Genetic analysis of late blight resistance in Solanum pimpinellifolium accession PI 270441: Heritability and response to selection

Abstract

Late blight (LB), caused by Phytophthora infestans, is a destructive disease of tomato (Solanum lycopersicum) worldwide. Currently, there are few commercial cultivars of tomato with resistance to LB, and the disease is mainly controlled by heavy use of fungicides. Due to the emergence of fungicide‐resistant pathogen isolates, there is a concerted effort to identify new genetic sources of resistance and breed new resistant cultivars. A recent screening identified several new tomato accessions with strong resistance to LB. Here, we report on the genetic basis of LB resistance in S. pimpinellifolium accession PI 270441, as determined by generation means analysis and analysis of response to selection, using populations derived from crosses with LB‐susceptible breeding line Fla. 8059. Heritability of LB resistance ranged from 0.76 to 0.78, and the minimum number of genes was estimated 1—few. These results suggest that transfer of LB resistance from PI 270441 to the cultivated tomato should be feasible via a traditional backcross breeding approach. Genetic mapping studies are underway to identify molecular markers associated with resistance in this accession.

Identification of late blight resistance quantitative trait loci in Solanum pimpinellifolium accession PI 270441

“…The F 1 generation showed strong resistance, similar to the resistant control lines NC 63 EB ( Ph‐2 ) and NC 870 ( Ph‐3 ), though it exhibited less resistance than PI 270441 (Table 1). Overall, disease responses of the parental lines, F 1 generation, and control genotypes were consistent with previously reported data on these genotypes (Foolad et al., 2014; Sullenberger et al., 2018).…”

“…The latter observation supports potential involvement of a few resistance loci with dominance or partial dominance gene action. A previous inheritance study of an F 2 population of the same cross suggested the involvement of one or a few resistance loci, as determined by the Castle–Wright equation (Sullenberger et al., 2018). The QTL results of the present study are in agreement, identifying three major resistance loci, one of which had the largest effects and could explain most of the variation (discussed below).…”

“…The pathogen was maintained weekly in an incubator by transferring fresh isolate from infected leaflets with sporulation to leaflets of a susceptible genotype. The inoculum for disease screening experiments was prepared as described in detail elsewhere (Sullenberger et al., 2018). Briefly, the inoculum was transferred to leaflets from a susceptible genotype and maintained in an incubator for 1 wk.…”

Genetic analysis of late blight resistance in a new RIL population of tomato derived from LB‐resistant Solanum pimpinellifolium accession PI 270443

“…Unlike ANOVA, the P/O correlation analysis does not assume normal trait distribution or similar environmental variances in parental and progeny generations (Dudley & Moll, ; Foolad & Jones, ). P/O regression/correlation analysis has been reported as one of the most reliable and empirical methods for estimating h 2 , and it has been extensively used for estimating h 2 of different traits and in different plant species (Fernandez & Miller, ; Foolad & Jones, ; Foolad & Lin, ; Smith & Kinman, ; Sullenberger, Jia, Gao, & Foolad, ).…”

Genetic characterization of late blight resistance in Solanum pimpinellifolium accession PI 270442

“…Pathogen maintenance and inoculum preparation were as described elsewhere [47]. Disease pressure was partially influenced by external conditions, and therefore for each experiment, varying inoculum concentrations were needed to compensate with the average concentration being 6,400 sporangia/ml.…”