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Ecology and Epidemiology

Mycelial Growth and Infection Without a Food Base by Eruptively Germinating Sclerotia of Sclerotium rolfsii. Z. K. Punja, Graduate research assistant, Department of Plant Pathology, University of California, Davis 95616; R. G. Grogan, professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 71:1099-1103. Accepted for publication 9 February 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1099.

Sclerotia of Sclerotium rolfsii, which were induced to germinate eruptively by drying for 10 hr at 1520% relative humidity, infected bean and sugar beet plants at 25 or 30 C without an exogenous food base of nonliving organic material. On unsterilized field soil, eruptively germinating sclerotia infected sugar beet leaf petioles from a distance of 3.5 cm; on acid-washed and sterilized quartz sand, this distance was reduced to 1.5 cm. The maximum distance from which undried sclerotia could infect host tissue both on field soil and on quartz sand was 0.5 cm. Volatiles from various dried and remoistened plant tissues (hay) triggered eruptive germination of undried sclerotia and increased the competence distance on field soil and quartz sand from 0.5 cm to 3.5 cm and 1.0 cm, respectively. A directional growth of mycelium toward the source of volatiles was observed on all substrates tested. Infection of host tissue by dried sclerotia was greatly increased in the presence of moistened hay, and infection from distances up to 3.0 cm on quartz sand and 6.0 cm on field soil were recorded. The epidemiological significance of mycelial growth from eruptively germinating sclerotia of S. rolfsii is discussed.