Taxonomy Of Hirsutella Minnesotensis And Allied Species And Its Molecular Ecology

Plant-parasitic nematodes are a group of devastating crop pests and cause great losses in agricultural production. Biological control is one of the most promising approaches for management of the pests, but now is greatly limited by lacking of superior biocontrol agents and knowledge of their ecology in soil. Soybean cyst nematode is an important pest of soybean in China. Hirsutella rhossiliensis Minter & Brady and H. minnesotensis Chen, Liu, & Chen are two among the few endoparasitic fungi of mobile stage of nematodes. Both species produce infective, adhesive conidia that may attach to the cuticle of a passing nematode, and have showed great potential in soybean cyst nematode control. Hirsutella minnesotensis is the prominent juvenile parasite of soybean cyst nematode and has shown potential in biocontrol of nematodes. The purposes of the present study are to evaluate the taxonomy of Hirsutella and allied species, and to establish a real-time polymerase chain reaction (PCR) protocol for quantitative investigation of H. minnesotensis and its ecological behaviors in soil.Taxonomy of nematophagous species of Hirsutella and allied species. Differences among isolates of the nematophagous species of Hirsutella were investigated in respect to their morphology, parasitism, and nucleotide sequence. Hirsutella vermicola was proposed as a new species that is parasitic to bacteria-feeding nematodes but not or weakly pathogenic to plant-parasitic nematodes. The new taxon is distinguished from H. rhossiliensis by its shorter conidiogenous cells with swollen base, helical necks and slightly wider conidia. The species conception of H. thompsonii was emended and its three varieties were not recognized based on their morphology and DNA sequences of ITS regions and MAPK gene fragments.Development of real-time PCR protocol for monitoring H. minnesotensis in soil.A real-time PCR protocol assay was developed to quantify the fungal population density of H. minnesotensis, a prominent juvenile parasite of soybean cyst nematode, in soil. A primer set 5'-GGGAGGCCCGGTGGA-3' and 5-'TGATCCGAGGTC AACTTCTGAA-3' and TaqMan probe 5'-CGTCCGCCGTAAAACGCCCAAC-3' were designed according to its sequence of ITS region of the rRNA gene, and was demonstrated to be highly species-specific. The PCR reaction system was further optimized and could be used to detect as few as 4 conidia g^-1 soil.Detection of H. minnesotensis with real-time PCR in field soil samples. Twenty soil samples (most from monocultured fields) were taken from soybean fields in...