Studies On Biological Characteristics And Control Of Stem-end Rot In Ponkan Citrus

There are great economic losses in citrus due to postharvest disease. To control them, the major method is fungicides. But the effect of fungicides is different from pathogens. And the systemic resistance to fungicides occurs more frequently in orchards than the past. So, alternative, safe, no-toxic approaches are needed to use in the postharvest storage of citrus fruit.Ponkan fruit were used as materials to isolate the pathogen-Diplodia natalensis, from natural rotted fruit and analyse its biological characters. According to the pathogen characteritic, its controlling mathod was studied, which Hydroxy biphenyls had the remarkable effect on controlling D. natalensis. At the same time, conmmercial storage experiment was carried out to evaluate the effect of Hydroxy biphenyls. At the end of storage, the rot rate was controlled less then10%, and there has no difference in fruit quality during storage. The main results were as follows:1. From the natural rotted Citrus fruits, D. natalensis was separated and purified. The biological characteristics were observed in this study. We found that:the colony form, growth rate of mycelia and yield of conidia significantly varied with different culture media. D. natalensis grew best, and the conidia of D. natalensis amounted to9.08×107cells·mL-1in potato sucrose agar. The optimum temperature for the D. natalensis was30℃. Lighting or dark had not effect on the growth of D. natalensis. For the conidia of D. natalensis, the lethal temperature was75℃.2. Hydroxy biphenyls effectively controlled the occur of D. natalensis. Through in vitro and in vivo test, Hydroxy biphenyls had obvious effect against D. natalensis. In vitro experiment showed that200mg/kg Hydroxy biphenyls inhited the drowth of the pathogen, and in vivo inoculated experient showed that the rot rate was20%by inoculated with200mg/kg Hydroxy biphenyls and1.0×105spores·mL-1D. natalensis, there was obvious difference from CK.3. Storage effect was studied using200mg/kg Hydroxy biphenyls to ponkan fruit in this paper. The result showed that at the end the storage the rot rate was9.67%, there was obvious difference from CK(25.33%). Meantime, the content of TA, Vc and TSS was analysed, the result showed that there were no difference among treatments. At the end of 100d storage, there was no difference in fruit quality between200mg/kg Hydroxy biphenyls and CK. Therefore, there had no difference in fuirt nutrient continent using200mg/kg Hydroxy biphenyls.