VIEW ARTICLE

Ecology and Epidemiology

Sclerotial Survival and Apothecial Production by Sclerotinia sclerotiorum Following Outbreaks of Lettuce Drop. Y. Ben- Yephet, Department of Plant Pathology, Agricultural Research Organization, Bet Dagan, Israel 50250; A. Genizi(2), and E. Siti(3). (2)Department of Statistics and Experiment Design, Agricultural Research Organization, Bet Dagan, Israel 50250; (3)Extension Service, Ministry of Agriculture, Be’er Sheva, Israel. Phytopathology 83:509-513. Accepted for publication 27 October 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-509.

The number of sclerotia of Sclerotinia sclerotiorum gradually declined over the years following outbreaks of lettuce drop in four naturally infested fields. The rates of population decline did not differ significantly among the four fields tested. In two fields located in a semiarid region, 5.5 and 2% of the initial amounts of sclerotia were still viable after 7 yr. Sclerotia removed from soil samples were classified by weight into four groups: 14–40, 7–14, 3–7, and 1–3 mg per sclerotium. The frequency distribution of the four sclerotial weight groups changed over the years, as small sclerotia became increasingly predominant over large ones. This trend was significant according to a generalized logit model. The number of apothecia produced per sclerotium showed a significant nonlinear increase with increasing sclerotial weight. The percentage of apothecia-producing sclerotia decreased significantly with increasing depth of burial in the soil. In addition, apothecial production was delayed with depth. Of the apothecia produced by sclerotia in lettuce fields 80 days after planting, 94% were located in the top 5 cm of the soil. The highest relative frequency of carpogenically germinated sclerotia (24.6%) was found at a depth of 2 cm.