Biological Control of Common Root Rot of Spring Wheat by Coating Seeds with Bacillus or richoderma spp.

Common root rot of wheat (Triticum aestivum L.) causedby Fusarium graminearum and Cochliobolus sativus is the mostdestructive disease in Qassim region, Saudi Arabian fields. Theobjective of this work was to obtain and test new bioagents for controlof wheat root rot. Rhizobacteria isolated from healthy wheat rootswere tested for their antagonistic effect on F. graminearum and C.sativus in petri plates. Bacillus polymyxa and a new Bacillus sp. wereselected for their strong antagonists to F. graminearum and C. sativus.Bacillus isolates and two Trichoderma spp. were applied to wheatseeds and sown in soil infested with F. graminearum and C. sativusand tested in both greenhouse and field experiments for two successivegrowing seasons (1998/1999 and 1999/2000). Application ofrhizobacteria to wheat grains reduced incidence of seedlings foot rotin greenhouse experiments. Meanwhile, seed treatment with Bacillusspp. reduced severity of common root rot symptoms significantly andincreased wheat grain yield up to 102% compared to Vitavax treatedseeds in the field. Wheat seeds treated with Trichoderma spp.improved plant growth and increased wheat grain yield in the field upto 62%. The efficacy of the tested biocontrol agents was greatlyaffected by growing season.