Interaction of Near-Ultraviolet Light and Temperature on Sporulation of the Fungi Alternaria, Cercosporella, Fusarium, Helminthosporium, and Stemphylium

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.

In vitro production of conidia of Alternaria solani

“…In the present work, greater sporulation was obtained under alternated regime of light (12 h photoperiod). This alternation simulates conditions required for conidial formation, as conidiophore formation occurs under irradiation and conidium formation during the dark period (Lukens, 1960;Leach, 1967;Waggoner & Horsfall, 1969;Douglas, 1972;Walker, 1980). Wavelengths near 310 ηm, provided by black light, stimulate sporulation of A. solani and the conidiophores do not revert to vegetative hyphae when exposed to the dark, allowing conidial formation (Aragaki et al, 1973).…”

Effect of light on sporulation ofPlasmopara viticola

“…Ribeiro et al (1976) found that under a 12 h Iight/12 h dark regime, irradiation in the band 312-440 nm stimulated sporangium production by Phytophthora capsici Leonian and P. palmivora (Butler) Butler, but they did not test the effect of continuous irradiation. Leach (1967) pointed out that for some fungi, near-u. v. light can stimulate the inductive phase but inhibit the terminal phase of sporulation.…”

Botrytis cinerea in greenhouse vegetables: chemical, cultural, physiological and biological controls and their integration

“…It was recognized for fungi such as Alternaria, Cercospora, Fusarium, Helminthosporiurn and Sternphylium (Aragaki 1962;Leach 1967;Honda and Sakamoto 1968;Onesirosan and Banttari 1969;Vakalounakis and Christias 1981), B. squamosa (Bergquist et al 1972) and Verticillium agaricinum (Osman and Valdon 1979). The sporulation of colonies of B. cinerea is affected by light as well.…”