Inheritance of resistance to late blight in tomato and identification of SSR markers linked to resistance through bulked segregant analysis.

摘要

For efficient selection of desired agronomic traits, molecular markers can provide an effective tool since they are based on the plant genotypes and thus are independent of environmental variation. The objective of this study was to study the inheritance of resistance to late blight in two segregating populations and attempt to identify loci specifically responsible for resistance to late blight using 59 SSR molecular markers. IKR4 and HINZ4 segregating populations were developed by the crossing 'Ikram' x '163A' and 'Heinz H7155' x '163A', respectively. The parents, F₁ and F₂ generations in addition to two standard susceptible cultivars were artificially inoculated with mixture isolates of P. infestans with a concentration of 103 spores/ml. Total genomic DNA was isolated from leaf tissue. The genetic analysis indicated that resistance is inherited as a partially dominant trait. The values of disease rating indicated that HEN4 population was more resistant to P. infestans than IKR4 population. Out of 59 SSR primer pairs, 53 (89.8%) were able to produce the expected DNA fragments in their PCR products screened for resistant and susceptible parents genome. Of the 53 amplified primer pairs, 33 (55.9%) were polymorphic and 20 (33.9%) were monomorphic among the two parents of tomato. For the polymorphic SSR loci, 2-4 alleles were detected and the expected fragment sizes varied from 100 to 250 bp. Thirty-three primer pairs were used in scanning the parents and the closed bulk. Out of 33 primers, 13 produced amplification products that were too faint to score or could not be consistently reproduced in respect of the closed bulk. Only 7 out of 33 primer pairs produced polymorphic banding patterns for the parents and also the closed-bulks. The results primarily confirmed that late blight resistant gene linked with three SSR markers in the closed bulk.