Assessment of Parasitic Activity of Fusarium Strains Obtained from a Heterodera schachtii-Suppressive Soil.

This study assessed the potential impact of various Fusarium strains on the population development of sugarbeet cyst nematodes. Fungi were isolated from cysts or eggs of Heterodera schachtii Schmidt that were obtained from a field suppressive to that nematode. Twenty-six strains of Fusarium spp. were subjected to a phylogenic analysis of their rRNA-ITS nucleotide sequences. Seven genetically distinct Fusarium strains were evaluated for their ability to influence population development of H. schachtii and crop performance in greenhouse trials. Swiss chard (Beta vulgaris) seedlings were transplanted into fumigated field soil amended with a single fungal strain at 1,000 propagules/g soil. One week later, the soil was infested with 250 H. schachtii J2/100 cm(3) soil. Parasitized eggs were present in all seven Fusarium treatments at 1,180 degree-days after fungal infestation. The percentage of parasitism ranged from 17 to 34%. Although the most efficacious F. oxysporum strain 471 produced as many parasitized eggs as occurred in the original suppressive soil, none of the Fusarium strains reduced the population density of H. schachtii compared to the conducive check. This supports prior results that Fusarium spp. were not the primary cause of the population suppression of sugarbeet cyst nematodes at this location.