| Cyst nematode is a general term for Subfamily Heteroderine nematodes.It is a plant parasitic nematode of economic importance and can cause loss of crop productions including cereals,beans and potatoes.In this study,investigations of occurrence and distribution,species diversity,host diversity,genetic differentiation of different host populations and different geographical populations of the cyst nematode on alpine steppe grasslands in Gannan and Tianzhu regions of Gansu Province were researched.The results of the study were as follows:From June to September in 2017,random sampling was used to investigate the occurrence and distribution of cyst nematodes in the rhizosphere soils of forage grasses in different regions of Gannan and Tianzhu,and the occurrence situation of cyst nematode of the forage grasses in the oat growing area and natural grasslaand were investigated.The distribution of cyst nematodes in Gannan and Tianzhu was extensive.The detection rate of cyst nematode in Gannan was 42.29% and the density of cysts was 1.3/100 g soil.The rate of cyst nematodes was 34.68% and the cyst density was 3.1 heads/100 g soil Tianzhu: The average cyst detection rate of cyst nematode on pastures in oat fields was 64%,and the density of cysts was 8 per 100 g soil;the detection rate of cyst nematodes in pasture areas was 26%,and the density of cysts was 3.8 in 100 g soil samples,the detection rate of cyst nematode and the density of cysts in the oats cultivation areas were higher than that in forage grass growing areas.The morphological and molecular biological methods were used to identify the species of rhizospheric cyst nematodes in Gannan and Tianzhu.The phylogenetic tree of 18S-rRNA gene sequences of cyst nematode was constructed using ML method.Two types of cyst nematodes were identified as Heterodera avenae and Globodera from Gannan region according to morphological.The molecular biological identification results are H.avenae and Globodera artemisiae.Five types of cyst nematodes were isolated from the cyst nematode in Tianzhu region;which are H.avenae,H.geottingiana and three types of Globodera.The molecular biological identification results are: H.avenae,H.geottingiana and G.artemisiae,and the remaining two categories failed to determine its species.From 2016 to 2017,a random sampling method was used to investigate the hosts of cyst nematodes in Gannan and Tianzhu grasslands.The results of the investigation were as follows: white females were found to be parasitized in the roots of Elymus nutans Griseb.and Plantago depressa Willd.in Gannan,and the average parasitism rates were 2.3 per plant and 1 per plant respectively.After comparing the 18S-rDNA gene sequences and establishing a phylogenetic tree,the cyst nematode species of the Elymus nutans Griseb.was H.avenae,and the Plantago depressa Willd.was H.geottingiana.In Tianzhu grasslands,white females were found in the grass roots of 18 species of 8 families,including Gramineae,Cyperaceae,Polygonaceae,Asteraceae,Boragocaceae,Plantainaceae,Caryophyllaceae,and Leguminosae.Comparing the 18S-rDNA gene sequences and establishing a phylogenetic tree,it was determined that the species of the cyst nematode on Gramineae grasses was H.avenae.The cyst nematodes in the roots of Microula pseudotrichocarpa and Lappula myosotis Moench of Caryophyllaceae,Plantago depressa of Leguminosae were H.geottingiana.The genetic differentiation of the 28S-rRNA gene sequences of different geographic populations in the Gannan region of the H.avenae was analyzed.The results showed that the sequence of the 28S-rDNA gene of 19 H.avenae populations in Gannan Prefecture was about 968 bp in length.The average contents of the bases A,T,G,and C were 23.59%,20.79%,33.38%,and 22.24%,respectively.There were 961 conserved sequences,6 mutation sites,0.62% of the total sequence length,1 parsimony informative site,5 single mutation sites,and 0.5 conversion and conversion ratio.The nucleic acid diversity index was 0.00075,and the average number of nucleic acid differences was 0.725.There were 5 haplotypes,the haplotype polymorphism was 0.386,and haplotype 1(H1)was the subject haplotype.The five haplotypes were constructed using the ML method.The results were divided into three small branches.The genetic distances between the various groups were relatively close,ranging from 0.001 to 0.005.The genetic differentiation index among 19 different groups was-0.07678.There was no significant correlation between the genetic distance and the host species among 19 different geographical populations of H.avenae.The variation source of H.avenae was mainly from within-species variation,and there was no genetic differentiation among different populations. |
