Parasitism And Pathogenicity Of Nematode-endoparasitic Hirsutella Spp. Against Heterodera Glycines And Caenorhabditis Elegans

Soybean cyst nematode (Heterodera glycines Ichinohe) is a devastating phytoparasitic nematode. Caenorhabditis elegans is one of the important model organisms. Hirsutella rhossiliensis Minter & Brady and Hirsutella minnesotensis Chen, Liu, & Chen,two endoparasite fungi against soybean cyst nematode, have been intensively studied as potential biocontrol agents. In this study, Hirsutella spp. were employed as parasites, H. glycines and C. elegans were represented as hosts, to illustrate the infection process of green fluorescent protein transformants to H. glycines and C. elegans by slide culture, compare the parasitism of different fungal isolates between H. glycines J2 and C. elegans four larval stages (L1-L4) by agar assay and tube soil assay, and explore the competition relationship between Hirsutella species and nematode species with plate culture test and tube soil test.Compare to the wild type, the transformants of H. rhossiliensis (AS6G4, AS6R1) and H. minnesotensis (AS3G1) marked fluorescent protein are similar to wild type on morphology, growth and pathogenicity. Based on this, the transformant ASG1 was applied to study the infection process of fungus to H. glycines and C. elegans. From the results the infection process could be divided into eight stages as the following, adhesion stage, peg formation stage, appressorium formation stage, initial hyphae growth stage, hyphae extension stage, hyphae filling nematode body stage, hyphae growth out of nematode stage, and conidia formation stage. Though the parasitized processes are similar between H. glycines juvenile 2 and C. elegans larvae 2, the parasitized time are different. On C. elegans larvae 2, the whole cycle from conidia of H. minnesotensis adhere nematode to germinate new conidia need 144 hours to finish, while on H. glycines, the mycelium from the digested nematode could not produce conidia after 184 hours infection.The parasitism of Hirsutella to nematode relate to the pathogenicity of fungal species and nematode species. H. thompsonii H.t216, a parasite of arthropod, could not infect nematode. H. vermicola obtained from saprophytic nematode presented a little parasitism to the nematode used in this study. Nineteen strains of H. minnesotensis and H. rhossiliensis which isolated from H. glycines juvenile 2 originally showed high parasitic capability. Whereas the difference among the strains are significant (F = 22.720; df = 19, P<0.01). Hirsutella spp. parasitized a higher percentage of H. glycines than C. elegans, and the parasitized percentage negatively correlated with the larvae stage which caused increasing of locomotion, volume, and momentum of H. glycines.In nature, there are complex ecological relationships among species, such as parasitism competition. In our study, we find that there is an inter-specific competition between H. minnsotensis and H. rhossiliensis. The hypothetic reason is that one species of Hirsutella could produce some compounds which could interfere the other's conidia germination and hyphae growth.