Molecular mapping and identification of QTLs responsible for charcoal rot resistance in Castor (Ricinus communis L.)

Charcoal rot caused by Macrophomina phaseolina in castor is one of the major pathogenic determinants for extreme yield loss. The charcoal rot resistance trait is complex and controlled by quantitative trait locis (QTLs). This study was aimed to develop linkage map and to identify novel QTLs associated with charcoal rot resistance in castor. A mapping population (F2:3) derived from the cross between two castor inbred lines JI 357 (Resistant genotype) and SKI 338 (Susceptible genotype) was developed and screened in the sick plot using randomised block design. After screening 920 (520 RAPD, 100 ISSR, 300 SSR) primers among the parental lines, 336 polymorphic markers were identified to be used for genotyping the mapping population to develop genetic linkage map. The genetic map consisting of 10 linkage group covering a total map length of 1833.4 centimorgan (cM) with average marker interval of 6.93 cM was developed. The length of linkage groups varied from 121.5 cM for linkage group 10 (C10) to 278.7 cM for linkage group 9 (C9). The average marker interval was maximum in C3 (8.23 cM) while it was lowest in C10 (5.78 cM). Analysing genotypic data along with phenotypic data collected from mapping population against charcoal rot in sick plot, identified three novel QTLs explaining 11.3–71.2% of phenotypic variation. One major QTL with LOD score of 6.5 was identified on linkage group 2 explaining 71.2% of phenotypic variation, is a most promising QTL for molecular breeding. This is the first study reporting novel QTLs for charcoal rot resistance in castor and thus future studies will be conducted to refine these QTLs.