Role of root colonization ability of plant growth promoting fungi in the suppression of take-all and common root rot of wheat

Plant growth promoting fungal (PGPF) isolates - GS6-1, GS7-4 (Phoma sp.) and GU23-3 (non-sporulating fungus), from zoysiagrass rhizosphere, suppressed take-all and common root rot of spring wheat caused by Gaeumannomyces graminis var. tritici (Ggt) and Cochliobolus sativus (Cs), respectively, in the greenhouse. Barley kernels colonized with pathogens (0.1%, 0.5% or 1.0% w/w) and PGPF isolates (1.0%, 1.5% or 2.0% w/w) were added to soil individually and in different combinations of pathogen and PGPF. With an increase in the rate of PGPF amendment, all three PGPF isolates suppressed take-all and common root rot (P = 0.05), irrespective of the pathogen inoculum level. Among the PGPF isolates, GS6-1 and GS7-4 were more effective than GU23-3. When added to soil individually, PGPF isolates were recovered from 75 to 95% of root segments, and Ggt and Cs from 88-95% of root segments. Both Ggt and Cs were isolated less frequently from roots when the PGPF concentration was high (2.0%); however, the PGPF isolates were isolated from roots in high frequencies even when the pathogen inoculum level was high. Isolate GS6-1 promoted plant growth even when the pathogen inoculum rate was high, as did GS7-4, but to a lesser amount. These fungal isolates suppressed take-all and common root rot, and two of them also increased plant growth. The suppression of take-all and common root rot appeared to be due to the competitive root colonization by PGPF isolates, thus blocking sites available for infection by pathogens. Copyright (C) 1996 Elsevier Science Ltd.