Abstract
Alternaria dauci, A. tomato, Cercosporella herpotrichoides, Fusarium nivale, Helminthosporium catenarium, and Stemphylium botryosum, all Fungi Imperfecti, were grown on temperature gradient plates (5–40 °C) under different regimes of near-ultraviolet radiation (320–420 nm) and darkness. None of the fungi normally sporulated in darkness on the media used. The effects of interaction of temperature and near-ultraviolet radiation (NUV) on sporulation were significant for all six fungi. The fungi were grouped into two categories, "Diurnal Sporulators" (A. dauci, A. tomato, and S. botryosum) and "Constant Temperature Sporulators" (F. nivale, H. catenarium, and C. herpotrichoides). The "Diurnal Sporulators" have two distinct phases of photosporogenesis, an "inductive phase" leading to the formation of conidiophores, and a "terminal phase" resulting in the formation of conidia. The "inductive phase" is stimulated by NUV and operative at relatively high temperatures, while the "terminal phase" is strongly inhibited by NUV and blue light, and is operative at lower temperatures. In S. botryosum the "terminal phase" was completely inhibited by light at high temperatures but only partially inhibited at low temperatures.The "Constant Temperature Sporulators" in contrast, have a lower optimum temperature range for sporulation and show no clear separation of photosporogenesis into two distinct phases. Sporulation in this group is abundant under continuous exposure to NUV though it is even more abundant when exposure is followed by darkness.A new phenomenon, that of "high temperature induction" of sporulation, was observed in colonies of A. tomato and A. dauci. Relatively high temperatures caused these fungi to produce conidiophores in darkness, though only when the temperature was lowered did conidia form on the conidiophores. The amount of sporulation caused by "high temperature induction" was less than that caused by exposure to NUV.
Publisher
Canadian Science Publishing