Influence of different irrigation regimes on carpogenic germination of sclerotia of Sclerotinia sclerotiorum

The effects of irrigation level, irrigation interval, length of irrigation break and of soil type on apothecial production, apothecial survival and sclerotial survival of Sclerotinia sclerotiorum were studied in field experiments in 1991 and 1992. The experimental area was sown with spring rapeseed and naturally produced sclerotia were placed 1 cm deep in the soil. Apothecia production started after 25-30 days of continuous soil moisture and was strongly influenced by the irrigation regime. Apothecia development was delayed if an irrigation break occurred before the start of apothecia production. The delay was approximately of the same length as the irrigation break. A high irrigation level caused more abundant apothecia production in the sand than in the loam, while at a low irrigation level, more apothecia were produced in the loam than in the sand. The maximum lifespan of apothecia was 33 days which was measured in the sand irrigated at 5 mm/day. The length of the moist period needed for carpogenic germination and the influence of dry periods are shown in this study and can be used when predicting the start of apothecia development. It is also shown that both soil type, amount of irrigation or rainfall and its distribution must be considered when estimating the number of apothecia and apothecia longevity.