Effect of Temperature on Antagonistic Fungi and Their Biological Control of <I>Alternaria brassicicola</I> (Schweinitz)

Abstract

Epiphytic fungi for the biological control of  Alternaria brassicicola (Schweinitz)  causing agent of   Chinese kale leaf spot  were collected from healthy leaves of  cabbage, Chinese cabbage, Chinese mustard, broccoli and Chinese kale form four different locations. Two hundred and twelve isolates were detected by hyphal tip isolation technique and only four isolates showed the best potential  antogonistic to A. brassicicola in vitro uisng dual culture technique . They  were identified  as Fusarium sp. (isolate 011),    Fusarium sp. (isolate 170), Penicillium sp. (isolate 075)  and Penicillium sp. (isolate 173). Culture filtrates of these isolates were tested for their effects to A. brassicicola  in terms of spore germination and spore production. The results revealed that Penicillium sp. (isolate 075) showed the highest inhibition of spore  germination with the reduction of 76.72%  whereas  Fusarium sp. (isolate 011)  gave the highest inhibition of spore production with the  reduction of 98.23%. All other antagonistic isolates showed the effects on both spore germination and spore production with the reduction indicated more than 50%.  The inhibition test of four antagonists to A. brassicicola by dual culture was also performed in different temperature conditions (19 , 27  and 32 ^oC). The result showed that temperature had an effect on the strength of antagonistic isolates, antagonists were more vigorous  when grown in warm condition, and the growth of the pathogen, there was the reduction of the number of spores and the spore size and the mycelia turned to lean as well.  The most efficient antagonist  of  A. brassicicola  was Fusarium sp. (isolate 011) when the dual culture test was performed at  32 ^oC with  48.24 % inhibition.