Hypovirulent Rhizoctonia spp. isolates from New Zealand soils protect radish seedlings against damping-off caused by R. solani.

Of the 206 Rhizoctonia spp. isolates obtained from 135 soil samples collected from different fields in the North and South Islands of New Zealand, 55% were pathogenic on radish (Raphanus sativus cv. Rex) seedlings. Only 27% of the isolates that were strongly pathogenic on radish were also pathogenic on ryegrass (Lolium perenne). While 13 of the 92 hypovirulent isolates provided >50% protection to radish seedlings against damping-off caused by Rhizoctonia solani in a screening experiment, only three provided >50% protection in the final, more detailed experiment. The best protective isolates, R85-10 and R30-8, consistently protected approximately 70% of radish seedlings in at least two separate experiments. There was no correlation between the growth rates of the hypovirulent Rhizoctonia spp. isolates and their percentage protection of radish seedlings against damping-off.