Identification And Infection Research Of Nematophagous Fungus Esteya Vermicola NKF 13222 Strain

Esteya vermicola was the first reported endoparasitic fungi of Bursaphelenchus xylophilus. In this study, a fungal strain NKF 13222 isolated from Bursaphelenchus rainulfi intercepted from wood packaging materials originating in Brazil, was identified as a new strain of E. vermicola by morphological and molecular characterrisitics. In order to explore the biocontrol potential of this fungus against nematode diseases and to provide the theoretical basis for possible industrial utilization, biological characters of the NKF 13222 strain and its infection ability for several important plant parasitic nematodes were evaluated. The main results are as follows:The strain produced lunate conidia and bacilloid conidia, each with different germination modes, but only lunate adhesive conidia were adhesion and infectious. Morphological comparisons revealed the NKF 13222 strain were found to be closely resembled with the E. vermicola Taiwan strain ATCC 74485 which isolated from B. xylophilus, while differed from Czech Republic strain CBS 115803 and South Korea strain CNU120806 with respect to sporulation and spore germination mode. Phylogenetic analyses based on β-tubulin and EF1-α gene sequences indicated that the NKF 13222 strain showed the closer relationship with the Taiwan strain ATCC 74485.The effects of the culturing factors on colony growth, sources, ratio of carbon and nitrogen on sporulation of the E. vermicola strain NKF 13222 were evaluated. The results showed that nutrient-rich PDA medium was more suitable for mycelial growth and on which more bacilloid conidia were produced, while on nutrient-poor WA medium, more lunate adhesive conidia were produced. The suitable temperature and pH for colony growth of the NKF 13222 strain was ranged from 20℃ to 30℃ and from 4.5 to 8.5, respectively. The strain cultured under dark condition was growing faster than that under light condition. No significant differences were observed for the effects of the sugar concentration in media on fungal growth. The comparisons of fungal sporulation in different liquid media revealed that the suitable source for carbon and nitrogen were galactose and peptone, repectively. When the strain cultured in medium with galactose and peptone by ratio of 100 and 1, maximum 8.52×10/mL spores were produced.The attraction, adhesion and infection ability of E. vermicola NKF 13222 strain on seven plant parasitic nematodes were evaluated. The results showed that mycelia of the NKF 13222 strain attracted worms of Bursaphelenchus xylophilus, B. mucronatus, Ditylenchus destructor and Aphelenchoides besseyi instead of Meloidogyne incognita, Heterodera avenae and Pratylenchus penetrans. The lunate conidia of NKF 13222 strain was found to be attached to the bodies of four attracted nematode species, with the attachment rates at 24 hour inoculation raged from 82% to 99%. No attachments were observed on the bodies of non-attracted nematode species by the lunate conidia. The infection ability of lunate conidia was significantly different in nematode species. The infection rate of spores at 7 days inoculation for B. xylophilus were 98%, however, for B. mucronatus, D. destructor and A. besseyi, were 43%,35% and 9%, respectively. The tests proved that E. vermicola NKF 13222 strain not only has a high infectivity against B. xylophilus, but also provide an alternative agent for biocontrol of some plant parasitic nematodes.