Proliferation ofTalaromyces flavusin Soil and Survival in Alginate Pellets

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Abstract
Conidia of Talaromyces flavus in alginate-bran pellets stored for 15 wk survived better at 5 and 15 than at 25.degree. C. Survival of ascospores was affected less by temperature than was survival of conidia. Ascospore viability declined moderately during the first 3 wk, with no further decline from the 3rd to the 15th wk. The propagule type and initial inoculum level in pellets, the type of bulking agent used to make the pellets, and the initial concentration of pellets added to soil each significantly affected fungal survival in and proliferation into soil from the pellets. Population densities in soil originating from conidia in alginate-bran pellets were higher than those originating from ascospores, especially when the former propagule was added initially at 5 .times. 107 or 1 .times. 108 conidia per gram of dry pellets or when pellets were added to soil at 0.25 and 0.5% (w/w) rather than at 0.1%. For instance, at 16 wk, recovery of colony-forming units from soil was about 800% of the original numbers of conidia added with bran in the pellets. Although ascospores in alginate-bran pellets also resulted in greater numbers in soil, the total number of colony-forming units recovered was always smaller than that obtained with conidia. In no case did conidia or ascospores added with Pyrax as the bulking agent result in great numbers in soil. In contrast, dried fungal biomass (largely mycelium) of T. flavus proliferated in soil when added as alginate-Pyrax pellets but not as alginate-bran pellets. Yellow-orange, fertile cleistothecia of T. flavus developed within 3-5 days on alginate-bran pellets containing conidia or ascospores placed on or in soil, but not on alginate-Pyrax pellets containing fungal biomass. The metabolic activity of soil was high when amended with pellets containing bran (with or without propagules) and low when amended with pellets containing Pyrax as the bulking agent. Bran was the best bulking agent in all tests performed with conidia or ascospores.