Study On Pathogens And Control Of Walnut Leaf Spot Disease In Southern Xinjiang

Walnut leaf spot is a new disease in recent years occurring in Hotan,Kashi and Aksuregions of southern Xinjiang. The round or nearly round,brown to dark brown necrotic spotsare originally found in leaf tip, leaf margin,then the lesion area gradually expanding to inward,finally they get together resulting in a large area withered necrosis. This disease can decreaseyield and plumpness of walnut, bring losses to local walnut production and farmers’ income.This study determined the leaf necrotic yellow Pathogen of walnut in Southern XinjiangWalnut Orchards by isolating, culturing, purifying and inoculation tests. It also studied theinfluence of temperature and moisture times on the pathogens of inoculation. The taxonomicstatus of pathogens was determined by observing the morphologic characteristics combinedwith molecular biological methods. Indoor bactericidal screening was conducted by colonygrowth and spore germination. And on this basis, the effectiveness of drug was conducted infield plot experiment, thus providing basis for disease control in field. The main results are asfollows:Typical leaf spot disease samples were collected from Hotan, Kashi and Aksu regions ofsouthern Xinjiang. After isolation, cultivation and purification obtained105strains, dependedon the colony characteristics of all strains were roughly divided into three types, they allbelonged to genus Alternaria sp. by observing under a microscope.Field inoculation test was conducted in30typical isolates selected from the above threeareas. The results showed that they all could cause disease in the inoculum except the strainI-11, indicating that most strains are pathogenic. While the strain virulence of the same regionwas different, also to the strain in different regions, so there was differences between thepathogenic of strains. Bacteria on different organs and tissues can interact infection. Thewounds were inoculated with a high incidence in the vaccinated without injury incidence,field inoculation onset of the incubation period for7days. Temperature and moisture timeshad great impact on the incidence of walnut leaf spot inoculation. The optimal combination oftemperature and moisture good for morbidity was:temperature28℃, moisture time48h,inoculation onset of the incubation period as short as6h.By observing and measuring the mycelium, colony characteristics, conidiophores, thebeak, conidia and a chain of pathogen, initially defined the taxonomic status of pathogens.Using fungal rDNA-ITS universal primers (ITS1F-ITS4) were used for PCR amplifying andsequencing. Put the results of sequences to GenBank for comparison analysis andphylogenetic tree, further validate the results of the morphological identification. Walnut leafspot pathogens were identified as Alternaria alternata(Fr.：Fr.)Keissler.The colony growth inhitory method and spore germination method were used to measureand compare the laboratory toxicities of8kinds of fungicides on walnut leaf spot disease(Alternaria alternata). The EC50values of prochloraz10%ME and difenoconazole10%WGare both less than0.30mL/L. The EC50values of propiconazole25%EC,iprodione50%WPand prochloraz-manganese50%WP are all lower than2mg/L. The inhibition rate of4kindsof fungicides including propiconazole25%EC, prochloraz10%ME, iprodione50%WP, anddifenoconazole10%WG suppressing spore germination all reached more than80%. On thisbasis,4fungicides: prochloraz10%ME,difenoconazole10%WG, Propiconazole25%EC andiprodione50%WP were selected to be tested in field trials. Trials results showed thatprochloraz10%ME and difenoconazole10%WG had better control effect on the leaf spotpathogen of walnut in Xinjiang, the control efficiency was more than78.88%.