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°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°C, and was slightly affected by the vacuum used to reduce the O2 level. After 17 weeks of storage at 5°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°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 of 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.