Identification of Meloidogyne incognita resistance QTLs using high density GBS linkage map in bittergourd

Abstract

The root knot nematode (RKN; Meloidogyne incognita ) is a very serious biotic constraint that limits the yield potential of bittergourd. The resistance within the cultivated germplasm of bittergourd is limited, therefore, introgressing resistance from related species of bittergourd offers a sustainable breeding solution. In this study, a RKN-susceptible cultivated parent M . charantia cv. Punjab-14 was crossed with resistant wild species of M . balsamina cv. Punjab Jhaar Karela-1 to generate F 2:3 mapping population. A genetic linkage map was constructed via Genotyping-by Sequencing (GBS). Joint phenotyping and genotyping analysis identified a total of five quantitative trait loci (QTLs) governing RKN resistance. Under artificial screening, two QTLs namely QTLs qRKN_pau6.1 (chromosome 6) and qRKN_pau11.1 (chromosome 11) were detected, explaining 10.11% and 7.53% of phenotyping variance (PVE), respectively. Under field conditions, three QTLs namely, qRKN_pau3.1 , qRKN_pau6.2 and qRKN_pau9.1 were mapped on chromosome 3, 6 and 9 accounting for 9.09%, 6.49% and 9.16% PVE respectively. The major artificial screening locus qRKN_pau6.1 was successfully validated using kompetitive Allele-Specific PCR (KASP) assays. One diagnostic KASP marker, BGST_19012274 and one linked marker BGST_29234979 located within the resistance-associated genomic region, narrowed the genetic interval to 4.23 cM and 19.05 cM, respectively. To our knowledge, this is the first report on pathogen resistance introgression from M . balsamina into M. charantia and provides the first SNP-validated blueprint for marker-assisted selection against M . incognita in bittergourd.