Research Projects

Apple (Malus × domestica) scab can reach up to 70% in susceptible cultivars if left unmanaged, making it one of the most economically damaging diseases in apple cultivation (Masoodi et al., 2022; Zelmene et al., 2022). This at times can result in devastation of entire fruit economy of Jammu and Kaashmir to the tune of 10000 Cr. Traditional scab management strategies involve the frequent application of fungicides, with 20 to 30 sprays per growing season being typical in many commercial orchards. One of the apple scab controlling strategies is gene pyramiding—especially the combination of R genes and quantitative trait loci (QTL, ensuring new cultivars with at least two or more resistance genes ensure long-lasting resistance to apple scab (Bus et al., 2011; Peil et al., 2011). A deeper understanding of the genetic mechanisms underlying scab resistance in Shalimar Apple 1, an apple cultivar developed at SKUAST-Kashmir, exhibits robust scab resistance derived from its unique genetic background will be obtained. 'Gala' is noted for its great quality, red colour and popular high-yielding apple variety that but on the other hand, partially resistant to apple scab. Ambri an indigenous (unique aromatic) apple cultivar on the other hand, is a popular apple variety that is noted for its great aroma but is prone to apple scab. The 'Gala' and 'Ambri' varieties with contrasting responses to scab were crossed to develop an F1 mapping population of 300 plants. This population is particularly valuable for mapping resistance traits due to the contrasting phenotypes of the parents and the presence of novel QTLs. We have also crossed ‘Gala’ with another parent ('Shalimar Apple 1') (male parent) having Rvi6 gene imparting resistance through major gene. Indeed, major genes are totally effective to control the avirulent fraction of the pathogen population, whereas QTL reduce the pathogen population size, which limits the selection for virulent isolates and maintains a partial effectiveness of the resistance towards the virulent isolates (Delourme et al., 2014). We have developed a protocol to fasten the growth of apple plants and reduce its juvenility. Here our aim is to map the QTLs in the shortest possible time, expression studies to identify of novel resistance pathways, investigate the effectiveness and durability of combining/ pyramiding one major gene (Rvi6) or gene(s) with QTLs in the apple scab pathosystem of unsprayed orchards where resistance effectiveness to other major gene has already been challenged. We are expecting a high-quality apple with major resistance genes and QTLs which has also been validated by our preliminary studies. The apple cultivars developed ion current study shall have the potential to help in apple production with least residual fungicides and high value crop. We presumed that resistance to scab in 'Gala' is conditioned by QTLs and could be mapped in the F1 (Pseudo-backcross) population. It’s largely due to presence of a substantial number of candidate defence genes inside the confidence intervals of the mapped QTLs. The molecular mechanism underlying such resistance can further be validated through transcriptomic analyses that can uncover differentially expressed genes (DEGs) involved in defense responses, enabling the discovery of novel resistance pathways on an individual basis. Our primary hypothesis is that resistance to apple scab in the cultivar ‘Shalimar Apple 1’ is polygenic, and combining major resistance genes (e.g., Rvi6) with partial resistance loci (QTLs) can enhance the durability of scab resistance across diverse environmental conditions. We further hypothesize that differentially expressed genes (DEGs) identified through transcriptomics are involved in key defense pathways and can serve as potential targets for breeding. Lastly, we hypothesize that pyramiding multiple resistance genes and QTLs will reduce the selection pressure on V. inaequalis and delay the breakdown of resistance.