Dissection of race 1 anthracnose resistance in a watermelon (Citrullus lanatus var. lanatus) biparental mapping population

Abstract

Anthracnose, caused by the fungal pathogen Colletotrichum orbiculare (Berk. & Mont.) Arx syn. lagenaria, is one of the most important diseases of watermelon in the United States and worldwide. The study was conducted to identify C. orbiculare race 1 resistance quantitative trait loci (QTL) in a 'Charleston Gray', resistant parent, and 'New Hampshire Midget', susceptible parent, biparental mapping population. The mapping population consisted of 228 F 2 and the validation population consisted of 60 individuals each in BC 1 P 1 and BC 1 P 2 . The disease severity was rated using a disease index comprising a rating scale of 0 to 100%. IciMapping was used to draw the linkage map and R/qtl non-parametric method ('model = np') was used to identity QTL. We identi ed a major disease resistance QTL, Qar1-8, on chromosome 8. The signi cant SNP marker S8_5149002, part of a putative coiled-coil (CC)-nucleotide-binding site (NBS)leucine-rich repeat (LRR) (CC-NBS-LRR or CNL; ClCG08G002410), had a LOD of 14.06. The signi cant marker was validated on mapping populations using R package functions 'chisq.test ', 'wilcox.test', 'kruskal.test', and 'dunn.test'. The signi cant marker S8_5149002 was also tested for its ability to differentiate race 1 anthracnose resistance on 61 watermelon germplasm including 41 plant introduction (PI) lines. Hence, the diagnostic SNP marker S8_5149002 could be used for marker assisted selection (MAS) for race 1 anthracnose resistance in watermelon breeding programs.

Recent Advances and Challenges in Management of Colletotrichum orbiculare, the Causal Agent of Watermelon Anthracnose

“…They hypothesized that residue 18 of a conserved motif, IxxLPxSxxxLYNLQTLxL, could govern resistance in 'DrHs7250'. An independent study conducted in the U.S. using a biparental mapping population, 'Charleston Gray' (female parent, resistant) and 'New Hampshire Midget' (male parent, susceptible), found a major C. orbiculare race 1-resistance QTL in the same region on chromosome 8 [62]. A PACE SNP marker designed from the SNP marker CL 14-27-9, identified earlier [61], was also the diagnostic marker for the QTL (LOD = 14.06) in the study.…”