PROJECT TITLE: Lettuce Breeding, USDA-ARS
PRINCIPAL INVESTIGATORS: E. J. Ryder, R. C. Grube, & J. D. McCreight
PROJECT TITLE: Breeding Crisphead Lettuce
PRINCIPAL INVESTIGATORS: Richard W. Michelmore, Oswaldo E. Ochoa, & Maria Jose Truco
PROJECT TITLE: Leaf Lettuce Breeding
PRINCIPAL INVESTIGATORS: Richard W. Michelmore, Maria Jose Truco, and Oswald E. Ochoa
PROJECT TITLE: Genetic Variation in Lettuce
PRINCIPAL INVESTIGATOR: Richard W. Michelmore
PROJECT TITLE: Basic Approaches to Lettuce Virus Disease Control
PRINCIPAL INVESTIGATOR: Bryce W. Falk
PROJECT TITLE: Examination of the Current Monterey County Seed Testing Protocol and Comparison of Various LMV Antisera and LMV Seed Testing Organizations for Detecting LMV-infected Seed Lots
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
PROJECT TITLE: Lettuce Mosaic Virus (LMV) Studies - Characterization of a Resistance Breaking Isolate of LMV
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
PROJECT TITLE: Characterization of a Severe Strain of Lettuce Mosaic Virus
PRINCIPAL INVESTIGATOR: William M. Wintermantel
PROJECT TITLE: The Etiology, Epidemiology, and Management of a New Soil-Borne Virus Disease of Lettuce in California
PRINCIPAL INVESTIGATOR: William M. Wintermantel
PROJECT TITLE: Biology and Epidemiology of Verticillium Wilt of Lettuce
PRINCIPAL INVESTIGATOR: Krishna V. Subbarao
PROJECT TITLE: Epidemiology and Control of Lettuce Drop Caused by Sclerotina Species
PRINCIPAL INVESTIGATOR: Krishna V. Subbarao
PROJECT TITLE: Investigations on Bottom Rot of Lettuce
PRINCIPAL INVESTIGATOR: Frank Martin
PROJECT TITLE: Fungicide Insensitivity in Lettuce Downy Mildew
PRINCIPAL INVESTIGATORS: Richard Michelmore, Oswaldo Ochoa, & Steven T. Koike
PROJECT TITLE: Ecology and Management of Bacterial leaf Spot of Lettuce
PRINCIPAL INVESTIGATOR: Carolee T. Bull
PROJECT TITLE Investigation of Bacterial Leaf Spot of Lettuce
PRINCIPAL INVESTIGATORS: Steven T. Koike, Bob Gilbertson, & Jeri Barak
PROJECT TITLE: Developing an Integrated Disease Management Program for Lettuce Anthracnose
PRINCIPAL INVESTIGATORS: Steven T. Koike, Krishna Subbarao
PROJECT TITLE: Developing an Integrated Disease Management Program for Gray Mold
PRINCIPAL INVESTIGATORS: Steven T. Koike & Krishna Subbarao
PROJECT TITLE: Investigation of a New Crown Rot Disease of Lettuce
PRINCIPAL INVESTIGATORS: Steven T. Koike & Krishna Subbarao
PROJECT TITLE: Powdery Mildew Management
PRINCIPLE INVESTIGATORS: Thomas Turini
PROJECT TITLE: Control of Downy Mildew of Lettuce With Fungicides
PRINCIPAL INVESTIGATOR: Albert O. Paulus
PROJECT TITLE: Insect Management for Central Coast Lettuce
PRINCIPLE INVESTIGATOR: William E. Chaney
PROJECT TITLE: Weed Management Systems for Lettuce
PRINCIPAL INVESTIGATORS: Steven A. Fennimore & Richard F. Smith
PROJECT TITLE: Plant-Soil Relationships in Lettuce
PRINCIPAL INVESTIGATOR: Louise E. Jackson
PROJECT TITLE: Efficient N and Irrigation Management for Lettuce Production
PRINCIPAL INVESTIGATOR: Tim Hartz
PROJECT TITLE: Evaluation of controlled Release Fertilizers for Winter Lettuce
PRINCIPAL INVESTIGATOR: Richard F. Smith
PROJECT TITLE: Pre-incorporation Transfer of Indicator Bacteria From Stacked Manure to Existing Lettuce
PRINCIPAL INVESTIGATOR: Trevor Suslow
PROJECT TITLE: Production Costs for Head (Wrapped Iceberg) and Leaf (Romaine) Lettuce in Monterey and Santa Cruz Counties
PRINCIPAL INVESTIGATORS: Laura tourte & Richard Smith
ABSTRACT
CALIFORNIA LETTUCE RESEARCH BOARD
for the period
(April 1, 2000-March 31, 2001)
PROJECT TITLE: Lettuce Breeding, USDA-ARS
PRINCIPAL INVESTIGATORS: E. J. Ryder, R. C. Grube, J. D. McCreight
SUMMARY:
In preliminary screening, 18 PI lines were identified as possibly resistant to big vein.
Six lines were confirmed resistant in a replicated test. From a cross between two resistant cultivars, we identified families with resistance equivalent to the more resistant parent.
Field selection of resistant breeding lines continued. Selection for quantitative resistance
to downy mildew continued. Breeding lines developed to date showed resistance
intermediate between the original resistant parents and susceptible cultivars. Resistance
is manifested as either smaller or fewer lesions or both. Sclerotinia tolerant lines were
backcrossed to Salinas for better head type. Several breeding families and PI accessions were identified with moderate tolerance. In Verticillium resistance studies, additional sources of resistance were identified and selections for resistance iceberg types were made. Segregating populations from crosses with pea leafminer resistant cultivars have been planted for evaluation and selection.
In powdery mildew resistance work, 10 highly resistant and 14 moderately resistant cultivars were identified. Crosses have been made for selection. Crosses have been made with lettuce aphid resistant cultivars and other sources of resistance are being explored. Breeding and selection for combining genes conferring resistance and mild reaction to lettuce mosaic virus continued. Crosses have been made with a romaine type PI line resistant to lettuce dieback, and selection has begun for a resistant commercial type romaine cultivar. Selection for several combined resistances are continuing. Selection for a dark green leaf lettuce continues. Selection for improved desert type lettuces continues. Genetic studies for inheritance of resistance to big vein, lettuce mosaic, downy mildew and lettuce drop are continuing. Screening, collection and distribution of germplasm continues.
CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM
April 1, 2000 to March 31, 2001
BREEDING CRISPHEAD LETTUCE
Richard W. Michelmore
Oswaldo E. Ochoa
Maria Jose Truco
Department of Vegetable Crops
University of California, Davis
rwmichelmore@ucdavis.edu
oeochoa@ucdavis.edu
mjtruco@vegmail.ucdavis.edu
SUMMARY:
The program emphasizes the identification and incorporation of genes for disease
resistance, particularly to downy mildew, lettuce mosaic virus, anthracnose and corky
root, into horticultural types suitable for California. Resistance for downy mildew is
being introduced from several new sources into cultivated genotypes suitable for
California and combined with resistance to LMV and corky root. Utilization of multiple
new sources will minimize the chances that changes in the pathogen will render all
cultivars susceptible simultaneously. Advanced lines with resistance to these diseases
are trialed in commercial fields. We anticipate releasing another set of advanced multi-
disease resistant lines that are close to commercial crisphead type in the coming year.
CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM
April 1,2000 to March 31,2001
LEAF LETTUCE BREEDING
Richard W. Michelmore
Maria Jose Truco
Oswaldo E. Ochoa
Department of Vegetable Crops
University of California, Davis
rwmichelmore@ucdavis.edu
mjtruco@vegmail.ucdavis.edu
oeochoa@ucdavis.edu
SUMMARY:
Backcross programs are underway that emphasize the identification and
introduction of genes for disease resistance, particularly to downy mildew, corky root,
lettuce mosaic virus and anthracnose, into the four leaf lettuce types. Resistance for
downy mildew is being introduced from eighteen new sources into cultivated genotypes
suitable for California and will ultimately be combined with resistance to LMV,
anthracnose and corky root. Utilization of multiple new sources and introduction of
different resistances into the different types will probably increase the longevity of
individual resistances and minimize the chances that changes in the pathogen will render
cultivars of different lettuce types susceptible simultaneously. Genetic studies are in
progress to determine the genetic basis for the resistance and to increase the efficiency of generating resistant lines.
CALIFORNIA LETTUCE RESEARCH PROGRAM
April 1, 2000, to March 31, 2001
GENETIC VARIATION IN LETTUCE
Richard W. Michelmore
Department of Vegetable Crops
University of California, Davis
rwmichelmore@ucdavis.edu
SUMMARY:
Novel methods for detecting, analyzing, and manipulating genetic variation are
being applied to lettuce. The aim of this project is to ensure that lettuce does not lag
behind other crops in benefiting from the application of biotechnological techniques. We have continued three projects: (i) Introduction of genes into lettuce using Agrobacterium tumefaciens and analysis of their expression, (ii) Cloning and characterization of disease resistance genes, (iii) Genetic mapping using a variety of molecular markers with the goal of locating most of the disease resistance genes known in lettuce.
This year we have initiated a fourth project: a comparative genomics approach to identification of candidate genes controlling horticultural traits. The map-based cloning of Dm3 has been confirmed and we have initiated studies to clone functional homologs from other genotypes. We are currently analyzing the stability of expression of Dm3 as a transgene. In parallel, we are utilizing a PCR-based approach to identify resistance gene candidates. A comprehensive map that integrates data from the major mapping projects completed to date is nearing completion. The map position of corky root resistance, cor has been refined and several linked markers identified that are informative in the breeding germplasm. We have developed and are creating database for the Composite (http://compositdb.ucdavis.edu/) that includes lettuce that contains genetic, molecular marker, cultivar, and sequence information.
RESEARCH ABSTRACT
TO THE
CALIFORNIA LETTUCE RESEARCH BOARD'S RESEARCH PROGRAM
for the Period
April 1, 2000 - March 31, 2001
PROJECT TITLE: Basic Approaches to Lettuce Virus Disease Control
PRINCIPAL INVESTIGATOR:
Bryce W. Falk
Department of Plant Pathology
University of California
Davis, CA 95616
SUMMARY:
Our efforts for this past year were concentrated on lettuce big-vein (LBV), caused by a
suspected virus which is transmitted by the soilborne fungus, Olpidiwn brassicae. This work was a carryover, completing work from the previous years' grant with no additional funding. Our work was applied in nature, trying to develop consistent, efficient means to screen for LBV resistance and to then screen cultivars and breeding lines for LBV relative resistance/susceptibility. We have now completed our work on LBV and here give a final report of our own work. In addition a summary of recent information on LBV from other parts of the world is presented. Recent work from Japan and Italy confirm the complexity of LBV as at least two distinct, unrelated viruses have now been presented as being specifically associated with LBV. However, in both cases the researchers appear to have made important discoveries relative to understanding the etiology of LBV. There is no question that understanding the etiology of LBV will be essential for developing long-term, effective strategies to control this disease.
RESEARCH ABSTRACT TO THE
CALIFORNIA LETTUCE RESEARCH
BOARD'S RESEARCH PROGRAM
for the period
April 1, 2000 - March 31, 2001
PROJECT TITLE: Examination of the Current Monterey County Seed Testing
Protocol and Comparison of Various LMV Antisera and LMV Seed Testing Organizations for Detecting LMV-infected Seed Lots
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
SUMMARY:
There is no single standardized ELISA procedure that is universally used for detecting LMV in lettuce seed. Thus there is a possibility of obtaining conflicting results from different tests/labs due to different tests being used. Alternatively, different tests may provide similar results, but variability may be due to differences in the training/experience of the individuals conducting the tests. In 1997, there were a number of documented discrepancies in tests performed by different labs, which lead to a concern about reliability of tests and questions regarding the need to standardize the LMV seed assay.
The first objective of the project was to identify the organizations/companies doing LMV seed testing. Following this identification we evaluated the various reagents used by different groups, and checked their efficacy and reliability. We carried out controlled experiments on plant seed and plant sap and it became apparent that there was a disparity between efficacy of reagents of different groups. Comparison tests (based on Agdia specifications) did not work well with antibody and conjugate from other groups. Agdia conditions were designed for a monoclonal antibody and did not work well for polyclonal antiserum. We then created a set of compromise conditions taking into account coating, conjugate dilution and washing buffer specifications. Tests using these compromise conditions, and under three different incubation temperatures (4°C overnight, room temperature for 4 hours or 37°C for 4 hours) on plant sap and seed extract, once again illustrated that it was not possible to mix and match polyclonal and monoclonal reagents or antibodies.
RESEARCH ABSTRACT TO THE
CALIFORNIA LETTUCE RESEARCH
BOARD'S RESEARCH PROGRAM
for the period
April 1, 2000 - March 31, 2001
PROJECT TITLE: Lettuce Mosaic Virus (LMV) Studies: Characterization of a
Resistance Breaking Isolate of LMV
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
SUMMARY:
Historically, lettuce mosaic virus (LMV) has been the most important and potentially
damaging virus disease of lettuce. Through a series of disease management strategies, most notably the mandatory LMV seed testing program, LMV has not been a problem in California. However, since 1986, LMV has been appearing with greater frequency in the Salinas Valley and other lettuce growing regions and there has been some concern that new strains of LMV have appeared. In work previously carried out by the lab on transgenic lettuce plants, based on the LMV coat protein gene, transgenic plants that showed evidence of resistance in early generations (R2) became susceptible in advanced generations (R3 and R4). In an attempt to determine the basis for the apparent loss of resistance in these transgenic lines, detailed molecular characterizations were carried out: RNA extractions for Northern blot analyses (gene expression) showed varied RNA expression levels, ranging from low to high levels, and protein expression studies in the form of Western blot analyses illustrated that the CP gene was still being expressed, at least for R2 plants and for some R3 plants.
During the course of these experiments, a severe resistance-breaking LMV isolate
was identified that presumably emerged by mutation of an existing strain. To determine if this was indeed the case, the susceptibility of ten different lettuce cultivars (varying in the complement of resistance genes) and the two susceptible host species (Chenopodium quinoa and Nicotiana benthamiana) were inoculated with the new virulent LMV isolate (LMV-R*), the stored isolates LMV-R95' and LMV-R952 and LMV-ER, another typical pathotype II LMV isolate provided by Ed Ryder. The coat protein gene from four different cultivars (LMV-R*, -R95\ -R952 and -ER) as well as from LMV-F-OO (isolated from the same location as the original LMV-R) was sequenced and comparisons made. Sap-inoculation experiments conducted with LMV-F-OO confirmed that it was not a resistance breaking isolate of LMV. The mechanism of resistance in 'mo' and "g' gene varieties was investigated by carrying out differential ELISA’s. Resistant and susceptible plants were inoculated with LMV-ER or LMV-R*, leaves were harvested at 10, 14, 17, 21 and 28 dpi, and ELISA’s were carried out. LMV-R* replicated and moved more quickly than LMV-ER.
CALIFORNIA LETTUCE RESEARCH BOARD
April 1, 2000-March 31, 2001
CHARACTERIZATION OF A SEVERE STRAIN OF
LETTUCE MOSAIC VIRUS
William M. Wintermantel
USDA-ARS
Salinas, California
SUMMARY:
The Firestone (FS) isolate of Lettuce mosaic virus (LMV) causes severe necrosis
and stunting on lettuce compared with the standard (ER) isolate. Both isolates
were obtained from stocks maintained by the lettuce breeding program at the
USDA-ARS station in Salinas. Both isolates were passaged to the local lesion
host Gomphrena globosa, and several single local lesion isolates were obtained
from each original isolate. The local lesion isolates were compared to the original
sources and all produced identical symptoms under standard controlled
conditions.
Passage of selected local lesion isolates to lettuce and weed hosts
determined that both FS and ER had identical host ranges. Interestingly, the FS
isolates were more aggressive not only on lettuce, but on all hosts tested,
infecting plants several days earlier than ER isolates. Local lesion isolates of both
ER and FS were passaged to Chenopodium quinoa for purification of viral RNA.
Purified viral RNA was amplified by RT-PCR, using primers to selected regions
throughout the LMV genome. Amplified fragments will be sequenced and
compared to determine regions responsible for the increased severity of the FS
isolate.
CALIFORNIA LETTUCE RESEARCH BOARD
April 1, 2000-March 31, 2001
THE ETIOLOGY, EPIDEMIOLOGY, AND MANAGEMENT OF A NEW SOIL-
BORNE VIRUS DISEASE OF LETTUCE IN CALIFORNIA
W.M. Wintermantel, R.Grube, E.J. Ryder, S. Koike, and G.C. Wisler
USDA-ARS and University of California-Davis
Salinas, California
SUMMARY:
Lettuce dieback is responsible for losses in romaine and leaf lettuce production in areas
associated with rivers in California and Arizona. Losses vary, ranging from severe in
some years to mild in others. The disease is tightly linked to the presence of river water, being found commonly in areas where flooding has recently occurred, where river wateris used for irrigation of fields, and where dredge is deposited on fields. Characteristic symptoms include severe stunting, necrosis and dieback of lettuce plants.
The disease is
caused by isometric viruses in the genus Tombusvirus. Field isolates from lettuce have
been identified and characterized as both Tomato bushy stunt virus (TBSV) and the
newly described Lettuce necrotic stunt virus (LNSV). In addition, Cucumber necrosis
virus (CNV) has been identified from diseased fields, however this virus does not appear to contribute significantly to lettuce dieback. Methods are being developed for more rapid and efficient identification of tombusviruses directly from lettuce, through both RT-PCR and electron microscopy. Studies are in progress to diagnose disease directly from soil, identify the relationship between soil-type and disease development, and to identify factors that may remediate disease development in the field. Field trials have identified a number of promising PI lines for resistance in romaine, leaf, and stem lettuce.
CALIFORNIA LETTUCE RESEARCH PROGRAM
April 1, 2000 - March 31, 2001
BIOLOGY AND EPIDEMIOLOGY OF VERTICILLIUM WILT OF LETTUCE
Krishna V. Subbarao
Department of Plant Pathology
University of California, Davis
SUMMARY:
The research objectives this year included: (1) to survey lettuce fields in the Salinas Valley for Verticillium wilt, and to determine wilt incidence and assay soils for Verticillium dahliae microsclerotia; (2) to characterize isolates collected from Salinas for both host range and genetic relatedness relative to isolates from Watsonville; (3) to determine the seedbome nature of V. dahliae in lettuce; and (4) to continue the breeding program to identify and develop sources of resistance to Verticillium wilt in crisphead, leaf, and other lettuce types. The major development this year was the spread of Verticillium wilt on lettuce to Salinas Valley fields. After extensive surveys in the Salinas Valley, the disease was confirmed in three fields. Incidence in these fields ranged between 20-60% and the numbers of microsclerotia between 55-800 per gram of dry soil.
The second objective could not be completed for lack of adequate number of isolates from Salinas for valid comparison. Another major discovery in the project this year was the elucidation of the seedborne nature of V. dahliae in lettuce. The pathogen was recovered from nearly 100% of seeds collected from infected plants. Both surface-sterilized and non-sterilized seeds yielded V. dahliae implying that the pathogen is internally seedborne. Planting infested seed or healthy seed soaked in a spore suspension from the lettuce isolate produced typical infected plants, and seed collected from these plants yielded the pathogen. We screened 41 lines that included commercial cultivars as well as breeding lines and identified additional sources of resistance. Resistance selections from the breeding lines have also been made for further progeny testing.
CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM
April 1, 2000 - March 31, 2001
EPIDEMIOLOGY AND CONTROL OF LETTUCE DROP CAUSED WSCLEROTINIA SPECIES
Krishna V. Subbarao
Department of Plant Pathology
University of California, Davis
SUMMARY:
The research objectives for the current year included: (1) to continue the evaluation of the existing and potential fungicides for lettuce drop control; (2) to determine other environmental factors that contribute to the geographical isolation of the two species; (3) to determine the survival of sclerotia from the two species at different soil temperatures; and (4) to evaluate breeding lines for Sclerotinia minor resistance both in the field and in the greenhouse. We began a long-term study on the evaluation of the existing and potential fungicides for the control of lettuce drop last year. The fungicides included this year were Botran, Rovral, Ronilan, Elevate, BAS 510, Serenade, and Fludioxonil. The last two fungicides were evaluated only during the fall on plots artificially infested prior to planting lettuce. The fungicide treatments were imposed immediately after thinning lettuce. During the fall, a second application of BAS 510, Elevate, and Serenade was made three weeks after the first. Lettuce drop incidence was nearly identical in Elevate, Rovral, Ronilan, and untreated control treatments during both spring and fall seasons. Control was not evident with BAS 510 during the spring but two applications during the fall reduced lettuce drop incidence relative to control by more than 50%. Control with Botran was intermediate.
Performance of both Fludioxonil and Serenade during the fall was encouranging. Extensive surveys were undertaken in the Salinas, Santa Maria and Central Valley production fields to assess the level of lettuce drop incidence and to identify both edaphic and environmental factors that encourage lettuce drop. Data are being analyzed and the results would be available in the near future. Several experiments to determine the survival of Sclerotinia minor and S. sclerotiorum sclerotia were initiated. Laboratory studies indicated that more than 90% of the sclerotia of both species survive temperatures of up to 40°C at least for three months. At two locations each in the San Joaquin Valley and Salinas Valley, we also are determining the effects of burial depth and duration on the survival of sclerotia. Preliminary results suggest that the survival ofS. minor is greatly reduced in the San Joaquin Valley after 15 months of burial, suggesting why we often see fewer infections by this species in that valley. Efforts to identify sources of resistance and using them in the breeding program were continued. Details of this work will be in the report by Ed Ryder.
RESEARCH ABSTRACT TO THE
CALIFORNIA LETTUCE RESEARCH
BOARD'S RESEARCH PROGRAM
For the period
April 1, 2000 - March 31, 2001
PROJECT TITLE: Investigations on bottom rot of lettuce
PRINCIPAL INVESTIGATOR: Frank Martin
SUMMARY:
Attempts to clarify which pathogens are responsible for lettuce bottom rot in California and Arizona production areas is in progress. Of the isolates that have been recovered from diseased plants in the field, 75% were multinucleate Rhizoctonia solani, 14% were binucleate Rhizoctonia and 11% were Pythium species (the predominant species was P. ultimum). The anastomosis determinations of the R. solani isolates are in progress, but it is clear that the isolates group into several different AGs. Thus far the most common AG identified is AG 4, a broad host range A that is capable of attacking a number of the host crops, some of which are commonly grown in rotation with lettuce. From one collection location isolates of this AG were recovered from bottom rotted lettuce as well as diseased celery and radicchio in adjacent fields. Pathogenicity tests with isolates of R. solani revealed that these isolates exhibited a range in virulence, with some causing only minor levels of infection while others caused significant rot of the leaf base of the host.
Additional pathogenicity tests to confirm the involvement of recovered pathogens on disease expression are in progress. Environmental conditions have been found to influence disease expression in growth chamber trials. While plant infection was observed at temperatures ranging from 23-28 C, symptom expression and disease progress was more pronounced at the higher temperatures. Humidity was found to be important for disease expression as well, with low levels of disease encountered under low humidity. In an effort to determine if genetic tolerance to the disease exists in the germplasm, growth chamber evaluations of germplasm provided by Ed Ryder are currently in progress.
CALIFORNIA LETTUCE RESEARCH PROGRAM
April 1, 1999 to March 31, 2001
Final Report
FUNGICIDE INSENSITIVITY IN LETTUCE DOWNY MILDEW
Richard Michelmore, Oswaldo Ochoa, Sarah Brown
Department of Vegetable Crops
University of California, Davis
Steve Koike
University of California Cooperative Extension
Monterey County
1432 Abbot Street, Salinas, CA 93901
SUMMARY:
During the 18 months of this survey, 134 isolates of Bremia lactucae were collected and characterized for insensitivity to Aliette and Maneb as well as for virulence phenotype and mating type. These were sampled from throughout the coastal growing areas in both objective surveys and opportunistically. This project has now been completed and therefore the results from both years of the survey are summarized to provide a full overview of the data. No differences were detected in sensitivity of isolates of downy mildew to Maneb. There are clear differences in sensitivity to Aliette in tests involving both seedlings and older plants. With heavy inoculum and under ideal conditions for disease development, some isolates caused significant disease, including on plants treated with above field rates of Aliette. However, in screens utilizing 6 week-old plants rather than seedlings, disease was reduced compared to Aliette-untreated plants. Therefore, under heavy disease pressure, failures of control can be expected in the field. However, under low inoculum pressure Aliette would be expected to provide some protection.
There was no correlation between virulence phenotype and Aliette insensitivity and
therefore it is not possible to combine the use of resistance genes and Aliette to provide
protection against all isolates. Aliette insensitive isolates were identified from all
California regions sampled. Pathotype V remained the most common pathotype, although only by a small margin. Novel 18 was the next most common. Dml8 remains the most effective resistance gene. Thirty isolates were tested for Ridomil sensitivity; all were insensitive. All 134 isolates were of the B2 mating type. We will continue our
opportunistic collection and characterization of isolates as part of our programs for
breeding for downy mildew resistance.
Research Abstract to the California Lettuce Research Board's Research Progam
November 2000 to March 2001
Project Title: Ecology and management of bacterial leaf spot of lettuce
Principle Investigator: Carolee T. Bull
USDA/ARS, Salinas CA
Summary:
Bacterial leaf spot of lettuce caused by Xanthomonas oxonopodis pv. vitians
(Xav: formerly X. campestris pv. vitians ) is an important pathogen of lettuce in
California's coastal and inland counties. Field trials were conducted in Santa Maria to
determine if commercially available products can provide control of this disease on
iceberg lettuce. Additionally, a trial was conducted to screen breeding lines for resistance to this disease.
In two field trials, chemicals (Quadris, Actigard-Blockade, Serenade, Serenade +
copper, copper, and Messenger) were applied according to the manufactures
recommendations. Materials were applied at thinning, followed by applications
approximately 7, 14,21,35, and 49 days after thinning. At harvest chemically treated and control plots were evaluated for bacterial leaf spot. Additional diseases including downy mildew, big vein, and lettuce drop were also evaluated.
The incidence of bacterial leaf spot of lettuce in Santa Maria was very low this year.
None of the research plots had bacterial leaf spot. None of the chemicals tested
influenced the incidence of the other diseases evaluated. No bacterial leaf spot occurred
in the trial with the breeding lines in Santa Maria and therefore no data was collected on
this plot.
Identical plots have been planted at two research locations in Salinas and the pathogen
will be applied at thinning to insure adequate disease pressure to evaluate the treatments.
Research Abstract to the
California Lettuce Research Board's Research Program
April 1, 2000 to March 31, 2001
Project Title: Developing an integrated disease management program
for lettuce anthracnose
Project Investigators:
Steven T. Koike
University of California Cooperative Extension
Monterey County
Krishna Subbarao
Department of Plant Pathology
University of California at Davis
Oswaldo Ochoa and Richard Michelmore
Department of Vegetable Crops
University of California at Davis
Summary:
Anthracnose disease (also known as ringspot and shothole) can be a serious,
damaging disease of lettuce when spring weather is cool and rainy in California. The
goals of our continuing project were to further refine fungicide spray programs,
develop detection methods for finding the Microdochium panattonianum pathogen in
soils, obtain information on how the disease develops, and test cultivars for possible
resistance. The compilation of all this information would help us assemble an
integrated disease management program for lettuce anthracnose. However, rainfall was limited in the spring of 2000. Anthracnose failed to develop in commercial fields and in our trials, so experiments involving the disease were not completed.
When Quadris was successfully registered for the control of anthracnose, various
field personnel reported possible burn and phytotoxicity when lettuce was sprayed
with tank mixes of Quadris and various insecticides. A field trial was conducted in
which we tried to reproduce such damage with Quadris + insecticide combinations. In
our trial no such damage was observed. If such damage does occur, it may vary
considerably based upon time of year, environmental conditions at the time of
application (such as temperature and light intensity), type or cultivar of lettuce, and
other factors.
Research Abstract to the
California Lettuce Research Board's Research Program
April 1, 2000 to March 31, 2001
Project Title: Developing an integrated disease management program
for gray mold of lettuce
Project Investigators: Steven T. Koike
University of California Cooperative Extension
Monterey County
Krishna Subbarao
Department of Plant Pathology
University of California at Davis
Summary:
Because of the widespread use of transplants in the early spring, Botrytis gray
mold at times can cause significant stand losses in leaf lettuce plantings. This effect is
particularly evident with Romaine cultivars as this lettuce type is very susceptible to the
disease. The initial symptom of gray mold is a water-soaked, brownish-gray rot that
occurs on transplant leaves and stems that are damaged during the normal practice of
handling and planting. Damaged tissues that are wet or in contact with the soil are
especially susceptible. From infected leaves and stems, the pathogen progresses into
the healthy crown of the lettuce plant, causing a decay and eventual death of the main
stem. A characteristic fuzzy gray growth of the Botrytis cinerea fungus can cover
diseased areas.
We conducted field trials to evaluate the effectiveness of various fungicides
against the B. cinerea pathogen. Fungicides were applied both preplant (to transplants
in trays, one day prior to field planting) and postplant (immediately after transplants
were placed in the ground) onto Romaine lettuce transplants. For the pre-plant
treatments made to plants in trays, Rovral- and Ronilan-treated plants had significantly
less disease than untreated plants in one of two locations. For post-plant treatments
made to Romaine right after transplanting, there were no statistically significant
differences between untreated plants and any of the fungicides. However, some
treatments did result in less Botrytis crown rot than untreated controls: Botran, Ronilan,
and Elevate. While experimental results were inconsistent, fungicides potentially can
help control this disease.
Research Abstract to the
California Lettuce Research Board's Research Program
April 1, 2000 to March 31, 2001
Project Title: Investigation of a new crown rot disease of lettuce
Project Investigators: Steven T. Koike
University of California Cooperative Extension
Monterey County
Krishna Subbarao
Department of Plant Pathology
University of California at Davis
Summary:
In the spring of 2000, a potentially new crown rot disease of lettuce was
discovered in both Monterey and Santa Cruz counties. Early symptoms consisted of
yellowing and wilting of lower leaves. Affected plants later had an uneven appearance
because one side of the foliage grew normally while the diseased side of the plant was
stunted and short. As plants matured, the entire plant became affected and eventually
wilted and collapsed. These above ground foliar symptoms were very similar to those
caused by Sclerotinia minor (causal agent of lettuce drop) and Botrytis cinerea (causal
agent of gray mold of lettuce).
However, examination of affected plants revealed distinct, black cavities (sunken
areas) on the crown and upper tap root. These cavities extended far into the crowns
and roots, resulting in extensive weakening of the plant; these plants could be broken
off easily at ground level. The black cavities were characteristically firm and lacked any
sign of fungal growth or spores. Thus, symptoms at the base of the crown differed
significantly from other lettuce crown diseases. The disease was most commonly found
and most severe on Romaine cultivars. A few plants of greenleaf and iceberg lettuces
were also confirmed to be infected.
Extensive isolations resulted in the recovery of the same gray-green fungus from
all samples at all locations. The fungus did not readily form spores or other structures,
so identification of the agent has not yet been completed. Known lettuce pathogens
such as Sclerotinia minor, Botrytis cinerea, Rhizoctonia solani, and Verticillium dahliae were never recovered from plants having crown rot.
When this new fungus was inoculated onto Romaine test plants, the same crown
rot symptoms developed and the fungus was reisolated. These initial tests indicate that
the recovered fungus is likely involved with crown rot disease.
RESEARCH ABSTRACT
TO THE CALIFORNIA LETTUCE ADVISORY
BOARD'S RESEARCH PROGRAM
for the period
April 1, 1999 - March 31, 2000
PROJECT TITLE: Powdery Mildew Management
PRINCIPLE INVESTIGATORS: Thomas Turini
University of California Cooperative
Extension, Imperial County
Steven Koike
University of California Cooperative
Extension, Monterey County
Ed Ryder and Becky Grube
USDA
Monterey County
SUMMARY:
Powdery mildew of lettuce, caused by Erysiphe cichoracearum, is a common problem in lettuce grown in the low desert and is an emerging problem in coastal production areas. Currently, there are few fungicides registered for control of this disease. To address this problem, fungicide activity and relative susceptibility of common lettuce varieties were compared in Imperial and Monterey Counties.
Two trials in Imperial and 3 trials in Monterey were initiated to compare activity of
fungicides against powdery mildew. Under the conditions of these fungicide efficacy
trials, materials that consistently provided excellent powdery mildew control included
Flint, Microthiol, Rally and Procure. Quinoxyfen, KP 481 and KQ 667 provided
excellent control, although these materials were only tested in one trial this season.
Downy mildew, which is caused by Bremia lactucae, was present at levels the enabled us to see treatment differences. Maneb, Aliette, and Acrobat, alone or in combination,
consistently reduced downy mildew severity as compared to the untreated control. KQ
667, KQ 667 applied with Curzate, and Maneb applied with Curzate provided excellent
control of downy mildew. In general, the materials considered powdery mildew
fungicides were not effective against downy mildew.
In the variety trial conducted in Imperial County, Cindy, Clarion and Big Boston, which
are known powdery mildew resistant varieties, and Deep Red had the lowest levels of
powdery mildew. In this study, the two red leaf varieties included were among the
varieties least affected by powdery mildew and iceberg varieties were the most affected-varieties with the lowest downy mildew severity included Royal Green, Cindy, Clarion and Vulcan. Downy mildew severity on Cindy, Clarion and Vulcan were not different than on Esmeralda.
RESEARCH ABSTRACT
CALIFORNIA LETTUCE ADVISORY BOARD'S RESEARCH PROGRAM
for the period
April 1, 1999 to March 31, 2001
PROJECT TITLE: Control of Downy Mildew of Lettuce with Fungicides
PRINCIPAL LEADERS & COOPERATING PERSONNEL:
Albert Paulus, Miguel Vilchez, and Frank Laemmlen
Plant Pathology Department, University of California,
Riverside and Cooperative Extension, Santa Barbara County
Lettuce Growers of the Santa Maria area
SUMMARY:
Propamocarb/Aliette at 3 pints/acre consistently provided excellent control of lettuce
downy mildew on a 10-day spray schedule. The same rate was used on downy mildew
(Peronospora statices) of hybrid statice, which is an ornamental plant grown in coastal
counties of California and excellent control was obtained. Bayer 3714, an experimental
unregistered fungicide, inhibited sporulation of the downy mildew fungus under high
disease intensity. Blockade (Actigard) used singly or in combination with Maneb
provided somewhat erratic control of downy mildew of lettuce.
Research Abstract to the
California Lettuce Research Board
for the period
April 1, 2000 to March 31, 2001
TITLE: Insect Management for Central Coast Lettuce
PRINCIPLE INVESTIGATOR: William E. Chaney
Farm Advisor - Entomology
U.C. Cooperative Extension - Monterey County
1432 Abbott Street
Salinas, CA 93901
Summary:
The pea leafminer problem has become less severe in recent years while lettuce aphid problems have become sporadic. Several new insecticides aimed at the lettuce aphid were tested and found to be effective, including the existing and new chloronicotinyls about to enter the market. Lab and field work showed that the key leafminer materials, Agrimek, Trigard and the neem-based products are still effective at reducing larval leafminer populations, but that the residual period of the first two are shortening.
The Central Coast Vegetable IPM (CCVIPM) Project, which began in 1997, wrapped up in March 2001. The project, which the Lettuce Board supported and cooperated with throughout, focused on new strategies of pest control using commercial-scale field demonstrations in head lettuce, romaine, and celery. Field trials were conducted in grower fields using side-by-side comparisons of different pesticide regimes. The IPM treatments excluded organophosphates (OP's), carbamates, and pyrethroids, except when alternatives weren't available. From 1997 to 2000, the CCVIPM project conducted 46 field demonstrations covering 667 acres. In these fields, the reduction in the number of applications of OP's, carbamates, and pyrethroids for the IPM treatments compared to the standard was 72 to 88%. However, the project clearly shows that eliminating these FQPA targeted materials is not possible at this time.
One or more of the excluded pesticides was required on the IPM treatment to manage a pest with no alternative control available in 38% of the head lettuce, 29% of the romaine, and 100% of the celery trials. Many of the "softer" IPM materials are more expensive than older OP's, carbamates, or pyrethroids. Thus, there was a higher cost for the IPM treatments, from $0.02 to $0.08 per carton. More information is available on the project website, http://ccvipmp.ucdavis.edu. Future work continues to look toward lettuce aphid resistant varieties and improved chemical and biological means of control for both lettuce aphid and leafminers.
CALIFORNIA LETTUCE RESEARCH BOARD
April 1, 2000 - March 31, 2001
WEED MANAGEMENT SYSTEMS FOR LETTUCE
Steven A. Fennimore
Dept. of Vegetable Crops and Weed Science
University of California, Davis
Salinas, CA
Richard F. Smith
University of California Cooperative Extension
Monterey County
Salinas, CA
SUMMARY:
Weed management activities in 2000 were focused on characterization of a potential new lettuce herbicide, and improvement of herbicide use efficiency on 80-inch beds. Specific objectives were: (1) to evaluate new potential herbicides for lettuce; (2) to evaluate Raptor herbicide for weed control in iceberg and leaf lettuce; (3) to compare herbicide use efficiencies in 80-inch bed production systems; (4) to evaluate the brush hoe cultivator as a tool to reduce labor inputs in 80-inch bed production systems; (5) to develop improved common purslane management systems. Nine new herbicides were evaluated in lettuce for preemergence or post emergence selectivity. None of the herbicides were found to be safe in lettuce. Raptor herbicide was identified as a potentially safe herbicide for lettuce in 1999. Five additional studies were conducted in 2000 to better characterize the selectivity of Raptor in lettuce, as well as the weed control efficacy. Raptor was selective in iceberg lettuce at rates up to 0.016 lb ai/A, but tolerance in romaine lettuce was not acceptable. Raptor was effective on hairy nightshade.
Three studies were conducted in 2000 to compare band, bed top and combination spray patterns on 80-inch beds. The combination spray pattern was a hybrid between the band and bed top spray patterns. Where weed densities were high, bed top applications were the most cost- effective, but where weed densities were lower, band applications were the most efficient. The brush hoe cultivator was evaluated on 80-inch beds to determine if it could be used to reduce labor inputs for hand weeding. Overall the brush hoe was found to remove more weeds than a standard cultivator, and in some cases did reduce labor inputs. Common purslane is tolerant to desiccation, and after uprooting by cultivation, some plants are transplanted to the furrow where they continue to grow and set seed. Common purslane control can be improved with the use of bed top herbicide applications that minimize weed emergence and reduce the probability of additional seed set.
RESEARCH ABSTRACT TO THE CALIFORNIA ICEBERG LETTUCE ADVISORY BOARD'S RESEARCH
PROGRAM
for the period
April 1, 2000 - March 31, 2001
PROJECT TITLE: Plant-Soil Relationships in Lettuce
PRINCIPAL INVESTIGATOR: Louise E. Jackson
Department of Vegetable Crops
University of California, Davis
SUMMARY:
Iceberg lettuce is shallow-rooted and is not able to access water that is deep in the
soil profile. Deeper roots would allow it to use a deeper water supply, and could reduce
the amount and frequency of irrigation. Wild lettuce (Lactuca serriola) is a deep rooted
and highly drought tolerant plant, and is closely related to cultivated lettuce. Genes
(quantitative trait loci or QTLs) were identified in previous work for taproot length, and
for the number of lateral roots at the tip of the taproot, using a cross between cultivated
and wild lettuce.
In this year's research program, there were three main goals: confirm the QTLs,
determine the cost of deep roots for shoot growth and yield, and begin to create near-
isogenic lines of cultivated lettuce for different gene combinations with marker-assisted
selection F7, recombinant inbred lines (RILs) were derived from the original cross of
cultivated lettuce (L. sativa cv. 'Salinas') by wild lettuce (L. serriola) that was used in
gene identification and mapping. These F7, RILs are very different in size and form from one another. Forty F7, RILs were chosen for study using DNA markers for the taproot and deep lateral genes. Some refinements need to be made in the procedures for the molecular markers, so only preliminary data are presented here. A field experiment at UC Davis on silt loam soil was conducted.
The preliminary data indicate that across the wide range of lettuce shoot sizes and
morphologies represented by the F7, RILs, highest shoot growth tended to occur in plants with the gene for short taproot from cultivated lettuce and the gene for deep laterals at the tip of the taproot from wild lettuce. These plants also tended to extract more water from deeper in the profile. A breeding program has begun to produce cultivated lettuce with the deep rooting traits.
Research Project Report
California Lettuce Research Board
April 1, 2000 to March 31, 2001
Project title: Efficient N and irrigation management for lettuce production
Project leader: Tim Hartz
Department of Vegetable Crops
University of California
Davis. CA 95616
(530)752-1738
Objectives: 1. Evaluate pre-sidedressing soil nitrate testing (PSNT) as an N management practice in romaine lettuce production
2. Develop efficient drip irrigation management practices for lettuce
Summary:
Four PSNT trials were conducted in commercial romaine fields in the Salinas Valley
during the summer of 2000. Two large PSNT plots were established in the middle of
each field. Prior to each sidedressing residual NOa-N in the top foot of soil was
determined in these plots, and the amount of N fertilizer to be applied was determined by that residual level. In one plot per field a 20 PPM N03-N threshold was used, in which no fertilizer was applied as long as the residual N03-N level was greater than the
threshold. If residual N03-N was less than the threshold, then only enough sidedress N
was applied to bring the soil available N up to that level. In the other plot a 30 PPM
N03-N threshold was used. The productivity of the PSNT plots was compared to that of adjacent plots fertilized by the growers' standard practice.
Three drip irrigation trials were conducted in drip-irrigated commercial lettuce fields
(2 romaine, I head lettuce) in the Salinas Valley. After the surface drip system was
installed, replicated plots of drip tape of different flow rates (both higher than and lower
than the field system) were spliced into the field system. As the grower managed the
field according to his normal practices these plots received either more or less water than
the rest of the field. Water meters were installed to monitor application volume in these
plots, and soil moisture sensors were installed to monitor changes in soil moisture. Yield
and quality comparisons were made among the three irrigation regimes. There were no differences in crop productivity among the three N regimes tested. Following the 20 PPM N03-N PSNT threshold reduced sidedress N application 54 lb/acre. These results agree with those of numerous PSNT trials conducted on head lettuce in prior years.
The drip irrigation management practices of the cooperating growers varied
substantially, but several inefficient practices were common. These included excessive
intervals between irrigations, individual applications heavy enough to cause substantial
leaching, and failure to match irrigation volume to real-time ETo and crop canopy size.
These results, similar to those obtained in commercial field trials with drip irrigated
celery, confirm that lettuce growers do not consistently manage drip irrigation for
maximal efficiency.
Research Project Report
California Lettuce Research Board
April 1, 2000 - March 31, 2001
Project Title: Evaluation of Controlled Release Fertilizers for Winter Lettuce Production
Project Leader: Richard Smith
Vegetable Crop and Weed Science Farm Advisor
University of California Cooperative Extension, Salinas
Cooperating personnel: Tim Hartz
Extension Specialist
Dept. of Vegetable Crops, University of California, Davis
SUMMARY:
Slow release fertilizer trials were conducted in 3 commercial head lettuce fields in
the Salinas Valley in 2000-01. Early planted fields on light soils were selected for these
trials to provide the greatest potential for exposure to the high rainfall months and
greatest potential for nitrogen movement from the root zone. 200 pounds of nitrogen was applied as all slow release fertilizer or as combinations of slow release fertilizer and
sidedress applications of conventional fertilizer. These treatments were compared with a standard treatment of 200 Ib. N/A and an untreated control.
Slow release fertilizers gave yields comparable to the standard fertilizer treatments in both trials. The best controlled release treatment was a combination of 100 Ibs. N of slow release fertilizers applied prior to planting followed by a total of 100 Ib. N applied in two sidedress applications. Applying all nitrogen as slow release fertilizer prior to planting yielded less than the combinations with conventional fertilizers. There were high levels of nitrate-nitrogen in the top foot of soil at the initiation of the trials.
Over the course of the trials most of the initial nitrogen was taken up or leached to deeper levels in the soil profile. Slow release fertilizers did not appear to have less nitrate to the 2-3 foot depth of the soil than standard fertilizer treatments. Slow release fertilizers generally maintained amounts of nitrate-nitrogen in the top foot of the soil over the course of the season, which were comparable with or higher than the standard fertilizer treatment. In addition, the levels of tissue nitrogen were also adequate in the slow release treatments.
No yield advantage was observed for slow release fertilizers in these trials. They
did however, in combination with conventional fertilizers, provide comparable yields
with conventional fertilizers. Because no significant differences in yield were detected,
no economic benefit from slow release fertilizers can be inferred from these trials. There may be intangible benefits from the use of slow release fertilizers such as reducing the risk of being rained out of a field during wet years.
PROJECT REPORT
CALIFORNIA LETTUCE RESEARCH BOARD
For the period
April 1, 2000 - March 31, 2001
PROJECT TITLE: Pre-incorporation Transfer of Indicator Bacteria from Stacked Manure to Existing Lettuce
PROJECT LEADERS: T.V. Suslow, UC Davis Vegetable Crops
COOPERATING PERSONNEL: R. Smith, S. Koikc - UCCE, Salinas
S. Goerge, M. Zuniga - UCD, Vegetable Crops
OBJECTIVES: To determine the potential for transfer and survival of non-pathogenic E. coli correlated nonpathogenic indicator bacteria from stacked (aged) dairy manure stored adjacent to an existing lettuce crop.
ABSTRACT: Dairy manure, containing a mean viable generic E. coli count of approximately log 3.5 CPU/g, was deposited as an approx. 4mm pile within a planting of crisphead lettuce. The lettuce, in general, had 4 to 6 true leaves at the time of pile deposition. At the first sampling, the manure had residual moisture content of approx. 20% and was kept covered during irrigation to prevent significant wetting. After two weeks, the dairy manure was determined to have a viable E. coli content of less than log 1.0 CFU/g. No detectable transfer to or survival on lettuce plants was detected in two trials. Populations of thermo tolerant coliforms were highest on lettuce plants immediately to the downwind side of the pile at the first sampling but not the second. To simulate the potential for transfer, a dry fluorescent marker was incorporated into dry dairy manure (mixed in 5-gal buckets and applied as an approx. 2.0cm layer to the existing stack).
By monitoring the fluorescence of particulate manure, under long-wave UV light, a steep, decreasing gradient of transfer to lettuce plants was observed. Negligible detection of UV fluorescing particles on leaves was encountered beyond 1.0m from the pile. Within this experiment, we can only demonstrate the likely distribution of very small aggregates that are blown off the pile. The distance and distribution of spread would be strongly influenced by the height of the pile, the aggregate and particulate properties of the manure, weather, vectors, and other potential means of mechanical dispersal. Model lab studies, with manure inoculated with marked strains of Salmonella and E. coli, demonstrated that rapid drying of the surface of a stacked pile would likely result in cell death or no recovery using standard techniques. Dry, surface particulates or aggregates would be most likely dispersed during field-side storage. No E. coli were detected in COOL air samples taken near the manure pile and the surrounding plot area. Low levels of potential indicator bacteria, thermo tolerant coliforms, were detected in COOL air samples and on lettuce surfaces.
Research Abstract to the
California Lettuce Research Board
April 1, 2000 to March 31, 2001
Project Title: Production Costs for Head (Iceberg) and Leaf(Romaine) Lettuce
in Monterey and Santa Cruz Counties
Project Investigators: Laura Tourte
Farm Advisor
University of California Cooperative Extension
Santa Cruz County
Richard Smith
Farm Advisor
University of California Cooperative Extension
Monterey County
Summary:
The overall objective of this project was to determine production costs and returns for head (iceberg) and leaf (romaine) lettuce in Monterey and Santa Cruz Counties to provide growers and the lettuce industry with up-to-date economic information for the two lettuce types. To accomplish this, data was collected through interviews with growers and relevant industry personnel. The practices and costs described in the final reports are considered common for production of the two lettuce types. In addition, the studies further delineated practices and costs of the two lettuce types to two different locations. North Monterey/South Santa Cruz County and South Monterey County. This delineated format enabled production costs to more accurately reflect variation in land rents, water costs and pest management for the area.
The completed studies are intended as estimates or guides, which can be helpful in making production decisions, determining potential returns, preparing budgets and evaluating production loans. Estimated cash costs for head (iceberg) lettuce range from $7,411 to $8,069 per crop per acre, with breakeven costs per 24-count 42-pound carton ranging from $8.35 to $10.19 depending on production conditions, yield and price received. Estimated cash costs for romaine lettuce range from $6,512 to $7,170 per crop per acre, with breakeven costs per 24-count 35- pound carton ranging from $7.01 to $8.81 depending on production conditions, yield and price received.
The costs and practices detailed in each study may not be applicable to all situations. However, individual growers may use the studies as templates and modify them to more accurately reflect their own situations.
Acknowledgements. Appreciation is expressed to the growers, packers and other industry representatives who provided information, assistance and expertise for this study. This study was funded by the California Lettuce Research Board.