Effect of crop extracts on carpogenic germination of sclerotia, germination of ascospores and lesion development of Sclerotinia sclerotiorum

Experiments were conducted to determine the effect of 1, 2 or 4% (w/v) aqueous crop extracts of barley, canola, lentil, oat, rye, sweet clover and wheat on carpogenic germination of sclerotia, germination of ascospores and lesion development of Sclerotinia sclerotiorum on detached bean leaves. The sclerotia germination was significantly (P < 0.05) reduced by 1% canola extract, 2% extracts of barley, canola, oat and lentil and by all extracts of 4% concentration, compared to the water control. Germination of ascospores was significantly (P < 0.05) lower in 1, 2 and 4% extracts of barley, or in 1 and 4% extracts of oat, but significantly higher with 1, 2 and 4% extracts of canola, lentil, rye, sweet clover and wheat than control. Inoculation of detached bean leaves with ascospores of S. sclerotiorum mixed with 4% crop extracts of barley, oat or sweet clover significantly reduced the lesion severity index compared to leaves inoculated with water + S. sclerotiorum, whereas inoculation with 4% wheat extract resulted in a significantly increased the lesion severity index. The studies demonstrate that aqueous extracts of certain crop plants have suppressive or stimulatory effects on the plant pathogen, S. sclerotiorum, depending upon the (i) crop plant, (ii) concentration of the extract and (iii) the type of pathogen inoculum (sclerotia or ascospores). The possible application of these findings for biological control, crop rotation and sustainable disease management are briefly discussed.