Studies On The Pathogen Causing Dark Leaf Spot Disease Of Atractylodes Lancea

Dark leaf spot is a devastating disease of Atractylodes, which is badly affecting quality and production of Atractylodes. So far, more researches on medical value have been carried out, but fewer on the pathogen. So it is important to identify the pathogens, to know the genetic diversity of pathogen population and the biological characteristics of pathogens.Pathogens were isolated from diseased leaves of Atractylodes in Xiaochang county of Hubei province. Firstly, we pathogenicity test was conducted based on Koch's rule. Secondly, we described the morphological characteristics of the conidia, conidiophore and beak of the pathogens growing on diseased leaf land PCA. Based on pathogenicity test, morphological characteristics and the sequence of ribosomal DNA-ITS, the pathogens were identified as Alternaria tenuissima and Alernaria solani. The studies of biological characteristics revealed the temperature for mycelium growth ranged from 15 to 35°C, with optimum temperature at 25°C; and the pH value ranged from 4.0 to 11.0, with optimum pH from 6.0 to 7.0. On defined Czapek media, glucose was the optimum carbon sources, while KNO₃ being the optimum nitrogen source.Both A. tenuissima and A. solani could infect Atractylodes, tomato, pimiento, eggplant. A. tenuissima could infect leaves of wheat and maize; however, A. solani could not infect leaves of wheat and maize.30%Armure EC and 10%Score WG had better inhibition to mycelium growth; while 75%Mancogel sulfur WG and 75%Chorothalonil WG had worse inhibition.Compared with RAPD patterns, 8 primers were selected from 60 arbitrarily primers. RAPD profiles of 40 pathogens isolated from diseased leaves of Atractylodes in Xiaochang and Yingshan of Hubei province, obtained using the selected primers. Among them,A. tenuissima, a small-spored species of Alternaria genus, were differentiated from A. solani, a large-spored species of Alternaria genus, at genetic distance 0.48. There were both A. tenuissima group and A. solani group in Xiaochang and Yingshan of Hubei province. Among large-spored species group, Yingshan sub-group were differentiated from Xiaochang sub-group at genetic distance 0.71. Among small-spored species group, Xiaochang sub-group were differentiated from Yingshan sub-group at genetic distance 0.64. These indicated that the RAPD analysis method used was adapted to analying the phylogenetic relationship of Alternaria species. The RAPD analysis also reflected abundant polymorphic among all strains of dark leaf spot.