Trichoderma spp. from New Zealand soils were evaluated (in greenhouse experiments and one field trial) for Rhizoctonia disease suppression and plant growth promotion of potato plants. Trichoderma virens LU549, T. atroviride LU144 and T. barbatum LU1482 demonstrated the greatest suppression of cankers on potato plants; the percentage of diseased stolons was reduced by 41–46%, compared with the R. solani control. Trichoderma virens LU549 also increased average tuber weight by 210%, and T. atroviride LU144 by 146%, compared with the R. solani control (in which tuber formation was highly suppressed). In plant growth promotion pot trials, the greatest proportional increases for three plant growth parameters (compared with the untreated control) were elicited by: T. harzianum LU1491 (number of tubers), T. barbatum LU1489 (total tuber weight), and Trichoderma sp. 792 LU1483 (average tuber weight). All six of these strains were selected and evaluated in all combinations in a 26 factorial greenhouse experiment. Trichoderma atroviride LU144 had positive impacts on several Rhizoctonia disease and plant growth parameters. Four of the strain combinations were subsequently tested in a field trial during the 2011/12 growing season, in which two Trichoderma strain combinations increased potato tuber yields. This research has shown potential for use of New Zealand Trichoderma strains to suppress Rhizoctonia diseases of potato and increase crop productivity.
biological control; combination