Relationship between foliar endophytes and apple cultivar disease resistance in an organic orchard

Many studies have shown that foliar endophytes enhance host resistance to leaf pathogens. Although plants show large genotype-related intraspecific variation in pathogen resistance, few studies have examined whether disease resistance is also influenced by the endophyte community. In the present study, we tested the hypothesis that apple cultivar differences in leaf pathogen resistance are related to their respective foliar endophyte communities. We inoculated spores of Alternaria leaf spot (Alternaria mali) in an organic orchard that had not been exposed to any chemical pesticide for over 30 years, and evaluated leaf damage in 18 apple trees belonging to three cultivars with differing levels of resistance. The richness, composition, and abundance of the foliar endophyte communities in the same 18 trees were also examined using terminal restriction fragment length polymorphism. We found that cultivar resistance to lower leaf damage correlated significantly with the abundance of endophytic fungal species. These results suggest that endophytic fungi can promote leaf spot resistance in apple cultivars.