Decrease in incidence of Pythium damping-off of field pea by seed treatment with Bacillus spp and metalaxyl

Strains of Bacillus subtilis (Ehrenberg) Cohn and B. polymyxa (Prazmowski) Mace were screened for their antagonistic effect on Pythium ultimum Trow and irregulare Buisman in vitro. Of 10 strains tested in paired cultures, four strains of B. subtilis and two strains of B. polymyxa had an inhibitory effect on Pythium. Culture filtrates and bacterial suspensions of B. subtilis or B. polymyxa were also antagonistic to Pythium SPP in in vitro. Growth of P. ultimum and P. irregulare was reduced significantly by metalaxyl at concentrations of 0.01 and 0.10 mu g/ml, respectively, whereas growth of B subtilis and B. polymyxa was nor affected at the same concentration. The biocontrol agents B. subtilis and B. polymyxa, and the fungicide metalaxyl, were evaluated alone and in combination for reducing seed and root rot of field pea (Pisum sativum L. var. arvense (L.) Poir.) cv. 'Radley' caused by P. irregulare or P. ultimum. Seed inoculation with B. subtilis or B. polymyxa caused significant increases in percent seedling survival and shoot dry weight compared to nontreated seeds in infested soil. Greater seedling survival, plant height, and shoot and root dry weights were observed for seed treated with metalaxyl at the recommended. application rate than for seed coated with B. subtilis or B. polymyxa. However, the combination of B. subtilis or B. polymyxa with metalaxyl at one-half the recommended rate was the most effective method for reducing Pythium seed and root rot. Percent seedling survival, plane height, and shoot dry weight did not differ significantly for seed created with B. subtilis or B. polymyxa plus metalaxyl at the half rate compared with metalaxyl alone at the full rare. This study suggested that a combination of Bacillus spp. and metalaxyl at a low rare could be used to improve the establishment and growth of field pea in Pythium-infested soils.