| Arthrobotrys oligospora is a kind of important nematode-trapping fungus,which is capable of preying on nematodes through three-dimensional network formed by mycelialization.It is a model strain that can be used to study the interaction between nematode-trapping fungus and nematodes,which has important ecological significance and value.The genetic differentiation and diffusion of A.oligospora from different ecological environments and geographical areas in China were analyzed by ITS,TUB and RPB2.It was found that it contained at least three distinct phylogenetic branches(ie,Cryptic species).In this study,73 strains of A.oligospora were used to explore the intraspecific differentiation by studying the size of the conidia,the growth rate of the colony under the experimental conditions,nematicidal activity of fermentation broth,and the characteristics of mating-type genes.In addition,screening of nematocidal active strains was carried out among the endophytic fungi of aquatic plants and the toxic metabolites of the nematode resistant strains were explored.The main findings are as follows:1.We selected the conidium length-width ratio of A.oligospora as the morphological characteristics analysis in study,found that the conidium length-width ratio of C-clade strain was significantly greater than strains of A-clade and B-clade,and the conidium length-width ratio between Al-clade and C-clade was the largest,they are also the most distant in the phylogenetic analysis.2.The growth rate of colonies in strains in different cultures medium and under different temperatures was shown:growth speed of strains from B-clade and C-clade under higher temperature was significantly weaker than A-clade.The growth rate of strain of B-clade and C-clade under 28℃ was obviously slower than that at 25℃,and the hyphae absolutely don’t grow under 30℃.Strains of A-clade can be grow normally outward to be dendritic under the three temperatures.The grow rate on poor nutrient medium CMA and PDA faster than the rich nutrient medium TYGA3.There were significant differences among clades with conidiation,nematicidal activity of fermented liquid on the solid plate,but did not reveal the correlation between clades of different phylogenetic branches.4.Mating-type gene annotation of A.oligospora showed that the single strain contained only one mating-type,MAT1-1 or MAT1-2,and each mating site contained only one gene,in which MAT1-1-1 gene contains two introns,encoding 1008 amino acids,MAT1-2-1 gene contains four introns,encoding 1142 amino acids.The proportion of mating-type in A.oligospora population is close to 1:1,which is a random mating group,and A.oligospora is a heterothallic species.The phylogenetic analysis of partial sequence of A.oligospora population mating-type gene is consistent with that of house-keeping gene.Based on the above results,it was concluded that there were at least two cryptic species in the populations of the A.oligospora isolated from different ecological environments and geographical areas.The morphological and biological differences were observed in the cryptic species.5.262 strains endophytic fungi isolated from aquatic plant were screened for their nematicidal activity,results showed that obtained 10 strains fungi with good poison nematicidal activity,included 5 Trichoderma strains.Preliminary study of toxic metabolite RH1 strain revealed that it was substances of thermal stability,non-acid,non-alkali and non-volatile. |
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