BIOLOGICAL-CONTROL OF PHYTOPHTHORA-PARASITICA VAR. NICOTIANAE ON TOBACCO SEEDLINGS WITH NONPATHOGENIC BINUCLEATE RHIZOCTONIA FUNGI

Nonpathogenic binucleate Rhizoctonia fungi (BNR) controlled black shan k caused by Phytophthora parasitica var, nicotianae on greenhouse-grow n tobacco seedlings in styrofoam float trays. Three BNR isolates were incorporated into a soil-less mix on colonized, pulverized, sifted ric e particles; colonized whole rice grains; or on pelleted tobacco seeds coated with 0.5% methyl cellulose. Five-wk-old seedlings were inocula ted with zoospores of P. parasitica var. nicotianae and disease rated over 10 d. The level of protection varied with method of BNR applicati on, ranging from 40 to 70%. Overall, control was better when BNR isola tes were applied on rice inocula rather than on BNR-colonized tobacco seeds. From 15% to 80% of individual roots from seedlings grown in soi l-less mix amended with BNR-colonized rice grains were colonized while only 0-20% of roots from seedlings grown from BNR-colonized tobacco s eeds were colonized. Likewise, 37-100% of soil-less mix amended with B NR-colonized rice grains contained BNR's while less than 3% of soil-le ss mix was colonized when seedlings emerged from BNR-colonized tobacco seeds. This is the first demonstration of biocontrol of Phytophthora by BNR fungi. (C) 1998 Elsevier Science Ltd. All rights reserved.