Combinatorial approach based on conventional and molecular methods for identification of scab resistance genes in apple germplasm of Jammu and Kashmir, India

Management of scab through resistant varieties represents a cost effective and eco-friendly alternative to chemical control. The accurate identification of resistant genotypes is carried out both at phenotypic as well as genotypic levels and most of the previous studies on resistance screening have been carried out using only one of these strategies. We used a combination of conventional and molecular marker based approaches for screening of 75 apple genotypes, in Kashmir region of India, to get more reliable results. We identified 17 genotypes carrying major scab resistance genes Rvi2, Rvi6, Rvi8 and Rvi11 with genotypes like Shalimar 2nd, Liberty and Sangerwan Delicious carrying multiple scab resistance genes, a finding that bypasses the use of tedious and time consuming procedure of gene pyramiding and could save researchers invaluable resources and time. We also identified two genotypes of Indigenous Ambri cultivars carrying Rvi11 scab resistance gene, a finding that may play an important role for revival and commercialization of Ambri cultivars which is considered as native of Kashmir valley of Jammu and Kashmir but are under serious threat from other commercially viable cultivars. Earlier scales used for resistance screening lack a separate category for identification of quantitative resistance. We introduce a separate class for genotypes carrying quantitative resistance because we believe it can be very important for disease management especially when present alongside a major scab resistance gene. We also conclude that genetic background in which a scab resistance gene is embedded is the major factor for the phenotypic response it shows upon inoculation with the pathogen.