Mapping of quantitative trait loci for scab resistance in apple (Malus × domestica) variety, Shireen

Background Scab caused by Venturia inaequalis (Cke.) Wint. is the most important fungal disease of apple. Fungicide application is a widely practiced method of disease control. However, the use of chemicals is costintensive, tedious, and ecologically unsafe. The development of genetic resistance and the breeding of resistant cultivars is the most reliable and safest option. One such source of scab resistance happens to be the variety ‘ Shireen ’, released from SKUAST-Kashmir. However, to date, the nature of resistance and its genetic control have not been characterized. Objective This research aimed to elucidate the genetic basis of scab resistance in Shireen . Methods Genetic mapping of quantitative trait loci (QTL) for resistance to apple scab disease was performed using an F1 cross developed between the susceptible cultivar ‘ StarKrimson ’ and the resistant cultivar ‘ Shireen ’. The population was evaluated for two consecutive years. Further, six candidate genes were analyzed via quantitative real-time PCR, to determine their expression level in response to the pathogen infestation. Results Genotyping and disease phenotyping of populations led us to identify two quantitative trait loci (QTLs), namely qRVI.SS-LG2.2019 and qRVI.SS-LG8.2019 on chromosomes 2 and 8 with LOD-values of 7.67 and 4.99 respectively, and six potential CDGs for the polygenic resistance in ‘ Shireen ’. The genomic region corresponding to the mapped QTLs in LG 2 and LG 8 of ‘ Shireen ’ was examined for candidate genes possibly related to scab resistance using in silico analysis. Conclusion The QTLs mapped in the genetic background of Shireen are the novel QTLs and may be transferred to desirable genetic backgrounds and provide opportunities for isolation and cloning of genes apart from their utility to achieve durable resistance to scab.