Stem rot disease incidence on faba beans in an artificially infested field

Abstract

Stem rot, a destructive fungal disease caused by Sclerotinia trifoliorum Eriksson, is a serious problem for many important crops including faba beans (Vicia faba L.). Field experiments were carried out for five consecutive years in northern Greece to study the period of infection of S. Trifoliorum and the disease incidence in faba beans grown in a field that was artificially infested by placing various numbers of fungal sclerotia into the soil during the sowing period. Disease severity was very low (< 4%) in all growing seasons, whereas a high percentage of infection (13.3 to 95.0%) was observed under controlled environment. Apothecial production in the field occurred from November to early January. Symptoms of fungal infection on faba bean plants were observed from early February to early April, with the most infection occurring during March. Faba bean plants were infected by mycelium, after myceliogenic germination of sclerotia, at the base of the stem close to the soil surface. Visible, water-soaked lesions appeared before flower initiation. Disease severity was not significantly correlated with monthly rainfall (r = 0.11) nor with mean monthly temperature (r = 0.15) over five growing seasons. The growth stage of plants and the absence of an energy source during ascospore release, as well as the mode of sclerotial germination (myceliogenic), may have been the critical factors responsible for the low disease severity in the field.