Influence of temperature and water potential on growth of Botrytis allii

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Abstract
Water potentials for optimum growth varied with temperature and with the material used to alter water potential. On prune extract – lactose – yeast extract (PLY) agar adjusted with KCl, sucrose, NaCl, or polyethylene glycol (PEG) 8000, growth rates were optimal at 20 or 25 °C and at water potentials of −5 to −10 bars (1 bar = 100 kPa). At 30 °C growth rates were optimal at −35 to −45 bars in the presence of KCl or sucrose and at −10 to −20 bars with NaCl or PEG 8000. Radial growth rates in dried onion leaves, adjusted to various water potentials over salt solutions in sealed chambers, corresponded to those on PLY media adjusted to the same water potentials with KCl or sucrose. Growth was halted at water potentials below −95 to −100 bars in onion leaves or in PLY agar containing KCl or sucrose osmotica, but it was halted at −50 to −60 bars in the presence of NaCl or PEG 8000. Growth of Botrytis allii in onion bulb tissue was optimal at 20 °C. Extent of bulb colonization increased linearly with the logarithm of increasing inoculum concentrations applied to small wounds in bulbs. Survival of B. allii in dead leaf tissue declined rapidly after 3 and 9 days at 37 and 32 °C, respectively.