In vitro screening of new strains of predacious nematophagous fungi for biocontrol suitability when produced in liquid culture

Abstract

Aim. To isolate, identify, and evaluate in vitro the predacious ability of nematophagous fungi strains, to determine their eligibility for mass production under submerged cultivation; to select the most efficient isolates of predacious nematopha- gous fungi as promising producers of the biopreparation to control plant-parasitic nematodes. Methods. Microbiological, microscopical, cultural-morphological, statistical. Results. The screening to determine the presence of predacious nema- tophagous fungi in different soils from different regions has been conducted for the first time in Ukraine. Out of 75 soil samples, isolated in Kyiv, Chernihiv, Dnipropetrovsk, Volyn and Odesa regions, 88 isolates of predacious nematophagous fungi were obtained which belong to 11 genera by their cultural-morphological characteristics: Arthrobotrys oligospo- ra – 39 isolates, A. musiformis – 25, A. conoides – 11, Drechslerella dactyloides – 3, A. artrobotryoides –2, A. superba – 2, A. megalospora – 2, A. sphaeroides –1, A. flagrans – 1, A. amerospora – 1, A. thaumasia – 1. High nematophagous activity in vitro (90–100 % trapping) regarding free-living nematodes (Rhabditis spp). was demonstrated by 4 isolates of A. oligospora, 18 isolates of A. musiformis, 5 isolates of A. conoides, 3 isolates of D. dactyloides, and one isolate of A. megalospora. Among the 47 most active isolates, 4 isolates of predacious fungi formed chlamydospores under submerged cultivation on two types of liquid media – wort medium and corn-molasses medium: A. musiformis-711, A. musiformis-911, A. conoides-90, D. dactyloides-19. It was found that isolate A. musiformis-911 and A. conoides-90 could form conidia in the submerged culture. Further experiments in determining the character of development for two latter isolates in different types of media under submerged cultivation established that the largest number of chlamydo- spores and conidia were formed by the isolates of A. conoides 90 and A. musiformis 911 on potato dextrose medium, 7.6·105 and 6.5·105 spores/ml respectively. In the wort medium, the productivity of spore formation for the isolate of A. conoides 90 was 35 times lower, amounting to 2.2·104 spores/ml, and in peptone-glucose medium – 90 times lower (8.5·103 spores/ml). The isolate of A. musiformis 911 in the wort medium produced 325 times fewer spores (2.0× ×103 spores/ml) than in potato-dextrose medium, while no chlamydospores and conidia were formed in the peptone- glucose medium. More detailed study of the ratio between isolates-producers and different sources of nutrition as the basis for the optimization of liquid media is required. Conclusions. According to the results of determining nematoph- agous activity regarding free-living nematodes, isolated from different soils in Ukraine and evaluating the character of development under submerged cultivation, two isolates of predacious fungi were selected – Arthrobotrys conoides-90 and A. musiformis-911, which are promising producers of a biological preparation eventually to be used in the biocon- trol of plant-parasitic nematodes. Conidia formation of the two isolates in liquid culture under mass production condi- tions was observed for the first time and could also contribute to their suitability for mass production and biocontrol.