DEVELOPMENT OF LETTUCE CULTIVARS ADAPTED TO FLORIDA'S SUBTROPICAL CLIMATE CONDITIONS AND ORGANIC SOILS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0226303
• Project Start Date: Jul 11, 2011
• Project End Date: Oct 1, 2016
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611

Performing Department
Everglades Research and Education Center, Belle Glade

Non Technical Summary
This project aims at development of lettuce cultivars adapted to Florida's sub-tropical climate conditions and organic soils. The objectives include high yield, big heads with dark green thick leaves, compactness, long shelf life, and resistance to major diseases/insects. Traditional breeding approaches and molecular technology will be used for improvement of lettuce. It is expected that lettuce cultivars with high yield, desirable horticultural characteristics, resistance/tolerance to disease(s)/insect(s)will be developed and released. With development and release of new cultivars, the sustainable lettuce production in Florida will be secured. In addition, refereed journal papers, conference presentations, and other technical papers will be published.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
201	1430	1080	100%

Knowledge Area
201 - Plant Genome, Genetics, and Genetic Mechanisms;

Subject Of Investigation
1430 - Greens and leafy vegetables;

Field Of Science
1080 - Genetics;

Keywords

plant breeding

yield

horticultural traits

resistance

disease

insect

lettuce cultivars

conventional methods

molecular technology

Goals / Objectives
The goal of lettuce breeding at the University of Florida is to develop cultivars well-adapted to Florida's sub-tropical climate conditions and organic soils. The breeding objectives include high yield, big heads with dark green thick leaves, compactness, long shelf life, and resistance to major diseases/insects. One to two lettuce cultivars with high yield, desirable horticultural characteristics, resistance/tolerance to disease(s)/insect(s)will be released. Refereed journal papers, conference presentations, and other technical papers will be published.

Project Methods
The UF lettuce breeding program currently has approximately 350 germplasm lines and cultivated varieties. New germplasm will be collected from public and private sectors to increase the genetic diversity. The germplasm lines will be evaluated for yield, horticultural traits, and other traits like disease resistance. We are particularly interested in resistance to bacterial leaf spot because this disease is a serious threat to the lettuce industry in Florida. Each year, approximately 100 crosses will be made between current cultivars, or between improved germplasm lines, or between cultivars and improved germplasm lines. The parents used for crosses should have high yield potential or disease/insect resistance or other desirable traits such as good nutrition. The crosses will be progressed to F2s from which single plant selections will be made. Then in each subsequent generation single plant selection continues until the progenies become stable and uniform in traits. The stable lines will be tested against the standard cultivars for yield performance and horticultural traits as well as resistance to diseases (such as downy mildew and bacterial leaf spot) using randomized complete block design with replications in a field at EREC. The lines will also be evaluated for reaction to corky root rot in the EREC corky root rot nursery. Those that have high yield potentials, good horticultural traits, and disease/pest resistance will be further tested in variety trials which will be conducted at two-three locations for two-three years using randomized complete block design. Since the main lettuce production is in the Everglades Agricultural Area, two locations will be chosen from this area. The best lines will be released as new cultivars following the IFAS variety release procedures. Lettuce lines that are identified to be resistant to diseases such as bacterial leaf spot and resistant to insects will be crossed with susceptible lines for development of segregating populations such as F2:3 families. These will be used to delineate resistance genes and to identify markers closely linked to the genes. Molecular markers will be developed for gene (QTL-quantitative trait loci) mapping and marker-assisted selection. There are only a limited number of markers publicly available in lettuce. We will test the RAPD and SNP markers to identify those that are useful in lettuce. DNA will be isolated from a number of lettuce varieties. PCR amplification will be performed in the varieties with the RAPD primers. The polymorphic markers are chosen for gene mapping and the closely linked markers will be used for marker-assisted selection in the breeding program. The new cultivars should be beneficial to Florida lettuce producers as well as consumers. The results will be published in refereed journals, national and international conferences, or as technical papers, which will provide new infomation to scientific societies and communities with relation to lettuce production.

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:Growers, community in plant science, and the general public Changes/Problems:The project is going as planned. There were no major problems. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?The results were presented at national conference, local meetings, field trips, face-to-face talks, and handouts. In addition, anyone interested in this area has access to my publications in journals, UF/IFAS EDIS website, and conference websites. What do you plan to do during the next reporting period to accomplish the goals?In 2016, I will continue my research in the following areas: 1) development of cultivars suitable for commercial use in lettuce production; 2) Selection of lettuce lines with resistance to bacterial leaf spot; and 3) development of molecular markers useful for marker-assisted breeding for improvement of lettuce for resistance to BLS.

Impacts
What was accomplished under these goals? A part of the program is to improve lettuce for resistance to bacterial leaf spot. Bacterial leaf spot (BLS), caused by the pathogen Xanthomonas campestris pv. vitians, is a devastating disease of lettuce in the world and is the most damaging disease of lettuce in Florida. This disease is highly unpredictable about where and when an outbreak will occur during the lettuce growing season. There are no chemicals for control of the disease when it is epidemic in the field. Use of host-plant resistance is the only ultimate solution to the problem. We have identified one source of good resistance and several sources of moderate resistance. A segregating population derived from a cross between the bacterial leaf spot (BLS) resistant line and the susceptible romaine lettuce variety `Valmaine' was used for inheritance analysis of the resistance and for determination of the resistance gene(s). About 230 F2 seeds were planted and 187 germinated to form a F2 population. The F2 population was screened for BLS-resistant plants with bacterium Xanthomonas campestris pv. vitians (Xcv). Of 187 F2 plants inoculated, 142 were resistant and 45 were susceptible. Segregations among the 187 F2 plants conformed to 3(resistance) : 1 (susceptibility) ratios (χ2 = 0.086, P = 0.769), indicating that a single dominant gene controls BLS resistance in the resistant line. The individual F2 plants were then selfed to produce F3 families. A total of 162 F3 families were generated. The segregation ratio of reaction to disease by seedling inoculation with Xcv L7 strain in the F3 families was showed to be 32 homozygous resistant: 82 heterozygous: 48 homozygous susceptible, fitting to 1:2:1 (n=162, χ2=3.19, p=0.20), a confirmation of a single dominance gene inheritance. The resistant gene was named Xcvr.? Genomic DNA was extracted from leaf tissues collected from 124 randomly selected F2 plants for molecular mapping of the resistance gene. The F2 population was genotyped with more than 6,000 AFLP, 12 SSR, and 2 CAPS markers. The resistant gene Xcvr was mapped to linkage group 2 (LG2) with the closest molecular marker being12.9 cM from the gene. An association analysis was also conducted to identify molecular markers that are associated with resistance using additional 179 germplasm lines and 384 single nucleotide polymorphism (SNP) markers. We found one marker (QGB19C20.yg-1-OP5) to be associated with disease severity. Two additional SNP markers (Contig15389-1-OP1 and Contig6039-19-OP1) were associated with the resistance in the germplasm line that has been used for development of the segregating population described above. Combining the results of inheritance analysis with those of linkage mapping and association analysis, we found that the chromosome 2 carries a single dominant gene (i.e. Xcvr) for high resistance in the germplasm line with high level of resistance. Due to the nature of a single gene inheritance in the high resistant line, this resistance should be transferable from the resistant line to adapted cultivars for commercial use in lettuce production in Florida. In 2015, we made another 20 crosses between the BLS resistant line and different adapted cultivars and breeding lines. In spring 2015, 35 F3 lines with resistance and romaine performance were selected, indicating that the resistance has been successfully incorporated into romaine letter which is predominate lettuce type grown and consumed in the U.S. Seeds (F4 generation) produced from the 35 F3 lines were planted in fall 2015 in a local lettuce grower's field for observation of yield potential and horticultural performance in these F4 lines and also for continuing plant selection for development of commercial cultivars with resistance. In addition, 10 of the 35 F4 lines were compared with 'Manatee', a major commercial variety used in Florida lettuce production, for yield and other characteristics in fertilizer experiments in fall 2015. Some of the F4 lines had yield potentials higher than or similar to that of 'Manatee'. These results suggest that the BLS resistance and high yield can be combined in a variety through breeding and plant selection. Another part of the lettuce breeding program is to understand genetics of the resistance to insects in 'Valmaine' lettuce. The serpentine leafminer (Liriomyza trifolii Burgess) is an economically important pest of lettuce in the US. Historically, lettuce growers in Florida have relied on insecticides to control the pest. However, L. trifolii developed resistance to frequently used insecticides within a few years. Host plant resistance (HPR) is an ecologically sound and economically viable strategy to control insect pests. The identification of Quantitative Trait Loci (QTL) associated with L. trifolii resistance-related traits was the primary goal of this project. The study was conducted on a population of 125 F2 individuals from a cross between 'Valmaine' (resistant) and 'Okeechobee' (susceptible) romaine cultivars. Progeny testing exhibited continuous variation in damage scores among the corresponding F3 families. A total of 251 SNP, 86 AFLP, and 6 SSR markers were used to genotype the F2 individuals. QTL mapping revealed two major novel QTLs on LG1 and LG2 for damage score, which together explained over 85% of total phenotypic variation. It detected one major novel QTL on LG1 for survival of adult L. trifolii, which explained 39% of total phenotypic variation. The QTLs for both traits on LG1 were flanked by SNP188 and SNP187. Identification of resistant QTL will facilitate development of resistant cultivars suitable for commercial use to protect lettuce crop from damage by serpentine leafminer. The cultivar development effort started from scratch with no germplasm five years ago. In 2015, the highest generation was F6. A total of 86 breeding lines (64 F6, 21 F5, and 1 F4 lines) were compared with the commercial cultivars 'Manatee' and 'Okeechobee' for yield and horticultural traits. Several lines showed promising to be released as cultivars for lettuce industry to use in commercial production in near future.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Wang, Yunwen, Huangjun Lu, Richard Raid, Gregg Nuessly, and Georgy Faroutine. 2015. Diverse responses of lettuce cultivars and germplasm lines to infections of three isolates of Xanthomonas campestris pv. vitians. HortScience 50:650-655.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Lu, Huangjun. 2015. Construction of a linkage map with AFLPs to identify genes for bacterial leaf spot resistance in lettuce (Lactuca sativa L.) Plant & Animal Genome XXIII, The International Conference on the Status of Plant & Animal Genome Research (Jan 2015), San Diego, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Lu, Huangjun. 2015. Discovery of the Bacterial Leaf Sport Resistant Gene and Its Impact on Floridas Lettuce Production. Florida Lettuce Advisory Committee Meeting (Mar 2015). Belle Glade, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Wang, Yunwen, and Huangjun Lu. 2015. Mapping of the bacterial leaf spot resistance gene in lettuce PI358001-1. 2015 American Society for Horticultural Science Conference Aug 2.15). New Orleans, LA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Lu, Huangjun, Ramkrishna Kandel, Gregg Nuessly, Heather McAuslane, and J. Hu. 2015. A dominant gene for the banded cucumber beetle resistance in lettuce. 2015 American Society for Horticultural Science Conference. New Orleans, LA. Aug. 4-7, 2015.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Kandel, Ramkrishna, Huangjun Lu, Gregg Nuessly, and Heather McAuslane. 2015. Inheritance and molecular mapping of serpentine leafminer (Liriomyza trifolii Burgess) resistance in romaine lettuce (Lectuca sativa L.) Valmiane. 2015 American Society for Horticultural Science Conference. New Orleans, LA. Aug. 4-7, 2015.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Lu, Huangjun, Ramkrishna Kandel, Gregg Nuessly, Heather McAuslane, and J. Hu. 2015. Molecular mapping of the banded cucumber beetle resistance in romaine lettuce Valmaine. Plant & Animal Genome XXIII, The International Conference on the Status of Plant & Animal Genome Research, San Diego, CA. Jan. 10-14, 2015.

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Growers, community in plant science, and the general public Changes/Problems: The project is going as planned. There were no major problems. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? The results were presented at national conferences, local meetings, field trips, face-to-face talks, and handouts. In addition, anyone interested in this area has access to my publications in journals, UF/IFAS EDIS website, and conference websites. What do you plan to do during the next reporting period to accomplish the goals? In 2015, I will continue my research in the following areas: 1) molecular mapping of the Bcb1 gene and investigatinng the relationships between beetle resistance and serpentine leafminer resistance in lettuce cultivar 'Valmaine'; 2) Genetic study of the bacterial leaf spot resistance and development of resistant varieties; and 3) development of cultivars suitalbe for commerical use in Florida lettuce production.

Impacts
What was accomplished under these goals? A part of the program is screening lettuce germplasm for resistance to bacterial leaf spot. Bacterial leaf spot (BLS), caused by the pathogen Xanthomonas campestris pv. vitians, is a devastating disease of lettuce in the world and is the most damaging disease of lettuce in Florida. This disease is highly unpredictable about where and when an outbreak will occur during the lettuce growing season. There are no chemicals for control of the disease when it is epidemic in the field. Use of host-plant resistance is the only ultimate solution to the problem. We have identified one source of good resistance and several sources of moderate resistance. A segregating population derived from a cross between the bacterial leaf spot (BLS) resistant line and the susceptible romaine lettuce variety ‘Valmaine’ was used for inheritance analysis of the resistance and for determination of the resistance gene(s). The population was screened for BLS-resistant plants with bacterium Xanthomonas campestris pv. vitians (Xcv). Of 187 F2 plants inoculated, 142 were resistant and 45 were susceptible. Segregations among the 187 F2 plants conformed to 3(resistance) : 1 (susceptibility) ratios (χ2 = 0.086, P = 0.769), indicating that a single dominant gene controls BLS resistance in the resistant line. The resistant gene is designated as Bls1, which means the first BLS resistant gene identified in lettuce. An association analysis was conducted to determine chromosomal locations for BLS resistance and to identify molecular markers that are associated with resistance using 179 germplasm lines and 384 single nucleotide polymorphism (SNP) markers. We found one marker (QGB19C20.yg-1-OP5) to be associated with disease severity. Two additional SNP markers (Contig15389-1-OP1 and Contig6039-19-OP1) were associated with the resistance in the germplasm line that has been used for development of the segregating population described above. The marker QGB19C20.yg-1-OP5 is located on chromosome 2, while both of the markers Contig15389-1-OP1 and Contig6039-19-OP1are on chromosome 4. The interpretations of these discoveries are that a region of chromosome 2 is responsible for moderate resistance existing in several germplasm lines with moderate resistance, while chromosome 4 contains a gene for high resistance in the line with high level of resistance. Combining the result of inheritance analysis with that of association analysis, we found that the chromosome 4 carries a single dominant gene (i.e. Bls1) for high resistance in the germplasm line with high level of resistance. Due to the nature of a single gene inheritance in the high resistant line, this resistance should be transferable from the resistant line to adapted cultivars for commercial use in lettuce production in Florida. In 2014, 20 crosses were made between the BLS resistant line and different adapted cultivars and breeding lines. These crosses will be used for plant selection for development of BLS resistant cultivars. The second part of the lettuce breeding program is to understand genetics of the resistance to insects in ‘Valmaine’ lettuce. Banded cucumber beetle (BCB) is one of insect pests that can cause significant damage to lettuce and result in economic losses to growers. The romaine lettuce ‘Valmaine’ is known to have a high level of resistance to the insect. A lettuce population segregating for resistance was developed from a cross between ‘Valmaine’ and ‘Okeechobee’. ‘Okeechobee’ is susceptible to banded cucumber beetle. The derived F1 plants were infested with banded cucumber beetles in the laboratory and results showed that they performed similarly to ‘Valmaine’ in resistance to the insect. The segregation ratio was 3 (resistance) : 1 (susceptibility) in F2 population and 1(homozygous resistance) : 2(heterozygous) : 1(homozygous susceptibility) among F3 families, indicating that the banded cucumber beetle is controlled by a single dominant gene. This gene was designated as Bcb1. Identification of the Bcb1 gene will facilitate development of resistant cultivars suitable for commercial use to protect lettuce crop from damage by banded cucumber beetles. Besides, ‘Valmaine’ is also resistant to serpentine leafminer, cabbage looper, and beet armyworm. I am conducting experiments to determine if there are genetic relationships between beetle resistance and resistance to other insects. In 2014, 58 crosses were made to develop new cultivars that are suitable for commercial production in Florida. To date, the breeding program has generated 263 F2 populations, 730 F3, 223 F4, and 84 F5 lines. Selection will continue in 2015 and F6 lines will be used for seed increase for variety trials in the following years. In February 2014, a BLS outbreak was reported in a 36-acre field in which an iceberg variety and a romaine variety were grown. When the disease outbreak occurred, the iceberg cultivar had matured and was thus harvested, but the romaine lettuce was not at the maturity stage and was disked to destroy the pathogen inoculum that could further spread to other lettuce fields. In addition, there were more than 100 acres of field nearby left without planting any lettuce since then due to presence of the pathogen in the adjacent field. The total (direct and indirect) economic losses were estimated to be over $500,000. In late April, disease was spotted in another field about 30 miles from the first outbreak field. This occurrence of the disease did not result in economic losses because it was the end of the lettuce growing season and nearly all lettuce had been harvested at that time. These two disease incidents indicate that the bacterial pathogen can be in the lettuce field to cause BLS anytime in the spring. Since there are no chemicals available to control the disease, use of host plant resistance (resistant varieties) is the only solution to the problem.

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: Lu, H., J. Hu, and S.-J. Kwon. 2014. Association analysis of bacterial leaf spot resistance and SNP markers derived from expressed sequence tags (ESTs) in lettuce (Lactuca sativa L.). Molecular Breeding 34:997-1006.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Lu, H., and J. Hu. 2014. Association analysis of response to bacterial leaf spot with single nucleotide polymorphism markers in lettuce. Plant & Animal Genome XXII, The International Conference on the Status of Plant & Animal Genome Research, San Diego, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Kandel, R., H. Lu, G. Nuessly, and H. McAuslane. 2014. Genetic study of serpentine leafminer resistance in Valmaine romaine lettuce. 2014 American Society for Horticultural Science Conference , Orlando, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Lu, H. 2014. Lettuce Bacterial Leaf Spot Resistance Breeding Efforts and Variety Selection for Commercial Production. Florida Lettuce Advisory Committee Meeting (March 2014), Belle Glade, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Lu, H. 2014. A Putative Gene for Bacterial Leaf Spot Resistance in Lettuce. Florida Lettuce Advisory Committee Meeting (Nov. 2014), Belle Glade, FL.

Progress 10/01/12 to 09/30/13

Outputs
Target Audience: The target audiences include lettuce growers,lettuce seed industry representatives,research scientistsin plant breeding and genetics, students (undergraduate students, graduate students, and postdocs), and general publics. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? In 2013, I continued the research on genetics of the resistance to insects in ‘Valmaine’ lettuce. Banded cucumber beetle is one of insect pests that can cause significant damage to lettuce and result in economic losses to growers. The romaine lettuce ‘Valmaine’ is known to have a high level of resistance to the insect. A lettuce population segregating for resistance was developed from a cross between ‘Valmaine’ and ‘Okeechobee’. ‘Okeechobee’ is susceptible to banded cucumber beetle. The derived F1 plants were infested with banded cucumber beetles in the laboratory and results showed that they performed similarly to ‘Valmaine’ in resistance to the insect. Ninety seven F2 plants were screened with banded cucumber beetles to determine response of each plant to the insect using a choice test in the laboratory. Sixty nine were resistant and 28 were susceptible, which indicated a single dominant gene inheritance for the banded cucumber beetle resistance. This gene was named as Bcb1. Identification of the Bcb1 gene will facilitate development of resistant cultivars suitable for commercial use to protect lettuce crop from damage by banded cucumber beetles. Besides, ‘Valmaine’ is also resistant to serpentine leafminer, cabbage looper, and beet armyworm. I am conducting experiments to determine if there are genetic relationships between beetle resistance and resistance to other insects. The second project was identification of commercial cultivars that are best adapted to the sub-tropical climate and organic soil in Florida. Seven cultivars including three crisphead and four romaine were evaluated for yield performance, horticultural characteristics, disease and insect responses in the field in a two-year period (2011-2012). In the crisphead variety trials, the cultivar ‘Gator’ had the highest yield (14,700 lbs/acre) in 2011, while ‘Raleigh’ had the highest yield (20,500 lbs/acre) in 2012. In the romaine variety trials, ‘Terrapin’ yielded more than any other cultivars in both years and was 14.5% higher in yield than the second highest yielder ‘Okeechobee’. For other characteristics, ‘70096’ was resistant to frost, seed thermo-dormancy, and the insect banded cucumber beetle, and ‘Manatee’ was tolerant to aphids. The results indicate that ‘Gator’ and ‘8074’ can be still used as major cultivars in crisphead lettuce production but ‘Terrapin’ should replace other romaine cultivars to increase romaine lettuce production in Florida. The third project was screening lettuce germplasm for resistance to bacterial leaf spot. Bacterial leaf spot (BLS), caused by the pathogen Xanthomonas campestris pv. vitians, is a devastating disease of lettuce in the world and is the most damaging disease of lettuce in Florida. This disease is highly unpredictable about where and when an outbreak will occur during the lettuce growing season. There are no chemicals for control of the disease when it is epidemic in the field. Use of host-plant resistance is the only ultimate solution to the problem. Recently, a new method for fast and accurate evaluation of a large number of lettuce germplasm lines has been developed in my laboratory. Establishment of the new screening method has profound influence on two aspects. A great number of germplasm can be evaluated for response to the disease in a short period of time, which will lead to quick identification of resistant sources that can be used directly in lettuce production to combat the disease or used as germplasm for development of resistant cultivars. The second influence is usefulness of the method in a breeding program to facilitate development of resistant cultivars through distinguishing the resistant plants from the susceptible ones at the seedling stage in an early (F2) generation, dealing with only the resistant plants in later generations, which will save time and costs. Using this method, we have identified one source of high resistance and five sources of moderate resistance from screening 258 germplasm lines. In a further experiment, we discovered the putative chromosomes associated with the high and moderate resistance. How have the results been disseminated to communities of interest? The results were presented at national conferences, local meetings, field days, and handouts.In addition, anyone interested in this area has access to my publications in journals, UF/IFAS EDIS website, and conferences websites. What do you plan to do during the next reporting period to accomplish the goals? I will continue my research in the following areas: 1) molecular mapping of the Bcb1 gene and investigating the relationships between beetle resistance and resistance to other insects; 2) Genetic study of the bacterial leaf spot resistance and development of resistant cultivars; and 3) variety trials to identify cultivars suitable for use in lettuce production in Florida.

Impacts
What was accomplished under these goals? Lettuce is an economically important vegetable crop in South Florida. Florida lettuce growers plant approximately 10,000 – 11,000 acres of lettuce annually, which contributes a $50 million gate value to Florida economy and provides employment for hundreds of workers. The production costs are higher in Florida than in other lettuce production states such as California and Arizona in that there are higher insect and disease pressure in Florida. Banded cucumber beetle can cause significant feeding damage to lettuce and growers spray insecticides for one to two times to control the pest. With identification of the resistant gene Bcb1 from my research project, new resistant cultivars can be developed for growers to use, which could reduce the production costs by $400,000 per year through reducing use of insecticides. In the lettuce variety trials, the cultivar ‘Terrapin’ yielded at least 14.5% higher than other romaine cultivars. Because the romaine lettuce accounts for 60% of total lettuce acreage in Florida, the Florida growers should make 2.6 million dollars more when using the cultivar ‘Terrapin’ for production than using other cultivars such as ‘Okeechobee’ for production. In addition, my lab has identified resistant sources for bacterial leaf spot. Resistant cultivars are under development.

Publications

• Type: Journal Articles Status: Published Year Published: 2013 Citation: Lu, H., and R. Raid. 2013. A novel screening method for evaluation of lettuce germplasm for bacterial leaf spot resistance. HortScience 48(2): 171-174.
• Type: Other Status: Published Year Published: 2013 Citation: Lu, H. 2013. Lettuce Cultivars Suitable for Use on Organic Soils in Southern Florida. EDIS paper HS1225, http://edis.ifas.ufl.edu/hs1225
• Type: Other Status: Published Year Published: 2013 Citation: Santos, L., A. L. Wright, Y. Luo, H. Lu, and C. Odero. 2013. Nitrogen Cycling and Management for Romaine and Crisphead Lettuce Grown on Organic Soils. EDIS paper SL386, http://edis.ifas.ufl.edu/ss588.
• Type: Other Status: Published Year Published: 2013 Citation: Santos, L., A. L. Wright, Y. Luo, H. Lu, and C. Odero. 2013. Nitrogen Management for Lettuce Production on Muck Soils. The Vegetarian Newsletter. Issue No. 586.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Lu, H., and R. Raid. 2013. Evaluation of Lettuce Germplasm for Response to Bacterial Leaf Spot. ASHS Annual Conference. Palm Desert, CA
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Lu, H., R. Kandel, G. Nuessly, H. McAuslane. 2013. Genetic Study of the Banded Cucumber Beetle Resistance in Romaine Lettuce Cultivar Valmaine. ASHS Annual Conference. Palm Desert, CA

Progress 10/01/11 to 09/30/12

Outputs
OUTPUTS: The most interesting discovery in this project in 2012 was determination of inheritance of the banded cucumber beetle resistance in Valmaine lettuce. Banded cucumber beetle is one of insect pests that can cause significant damage to lettuce and result in economic losses to growers. The romaine lettuce Valmaine is known to have a high level of resistance to the insect. A lettuce population segregating for resistance was developed from a cross between Valmaine and Okeechobee. Okeechobee is susceptible to banded cucumber beetle. The derived F1 plants were infested with banded cucumber beetles in the laboratory and results showed that they performed similarly to Valmaine in resistance to the insect. Ninety seven F2 plants were screened with banded cucumber beetles to determine response of each plant to the insect using a choice test in the laboratory. Sixty nine were resistant and 28 were susceptible, which indicated a single dominant gene inheritance for the banded cucumber beetle resistance. This gene was named as Bcb1. Identification of the Bcb1 gene will facilitate development of resistant cultivars suitable for commercial use to protect lettuce crop from damage by banded cucumber beetles. The second significant discovery was identification of commercial cultivars that are best adapted to the sub-tropical climate and organic soil in Florida. Seven cultivars including three crisphead and four romaine were evaluated for yield performance, horticultural characteristics, disease and insect responses in the field in a two-year period (2011-2012). In the crisphead variety trials, the cultivar Gator had the highest yield (14,700 lbs/acre) in 2011, while Raleigh had the highest yield (20,500 lbs/acre) in 2012. In the romaine variety trials, Terrapin yielded more than any other cultivars in both years and was 14.5% higher in yield than the second highest yielder Okeechobee. For other characteristics, 70096 was resistant to frost, seed thermo-dormancy, and the insect banded cucumber beetle, and Manatee was tolerant to aphids. The results indicate that Gator and 8074 can be still used as major cultivars in crisphead lettuce production but Terrapin should replace other romaine cultivars to increase romaine lettuce production in Florida. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: In 2012, I held 2 lettuce field days to show lettuce growers and others the lettuce variety trials at the Everglades Research and Education Center in Belle Glade, FL. A total of 42 people attended these events. They observed the performance of lettuce cultivars and knew which cultivars were the best in yield, horticultural characteristics, resistance to diseases and insects. This should help the growers to make decision on which cultivar(s) they can use in lettuce production in Florida to maximize their profits and to provide the market with the best produce. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Florida lettuce growers plant approximately 10,000 - 11,000 acres of lettuce annually, which contributes a $40 million gate value to Florida economy and provides employment for hundreds of workers. The production costs are higher in Florida than in other lettuce production states such as California and Arizona in that there are higher insect and disease pressure in Florida. Banded cucumber beetle can cause significant feeding damage to lettuce and growers spray insecticides for one to two times to control the pest. With identification of the resistant gene Bcb1 from my research project, new resistant cultivars can be developed for growers to use, which could reduce the production costs by $400,000 per year through reducing use of insecticides. In the lettuce variety trials, the cultivar Terrapin yielded at least 14.5% higher than other romaine cultivars. Because the romaine lettuce accounts for 60% of total lettuce acreage in Florida, the Florida growers should make 2.6 million dollars more when using the cultivar Terrapin for production than using other cultivars such as Okeechobee for production.

Publications

• Lu, Huangjun, Gregg Nuessly, and Alan Wright. 2012. Identification of lettuce germplasm lines resistant to Banded cucumber beetle. ASHS Annual Conference. Miami, FL. Jul. 31- Aug. 3, 2012.
• Lu, Huangjun, Gregg Nuessly, and Alan Wright. 2012. Host-Plant Resistance as a Component of Insect Pest Management for Control of Banded Cucumber Beetle on Lettuce. The Vegetarian Newsletter. Issue No. 577.
• Lu, Huangjun, and David Sui. 2012. Field performance of lettuce cultivars used in southern Florida. FSHS Annual Meeting. Delray Beach, FL, June 3-5, 2012.
• Lu, H., A. Wright, and D. Sui. 2012. Lettuce Cultivars for Insect Resistance in Southern Florida. EDIS paper HS1196, http://edis.ifas.ufl.edu/review/hs1196version=1.
• Wright, Alan, David Sui, Calvin Odero, and Huangjun Lu. 2012. Update on Soil Fertility Program. Lettuce Advisory Committee Meeting, Belle Glade, FL, Feb. 29, 2012.
• Lu, Huangjun, Joubert Fayette, Jinguo Hu, Carolee Bull, Richard Raid, Soon-Jae Kwon, Jeffery Jones. 2012. Association study of response to bacterial leaf spot with single nucleotide polymorphism markers in lettuce. Plant & Animal Genome XX, The International Conference on the Status of Plant & Animal Genome Research, San Diego, CA, Jan. 14-19, 2012.
• Lu, Huangjun. 2012. Bacterial leaf spot in lettuce -- Can the problem be solved by plant breeding approach 2012 Florida Lettuce Advisory Committee Meeting, Belle Glade, FL, Feb. 29, 2012.

Progress 10/01/10 to 09/30/11

Outputs
OUTPUTS: The most interesting discovery in this project in 2011 was the identification of a lettuce cultivar with resistance to banded cucumber beetle. Banded cucumber beetle is one of insect pests that can cause significant damage to lettuce and result in huge economic losses to growers. In the field experiments that included four romaine and three iceberg cultivars currently used by growers in lettuce production, the cultivar 70096 had as low as 3.7% of banded cucumber beetle feeding damage compared with 12.1 - 19.8% of damage in other cultivars. In food no-choice test conducted in the laboratory, the percentage of the damaged leaves was 17 for 70096 and 92 for susceptible cultivar Okeechobee. Yield was decreased by 3% to 37% for six of the seven cultivars grown under the adverse environmental conditions of banded cucumber beetle infestations, while yield of 70096 did not decline, indicating that 70096 was highly effective to protect the crop from feeding damage by banded cucumber beetles. Another important progress I made was the development of a method for fast screening of lettuce germplasm for response to bacterial leaf spot which is the most destructive disease on lettuce. I demonstrated that there is a lack of resistant source in our lettuce germplasm collection, which could potentially hinder the breeding effort to develop cultivars for resistance to bacterial leaf spot. Based on this result, I requested 179 more germplasm lines from the USDA-ARS unit in Pullman, Washington, to increase genetic diversity of my germplasm collection. These new lines are currently under evaluation for response to bacterial leaf spot. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Florida lettuce growers plant approximately 10,000 acres of lettuce annually, which contributes a $30 million gate value to Florida economy and provides employment for hundreds of workers. The production costs are higher in Florida than in other lettuce production states such as California and Arizona in that there are higher insect and disease pressure in Florida. Banded cucumber beetle can cause significant feeding damage to lettuce and growers often spray insecticides for one to two times to control the pest. With the identification of resistant cultivar from my research project, growers can use the resistant cultivar for lettuce production and do not have to apply pesticides to lettuce for controlling banded cucumber beetles, reducing the production costs by $400,000 per year as well as enhancing the environment. Bacterial leaf spot, caused by Xanthomonas campestris pv. vitians, is a highly destructive disease of lettuce. There are no chemicals available to control the disease when it becomes epidemic in the field. Thus growers have great interest in using host plant resistance to protect their lettuce crop from damage caused by the bacterium Xanthomonas campestris pv. vitians. The screening method that I developed will facilitate identification of resistant sources that can be integrated into cultivars.

Publications

• Lu, Huangjun, Alan Wright, and David Sui. 2011. Response of lettuce cultivars to insect pests in southern Florida. HortTechnolgy 21: 773-778.
• Wright, Alan, David Sui, Calvin Odero, and Huangjun Lu. 2011. Use of soil pH amendments for leafy greens production in South Florida. The Vegetarian Newsletter. Issue No. 567.
• Lu, Huangjun. 2011. A Method for Fast Screening of Lettuce for Response to Bacterial Leaf Spot. 2011 Florida Lettuce Advisory Committee Meeting, Belle Glade, FL.
• Lu, Huangjun, Richard Raid, and Alan Wright. 2010. Identification and utilization of resistance to economically important diseases in lettuce. FL Lettuce Advisory Meeting. Belle Glade, FL