Progress 09/15/06 to 08/31/09

Outputs
OUTPUTS: An F2 population between tomato (Solanum lycopersicum L.) and S. habrochaietes accession LA1777 was made and 171 F2 plants were assayed for SLWF mortality and oviposition by confining 10 adult females in one clip cage per plant for 24 hours and the numbers of living and dead whiteflies and eggs deposited were counted. The lateral leaflet opposite to the one used for the insect assay was used to count the numbers of type IV and type VI trichomes for each plant. Eleven plants from the population were selected as resistant based on their low oviposition (0-12 eggs), high adult mortality, and high number of type IV trichomes; ten susceptible plants were selected based on their low mortality, high oviposition, and 0 to very few type IV trichomes. Four hundred twenty-one molecular markers spanning the tomato genome were screened using a modified bulk segregant analysis (MBSA) of the resistant and susceptible selections. MBSA revealed five putative regions associated with resistance, designated R1, R2, R3, R4 and R5 on chromosomes 10, 9, 11, 11 and 8, respectively. To verify these results, a QTL analysis was done using 138 of the 171 F2 plants. Significant associations were found for oviposition and type IV trichomes for R1-R4 but not for R5. Resistance was only recovered in plants that had multiple regions present, but never in plants with only a single region. A manuscript has been submitted to the Journal of the American Society of Horticultural Science describing these results. Crosses were made primarily using recombinant inbred lines (RILs) to combine the four regions in all possible combinations to determine which combinations provide resistance. Some combinations were bioassayed and it was found that R1 plus R2 did not give resistance, but R2, R3, and R4 combined provided high resistance. To obtain a more complete set of genotypic combinations plants heterozygous for all four loci and plants heterozygous for three of the four loci were self-pollinated and sib-mated, and more than 800 progeny were genotyped. Recovery of particular genotypes does not appear to be random, and not all genotypic combinations were recovered. The selected genotypes were bioassayed in late fall 2008. Results suggested that: all 4 regions in combination provided high resistance; R1, R3 and R4 combined provided high resistance; R2, R3 and R4 combined provided high resistance in 11 of 14 plants tested; R1 plus R2 provided resistance in only three of seven plants tested; R2 plus R4 appeared to provide acceptable resistance; neither the combination of R2 plus R3 or the combination of R3 plus R4 provided adequate resistance. Thus, it appears resistant alleles is needed at a minimum of three regions to consistently provide adequate resistance; however, some two-locus combinations may also suffice. More testing is needed to confirm these data, since all genotypic combinations were not recovered, and several combinations had only a single representative plant. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The information developed will be useful as a foundation to determine the combination of loci needed to obtain resistance to sweet potato whitefly. Fine mapping of these genes should then eliminated the linkage drag associated with this trait and allow for resistant varieties to be deployed. The economic impact of such releases would be in the hunderds of millions of dollars per year. However, the work accomplished was only the first important step on this road and more work is required.

Publications

• Momotaz, A., Scott, J.W. and Schuster, D.J. 2007. Begomovirus resistance genes not found in recombinant inbred lines developed from Solanum habrochaites accession LA1777. HortScience. 42(5): 1149-1152.
• Momotaz, A., Scott, J.W. and Schuster, D.J. 2008. Identification of QTLs conferring resistance to Bemisia argentifolii in a F2 population of Solanum lycopersicum x Solanum habrochaites accession LA1777. Plant & Animal Genome XVI Conf., San Diego, CA. Jan. 12-16, 2008. http://www.intl-pag.org/16/abstracts/PAG16_P05g_431.html. [Abstract].
• Momotaz, Aliya, Jay W. Scott, and David J. Schuster. 2010. Identification of QTLs Conferring Resistance to Bemisia tabaci in an F2 Population of Solanum lycopersicum x Solanum habrochaites Accession LA1777. J. Amer. Soc. Hort. Sci. 135: (In Press)
• Momotaz, A., Scott, J.W. and Schuster, D.J. 2005. Searching for silverleaf whitefly and begomovirus resistance genes from Lycopersicon hirsutum accession LA1777. Acta. Hort. (ISHS) 695:417-422.
• Momotaz, A., Scott, J.W. and Schuster, D.J. 2006. Identification of Silverleaf Whitefly Loci In Lycopersicon hirsutum accession LA1777. Tomato Breeders Roundtable and Tomato Quality Workshop. Tampa, Florida, USA May 7-11, 2006. http://roundtable06.ifas.ufl.edu/ [Abstract].
• Momotaz, A., Scott, J.W. and Schuster, D.J. 2006. Identification and introgression of Silverleaf Whitefly resistance from Lycopersicon hirsutum accession LA1777. 4th International Bemisia Workshop and International Whitefly Genomics Workshop, December 3-8, 2006 in Duck Key, Florida USA. http://www.conference.ifas.ufl.edu/bemisia/Abstract 20book.pdf;P67.[Abstract].
• Momotaz, A., Scott, J.W. and Schuster, D.J. 2007. Begomovirus resistance not found in Solanum habrochaites accession LA1777 recombinant inbred lines of tomato. HortScience Vol. 42(4): 1015. [Abstract].

Progress 09/15/07 to 09/14/08

Outputs
OUTPUTS: An F2 population between tomato (Solanum lycopersicum L.) and S. habrochaietes accession LA1777 was made and 171 F2 plants were assayed for SLWF mortality and oviposition by confining 10 adult females in one clip cage per plant for 24 hours and the numbers of living and dead whiteflies and eggs deposited were counted. The lateral leaflet opposite to the one used for the insect assay was used to count the numbers of type IV and type VI trichomes for each plant. Eleven plants from the population were selected as resistant based on their low oviposition (0-12 eggs), high adult mortality, and high number of type IV trichomes; ten susceptible plants were selected based on their low mortality, high oviposition, and 0 to very few type IV trichomes. Four hundred twenty-one molecular markers spanning the tomato genome were screened using a modified bulk segregant analysis (MBSA) of the resistant and susceptible selections. MBSA revealed five putative regions associated with resistance, designated R1, R2, R3, R4 and R5 on chromosomes 10, 9, 11, 11 and 8, respectively. To verify these results, a QTL analysis was done using 138 of the 171 F2 plants. Significant associations were found for oviposition and type IV trichomes for R1-R4 but not for R5. Resistance was only recovered in plants that had multiple regions present, but never in plants with only a single region. A manuscript is in preparation describing these results. Crosses were made primarily using recombinant inbred lines (RILs) to combine the four regions in all possible combinations to determine which combinations provide resistance. Some combinations were bioassayed and it was found that R1 plus R2 did not give resistance, but R2, R3, and R4 combined provided high resistance. To obtain a more complete set of genotypic combinations plants heterozygous for all four loci and plants heterozygous for three of the four loci were self-pollinated and sib-mated, and 823 progeny were recently genotyped. Select combinations will be bioassayed in late fall 2008. More genotyping will be done soon since recovery of particular genotypes does not appear to be random, and not all genotypic combinations were recovered. Results will be presented next year. PARTICIPANTS: J. W. Scott, Professor of Horticultural Sciences was the principal investigator, his role was in developing the overall design of the research; first using recombinant inbred lines (RILs) and then developing the interspecific F2 which was the population used in the MBSA and QTL studies when resistance was not found in the RILs. He is guiding the present research and breeding approach as resistance genes are verified and linkage drag is removed from each locus. Aliya Momotaz was the Post-Doctoral Scientist who carried out much of the work, from bioassays to molecular marker development and screening. She analyzed all the data and conducted the MBSA and QTL analyses. She also oversaw pollination and seed production activities. D.J. Schuster, Professor of Entomology oversaw the mainanence of the sweet potato whitefly colony used in the bioassays and provided expertise in trichome morphlogy and the bioassay procedure. He provided labor to assist with the bioassays. TARGET AUDIENCES: Target audience for this work are scientists working in the area of (tomato) breeding and genetics. These are the people who may be able to take germplasm developed in the project to develop whitefly tolerant cultivars for tomato growers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
This is a long-term project and there will be no economic impact for some time. If the project is successful savings to tomato growers in reduced pesticide costs, reduced geminivirus infection, and elimination of irregular ripening could be worth 30 million per year to Florida growers.

Publications

• Momotaz, A., Scott, J.W. and Schuster, D.J. 2008. Identification of QTLs conferring resistance to Bemisia argentifolii in a F2 population of Solanum lycopersicum x Solanum habrochaites accession LA1777. Plant & Animal Genome XVI Conf., San Diego, CA. Jan. 12~16, 2008. http://www.intl-pag.org/16/abstracts/PAG16_P05g_431.html. [Abstract].

Progress 09/15/06 to 09/14/07

Outputs
See previous CRIS reports for studies that lead up to last years' work. To verify chromosome regions with silverleaf whitefly (SLWF) resistance, a QTL analysis was done using molecular markers flanking regions identified in a modified bulk segregant analysis of an interspecific F2 population. Of the six regions identified earlier, four major QTLs (regions R1~R4 on three different chromosomes) had LOD values of 4.87~5.95 and the other two QTLs (R5 & R6) had LOD scores of 2.97 & 2.11 respectively. Next, LA1777 recombinant inbred lines (RILs) spanning the six regions were screened with molecular markers linked to resistance in the F2 population. Only 3 regions (R1, R4, R6) had markers expressed in the RIL plants. Markers in two of the remaining three regions (R2, R3) were found in respective RILs derived from Solanum pennellii accession LA716. Crosses were made and F1s were self-pollinated to the F2 to combine putative resistance regions. For regions R1 and R4 on chromosome 10 and 9 we screened 188 F2 plants with two closely linked markers to these two QTLs. We have found nine plants with homozygous for both loci. Then we made four groups based on availability of loci in homozygous for two loci (Group1), homozygous for first locus and heterozygous for 2nd locus (Group2), heterozygous for first locus and homozygous for 2nd locus (Group3), heterozygous for both loci (Group4). An assay of 18 F2 plants (9 plants from group1, 3 plants each from groups 2~4) for SLWF mortality and oviposition was done along with 3 plants each of LA1777 and S. lycopersicum. Type IV trichome counts were also done. No increased level of resistance was found in any plants of any groups and there was no plants having typeIV trichome on their leaves. Crosses were also done to combine other regions two by two and now to add third regions to the chromosome 9 and 10 homozygous regions. Since markers for 3 putative QTLs were not found in LA1777 RILs, resistant F3 plants were crossed with susceptible tomato lines and BC1F2 populations were made. This fall these BC1F2 will be screened using the appropriate molecular markers and will be bioassyed. Crosses are also being made with the S. pennellii RILs to see if resistance can be recovered when combined with LA1777 RILs cantaining putative resistant loci.

Impacts
Silverleaf whitefly resistance would be a huge benefit to organic and traditional tomato growing systems by limiting yield reductions due to geminivirus infection and irregular ripening which results from whitefly feeding itself. The research being conducted is the first step needed to make resistant cultivars a reality but the deveopment of such cultivars is beyond the scope of the present research.

Publications

• Momotaz, A., Scott, J.W. and Schuster, D.J. 2007. Begomovirus Resistance Not Found in Solanum habrochaites accession LA1777 recombinant inbred lines of tomato. HortScience Vol. 42(4): 1015. [Abstract].
• Momotaz, A., Scott, J.W. and Schuster, D.J. 2006. Identification and introgression of Silverleaf Whitefly resistance from Lycopersicon hirsutum accession LA1777. 4th International Bemisia Workshop and International Whitefly Genomics Workshop, December 3-8, 2006 in Duck Key, Florida USA. http://www.conference.ifas.ufl.edu/bemisia/Abstract
• Momotaz, A., Scott, J.W. and Schuster, D.J. 2007. Begomovirus resistance genes not found in recombinant inbred lines developed from Solanum habrochaites accession LA1777. HortSci. 42(5): 1149-1152.