Combining Effective Strains of Trichoderma harzianum and Solid Matrix Priming to Improve Biological Seed Treatments. G. E. Harman, Professor, Department of Horticultural Sciences, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. A. G. Taylor, and T. E. Stasz. Associate Professor, and Research Associate, Department of Horticultural Sciences, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. Plant Dis. 73:631-637. Accepted for publication 17 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0631.

Two strains of Trichoderma harzianum (T12 and T95) were fused to give an array of progeny strains, two of which (22 and 106) were selected for further study. Seeds of several crops were treated with the parental or progeny strains with or without solid matrix priming. For comparison, some seeds were treated only with a sticker (Pelgel) used in all treatments or with a standard fungicide, usually thiram, again with or without solid matrix priming. Seeds of cotton (Gossypium spp.), cucumber (Cucumis sativus), pea (Pisum sativum), snap bean (Phaseolus vulgaris), sweet corn (Zea mays), and wheat (Triticum aestivum) were planted in soil infested with Pythium ultimum. Wheat seeds were also planted in soil containing Fusarium graminearum, cucumber and snap bean seeds in soil containing Sclerotium rolfsii, and radish (Raphanus sativus) and cucumber seeds in soil infested with Rhizoctonia solani. In all crop-pathogen combinations, Trichoderma strains increased stands relative to the untreated control and were as effective as the chemical fungicides, even in the absence of solid matrix priming. Priming of seeds treated with Trichoderma strains increased plant stands in soils infested with F. graminearum and P. ultimum but not in soils infested with R. solani or S. rolfsii. In soils infested with P. ultimum, strain T95 generally gave the poorest results, T12 was intermediate, and the progeny strains (22 and 106) gave improved stands. All four strains gave similar levels of protection against the other pathogens. In Pythium-infested soils, cucumber seedlings from seeds treated with strain 22 or 106 were more robust and had greater root volumes than those from seeds treated with T12 or T95. In field trials, stands of peas were not significantly enhanced by seed treatment with Trichoderma strains in the absence of priming but were improved by Trichoderma plus priming. The progeny strains were more effective than the parental strains in colonizing roots of mature pea plants. In two field trials with sweet corn, strain T12 increased plant stand, reduced seedling mortality, and increased plant growth relative to no treatment. The increased plant growth was evident for the entire duration (98 days) of the longest trial.

Keyword(s): protoplast fusion, soilborne pathogens, biological control.