Behaviour of a plant growth-promoting sterile fungus on agar and roots of rye-grass and wheat

Abstract

The radial extension of a plant growth-promoting sterile red fungus (SRF) after 3 d on various agars at 25 °C was most on wheat meal agar and least on water agar. Maximum growth on potato dextrose agar (PDA) was at 25° and minimum at 30°. The pH optimum for growth on PDA was 5·5 and minimum was 4·0 both after 3 d at 25° or 70 d at 5°. At 5° the SRF produced drops of exudate around the fungal disk in the centre of the plate. These appeared in all pH treatments after 20 d, with the exception of pH 4·0 and 4·5; most appeared between 50–60 d for all treatments, the amount exuded declining after this period. More exudate was evident at pH 7·5 between 50 and 70 d than in any other treatment. The exudate inhibited growth of Gaeumannomyces graminis var. tritici (Ggt) on agar. The SRF colonized roots of wheat ( Triticum aestivum cv. Gamenya) more aggressively than those of rye-grass ( Lolium rigidum cv. Wimmera) both in sterilized and non-sterilized soil. Ggt had no effect on the progression of the SRF on the roots of wheat or ryegrass when they were co-infested in sterilized and non-sterilized soils. The SRF colonized the entire root system and crown regions of both hosts 4 d after incubation in both soil treatments. The extent of colonization by the SRF, whether alone or with Ggt, was more in non-sterilized than sterilized soil. The SRF protected the roots of wheat and rye-grass from Ggt in sterilized and non-sterilized soil since most plants of wheat and rye-grass died in Ggt alone treatments.