FACTORS RELATING TO PEANUT YIELD INCREASES AFTER SEED TREATMENT WITH BACILLUS-SUBTILIS

Bacillus subtilis, when added as a seed treatment, consistently colonized the roots of peanut plants at rates exceeding 10(4) colony-forming units (cfu) per gram of root tissue when evaluated 120 days after planting. Yield increases from 1982 to 1985 ranged from -3.5 to 37%, with only two incidences of negative responses in 24 tests. Peanuts responded most favorably to the bacterial seed treatment when subjected to stresses, such as limited water availability, poor rotational practices, or cool soils, caused by early plantings. Treatment of peanut seed with B. subtilis was associated with improved germination and emergence, increased nodulation by Rhizobium spp., enhanced plant nutrition, reduced levels of root cankers caused by Rhizoctonia solani AG-4, and increased root growth. The means by which B. subtilis may affect yield in peanuts are multiple and are not operative at the same time, making predictions of degree of yield responsiveness difficult.