Low temperature induces decreased germinability of Cylindrocladium microsclerotia

Numbers of germinable Cylindrocladium crotalariae microsclerotia (assayed at 26 degrees C) decreased progressively over 4 weeks when naturally infested soils were incubated at 6 degrees C. Lower numbers of germinable microsclerotia were obtained from a soil incubated at--3 than at 5 degrees C, while no germinable microsclerotia were found for soils incubated at--10 degrees C. Significantly, when soils incubated at--10 or at 6 degrees C for 4 weeks were transferred to 26 degrees C for 4 weeks, the low-temperature effect was partially reversed. Incubation of naturally infested soils under field conditions from October to February indicated that a similar low-temperature induced phenomenon exists in nature. Germinability of axenic laboratory-grown microsclerotia of C. crotalariae, C. floridanum, and C. scoparium incubated 4 weeks at 6 degrees C ranged from 0 to 91% (mean = 38%) of the initial germinability. Partial recovery of laboratory-grown microsclerotia from the low-temperature effect, by incubation at 26 degrees C, was demonstrated. Conductivity measurements of solutions bathing microsclerotia incubated at 6 degrees C were higher than those incubated at 26 degrees C for 4 weeks and indicated that chilling injury may account, in part, for decreased germinability of microsclerotia.