Survival of sclerotia of sclerotinia sclerotiorum in soil

Abstract

Factors affecting longevity of sclerotia in sandy clay loam (s.c.l.) and sandy loam (s.l.) were examined, using sclerotia from a laboratory culture of S. sclerotiorum and from natural infestations on beans and lettuce. Survival of sclerotia from culture and lettuce was compared in s.l. Recovery and viability were less, and incidence of Fusarium, Mucor and Trichoderma spp. greater, in sclerotia from lettuce than from culture. Rinds of sclerotia from lettuce were more perforated than those from culture. Burial of sclerotia at 4 cm for 35 weeks reduced recovery of sclerotia to zero in s.c.l. and by 50% in s.l. At the soil surface recovery was reduced by 55% in s.c.l. and by 10% in s.l. Less than 50% of sclerotia recovered were viable. Neither a chloropicrin-methyl bromide fumigant nor a tomato compost treatment affected recovery or viability. Fumigation increased incidence of Trichoderma spp. and decreased incidence of Fusurium and Mucor spp. isolated from sclerotia. Apothecia were produced over 6 weeks in s.c.l. and over 20 weeks in s.l. Production was increased by the low rate of fumigant in s.c.l. and by tomato compost in s.l.