Occurrence of Species of Aspergillus and Penicillium in Roots of Wheat and Ryegrass and Their Effects on Root Rot Caused by Gaeumannomyces graminis var. Tritici

Abstract

Aspergillus fumigatus, A. terreus, Emericella nidulans, E, quadrilineata, Penicillium aculeatum, P. brevicompactum, P. chrysogenum, P. citreonigrum, P. corylophilum, P. fuscum, P. griseofulvum, P. janthinellum, P. nigricans, P. purpurogenum, P. restrictum, P. turbatum, P. verruculosum, Eupenicillium sp. and E. euglaucum were isolated from roots of wheat and ryegrass at seedling, tillering, stem extension, milky ripe and ripe for cutting stages. Frequency of occurrence of species of Aspergillus and Penicillium were higher in roots subjected to washing only and plated onto PDA or PDA amended with lactic acid. In general, species of these two genera were common at the stem extension stage. P. nigricans, P. janthinellum, P. griseofulvum, P. fuscum, Eupenicillium sp. and P. turbatum were isolated at a higher frequency than other species. When introduced at 1% inoculum level A. terreus, P. fuscum, P. griseofulvum and P. nigricans caused severe damage to wheat and ryegrass seedlings especially in sterilised Lancelin soil where they reduced the fresh shoot and root weights of the hosts. When these isolates were screened for antagonism towards Gaeumannomyces graminis var. tritici (Ggt) or agar the strongest antagonism was shown by P. griseofulvum, A. terreus, P. nigricans, P. fuscum and P. janthinellum, whereas other species of the two genera had little or no effect on Ggt. The presence of A. terreus, P. griseofulvum or P. fuscum. with Ggt decreased root rot of wheat and ryegrass caused by Ggt in sterilised and non-sterilised soil, while P. nigricans showed a similar effect in non-sterilised soil only. However, none of the isolates tested would be suitable as biological control agents.