Genetic mapping of Citrullus amarus for resistance to gummy stem blight in watermelon

Gummy stem blight affects several cucurbit crops and has emerged as a serious production constraint of watermelon cultivation globally. However, no commercial varieties are available possessing resistance against this disease. Identification of genetic determinants and underlying QTLs are prerequisites for resistant variety development. In this direction, an attempt was made to understand genetics and identify responsible loci using two resistant accessions viz., PI 482276 and IIHR 82. Inheritance analysis indicated that resistance to GSB is governed by polygenes in both accessions. Four QTLs were identified for the population derived from PI 482276 x Arka Manik, while six were observed in the cross IIHR 82 x Arka Manik employing QTL-seq approach. The QTL regions contained important genes putatively involved in resistance reaction such as NAC domain-containing protein 17-like, chitinase 2- like, Pectinesterase, Coiled-coil domain-containing protein 18, Kinase family protein expansin-like B1 protein etc. Our results offer further insight into the disease resistance genetics and its utilization in resistance breeding for gummy stem blight in watermelon.