| RESEARCH PROJECT REPORTS PROJECT TITLE & PRINCIPAL INVESTIGATOR(S)
2003 - 2004 LETTUCE BREEDING, USDA-ARS R. C. Grube, R. Hayes, B. Mou, & J. D. McCreight, USDA-ARS, Salinas BREEDING CRISPHEAD LETTUCE Richard W. Michelmore, & Oswaldo E. Ochoa, UC Davis LEAF LETTUCE BREEDING Richard W. Michelmore, & Maria Jose Truco, UC Davis GENETIC VARIATION IN LETTUCE Richard W. Michelmore, UC Davis CHARACTERIZATION AND MANAGEMENT OF LETTUCE DIEBACK DISEASE AND LETTUCE TOMBUSVIRUSES William M. Wintermantel, USDA-ARS, Salinas MANAGEMENT OF PHOMA BASAL ROT DISEASE OF LETTUCE Steven T Koike & Krishna V. Subbarao, UC Cooperative Extension, Salinas and UC Davis ECOLOGY AND MANAGEMENT OF BACTERIAL LEAF SPOT OF LETTUCE Carolee Bull, USDA-ARS, Salinas EPIDEMIOLOGY AND CONTROL OF LETTUCE DROP CAUSED BY SCLEROTINIA SPECIES Krishna V. Subbarao, UC Davis BIOLOGY AND EPIDEMIOLOGY OF VERTICILLIUM WILT OF LETTUCE Krishna V. Subbarao, UC Davis FUSARIUM WILT OF LETTUCE: MANAGEMENT THROUGH DETECTION, AVOIDANCE, AND DISEASE RESISTANCE Thomas R. Gordon, UC Davis INSECT MANAGEMENT FOR CENTRAL COAST LETTUCE William E. Chaney, UC Cooperative Extension, Salinas INSECT MANAGEMENT FOR LOW DESERT LETTUCE EricT. Natwick, UC Cooperative Extension, Holtville WEED MANAGEMENT SYSTEMS FOR LETTUCE Steven A. Fennimore & Jose Aguiar, UC Davis and UC Cooperative Extension, Indio INFLUENCE OF VARYING NITROGEN AND PHOSPHORUS FERTILIZATION ON POSTHARVEST QUALITY OF LETTUCE Husein Ajwa, UC Davis MUSTARD COVER CROPS TO OPTIMIZE CROP ROTATIONS FOR LETTUCE PRODUCTION Richard F. Smith, UC Cooperative Extension, Salinas SALINITY EFFECTS ON QUALITY AND YIELD OF DRIP IRRIGATED LETTUCE Michael Cahn & Husein Ajwa, UC Cooperative Extension, Salinas and UC Davis MEASURING AND ESTABLISHING EXPOSURE POTENTIAL OF PERCHLORATE IN LETTUCE Robert Krieger & Charles Sanchez, UC Riverside and University of Arizona, Yuma ASSESSMENT OF INDICATOR BACTERIA FROM RESERVOIR IRRIGATION WATER AND ON LETTUCE Trevor Suslow, UC Davis NUTRIENT, PHYTOCHEMICAL, ORAC ANALYSIS OF 5 LETTUCES: BUTTERHEAD GREEN LEAF, RED LEAF, ICEBERG, AND ROMAINE Gary Beecher & Joanne Holden, USDA-ARS, Beltsville, MD and Ronald Prior, Arkansas Children’s Center, Little Rock, AR ABSTRACT CALIFORNIA LETTUCE RESEARCH BOARD for the period (April 1, 2003-March 31, 2004) PROJECT TITLE: Lettuce Breeding, USDA-ARS PROJECT INVESTIGATORS: R. C. Grube, R. Hayes, B. Mou, J. D. McCreight, USDA/ARS Crop Improvement and Protection Unit, Salinas, CA SUMMARY: Our objectives are to incorporate resistance to several diseases and insects into crisphead and mixed lettuce cultivars and breeding lines. In 2003, major efforts targeted lettuce big vein (BV), lettuce mosaic virus (LMV), downy mildew/Bremia (DM), lettuce drop/Sclerotinia minor, Verticillium wilt, lettuce dieback/tombusviruses, Fusarium root rot, bacterial leaf spot (BLS), corky root (CR), lettuce aphid and leafminer. Minor programs addressed adaptation to desert conditions, dark green leaf color, nutritional content, resistance to Phoma basal rot and powdery mildew (PM), and combining multiple resistances. In all programs, horticultural traits, adaptation, and resistance to tipburn are considered essential. In 2003, we identified new candidate sources of resistance to CR, leafminer, Fusarium, Phoma, Verticillium, BLS, BV and lettuce aphid. In replicated tests, we confirmed resistance of previously identified germplasm to CR, leafminer, BV, dieback, BLS, PM and LMV. Advanced breeding lines were evaluated for resistances to BV, LMV, CR, DM, and Verticillium (crisphead), dieback (romaine), and dark green color (leaf). Genetic studies concurrent with breeding programs are being conducted to determine the inheritance of resistances to BV, LMV, lettuce drop, and field resistance to DM. Publications during 2003-2004 included reports of research on resistances to leafminer, lettuce drop, dieback, multiple disease resistances and nutritional content. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2003 to March 31, 2004 BREEDING CRISPHEAD LETTUCE Richard W. Michelmore Oswaldo E. Ochoa Department of Vegetable Crops University of California, Davis rwmichelmore@ucdavis.edu ochoa@vegmail.ucdavis.edu SUMMARY: The program continues to emphasize the identification and incorporation of genes for disease resistance, particularly to downy mildew, lettuce mosaic virus, anthracnose, verticillium and corky root, into crisphead horticultural types suitable for California. Resistance for downy mildew is being introduced from several new sources 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. We are also introducing delayed bolting from wild lettuce. We are initiating a program for resistance to Verticillium. Advanced lines are trialed at the USDA field station in Salinas. We have continued to monitor variation in the ability of the downy mildew pathogen to overcome resistance genes. There has been a continued increase in variation in the pathogen. Of the known resistance genes, only Dml 7 remained effective against all California isolates. The frequency of isolates in our non-random sample that were capable of overcoming all of the other characterized sources of resistance increased in 2003. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1,2003 to March 31, 2004 LEAF LETTUCE BREEDING Richard W. Michelmore Maria Jose Truco Oswaldo E. Ochoa Department of Vegetable Crops University of California, Davis rwmichelmore(S>ucdavis.edu mjtruco(a>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 varieties. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2003, to March 31, 2004 GENETIC VARIATION IN LETTUCE Richard W. Michelmore Department of Vegetable Crops University of California, Davis rwmichelmore(a>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 genomic and biotechnological techniques. We have continued four 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, (iv) Comparative genomics to identify candidate genes controlling horticultural traits. We are in the process of cloning functional homologs of Dm3 with different specificities from other genotypes with an initial focus on Dml8. We have shown using post-transcriptional gene silencing that Dml8 and Dml6 are probably encoded by homologs of Dm3. Over 66,000 ESTs have been generated representing over 19,000 unigenes and at least a third to a half of all genes in lettuce. QTL analysis has identified chromosomal regions controlling numerous horticulturally important traits. These are being mapped relative to candidate genes. We have developed and are curating a database for the Compositae (http://compositdb.ucdavis.edu/) that includes genetic, molecular marker, cultivar, and sequence data for lettuce as well as information on lettuce researchers. We are developing a new lettuce database, lettuce genetic map viewer, that will replace in time the old lettuce database version. This updated beta version is accessible at http://cgpdb.ucdavis.edu/database/Renome viewer/viewer/. PROJECT REPORT CALIFORNIA LETTUCE RESEARCH BOARD April 1, 2003-March 31, 2004 Project Title: Characterization and Management of Lettuce Dieback Disease and Lettuce Tombusviruses Project Leader: William M. Wintermantel, USDA-ARS, 1636 E. Alisal St. Salinas, CA 93905, Ph: (831) 755-2824; Fax: (831) 755-2814 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 water is 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 Lettuce necrotic stunt virus (LNSV), and Tomato bushy stunt virus (TBSV). Studies conducted previously demonstrated that conditions within the soil environment influence lettuce dieback symptom development under greenhouse conditions. Soil salinity, in particular, had a dramatic effect on disease incidence, and suggested that poor drainage such as occur in areas near rivers may lead to high salt concentrations, and that these conditions may lead to increased incidence of infection. New tests are in progress in field microplots to determine if the same effect occurs under field conditions. Preliminary tests conducted on lettuce dieback-resistant and susceptible seedlings indicated LNSV can accumulate in resistant lettuce. These studies do not indicate the level of accumulation, however. It remains possible that accumulation or even virus movement within plants may be reduced in resistant varieties even though some virus accumulation occurs. Laboratory studies have demonstrated that purified LNSV and TBSV are both highly stable in water. Virus extracts maintained at ambient temperature for up to two months in water remain highly infectious, confirming the ability of tombusviruses to survive and spread through movement of surface water. In order to more fully understand the causal agent of lettuce dieback, the complete nucleotide sequence of a well-characterized LNSV isolate is being determined. This information provides baseline information for future studies, and for comparison with other disease-causing isolates. RT-PCR primers and ELISA techniques are both available for confirmation of tombusvirus infection of lettuce. Recent studies have focused on the less expensive ELISA detection. Due to relatively low virus titer in lettuce, ELISA detection can be compromised by poor reactivity between some LNSV isolates and commercial antiserum. Research Abstract to the California Lettuce Research Board's Research Program April 2003 to March 2004 Project Title: Management of Phoma basal rot disease of lettuce Project Steven T. Koike Investigators: University of California Cooperative Extension Monterey County Krishna Subbarao Department of Plant Pathology University of California at Davis Collaborators: B. Grube, E. Ryder, G. Verkley, T. O'Neill, D. Fogle Summary.: The recently discovered Phoma basal rot disease of lettuce, first found in California in 2000, is now apparently established in various parts of coastal California. The pathogen is a fungus in the genus Phoma; the species is likely Phoma exigua. The Phoma group includes a large number of soil-borne species, some of which are weak pathogens that usually attack plant stems. Experiments showed that romaine isolates were able to consistently cause disease on romaine and crisphead cultivars, and crisphead isolates consistently caused disease on crisphead and romaine cultivars. Our field trials tested efficacy of fungicides for Phoma basal rot. Results from one 2002 and two 2003 experiments were consistent. When applied shortly after thinning, the products Quadris, Endura, and Switch were very effective in preventing Phoma basal rot from developing. However, timing of sprays may be critical; in a different 2003 trial, our first spray was applied seven days later than scheduled. For this location, the treatments (which consisted of various rates and timings of Quadris and Endura) did not perform well. Additional field trials are planned to investigate this timing factor. For a number of years, there has been an interesting correlation between Phoma outbreaks on lettuce and previous strawberry crops. For many romaine crops, significant disease has occurred when the lettuce is the first crop following strawberries from the previous season. We therefore conducted a preliminary analysis of strawberry transplants this past fall to see if the Phoma pathogen was present on such plant material. Strawberry transplants were obtained directly from nursery sources and were tested for the possible presence of Phoma. A total of 34 samples were collected and five replications were tested per sample. For each sample, roots were rinsed and then directly plated onto semi-selective medium. Another set of roots was placed into sterile distilled water and incubated on a rotary shaker; the resulting solution was filtered through cheesecloth and then dilution plated onto semi-selective medium. For all samples, no Phoma suspects were observed in any of the plates. We will continue this examination of strawberry as a possible factor in Phoma basal rot. CALIFORNIA LETTUCE RESEARCH BOARD 2003 FINAL REPORT MAY 15, 2004 Project Title: Ecology and management of bacterial leaf spot of lettuce Principle investigator: Carolee Bull, USDA/ARS Cooperators: Polly Goldman, USDA/ARS Ryan Hayes, USDA/ARS Steve Koike, UCCE Ed Ryder, USDA/ARS Summary: During the 2003 funding cycle we optimized and completed our field experiments on management of bacterial leaf spot (BLS) of lettuce, caused by Xanthomonas campestris pv. vitians (Xcv). Additionally we completed screening of 11 cultivars for disease resistance in field and greenhouse experiments as well as investigating the role of bacterial populations in disease development on susceptible and resistant cultivars. In one experiment we evaluated 4 commercially available chemical and biological products and combinations of these products for control of BLS. As we have seen in prior research, combinations of copper and Serenade (AgraQuest, Davis, CA) or Maneb resulted in significantly lower disease incidence and severity than that of a water control. Unlike our findings in previous years, the reduction in disease appeared to be due mostly to the copper in these mixtures. We also evaluated 11 lettuce cultivars for resistance to BLS in two replicated trials. Results were consistent with our prior research. Vista Verde and Pybus 251 were consistently the most susceptible cultivars. Several cultivars, including Little Gem, Batavia Reine de Glaces, Prizehead, and Iceberg, were resistant. Batavia Reine de Glaces and Holborn Standard were chosen as parents for breeding purposes and we are screening the progeny from this and other crosses. We screened additional cultivars and lines in non-replicated trials and identified several new potentially resistant lines. In a third group of experiments, we evaluated the influence of bacterial populations on disease development in field and greenhouse trials. In both experiments disease severity increased with increasing concentrations of applied bacteria. As expected, the maximum disease severity was greater in the susceptible than in the resistant cultivars. We are using these findings to further improve our methods for rapid screening of lettuce lines for resistance to BLS. CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM April 1, 2003 - March 31, 2004 EPIDEMIOLOGY AND CONTROL OF LETTUCE DROP CAUSED BY SCLEROTINIA SPECIES Krishna V. Subbarao Department of Plant Pathology University of California, Davis SUMMARY The research objectives for the current year included: (1) to evaluate existing and potential fungicides for lettuce drop control in commercial production fields; (2) to evaluate chloropicrin (C), telone+C, and methyl bromide+C for reduction of S. minor sclerotia in soil; (3) to compare the effects of 40-inch and 80-inch bed widths on the incidence of lettuce drop caused by S. minor and S. sclerotiorum; (4) to compare accumulation and survival of sclerotia, production of apothecia, ascospore release, and infection of lettuce by ascospores; (5) to continue to determine the efficacy of biocontrol agents in Imperial Valley for lettuce drop control; and (6) to evaluate breeding lines for resistance to Sclerotinia minor. We evaluated Rovral, Botran, BAS 510 (commercially available as Endura from April 2004), and two different application times of Switch (registration expected in late 2004), during the spring and fall seasons of 2003 in commercial lettuce fields. During the spring, lettuce drop incidence was less than 1%; hence no treatment differences were observed. During the fall, Endura applied at thinning and 2-wk post-thinning and Switch applied at 2- and 4-wk post-thinning provided equivalent control and was nearly 80% relative to unsprayed control. All fumigation treatments listed in objective 2 reduced the number of S. minor sclerotia, the numbers remained low even at the end of strawberry harvest, but increased in all three treatments during spring lettuce. On the spring and fall lettuce crops following strawberry, however, the incidence of lettuce drop varied between 2.5 - 5.8% and 8.6 - 11.2%, respectively relative to the untreated control plots (8.0 to 13.5%, respectively). In contrast, the incidence of basal rot in the spring crop was significantly higher in the fumigation treatments than in the untreated control plots. We also compared the effects of 40 and 80" bed configurations on lettuce drop caused by both S. minor and 5*. sclerotiorum in isolated plots. The preliminary results confirmed our hypothesis that the incidence of lettuce drop caused by S. minor was greater in 80" beds than in 40" beds. Similarly, the number of apothecia per square meter produced by S. sclerotiorum was significantly greater in the 80" beds than on 40" beds. These studies are being continued in 2004. Another major study completed this year included the genetic characterization of isolates of S. minor using mycelial compatibility groups (MCGs). About 240 isolates have been characterized and 7 MCGs identified. Majority of the isolates belonged to 4 MCGs and they were distributed differentially within the Salinas Valley. The implications of these findings for lettuce drop control remains to be determined. Once again, of all the biocontrol agents evaluated against both S. sclerotiorum and S. minor, none were effective against S. minor and Contans was highly effective against S. sclerotiorum. Efforts to identify' sources of resistance and using them in the breeding program were continued. Details of this work are in the report by Ed Ryder and Rebecca Grube. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2003 - March 31, 2004 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) continued monitoring of Verticillium wilt and soil inoculum density in coastal California; (2) to evaluate incidence of Verticillium wilt on lettuce following strawberry in plots treated with chloropicrin, telone+chloropicrin, and methyl bromide+chloropicrin (MBC); (3) to determine the efficacy of fumigation at different soil depths and follow the recolonization of soil by Verticillium dahliae; (4) to determine the effects of infested seed on soil infestation by Verticillium dahliae and on the incidence of Verticillium wilt of lettuce; (5) to develop a screening technique that can be used to evaluate Verticillium wilt resistance in lettuce in vitro; and (6) to continue the breeding program to identify and develop sources of resistance to Verticillium wilt in crisphead, leaf, and other lettuce types. Unlike in previous years, there were no dramatic losses from Verticillium wilt this year. However, the appearance of Verticillium wilt in fields previously fumigated with MBC was a worrying development. Soil assays from the field in which the disease reappeared revealed very high levels of microsclerotia g"1 soil consistent with previous observations. The lettuce crops following strawberries after fumigation with Chloropicrin, Telone+Chloropicrin, and MBC were evaluated for incidence of lettuce drop, crown rot and Verticillium wilt. No Verticillium wilt developed on these crops and the microsclerotia in the three treatments varied between 35-51 g"1 soil much below the threshold associated with Verticillium wilt on lettuce. However, the incidence of crown rot was significantly higher in the three fumigation treatments relative to the nonfumigated plots. In a field that had very high levels of Verticillium wilt in 2002, we began long-term studies to determine the efficacy of fumigation with MBC to reduce microsclerotia of V. dahliae at different soil depths. Another implicit objective of this study was to determine the effects of various cropping patterns on the microsclerotia at different soil depths. Following fumigation and strawberry planting, soil at four sites was sampled in 2-inch increments to a depth of 24 inches. At all sites, the number of microsclerotia was high near the surface and progressively declined. The incidence of wilt on strawberries was low. To determine the minimum number of infested seed required to infest uninfested soil with V. dahliae, 0, 5, 15, 60 and 100% infested plants were planted in replicated 1- x 1-m2 microplots. Unfortunately, S. minor induced lettuce drop despite fumigation prevented tangible data from being collected. We are currently developing a number of protocols to screen lettuce cultivars and Pis for resistance to Verticillium wilt. Test tube assays have proven successful in identifying resistance in genotypes and discriminating V. dahliae isolates. We also evaluated 22 cultivars and PI lines along with breeding lines in a commercial field. The screen was highly successful and confirmed the resistance in a number of previously identified cultivars and PI lines. Abstract Project title: Fusarium wilt of lettuce: management through detection, avoidance and disease resistance Principal investigator: Thomas R. Gordon Department of Plant Pathology University of California Davis, CA 95616 Layman's summary : Fusarium wilt of lettuce is caused by Fusarium oxysporum f. sp. lactucae. This fungus resides in the soil and infects plant roots. On susceptible lettuce plants, extensive damage to the root occurs, resulting in stunting and possibly death of the affected plant. Management of this disease problem requires practices that minimize levels of the pathogen in soil and the use of lettuce cultivars with resistance to the disease. Population levels of the pathogen in soil can usually be reduced by rotation to non-susceptible crops. With this in mind, we tested broccoli, cauliflower, celery and spinach to determine how extensively they were colonized by the lettuce wilt pathogen. The results showed that all these supported growth of the pathogen on their roots. The levels of colonization were not greatly different from what was observed on the lettuce cultivar 'Salinas'. Thus it will be possible for the pathogen to sustain itself in the absence of a susceptible lettuce crop. However, the inoculum levels used in our tests were relatively high, and it is possible that subtle differences between crops may be revealed at lower inoculum levels. Eighty cultivars of lettuce were tested for susceptibility to Fusarium wilt by inoculating seedlings with a spore suspension of the pathogen. For each cultivar, separate tests were conducted with two different isolates at two different inoculum levels. Ten plants were inoculated with each isolate at each inoculum level. The results indicated that most cultivars were highly susceptible to Fusarium wilt. However, several cultivars showed some level of resistance, including leaf, romaine and iceberg types. In general, romaine cultivars were the most resistant. Further tests will be required to confirm these cultivars are resistant under field conditions. Over 100 isolates of Fusarium oxysporum were tested on a known susceptible cultivar to determine if there were differences in virulence. Most isolates appeared very similar in these tests, but a small group had a significantly lower level of resistance than the majority of pathogen strains. Research Abstract to the California Lettuce Research Board for the period April 1, 2003 to March 31,2004 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 management of soil pests is a key issue of increasing concern for many growers. The key soil arthropods of concern in lettuce are springtails, bulb mites and garden centipedes (symphylans). The soil pests are especially difficult to research due to the difficulty in both sampling and predicting to occurrence of these pests. While some chemical alternatives may be available for soil pests, the data to support their registration is lacking. Sampling for symphylans is difficult and visible detection of any symphylans often indicates a population large enough to cause economic damage. We have been utilizing a sampling plan modified from one developed by researchers at Oregon State and it has proven very efficient and relatively easy. It involves using thick slices of raw potato placed on the soil surface at the level at which moisture is clearly visible in the soil. Then cover the bait with a solid plastic dome to protect the bait from drying out while it is allowed to attract symphylans. The bait is left in place for 24 to 36 hours then when the cap is removed, the symphylans can be counted when the potato slice is picked up, both on the potato and on the soil surface. Count the soil surface first as the symphylans there will quickly hide. Lettuce aphid continues to be a key insect concern for some lettuce growers in coastal production areas. Pest pressure continues to be highly variable both throughout the season and geographically. The reason for this variation is unknown, and while interesting, unlikely to affect management decisions. Chemical control continues to be effective for conventional growers. Organic growers have variable success with their control programs, but many have found hoverfly larvae to be effective at controlling lettuce aphid populations. Tests to look for changes in susceptibility of lettuce aphid populations to Provado still show no clear signs that this insect is becoming less susceptible to this product. Tests with the foxglove aphid, which became a problem in some lettuce fields last season, did show reduced mortality at some of the lower concentrations of Provado tested. This may be due to the fact that this is a larger aphid than lettuce aphid, to which it was compared, and the lower dose was simply too little material per unit of body weight to effect control. Research Abstract to the California Lettuce Research Board's Research Program April 1, 2003 to March 31, 2004 TITLE: Insect Management for Low Desert Lettuce PRINCIPAL INVESTIGATOR: Eric T. Natwick Farm Advisor - Entomology University of California Cooperative Extension - Imperial County 1050 East Holton Road Holtville, CA 92250 SUMMARY: Registered and experimental insecticides were evaluated for their efficacy against worm pests in lettuce in Imperial Valley, CA. Beet armyworm, Spodoptera exigua, and cabbage looper, Trichopulsia ni, are the two primary worm pests of lettuce in southern California. The continued reliance on a limited arsenal of insecticides to control these pests could lead to insecticide resistance problems. Beet armyworm resistance to carbamate insecticides was documented in the Imperial Valley by Dr. David Kerns, Yuma Agricultural Center in the 1990's. Several new insecticides aimed at beet armyworm and cabbage looper control, Intrepid 2 SC, Entrust 80 W (Spinosad), V-10132 2.58 EC (in the can mixture of Pyridalyl and Esfenvalerate), Pyridalyl (S-1812 35 WP and 4 EC), Proaxis 0.497 CS (gama-cyhalothrin) and resolved zeta-cypermethrin (F0570 0.8 EW, Mustang Max) were compared to industry standards, Avaunt 30 WG, Success 2 SC, Warrior 1 CS, and Asana XL. Several new insecticides, Entrust 80 W, Intrepid 2 SC, Pyridalyl, and V-10132 2.58 EC, were found to be comparable to the industry standards, Success 2 SC and Avaunt 30 WG, for beet armyworm control in lettuce. Research results showed that all insecticide treatments, except S-1812 4 EC, were effective against cabbage loopers. Registered and experimental insecticides were evaluated for their efficacy at controlling thrips in Romaine leaf lettuce in Imperial Valley, CA. Bean thrips, Caliothrips phaseoli, and western flower thrips, Frankliniella occidentalis, are the two primary thrips pests of lettuce in southern California. Insecticide resistance in western flower thrips has been well documented worldwide. Bean thrips has only recently become a common pest on lettuce in the Imperial Valley, but the continued reliance of a limited arsenal of insecticides to control this pest could lead to insecticide resistance problems. Insecticides included in the experiment for thrips control were Platinum 2 SC, Warrior 1 CS, Admire 2F, Assail 70 WP, Lannate LV, and Success. The best treatments for thrips control were Platinum 2 SC in-furrow at planting followed by foliar treatments with Warrior 1 CS, Warrior 1 CS alone, Lannate LV tank mixed with Warrior 1 CS, Success 2F and Assail 70 WP. The aphid experiment was not completed due to a lack of adequate numbers of aphids. CALIFORNIA LETTUCE RESEARCH BOARD April 1, 2003 - March 31, 2004 WEED MANAGEMENT SYSTEMS FOR LETTUCE Steven A. Fennimore Dept. of Vegetable Crops and Weed Science University of California, Davis Salinas, CA Jose Aguiar University of California Cooperative Extension Riverside County ,Indio, CA SUMMARY : Field and lab studies were undertaken to evaluate four aspects of lettuce weed management, hi the first series, field studies were conducted to evaluate the safety of herbicides on lettuce germplasm from the University of Idaho. The conventionally bred Idaho germplasm was reported to be tolerant to sulfonylurea herbicides. Preemergence and postemergence applications of Pursuit and Raptor as well as preemergence applications of Maverick and Upbeet were found to be safe on the Idaho germplasm. In a second experiment, we evaluated treatments to improve nutsedge control in fallow ground prior to lettuce planting. Nutsedge control was better where lettuce was planted in plots previously treated with sequential applications of Telone C35 followed by Eptam, compared to plots treated with Eptam alone, hi our third experiment series, we examined whether high magnesium in irrigation water might contribute to poor weed control from Kerb. Under certain circumstances, such as high levels of irrigation, Kerb herbicide can be washed from the upper soil layer resulting in poor weed control. We did not detect large effects of magnesium on Kerb soil mobility, hi the fourth trial series, Treflan applied post plant preemergence was evaluated as a potential lettuce herbicide. Treflan at 1 pint per acre was as safe to lettuce as Kerb, but at 2 pints per acre Treflan reduced lettuce stand. RESEARCH ABSTRACT CALIFORNIA LETTUCE RESEARCH BOARD For the period (April 1, 2003-March 31, 2004) PROJECT TITLE: PROJECT INVESTIGATORS: COOPERATING PERSONNEL: INFLUENCE OF VARYING NITROGEN AND PHOSPHORUS FERTILIZATION ON POSTHARVEST QUALITY OF LETTUCE Husein Ajwa Department of Vegetable Crops University of California, Davis M. Murshidul Hoque Department of Vegetable Crops University of California, Davis Susanne Klose Department of Vegetable Crops University of California, Davis Richard Smith UC Cooperative Extension Monterey County, California Michael Cahn UC Cooperative Extension Monterey County, California SUMMARY: The objective of the study was to evaluate changes in postharvest quality paramenters and nutritional composition of romaine (cul. Green Tower) and iceberg (cul. Sharp Shooter) lettuce in response to N, P and K fertilization. Sixteen treatment combinations of fertilizer were selected. N was applied at 0, 112, 225, and 337 kg/ha as ammonium nitrate; P was applied at 0, 112, and 225 kg/ha as super phosphate; and K was applied at 0 and 112 kg/ha as muriate of potash. Postharvest visual parameters (color, wilting, turgidity, glossiness, decay, brittleness, fringe burn, and salt burn) of lettuce stored in a cooler at 1° C were evaluated over a three week period. Fresh weight increased with increasing N fertilizer application rates, but was not affected by P or K rates. Our study suggests that lettuce can be stored in coolers up to 14 days without reduction in quality, regardless of fertilizer application rates. Decay and wilting, were the major parameters affecting lettuce quality if storage extends over 3 weeks. The best overall postharvest quality was found in medium N (200 lbs/ac) and P (100 lbs/ac) fertilizer application rates. Increasing the N and P rates increased glucose content in lettuce and decreased the shelf life. No significant correlations were found between soil fertilizer application rates and nutritional content of lettuce (lutein, beta-carotene, chlorophyll a, chlorophyll b, and vitamin C). CALIFORNIA LETTUCE RESEARCH BOARD April 1, 2003 - March 31, 2004 Title: Mustard Cover Crops to Optimize Crop Rotations for Lettuce Production Project Investigators: Richard Smith and Steve Koike, UCCE, Monterey County Krishna Subbarao and Steve Fennimore, University of California SUMMARY : Effective rotations are an essential part of lettuce production. Unfortunately, given economic pressures such as high land rents and lower returns for rotational crops, effective rotations are not always possible. As a result, Sclerotinia minor, lettuce drop, is the key soilborne disease in the Salinas Valley. Mustard cover crops {Brassica and Sinapis spp.) have been researched for a number of years in other parts of the world as a means of suppressing soilborne diseases and weeds. The beneficial effect of mustard cover crops on soilborne pests may be due to toxic chemicals that they release upon incorporation into the soil or due to soil microbiological effects. These studies were undertaken to determine if mustard cover crops are suppressive to lettuce drop and weeds in lettuce production. To evaluate the impact of mustard cover crops we established short-term and long-term trials. Three short-term studies were conducted with cooperating growers in which the mustard cover crop blend Caliente 119 (S. alba and B. juncea) was grown in comparison with Merced Rye or a no cover crop control. Lettuce was planted within 4-5 weeks following mustard cover crop incorporation. In addition, a long-term rotational plot was also established in which a set of fall grown cover crops were grown and followed by lettuce planted in the spring; the results contained in this report are of the first year of that study. Lettuce Head Drop Studies: Short-term plots: At one of the sites we observed significantly lower levels of lettuce drop infection in the mustard cover cropped plots. However, the levels of infection at each site were low. Long-term plot: There were moderate levels of sclerotia in the soil of the trial site in the pre-cover crop samples. No reductions in the levels of soil sclerotia were observed following incorporation of the cover crops. On the first of the two evaluation dates, there was significantly less lettuce drop infection in the Merced rye treatment, but at the second evaluation (at harvest), there was no difference among the treatments. Weed Studies: Short-term plots: There were slight but significant reductions in the number of weeds at each of the three short term plots. Long-term plot: We discovered that we have low weed densities at this site and may not be able to conduct detailed evaluations of the soil seedbank. Mustard cover crops did not reduce the number of weeds present at thinning over the no cover crop control or Merced Rye. All cover crops improved the yield of the lettuce at this site over the no cover crop control. California Lettuce Research Board Annual Report 2003 - 2004 Salinity Effects on Quality and Yield of Drip Irrigated Lettuce Michael Cahn Husein Ajwa Irrigation and Water Resources Advisor Cool Season Vegetable Specialist University California, Cooperative Extension Vegetable Crops Dept. 1432 Abbott St. University of California Salinas, CA 93901 1636 East Alisal Salinas, CA 93905 SUMMARY : Published thresholds of salinity tolerance for lettuce may not be reliable for the weather regime, water quality, cultivation practices, and varieties of the central coast. Because lettuce growers in the Salinas and the Pajaro Valleys face multiple challenges in managing salinity, including sea water intrusion, salinity TMDLs, and increased use of reclaimed water, there is a pressing need to establish salinity thresholds for currently grown lettuce varieties. We conducted a drip irrigated field trial to measure the effect of varying levels of salinity and sodium adsorption ratios (SAR) on the quality and yield of head lettuce at the USDA Spence Research Field Station during the 2003 season. The trial followed a split-plot, randomized complete block design with 4 replications, where variety (Salinas and Sniper) was the main plot and salinity was the sub-plot.. The salinity levels of the irrigation water treatments, measured by the electrical conductivity, ranged from 0.6 to 8.0 dS/m and the SAR levels ranged from 3 to 10. Salinity treatments had similar effects on both head lettuce varieties, though carton yields for 24-size heads were greater for Salinas than Sniper. Although salt toxicity symptoms were not present on margins of leaves, the results of the field trial showed that increased salinity in the irrigation water significantly reduced carton yield of 24-sized heads, total biomass, and head size for both varieties of lettuce. Likewise, salinity levels, measured in the top 6 inches of the soil 2 weeks before harvest, were correlated with a decrease in carton yield of 24-size heads and an increase in carton yield of 30-sized heads. Except for head weight, SAR level of the irrigation water d id n ot i nteract w ith t he e ffect oft otal s alinity o n 1 ettuce p roduction. U sing regression analysis, we determined that a 10% yield loss of 24-size heads occurred when the salinity level of water was greater than 1.8 dS/m or the salinity level in the upper 6-inches of the soil was above 2.7 dS/m. Levels of sodium and chloride in the wrapper leaves were found to be correlated to SAR and EC levels of the top 6-inches of the soil, but calcium in the wrapper leaves was not correlated to soil salinity. PCALIFORNIA LETTUCE RESEARCH BOARD APRIL 1, 2003-MARCH 31, 2004 PROJECT TITLE: MEASURING AND ESTABLISHING EXPOSURE POTENTIAL OF PERCHLORATE IN LETTUCE PRINCIPAL INVESTIGATORS: Robert I. Krieger, Ph.D. Personal Chemical Exposure Program Department of Entomology, University of California, Riverside Riverside, CA 92521 Charles A. Sanchez, Ph. D. Professor of Soil, Water, and Environmental Science Director-Yuma Agricultural Center 6425 W. 8th Street Yuma, Arizona 85364 ABSTRACT : Determine the occurrence and possible biologic significance of perchlorate in iceberg (crisphead) and leaf (romaine, butterhead, red leaf, and green leaf) lettuce in the food supply based upon residue analysis, and validated literature or certified reports. Potential human exposure from these sources was estimated using water standards suggested by the U. S. Environmental Protection Agency and the Office of Health Hazard Assessment, California Environmental Protection Agency. All fields selected for sampling were irrigated with water from the Colorado River, which is known to contain trace amounts of perchlorate. Iceberg and romaine lettuce samples were collected from three different production regions (Yuma, Bard, and Imperial Valley for iceberg and Yuma, Bard, and Coachella Valley for romaine) in mid-December and in early-February. An extraction procedure for plant material developed by the USEPA research laboratory was used with minor modifications. The samples were analyzed by ion chromatography. The method detection limit was 0.2 ug/L and the minimum reporting level was 1.5 ug/L depending on matrix. Spiked additions were used to guard against matrix errors. Trace perchlorate residues in lettuce result from low levels of perchlorate in irrigation water. Naked, wrapped, and bulk iceberg lettuce contained mean levels of 15, 9 and 8 ug/kg, respectively. The mean perchlorate levels for romaine were naked 28, bulk 13 and hearts 11 ug/kg respectively. The mean perchlorate levels for green leaf, red leaf, and butterhead lettuce were 33, 28 and 29 ug/kg, respectively. The tiny amounts of perchlorate potentially associated with human consumption are less than hypothetical exposures for water derived from water action levels of 1 ppb suggested by USEPA and of 6 ppb proposed by the state of California. Potential perchlorate exposures from lettuce are negligible relative to harmful amounts. California Lettuce Research Board Final Report Cumulative Research Report 2001 and 2003 ABSTRACT Project Title: Assessment of Indicator Bacteria from Reservoir Irrigation Water and on Lettuce Funding Year: April 1, 2001 to March 31, 2004 Project Leader: Trevor Suslow, UC Davis Dept. Vegetable Crops. Research Collaborator: Steve Koike; UCCE Monterey County Research Associate Staff: Misty Johnstone, Lorena Fernandez, and Rachel Maximo; UCD Veg Crops Katherine Kammeijer, UCCE Monterey County Summary of Accomplishments: Current methods to monitor the contamination of horticultural crops, by enteric pathogens, during preharvest, harvest and postharvest operations for fresh produce lack the required sensitivity and specificity to address food safety concerns and facilitate the optimal development of practical Recommended Management Practices. For this reason, various microbial indicators are monitored with the expectation that their presence is predictive of recent fecal contamination and the elevated potential for human enteric pathogens to be present. The application of contaminated water during irrigation has the uncharacterized potential to result in broad distribution and, at least temporary, establishment of undesirable levels of indicators of fecal contamination or the documented presence of a variety of known pathogens. The purpose of this on-going project is to develop baseline documentation of the regional presence and persistence of E. coli in on-farm reservoirs intended for irrigation of head lettuce and/or leaf lettuce, as an indicator of potential direct or indirect fecal contamination. This data has already proven highly instructional in defining future research directions in microbial food safety, environmental sources of potential contaminant indicators, and the development of Recommended Management Practices. This data and related research is helping to define parameters for both design and implementation of Good Agricultural Practices and future research needs to improve microbial food safety programs. During the period of this project the average recovery of nonpathogenic indicator E. coli from on-farm reservoir water used for irrigation of lettuce and other regional crops was typically low and variable. Single collection date populations were often below the limit of detection, or less than 1 detectable colony in 100 ml of sampled water. The maximum detected single collection date value was log 2.48 CFU/lOOml or 302 detectable colonies in a 100 ml water sample. The highest mean (average) and median (mid-point) values for a single reservoir were log 1.49 and 1.59 CFU/lOOml, respectively, or 31 and 39 detectable colonies/100 ml. The mean and median values across all reservoirs varied by only a small margin, which reflects the relative low level of fluctuation (data range) among samples and sample dates over the course of the project. A strong, general trend of lower nonpathogenic E. coli and thermotolerant coliforms levels were observed for sprinkler samples compared to the corresponding reservoir samples for a given date. In general, for plant samples, there were a greater number of samples below the limit of detection (LOD) for Romaine leaves than plants with positive detection of E. coli. Typically only 1-2 plants exhibited relatively high presumptive E. coli counts, > 300 CFU/25g. Standard microbial criteria for irrigation water quality do not currently exist in the U.S., although various guidance data is available and utilized. Rigorous criteria are established for treated reclaimed wastewater used for irrigation of edible crops but are not directly relevant or generally applicable to stored groundwater, as monitored in this survey. For the majority of locations and dates, the levels of E. coli observed in over 250 reservoir samples would not be considered hazardous for human contact. There were a very limited number of exceptions, but other factors appear to limit persistence on plants. In addition, the composite data strongly suggest that reservoir irrigation water, in the Salinas Valley, may not be the primary source of E. coli recovered from lettuce leave samples. Other sources of infrequent but comparatively high populations of indicator E. coli on approximately 10% of individual Romaine plants should be further investigated. RESEARCH ABSTRACT TO THE CALIFORNIA LETTUCE RESEARCH BOARD FOR THE PERIOD APRIL 1, 2003 TO MARCH 31, 2004 Project Title: Nutrient, Phytochemical, ORAC Analysis of 5 Lettuces: Butterhead, Green Leaf, Red Leaf, Iceberg, and Romaine Principal Investigators: Gary Beecher Research Chemist-Retired Food Composition Laboratory Beltsville Human Nutrition Research Center USDA-ARS, Beltsville, MD 20705 gbeecher@earthlink.net Joanne M. Holden Research Leader Nutrient Data Laboratory Beltsville Human Nutrition Research Center USDA-ARS, Beltsville, MD 20705 holdenj^ba.ars.usda.gov Ronald L. Prior Research Chemist Arkansas Children's Nutrition Center Little Rock, AR 72202 priorronald@uams.edu Summary : The analysis of traditional nutrients, phytochemicals and ORAC values in lettuce is important for,the promotion of lettuce as part of a healthful diet, support of research to determine the impact of diet on health, and development of Dietary Reference Intakes for carotenoids and flavonoids. As part of a study conducted by Agriculture Research Service of USD A that included 59 vegetables, fruits and nuts, samples of butterhead, green leaf, iceberg, red leaf, and romaine were taken in two seasonal passes from supermarkets across the United States. The nationwide sampling scheme was designed to ensure that data represent, to the greatest extent possible, what is eaten by consumers in the continental United States. Analyses were done for the full panel of nutrients used in USDA's Nutrient Database for Standard Reference, 8 carotenoids, 17 flavonoids and ORAC. Nutrient, carotenoid, and flavonoid data were reported in the California Lettuce Research Board Annual Report for April 1, 2001 to March 31, 2002. The ORAC analysis is reported in this annual report along with adjustments to the 2001-2002 phytochemical data based on the analysis of samples not contained in the earlier data. |