Identification Of The Pathogen Causing Brown Spot On Ziziphus Jujuba Mill. Cv. Hupingzao And Its Control

Brown spot in Ziziphus jujuba Mill. cv. Hupingzao was a serious fruit disease in Shanxi Province in recent years. The typical symptom was that red spots occurred on the top or shoulder parts of jujube fruits, then the spots changed into brownish and the edge was much clear. Fruit of other part neither rot nor turning color except spot part. The rate of diseased fruit can reached 50 % when it happened seriously. It destroyed yield and quality of Hupingzao. The pathogen was isolated and identificated by the morphological and molecule method. Antagonistic microorganism and fungicides were screened against pathogen. The main results are as follows:1 Isolation and identification of the pathogenOne hundred and thirty five isolates were obtained from 150 tissue pieces of 30 diaeased fruits and no distinct difference could be observed among them. After pathogenicity tests in lab and field, and pathogen re-isolation, the strain CN535 was determined to be responsible for the disease. The pathogen colony on PAD attained to 69.2~73.5 mm in diameter in seven days, with concentric rings in light-gray and dark-green color. The conidia are obclavate, obpyriform, ellipsoidal in form, and they are formed singly or in short chains, with a conical or cylindrical beak and transverse, longitudinal or oblique septa, 22.5~40.0×8.0~13.5μm, showing the typical morphology of the genus Alternaria. The character of porulation pattern was conidial chain with short branch formed on the top of the conidiophor and the branch chain was 1 to 5 spores which looks like boskage. Its rDNA-ITS sequence has 100% similarity with those of A. alternata, A. tenuissima, A. longipes, A. mali and A. citri searched in GenBank. The specific fragments of 341 bp and 450 bp were amplified with two pairs of sensitive primers AAF2/AAR3 and Aalt-F/Aalt-R. Based on the morphological characteristics and rDNA molecular analysis, the pathogen was finally identified as A. alternata (Fries) Keissler.2 Isolation of endophytic bacteria and screening of antagonistic microorganisms Isolated endophytic bacteria of the jujube on the PDA,KB and NA culture medium and culutring clony on the KB culture medium.The clony was in Kelly colour and the edge was smooth. Sixteen strains were obtaind after directly isolating and screening antagonistic microorganism and all these strains can not inhibit the mycelium growth of the pathogen. The rate of antagonistic microorganism isolated from the heated soil was larger than from the unheated, but the rate is not direct ratio to the temperature. At the same time, 4 strains whose inhibition rate were upon 90.0% of and 11 strains whose inhibition rate were upon 80.0% were obtained. Result of screening antagonistic microorganism shows that the mycelium growth inhibition rate of CHA0r,WCS358::phl and SB were 54.7%,51.2% and 46.5%. The inhibition zone diameter were 14.3 mm,12.7 mm and 12.7 mm.The mycelium growth inhibition rate of Wuyiencin Streptomyces and Streptomyces aureofaciens can reach 58.0% and 67.3%. The inhibition zone diameter were 30.0 mm and 25.3 mm. CN120 and CN121 not only inhibit the mycelium growth but also promote it.3 Chemical controlling of the brwon spot of Ziziphus jujuba Mill. cv. Hupingzao Toxicity test to Alternaria alternata of 9 familiar fungicides was studied. The in vitro inhibition to mycelium growth and spore germination of 9 fungicides against pathogen was tested by using growth inhibition of mycelium on PDA agar plates and spore germination on concave slides. Test control effect of 6 fungicides in lab and put the fungicides in good effect into field. The results indicated that Iprodion, Mancozeb, Propiconazole, Jianban and Carbendazim, could significantly inhibit mycelium growth with inhibiting rates of 90.0% or more, and the fungicides including Mancozeb, Jianban, Carbendazim, Tanzujue, and Propiconazole could greatly suppress spore germination with above 85.0% inhibition rates as well. Results from toxicity test showed that EC50 of Iprodion, Tanzujue, Propiconazole, Carbendazim, Jianban and Mancozeb was 0.2,11.1,14.5,20.8,28.5 and 149.9 mg/L, respectively, and Iprodion was the best with the lowest EC50 Mancozeb was the worst. The correlation coefficients of six fungicides were all above 0.90, indicating a highly positive correlation between fungicide concentration and its inhibition ability. Result of control effect in the lab shows that Propiconazole, Jianban, Mancozeb and Iprodion were good and Tanzujue and Carbendazim were not very well. Result of control effect in the field shows that Iprodion can reach 72.9%, Propiconazole and Jianban were worse, Mancozeb can only reach 25.6%.