A Rapid Greenhouse Screening Method to Identify St. John’s Wort (Hypericum perforatum) Accessions Resistant to Colletotrichum gloeosporioides

Abstract

Anthracnose is a major production constraint for st. john’s wort (Hypericum perforatum L.) caused by the fungus Colletotrichum gloeosporioides (Penz.). A greenhouse screening method based on mortality was developed to eliminate accessions susceptible to anthracnose in the early stage of breeding for resistant cultivars. The mortality of 22 accessions of st. john’s wort artificially inoculated with a strain of C. gloeosporioides was highly correlated between three greenhouse experiments (r = 0.799 to 0.923), even when done at two different places. The response of the greenhouse screening was equally highly correlated to the mortality in the field tested at two sites naturally infested with C. gloeosporioides (r = 0.700 to 0.865) but less well correlated with the mortality at a third field site (r = 0.495 to 0.672). Yield of st. john’s wort was highly correlated with mortality (r = –0.747 to –0.846) at all three field sites, but a significant interaction between accession and site was observed. Therefore, an improvement of anthracnose resistance of st. john’s wort should be based on a greenhouse screening of seedlings followed by multiple-site field testing of adult plants.