Germination of plant seeds is accompanied by the exudation of host nutrients into the soil environment, which frequently attract potentially damaging fungi such as Pythium spp., R. solani, and Fusarium spp. These fungi utilize the seed and root exudates as an energy source for germination and growth, and subsequently penetrate and colonize the seed and root hairs, causing rot and damping-off of emerging seedlings. These fungi are favored by cool (15-20°C) and moist conditions. Fungal biological control agents have been described which when applied to the surface of seed, to the planting substrate, or when applied shortly after seed germination, can utilize the host nutrient exudates and colonize the seed and developing roots to compete with and exclude the pathogenic fungi. In addition, many of these biocontrol agents secrete hydrolytic enzymes and antibiotics that inhibit the development of the pathogenic fungi. The most widely-researched of these biocontrol agents are species of Trichoderma and Gliocladium and to a lesser extent Penicillium spp. (Table 1).
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