Identification Of The Pathogenic Fungus Causing Leaf Spot Of Zizyphus Jujuba In Xinjiang And Its Control Funficides Screen

Objective:The leaf spot of Zizyphus jujuba is widely occurred in dwarf and close-planting orchards and has caused a great loss in Xinjiang. This research is aimed to clarify the pathogenic types and biological characteristics that caused leaf spot of Zizyphus jujuba, and screen out effective fungicides against leaf spot of Zizyphus jujuba, therefor providing theoretical basis and technological support for the prevention of leaf spot diseases of Zizyphus jujuba.Methods:Typical samples with leaf spot symptom of Zizyphus jujuba were collected from main cultivation districts in Xinjiang. Isolates were obtained by tissue isolation method. Morphological identification and18S rDNA-ITS, EF-1α and β-tubulin gene sequence analyze methods were combined to identify the main pathogen for leaf spot of Zizyphus jujuba after pathogenic test. The influences of temperature and pH on the mycelia growth rate were studied to identify the suitable living conditions for the pathogen. The effective preventing fungicide was confirmed by inhibition of mycelia growth and spore germination.Results:1. A total of161samples of leaf spot were collected from46jujube orchards of14farms in the south of Xinjiang and161isolates were obtained by tissue isolation method.141of these were Alternaria spp, occupied87.5%of the total isolates, which was the main pathogen for leaf spot of Zizyphus jujuba in Xinjiang.12of the isolates were Fusarium spp, accounted for7.45%and other8isolates accounted for4.97%. The pathogenic test showed that Alternaria spp and Fusarium spp separated from the jujube fruit and leaves can also contaminate jujube leaves.2. Five representative strains were selected to observe their cultivating shape in the medium and morphological characteristics under the microscope, and identified that KEL29-1, KS48-3and AKS6-1are representative strains of Alternaria spp; AKS6-3and KS50-8are representative strains of Fusarium spp. By referring to the method of Tianyu Zhang, the sporulation phenotype, Conidia, and morphological characteristics of conidiophores and beak of the Alternaria spp were observed under light microscope. Microspore growing way of Fusarium spp, Megaspore characteristic of Fusarium spp, and Chlamydospore of Fusarium spp were observed under light microscope, referring to the method of Zhenchen Wang. According to the morphological features and the ITS sequence, EF-la and P-tubulin gene sequence analyse, KEL29-1> KS48-3and AKS6-1were identified as A. alternata (Fries) Keissle; AKS6-3was identified as F. oxysporum{Schlecht);.KS50-8was identified as F. equiseti3. The influences of temperature and pH on mycelia growth of the main pathogen A. alternata causing leaf spot of Zizyphus jujuba were studied, and the suitable growth temperature was considered as25～30℃,28℃was the optimal temperature and suitable pH value is7～9. Domestic preventive fungicide selection was conducted through inhibition of mycelia growth and spore germination, the results showed that70%Mancozeb could significantly inhibit mycelium growth and could greatly depress spore germination with inhibition of the pathogen, the EC50values were0.053g·L-1and0.020g·L-1, which would be the first selection of preventive fungicide to control leaf spot of Zizyphusjujube in Xinjiang.Conclusions:The main pathogens causing leaf spot of Zizyphus jujuba are identified as A. alternata(Fries) Keissle, F. oxysporum (Schlecht.) and F. equiseti by morphological identification and18S rDNA-ITS, EF-1α and β-tubulin gene sequence analyze. By the biochemical feature test and domestic fungicide selection experiments of the main pathogen A. alternate, the suitable living temperature is considered as25～30℃, and suitable pH value is7～9;70%Mancozeb performs the best to restrain mycelia growth and spore germination of A. alternate. Therefore,70%Mancozeb can be identified as the primary preventing fungicide of leaf spot of Zizyphusjujube.