Evaluation ofTrichoderma koningiiandT. harzianumfrom New York Soils for Biological Control of Seed Rot Caused byPythiumspp.

Abstract

Some soils with low Fe levels are suppressive to Trichoderma spp. because of the activity of pseudomonads and their siderophores. Isolates of Trichoderma were obtained from a soil suppressive to these fungi. The abilities of these isolates to protect pea [Pisum sativum] seeds against Pythium spp. were determined. The 2 most effective isolates were identified as T. koningii (T8) and T. harzianum (T12). Both isolates grew well on seeds, and neither was affected by seed-colonizing pseudomonads. T8 grew better than T12 at 10.degree.-20.degree. C. The optimal pH for both isolates was 4.5, and both grew slowly at pH 2 and 8. Both isolates were inhibited by the partially-purified fluorescent pigment from a Pseudomonas sp., but T12 was less inhibited than T8. T12 grown on low-Fe (King''s B) medium produced a fluorescent pigment that was precipitated by the addition of FeCl3, but T8 did not. T8 produced 28% as much biomass on a medium with very low (17 ng/ml) Fe as on a less deficient medium, but T12 produced only 7.5% as much. Both isolates protected seeds against seed rots in soils naturally infested with Pythium spp. when applied either as a seed coating in various adhesives or when applied in gels used for fluid seed drilling. Polyvinyl alcohol tended to give less disease than other adhesives tested. Among gels, Poly Surf C (a hydroxyethyl cellulose) and Polytran A (a glucan) gave better results than the silica-based Laponite 508. In field trials, T8 consistently protected peas and beans [Phaseolus vulgaris] against seed rots. Materials tested as spreader-stickers for seed treatments or as gel carriers used in fluid seed drilling differ in suitability as delivery systems for biocontrol agents; polyvinyl alcohol works well as a spreader sticker, and Poly Surf C is useful in fluid seed drilling systems.