Variety Identification And Pathogenicity Determination Of Gaeumannomyces Graminis Of Wheat In Henan

Wheat take-all is a devastating disease on wheat.Recently, the disease caused severe damage in henan province leading to significant yield loss of wheat. In order to unravel the occurrence of the pathogen in henan province, samples showing typical symptoms were collected from seven regions including zhengzhou, xuchang, kaifeng etc, and74Gaeumannomyces strains were isolated from them. Morphological, physiological, molecular identification combined with pathogenicity determination and rDNA-ITS sequence analysis were applied to identify the variety of Gaeumannomyces graminisof wheat in Henan and and the pathogenicity differences between different regions or different strains.The morphological identification results were listed below:the colour of the colony was hoar during the early stage and then changed to taupe at the late stage on the PDA medium, the margin was curled to the center, the runner hypha of the74strains was brown and showed"∧"at the branch, all the strains can produce phialid and phialospores, the phialospore is lunular or semilunar, all the strains can only produce simple hyphopodium,which is olivary,claviform or near orbicular.The hyphopodium usually produce together and form sclerotic masses; All the strains can be artificially induced perithecium, which is produced immerge or semi-immerge and usually produced between the hypha of the bottles, orbicular or olivary. The mature ascus is clavate and the size is98.6～127.9μm×9～15μm.Ascospores are linear and slight curving.The mature ascospore has clear membrane and the size is98.6127.9μm×9～15μm.Physiological and biochemical characteristics study of the strains showed that the optimal temperature of most isolates is25℃,and the optimal pH is7.0.Growth rate of all the isolates was inhibited on PDA medium containing2.5%fresh oat leaves soap. Growth rate of all the strains showed great difference on PDA medium containing1%L-cysteine. Therefore, L-cysteine is unsuitable for the variety identification.According to the above characteristic,all the74strains were identified as Ggt (Gaeumanomyces graminis var. trifici)The primers designed by Rachadwong and Wang Meinan were used to identify the74strains.The results indicated that only the870bp fragment of Ggt was amplified, no other specific fragments obtained.By using the fungi universal primer ITS4and ITS5,the ribosomal DNA internal transcribed spacer (ITS) region of the genomic DNAs was amplified, sequenced, and analyzed using MEGA4.1software. The result of the clustering and analysis showed that all74isolates and6representative species of Ggt’s sequences from GenBANK were clustered together and showed close genetic relationships.74isolates can be separated clearly from other varieties. The research results of above two kinds of molecular technology conform to that of morphological identification.The pathogenicity of74isolates were tested in greenhouse. The virulence of Gaeumanomyces isolates showed significant difference, and Gaeumanomyces isolates in Henan could be divided into three pathotypes which is the highly aggressive isolates,the moderately aggressive isolates and the weakly aggressive isolates, respectively.The first two pathotypes accounting for63.89%and29.73%respectively were the main pathotype.The results also showed that the virulence of isolates exhibited certain difference among different regions. The virulence showed strong for isolates from Zhoukou,Shangqiu and Luohe regions and weak for those from Zhengzhou region. Besides in the same region(taking Kaifeng for example) the virulence of Gaeumanomyces isolates showed significant difference.