Begomoviruses vectored by the sweetpotato whitefly (Bemisia tabaci) are a major threat to tomato (Solanum lycopersicum) production in many regions around the world. Of the many begomoviruses, the strains that cause Tomato yellow leaf curl virus (TYLCV) are the most widespread and well known. TYLCV resistant cultivars are commercially available in production regions, and most of these use the dominant Ty-1 gene that was introgressed from S. chilense accession LA1969. Producers in Florida often prefer to grow susceptible cultivars because of linkage drag effects that lower marketable yield and increase foliar disease infections. The Ty-3 gene, introgressed from S. chilense accessions LA2779 and LA1932, was recently found to be allelic to Ty-1 (Verlaan et al., 2013). Linkage drag in the form of increased foliar disease and reduced yield has also been a problem in lines possessing Ty-3. Fla. 8923 is a large-fruited breeding line with a much reduced introgression that is free of the negative effects of linkage drag based on observations of several promising hybrids derived from it over three seasons and three locations (Hutton and Scott, unpublished data). It is potentially suitable as a parent in commercial hybrids or as a Ty-3 donor in tomato breeding programs where begomovirus resistant cultivars are the goal.
Origin
The pedigree of Fla. 8923 is shown in Fig. 1. Resistance was derived from S. chilense accession LA2779 that was crossed with Campbell 28 (C28) in 1990. Two interspecific F1s were obtained from the 66 fruit that set from this cross. The F1s were backcrossed to Fla. 7409 and a fair amount of seed was produced, but germination was less than 2%. The backcross to Fla. 7409 was advanced to the F7 generation) in the field after inoculation with Tomato mottle virus (ToMoV) and selection for resistant plants each generation. The F7 was highly resistant but wild in appearance. Seed was sent to Judith Milo at the Hebrew University in Rehovot, Israel, who crossed the F7 with a begomovirus-susceptible greenhouse tomato inbred and returned F2 seed from that cross. An F2 ToMoV-resistant selection without wild species characteristics was made and advanced to the F4 generation. The F4 was fixed for ToMoV resistance and crossed to Fla. 7833; selections were thereafter tested in separate trials for both ToMoV and Tomato yellow leaf curl virus (TYLCV). In 2002 the F8 Fla. 8680 was crossed to Fla. 7781 (Scott and Jones, 2000) and F2 seed were screened for molecular markers flanking the S. chilense introgression (Ji et al., 2007). The following map positions are based on the Tomato-EXPEN 2000 map (http://www.sgn.cornell.edu). Of 719 F2 plants, 30 recombinants were identified and genotyped for markers between 5 and 32 cM on chromosome 6, and recombinant inbred lines (RILs) were evaluated in the field for resistance to TYLCV. All RILs having introgressions that spanned 18–25 cM showed some resistance. Two of the resistant F5 RILs, each containing this region, were selected and used to develop fine-mapping populations; the introgression in RIL 554 spanned from 5 to 25 cM, and the introgression in RIL 157 spanned from 18 to 32 cM. These RILs were crossed to Fla. 7776 (Scott et al., 2006), and F2 populations were developed. Of nearly 11,000 plants genotyped with flanking markers, 299 recombinants were obtained, and 114 of these had crossovers between 18 and 25 cM. Phenotyping of cuttings from these recombinants in 2009 and genotyping with newly available single nucleotide polymorphism markers developed from sequences available through the tomato genome project mapped the Ty-3 gene to a 2.5 cM region. Further testing of informative RILs in 2010 located the gene within a 0.3 cM region (Verlaan et al., 2013). Two resistant RILs (i.e., E942-482 and E948-725), each resulting from a crossover within this 0.3 cM interval and immediately on either side of Ty-3, were intercrossed to develop a Ty-3 minimal introgression (Verlaan et al., 2013, Table S3). More than 2000 F2 plants from this cross were grown in 2010 and tested with flanking markers to identify recombinants; three plants were found to have resulted from crossovers within this region and were heterozygous for a Ty-3 introgression less than 70 kb in size. Progeny were grown and markers were used to select for homozygosity of the reduced region; one of these plants became Fla. 8879.
Pedigree of Fla. 8923. All 7000 and 8000 numbered lines in the pedigree should have a Fla. prefix, which was left off for spacing considerations.
Citation: HortScience horts 50, 8; 10.21273/HORTSCI.50.8.1257
Fla. 8879 was crossed to Fla 8111B (Scott, 2013), a globe-shaped tomato with large fruit size derived from Fla. 7777 (Scott et al., 2004). Fla. 8111B has a large vine and a number of good horticultural characteristics, but it is very susceptible to bacterial spot. The Fla. 8879 x Fla. 8111B F1 was crossed to Fla. 8626, another large-fruited globe-shaped tomato inbred that also had Fla. 8111B in its pedigree. Scott et al. (2009) reported that Fla. 8626 had resistance to bacterial wilt (Ralstonia solanacearum), but further testing showed this not to be the case (Scott, unpublished data). Marker assisted selection was used at the seedling stage in the F1 and subsequent generations to identify and select plants containing Ty-3. In Spring 2012, an F2 plant was selected that was heterozygous for Ty-3. A homozygous F3 line was obtained with a good yield of very large fruit. Yield data were taken on more advanced selections in 2013. Seed was increased in the F6 generation in Spring 2014 for release.
Description
Fla. 8923 has a determinate, open vine with intermediate vigor typical of most tomato vines with globe-shaped fruit. Fruit cover is fair. The deep round- (globe-) shaped fruit have jointed pedicels, shoulders are uniform green, and blossom scars are stellate and usually smooth. In two seasons of testing, total marketable yields of Fla. 8923 were similar to all the commercially available hybrids that were tested (Tables 1 and 2). Fla. 8923 has very large fruit. In Spring 2013 Fla. 8923 had extra-large fruit yield similar to ‘Sanibel’ but greater than that of ‘Sebring’, ‘Florida 47’, and ‘Solar Fire’, while overall fruit size was greater than that of all the commercial hybrids, except ‘Sanibel’ (Table 1). In Fall 2013 Fla. 8923 had total and extra-large yields statistically similar to those of commercial hybrids. Overall fruit size was greater than all three commercial hybrids (Table 2). Firmness was comparable to tomato cultivars grown in Florida in two seasons of testing (Table 3). Overall, the external and internal fruit color tended to be slightly pale red. In Spring 2013, the external L and hue angles of Fla. 8923 were similar to ‘Sebring’ but higher than those of Tasti-Lee® and ‘Florida 47’ suggesting a trend for the fruit to be lighter and paler red, respectively. Likewise, in Fall 2013 the external L and hue angles were significantly higher than those of the commercial hybrids. Internally, the L and hue angles for Fla. 8923 in Spring 2013 were similar to ‘Florida 47’ but higher than Tasti-Lee® and ‘Sebring’. The latter two are crimson (ogc gene) and have a deeper red color than Fla. 8923 or ‘Florida 47’. Likewise in Fall 2013, the internal L values and hue angles for Fla. 8923 and ‘Florida 47’ were similar and significantly higher than those of Tasti-Lee®, indicating the latter was a deeper red.
Marketable yield, extra-large yield and fruit size for tomato inbreds and control hybrids at the Gulf Coast Research and Education Center, Balm, FL, Spring 2013.
Total and extra-large marketable yield and fruit size for tomato inbreds and control hybrids at the Gulf Coast Research and Education Center, Balm, FL, Fall 2013.
External color, internal color, and firmness for fruit of Fla. 8923 and comparison of tomato cultivars over two seasons at the Gulf Coast Research and Education Center, Balm, FL 2013.
Disease Resistance
Fla. 8923 had intermediate resistance to both TYLCV and ToMoV under the heavy disease pressure that resulted when seedlings were inoculated for 2 weeks (Table 4). On grower farms in Florida, the resistance of the cultivar Tygress, heterozygous for Ty-1, would be rated very close to 0 on our severity scale. Observations for genotypes with Ty-3 have shown that when young plants are inoculated they show some disease symptoms, but often gradually improve as the plants continue to grow in the field. The inheritance is additive, so plants heterozygous for Ty-3 alone show more disease symptoms than plants homozygous for Ty-3 alone (Verlaan et al., 2013). When Ty-3 is combined heterozygously with other TYLCV resistance genes, a good level of resistance is often obtained which is evidenced in the (Fla. 8624 × Fla. 8923) hybrid (Table 4). Fla. 8923 is resistant to Fusarium wilt races 1 and 2 (Fusarium oxysporum f. sp. lycopersici), gray leafspot (Stemphyllium sp.), and Verticillium wilt race 1 (Verticillium dahliae). It is more sensitive to bacterial spot race T4 (Xanthomonas perforans) than many susceptible genotypes and it is similar to Fla. 8111B in that regard. However, hybrids of Fla. 8923 crossed with other bacterial spot susceptible parents do not show extreme susceptibility as is the case for crosses among many other very susceptible inbreds (Hutton and Scott, unpublished observations). The primary disorder has been zippering. It has a high level of resistance to graywall.
Tomato yellow leaf curl virus (TYLCV) and Tomato mottle virus (ToMoV) disease severityz for tomato genotypes inoculated at the seedling stage at the Gulf Coast Research and Education Center, Balm, FL, Spring 2014.
Availability
Fla. 8923 is an inbred breeding line release. Seed distribution is controlled by Florida Foundation Seed Producers, P.O. Box 309, Greenwood, FL 32443. Initial seed requests should be made to S.F. Hutton.
Literature Cited
Ji, Y., Schuster, D.J. & Scott, J.W. 2007 Ty-3, a begomovirus resistance locus near the Tomato yellow leaf curl virus resistance locus Ty-1 on chromosome 6 of tomato Mol. Breed. 20 271 284
Hutton, S.F., Scott, J.W. & Schuster, D.J. 2012 Recessive resistance to Tomato yellow leaf curl virus from the tomato cultivar Tyking is located in the same region as Ty-5 on chromosome 4 HortScience 47 324 327
Scott, J.W. 2013 Fla. 8111B a large-fruited, globe shaped tomato breeding line Rpt. Tomato Genet. Coop. 63 31
Scott, J.W. & Jones, J.P. 2000 Fla. 7775 and Fla. 7781: Tomato breeding lines resistant to Fusarium crown and root rot HortScience 35 1183 1184
Scott, J.W., Olson, S.M., Bartz, J.A., Maynard, D.N. & Stofella, P.S. 2004 Fla. 7964 hybrid tomato resistant to spotted wilt virus Rpt. Tomato Genet. Coop 54 51
Scott, J.W., Olson, S.M., Bryan, H.H., Bartz, J.A., Maynard, D.N. & Stoffella, P.J. 2006 ‘Solar Fire’ hybrid tomato: Fla. 7776 tomato breeding line HortScience 41 1504 1505
Scott, J.W., Vallad, G.E. & Jones, J.B. 2009 High level of resistance to bacterial wilt (Ralstonia solanacearum) obtained in large-fruited tomato breeding lines derived from Hawaii 7997 Acta Hort. 808 269 274
Verlaan, M.G., Hutton, S.F., Ibrahem, R.M., Kormelink, R., Visser, R.G.F., Scott, J.W., Edwards, J.D. & Bai, Y. 2013 The tomato yellow leaf curl virus resistance genes Ty-1 and Ty-3 are allelic and code for DFDGD-class RNA-dependent RNA polymerases PLoS Genet. 9 3 e1003399