Identity and frequency of occurrence ofTrichoderma spp. in roots of wheat and rye-grass in Western Australia and their effect on root rot caused byGaeumannomyces graminis var.tritici

Abstract

Trichoderma hamatum, T. harzianum andT. koningii were isolated from wheat and rye-grass roots from a field in Western Australia. Frequency of occurrence ofTrichoderma spp. was higher on roots subjected to washing only, for both wheat and rye-grass than the roots which were surface-sterilized with 0.6% or 1.25% NaOCl.Trichoderma spp. were recovered at a higher frequency on PDA amended with lactic acid (pH 4.5) than on PDA alone (pH 5.6) or PDA with streptomycin. In general,Trichoderma spp. were isolated at a higher frequency from roots of wheat than that of rye-grass.T. hamatum occurred at a higher frequency in rye-grass roots than in wheat, whereasT. harzianum was more common in roots of wheat than in rye-grass, especially in seedling and milky ripe stages.T. koningii was recovered at a higher frequency from roots at seedling stage of rye-grass than wheat, the reverse being true at tillering stage.T. koningii was not recovered from roots of either host in any sampling when they were surface sterilized with 1.25% NaOCl.

The take-all fungus was isolated from wheat and rye-grass roots more frequently at tillering and stem extension stages than others. It was severely pathogenic to both hosts in sterilized and non-sterilized soil.

Addition of lactic acid, HCl or streptomycin to PDA did not affect the growth of theTrichoderma spp. tested, but the growth was slower on Martin's medium than on other media. In generalT. harzianum andT. koningii grow faster thanT. hamatum. The growth of the three species were not different at 20 and 25°C, but at 15°c growing of all species was significantly reduced.

Incorporation of lactic acid into PDA prevented the bacterial growth in all treatments. Streptomycin too reduced but to a lesser degree than lactic acid. Surface sterilization with NaOCl decreased the recovery of both bacteria and fungi.

T. hamatum andT. koningii reduced the mortality of wheat and rye-grass plants inoculated with the take-all fungus in sterilized and non-sterilized soil, whereT. harzianum did not protect wheat or rye-grass from infection by the take-all fungus.