Characterization of Hypersensitive Resistance to Bacterial Spot Race T3 (Xanthomonas perforans) from Tomato Accession PI 128216

Abstract

Bacterial spot of tomato is caused by four species of Xanthomonas. The accession PI 128216 (Solanum pimpinellifolium) displays a hypersensitive reaction (HR) to race T3 strains (predominantely Xanthomonas perforans). We developed an inbred backcross (IBC) population (BC(2)S(5), 178 families) derived from PI 128216 and OH88119 (S. lycopersicum) as the susceptible recurrent parent for simultaneous introgression and genetic analysis of the HR response. These IBC families were evaluated in the greenhouse for HR to race T3 strain Xcv761. The IBC population was genotyped with molecular markers distributed throughout the genome in order to identify candidate loci conferring resistance. We treated the IBC population as a hypothesis forming generation to guide validation in subsequent crosses. Nonparametric analysis identified an association between HR and markers clustered on chromosome 11 (P < 0.05 to 0.0001) and chromosome 6 (0.04 > P > 0.002). Further analysis of the IBC population suggested that markers on chromosome 6 and 11 failed to assort independently, a phenomenon known as gametic phase disequilibrium. Therefore, to validate marker-trait linkages, resistant IBC plants were crossed with OH88119 and BC(3)F(2) progeny were evaluated for HR in the greenhouse. In these subsequent populations, the HR response was associated with the chromosome 11 markers (P < 0.0002) but not with the markers on chromosome 6 (P > 0.25). Independent F(2) families were developed by crossing resistant IBC lines to OH8245, OH88119, and OH7530. These populations were genotyped, organized into classes based on chromosome 11 markers, and evaluated for resistance in the field. The PI 128216 locus on chromosome 11 provided resistance that was dependent on gene dosage and genetic background. These results define a single locus, Rx-4, from PI 128216, which provides resistance to bacterial spot race T3, has additive gene action, and is located on chromosome 11.

Mapping and linkage disequilibrium analysis with a genome-wide collection of SNPs that detect polymorphism in cultivated tomato

“…For example, linkage disequilibrium between two genomic locations in a tomato mapping population resulted in a significant, but spurious marker–trait association that was not confirmed in subsequent populations (Robbins et al , 2009). Significant inter-chromosomal LD was identified within cultivated tomato that differed between fresh market and processing tomatoes.…”

“…These selections represent a sample of the alleles present in commercial hybrids, although they do not recreate the parents themselves. Also included were the parents of several important recombinant inbred and inbred backcross populations (Doganlar et al , 2002; Kabelka et al , 2002; Graham et al , 2004; Yang et al , 2005; Robbins et al , 2009). The collection also contained parents of populations utilized by the tomato research community such as segmental substitution lines (M82 and LA716; Eshed and Zamir, 1995) and a mutation library (Menda et al , 2004).…”

High-Density SNP Genotyping of Tomato (Solanum lycopersicum L.) Reveals Patterns of Genetic Variation Due to Breeding

“…The collection also contained germplasm that was considered commercially relevant, with several inbred lines that are parents of commercial hybrids [78]–[80]. The collection also included the parents of several important recombinant inbred and inbred backcross populations [45], [81]–[84], segmental substitution lines [85], and a mutation library [86]. Finally, two accessions that have been the subject of public sequencing efforts, Heinz 1706 and LA1589, were also included.…”

Transgenic Resistance Confers Effective Field Level Control of Bacterial Spot Disease in Tomato

“…For the survey of bacterial strains, the tomato lines Bonny Best, H7998, FL216, 3x-2-4, and VF 36-Bs2, and the pepper variety Early Calwonder (ECW) were used to identify bacterial races. The tomato variety Bonny Best is susceptible to Xanthomonas , whereas tomato lines H7998, FL216, 3x-2-4, and VF 36-Bs2 contain resistance loci Rxv, Xv3, Xv4, and Bs2, respectively [13], [33], [34], [35], [36], [37]. These resistance loci trigger a hypersensitive reaction (HR) in response to strains containing the corresponding effectors AvrRxv, AvrXv3, AvrXv4, and AvrBs2, respectively.…”