Identification Of Initial Pathogen Causing Fruit Shrinking Disease In Ziziphus Jujuba Mill. And Its Control

In this study, fungal pathogenic strains were isolated from jujube fruit shrinking disease (JFS) by improved isolation methods. The pathogen was identified through morphological observation and molecular identification. From 2009-2011 salicylic acid (SA) was investigated in induction of systemic resistance against jujube fruit shrinking disease in the jujube plantations, in which the optimum salicylate, optimal application method and optimal concentration were obtained, and the changes of enzymatic activities related to disease resistance were determined. Five kinds of fungicides and five plant growth regulators were applied for controlling this disease, and bags made from waxed paper and plastic film were used to cover the pruned branches to avoid the the primary infection by pathogen, in order to provide a practical basis for effective control of this disease.1 Isolation and identification of the initial infection pathogens causing jujube fruit shrinking diseaseThe pathogen was isolated and identified by morphological and molecular methods 210, 180, 144, 144 and 144 infected tissues were isolated from shrinking jujube fruits, collected from Tangxian and Xingtang in Hebei Province, Panzhuang village in Puyang city, Xuedian town in Xinzheng city and Neihuang county in Henan Province. 120, 135, 3, 16 and 22 isolates were obtained from each area, respectively. A typical strain was selected from each group and they were investigated further. Colony characteristics of the selected 5 strains were slightly different according to morphological observation. Based on the results of microscopical observation, all the 5 strains showed the typical morphology of the genus Alternaria. After pathogenicity tests in field, and re-isolation of the inoculated fungal strains, all the strains were determined to be responsible for the disease.The 26S rDNA ITS sequences of five strains had 100% similarity to those of A. alternata, A. tenuissima and A. brassicae in GenBank. Two specific primer pairs, AAF2/AAR3 for A. alternata, and Abre1/Abre2 for A. brassicae were applied to amplify 341 bp and 371 bp fragments, respectively. The specific fragment of 341 bp was amplifed from the DNA template of all 5 strains, but fragment 371 bp was not. Based on the morphological characteristics and molecular analysis, the pathogen was finally identified as A. alternata (Fries) Keissler.2 Induction of systemic resistance against Jujube fruit shrinking disease with salicylic acidTo understand the roles of salicylic acid (SA) in induction of systemic resistance against jujube fruit shrinking disease (JFS), SA and SA plus KH2PO4 and half micronutrients from MS medium (SA+) were investigated to test their inducing abilities by spraying and infusion, and the changes of enzymatic activities related to plant disease resistances, i.e.peroxidase (POD), poiyphenoloxidase (PPO) and phenyanine ammonialyase (PAL) were determined as well. The results showed that SA at 3-5 mmol/L could effectively induce systemic resistance against JFS and significantly reduce the percentage of diseased jujube fruits through spraying, but 1 mmol SA not. It was observed that SA at optimal concentration had better inducing effects when it was infiltrated into the xylem tissue of jujube stem compared with spraying. Neither spraying nor infusion of SA+ was capable of inducing systemic resistance against JFS. There was no significant difference among all the samples, collected after application of SA, for the change of PAL activities, but PPO activities in jujube showed significant difference when SA was infused into jujube stem. The activity of POD was significantly higher than that of control both by infusion with 3 mmol/L SA and by spraying SA at 1 mmol/L, 3 mmol/L and 5mmol/L, but no significance was detected with the application of SA+. It can be concluded that stem infusion could improve the absorption of SA solution, SA application could significantly increase resistance against jujube fruit shrinking disease, and POD activity is an important indicator for jujube disease resistance.3 Research on control of jujube shrinking diseaseThe in vitro inhibition to mycelium growth of 5 fungicides against pathogen was tested by growing the fungal strains on PDA agar plates with certain amount of each fungicide. The results indicated that 5 fungicides could significantly inhibit mycelium growth, whereas benzoyl propiconazole showed the highest inhibition rates, reaching 100%, and the others were all above 90%. The control results in the field indicated that the control effect were 59.3% and 64.8%, respectively, by spraying benzoyl propiconazole with 3000 dilution times and carbendazim with dilution times of 2000, A plant regulator, mepiquat chloride,showed significant control effect as well, with control rate of 64.1% compared with the control. Results from shoot bagging showed were not always stable. Generally, shoot bagging before the end of June could affect fruits setting rate negatively and sthat suppress fruit growth. The control effects would be much more obvious if shoot bagging was done one week before the end of July, preferably on July 30 in the tested fields.