Identification,Pathogenic Mechanism And Fungicides Of Pathogen Caused Leaf Spot Of Bletilla Striata In Jinyun Mountain

Bletilla striata(Thunb.ex A.Murray)Rchb.f.is a perennial herbaceous medicinal plant.The medicinal part is the pseudobulb of Bletilla striata in soil.The Jinyun Mountain Area of Chongqing is suitable for the cultivation of Bletilla striata and other traditional Chinese medicine.However,with the extendation of planting years,the expansion of planting scale,and the increase of spring-summer rainfall,the occurrence frequency of various diseases increases.The trend is increasing year by year.These diseases inhibit the growth of B.striata,lead to the decline of yield and quality,and are not conducive to the sustainable development of Bletilla striata industry.The purpose of this study is to identify the pathogen on leaf spots of B.striata in Jinyun Mountain Area of Chongqing,to understand the biological characteristics of the pathogen and the invasion process of the pathogen to B.striata leaves,the resistance response of B.striata leaves triggered by the invasion of the pathogen.Finnally,indoor toxicity test and pot efficacy test were carried out so as to further provide theoretical basis for the accurate control the disease of.striata leaf spot.The main results are as follows.Fresh disease leaves of B.striata were collected from the planting base of Chongqing Jinyun Mountain.Two strains(F1 and F2)were isolated and purified by plate marking method.The results of Koch’s rule test clarified that F1 was the pathogen on leaf spot of B.striata.Through morphological observation of the shape and size of large conidia and small conidia,it was preliminarily concluded that the pathogen belonged to the Fusarium.Combined with gene sequence analysis,the pathogen on leaf spot of Bletilla striata in Jinyun Mountain of Chongqing was identified as Fusarium oxysporum.The biological characteristics of the pathogen on leaf spot of B.striata were determined.Among the carbon sources in tests,the pathogen made use of the best utilization of maltose and the worst utilization of xylose.Among the nitrogen sources in tests,the pathogen made use of the best utilization of peptone from organic nitrogen sources,and the worst utilization of lysine and ammonium sulfate from inorganic nitrogen sources.The pathogen can grow in the temperature range of 10 ℃～40 ℃,and the optimal growth temperature is between 25 ℃ and 30 ℃.The pathogen can grow in the range of p H4～9,and the colony growth diameter is the largest at p H7.SA and Gzapek medium were the most suitable for mycelial growth.The lethal temperature of the mycelium was65℃.The leaves of B.striata were inoculated in vitro with mycelia.The samples of different inoculation time were collected for tissue transparency,staining and observation to clarify the infection process of pathogenic fungi on plants.The results showed that the conidia began to germinate and form germ tubes for 4 hours later after inoculation.Appressorium was formed for 6 hours after inoculation.After 10 hours of inoculation,the spores produced branching hyphae.After 18 hours of inoculation,the hyphae of the pathogen began to invade the epidermal cells of B.striata leaves.There were two ways for F.oxysporum to invade Bletilla striata leaves.They were direct invasion and stomatal invasion.The bifurcate branches and appressorium were special structures when F.oxysporum invaded leaves B.striata.In order to study the resistance response of B.striata to pathogen infection,the contents of soluble sugar,soluble protein,MDA and the activities of three antioxidant enzymes were detected at different inoculation time.The results showed that the physiological indexes,such as the contents of soluble sugar and soluble protein,and the activities of POD,CAT and SOD,were increased transiently at the beginning of infection.As the infection continued,the leaf pot symptoms of B.striata appeared.The physiological indexes,such as the contents of soluble sugar and soluble protein,the activities of POD,CAT and SOD,began to decrease.But the content of MDA has been increased.In order to provided scientific and technical support to control the leaf spot of Bletilla striata accurately and effectively,six chemical fungicides were selected for the indoor virulence test on the pathogen in the leaf spots of Bletilla striata.The results of PDA plate bacteriostasis test showed that the six chemicals had certain inhibitory effect on the mycelial growth of the pathogen.The inhibition effectsof Propiconazole and Tebuconazole were the best.The results of vivo toxicity test of potted plants showed that the control effects of Propiconazole and Tebuconazole were also the best.