VIEW ARTICLE

Ecology and Epidemiology

Effect of Water Potential and Temperature on Growth, Sporulation, and Production of Microsclerotia by Verticillium dahliae. N. Ioannou, Department of Plant Pathology, University of California, Davis, CA 95616; R. W. Schneider(2), R. G. Grogan(3), and J. M. Duniway(4). (2)(3)(4)Department of Plant Pathology, University of California, Davis, CA 95616, (2)Present address: Department of Plant Pathology, University of California, Berkeley, CA 94720. Phytopathology 67:637-644. Accepted for publication 3 December 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-637.

The minimum osmotic potential (φ_s,) which allowed conidial germination, mycelial growth, and sporulation of Verticillium dahliae was –100 to –120 bars. Radial growth on agar medium was maximal at φ_s values between –10 and –20 bars, but growth measured as increase in dry weight decreased linearly with decreased φ_s, of liquid medium from –2 to –120 bars. Likewise, the rate and final percentage of conidial germination decreased progressively with each decrease in φ_s below –2 bars. The production of conidia in liquid medium increased logarithmically as φ_s decreased from –2 to about –20 bars and was maximal at φ_s values as low as –50 bars. No (or very few) microsclerotia (MS) were produced at φ_s values between –70 and –80 bars, even though radial growth and production of dry weight were reduced by only 60% at these same φ_s values. The production of MS either was increased or remained unchanged by reduction of φ_s from –2 to about –20 bars and it decreased progressively with greater reductions in φ_s. The production of MS in infected tomato stems buried in nonsterilized soil was maximal at a water potential (φ) of –32 bars and at 24 C. Appreciable numbers of MS also were produced at 18, 27, and 30 C in soil at φ = –5 or –32 bars. However, in saturated soil and soil at φ = –100 bars the production of MS was greatly inhibited at all temperatures tested. When infected stems were adjusted by air-drying to φ values ranging from –5.8 to –98 bars and buried in soil at φ = –27.5 bars and 24 C, maximal numbers of MS were produced in tissue dried to φ = –18.7 bars. When similar tissues were buried in soil at φ = –0.8 bars only small numbers of MS were produced, regardless of the initial water status of the tissues.