Induction of defense genes and secondary metabolites in saskatoons (Amelanchier alnifolia Nutt.) in response to Entomosporium mespili using jasmonic acid and Canada milkvetch extracts

Entomosporium leaf and berry spot represent the most important disease of saskatoons (Amelanchier alnifolia Nutt.). This disease, caused by the ascomycete Entomosporium mespili (D.C.) Sacc., is difficult to control via conventional methods and no known saskatoon cultivar carries resistance to this pathogen. The aim of the present study was to enhance existing and induced defense responses of saskatoons using two host defense inducers, namely jasmonic acid and an extract from Canada milkvetch on two saskatoon cultivars, Smoky and Martin. Both inducers exhibited an ability to differentially induce the synthesis/accumulation of defense-related genes including those encoding for PR-1, PR-2, PR-5, LOX and PAL. Pre-treatment of saskatoon leaves with these inducers reduced the disease levels especially when applied to the moderately susceptible cultivar Martin. An accumulation of various hydroxycinnamic acid and proanthocyanidin derivatives also correlated with the disease levels recorded on both cultivars. Results are discussed on the basis of the induced pathways in an attempt to lay the ground for a better understanding of this host–pathogen interaction. In the meantime, we have shown that the use of defense enhancers may be useful in integrated management strategies to control entomosporium leaf and berry spot in saskatoons.