EFFECT OF GROWTH MEDIA, STORAGE ENVIRONMENT, SOIL-TEMPERATURE AND DELIVERY TO SOIL ON BINUCLEATE RHIZOCTONIA AG-G FOR PROTECTION OF POTATO FROM RHIZOCTONIA CANKER

Binucleate Rhizoctonia (BNR) isolates propagated for 20 days at 24-degrees-C on oat kernels and for 30 days on vermiculite amended with potato broth were recovered from an average of 62% of whole kernels, 100% of chopped kernels and 71% of vermiculite particles within the cultures, respectively. Viability of BNR isolates 232-CG and JF-3S4-3 was higher when stored at 5 than at 24-degrees-C, and was slightly affected by the vacuum used to reduce the O2 level. After 17 weeks of storage at 5-degrees-C in air, BNR isolates 232-CG and JF-3S4-3 maintained similar viability (75% viability on whole oat kernels and 100% viability on chopped oat kernels), but in vermiculite amended with potato broth, viability of isolate 232-CG remained at 100% while that of JF-3S4-3 was 28%. In the glasshouse, BNR isolates 232-CG and JF-3S4-3 protected potato plants from Rhizoctonia canker caused by R. solani in soil maintained at 11, 17 and 23-degrees-C. Protection from Rhizoctonia canker was greater when BNR was delivered to soil than when placed on seed pieces. BNR-colonized-whole oat kernels placed in soil (15 g/m or row) gave the greatest protection from Rhizoctonia canker in all experiments. In two field experiments in soil naturally infested with R. solani AG-3, the amount of BNR-colonized oat kernels was reduced from 15 g/m of row to 1.9 g/m of row without affecting protection of potato plants from Rhizoctonia canker.