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Ecology and Epidemiology

Improved Seedling Performance by Integration of Biological Control Agents at Favorable pH Levels with Solid Matrix Priming. G. E. Harman, Professor, Department of Horticultural Sciences, New York State Agricultural Experiment Station, Geneva 14456; A. G. Taylor, Associate professor, Department of Horticultural Sciences, New York State Agricultural Experiment Station, Geneva 14456. Phytopathology 78:520-525. Accepted for publication 15 September 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-520.

Solid matrix priming (matrix priming) is a process in which moistened seeds are mixed with an organic carrier and the moisture content of the mixture brought to a level just below that required for seed sprouting. Untreated seeds or seeds treated with Enterobacter cloacae without matrix priming of either cucumber or tomato produced few or no seedlings when planted in infested soil. Treatment of cucumber seeds with Trichoderma strains without matrix priming resulted in about 30% of seeds producing seedlings, but most succumbed to postemergence damping-off. About 90% of the cucumber seeds treated with thiram alone gave rise to seedlings, all of which died within 8 days of planting. Treatment of tomato seeds with Trichoderma strains or thiram without matrix priming resulted in 70–95% stands, with a low level of damping-off. Combining matrix priming, in Agro-Lig (pH 4.1), with any of the biological control agents, improved seedling performance markedly relative to seeds treated with the organism alone. All organisms, when combined with matrix priming on cucumber seeds, gave 80–96% initial seedling emergence, and with Trichoderma-treated seeds, postemergence damping-off was less than when seeds were treated with thiram. With tomato seeds, combining matrix priming with Trichoderma or thiram resulted in very good stands and little damping-off. E. cloacae worked poorly on tomato seeds primed in Agro-Lig. Substitution of sphagnum or a pH 6.6 bituminous coal for Agro-Lig in matrix priming altered the results: Trichoderma strains worked most effectively in sphagnum or the lignite material, whereas the performance of E. cloacae was markedly improved in the coal carrier. On tomato, E. cloacae did not survive matrix priming in Agro-Lig, whereas 10⁷ propagules per seed were recovered from matrix priming plus E. cloacae in the coal carrier. On cucumber, 10⁸ propagules of the bacterium were recovered per seed in the coal carrier, but only 10⁵ in Agro-Lig. Seeds could be dried after matrix priming with retention of enhanced microbal activity, but levels of E. cloacae on coal-primed tomato seeds declined from 10⁷–10⁸ to 10⁵ propagules per seed on drying, and Trichoderma numbers decreased four- to sixfold. A series of treatments were conducted to determine whether the carrier, priming of the seed, priming of the biocontrol agent, or some combination of these was responsible for the beneficial results noted. The best results were obtained with matrix priming when T. harzianum was primed on the seeds. Priming of seeds plus T. harzianum in a conventional liquid priming system using polyethylene glycol as the osmoticant resulted in no recovery of the organism and poorer performance in infested soil than when matrix priming was combined with this fungus. Matrix priming plus Trichoderma strains resulted in more rapid emergence from Pythium-infested soil and more rapid seedling growth than seeds given matrix priming alone or matrix priming plus thiram. In uninfested soil, seeds treated with matrix priming alone or matrix priming plus thiram emerged and grew at the same rapid rate as seeds treated with matrix priming plus Trichoderma. Addition of 0.5 N HCl to cucumber seeds (making the seed pH at 3.7) treated with T. harzianum markedly improved stands when planted in Pythium-infected soils relative to seeds treated only with T. harzianum.