QTL mapping for resistance to Pseudomonas syringae pv. actinidiae (Psa) in tetraploid Actinidia.

For fifteen years, bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), has severely impacted kiwifruit cultivation. To some extent, all cultivated varieties are susceptible, resulting in production losses and plant mortality, although different degrees of resilience to the disease are known. Current prevention relies on careful prophylaxis and cultivating less susceptible varieties, as no resistant varieties have been licensed yet. However, some genotypes within the genus Actinidia show resistance. Recent studies have focused on identifying genes associated with resistance or susceptibility to Psa. In this study, a high-resolution interspecific linkage map (A. chinensis var. chinensis × A. arguta) was constructed using SNP markers obtained through ddRAD sequencing. Controlled cane inoculations of the interspecific population were followed by lesion length and infection assessments over six weeks. QTL mapping identified a major QTL on Chr28 and two minor QTLs on Chr4 and Chr17 linked to resistance in A. arguta. A susceptibility-associated QTL was also detected on Chr9 in A. chinensis var. chinensis. RNA-seq analysis of infected sub-cortical tissues from parental genotypes revealed differentially expressed genes, highlighting candidate genes potentially involved in resistance and susceptibility mechanisms. These findings enhance our understanding of genetic resistance and provide valuable targets for breeding Psa-resistant kiwifruit cultivars.