Alginate Pellet Formulation of Hirsutella rhossiliensis for Biological Control of Plant-Parasitic Nematodes

Vegetative colonies of the nematophagous fungus Hirsutella rhossiliensis were grown in shake culture, rinsed free of media, macerated, and pelletized in 1% alginate. Nondried or dried (1 day at 22°C) pellets were added to 17 cm3 of loamy sand and packed into vials. After 14 days at 20°C, assay nematodes (healthy second-stage juveniles of Heterodera schachtii) were added to each vial, recovered after 66 h, and examined to determine the percentage with at least one fungal spore attached (transmission). Averaged over five experiments, transmission with four nondried or dried pellets per vial was 62 or 73%, respectively. Dried pellets were 1.7 mm in diameter, weighed 0.58 mg, and contained 0.14 mg dry wt of hyphae. Whereas transmission with dried pellets stored at 5°C for 13-195 days remained high, transmission decreased if dried pellets were stored at 22°C for longer than 13 days; this decrease was more rapid in nonheated than in heated soil, and in soil at −8 kPa than at −28 kPa. Transmission with dried pellets doubled if pellets were in soil for 28 days rather than 14 days before assay nematodes were added. Transmission with dried pellets was low when hyphal density was low or when hyphae were stored and macerated in water. Addition of dried pellets to soil suppressed invasion of roots by H. schachtii.