Control of damping-off in cress and sugar-beet by commercial seed-coating with Pythium oligandrum

Seeds of cress and sugar-beet were coated with oospores of Pythium oligandrum using commercial seed-pelleting or film-coating procedures. Following either procedure approximately 10⁴ oospores were recovered from both seed types, achieving 75.94% of the targeted dose. Oospore germination (9.19%) was unaffected by the coating treatments. Both types of treatment reduced damping-off of cress caused by P. ultimum in artificially infested sand and potting compost and by Rhizoctonia solani in artificially infested sand. In some cases, the level of control was equivalent to fungicide drenches. In general, pelleting of P. oligandrum on cress gave better control than film-coating treatments. P. oligandrum also reduced damping-off of sugar-beet in soil naturally infested with Aphanomyces cochlioides and Pythium spp. Control was equivalent to that achieved with hymexazol fungicide seed-coating treatments and was related to the inoculum potential of A. cochlioides in the soil; neither standard hymexazol coatings nor P. oligandrum treatments gave control at high inoculum potentials. P. oligandrum was not rhizosphere competent on cress or sugar-beet.