Study On Physiology Of Post-harvest Diseases Of 'Red Sun' Kiwifruit And Preservation Technology By Ozone

"Red Sun" kiwifruit(Actinidia chinensis Planch.var.rufopulpa Liang et Ferguson) is the first red flesh culture selected from Actinidia chinensis var.rufopulpa in Sichuan province, which is renowned as the "national variety protection resources". There were enormous economic losses each year due to post-harvest diseases and poor storage and transportation technology. However, there is not any report about how to prevent or control post-harvest diseases and valid storage technology of 'Red Sun' kiwifruit. In this paper, the following research were firstly and systematically studied:post-harvest pathogens isolation and identification of infective disease of kiwifruit, biological characteristics and indoor fungicides screening, host range investigation; the effect of pathogens on qualities and physiology of kiwifruit at 25℃were measured; the effect of ozone on colony growth of pathogens (in-vitro) and the qualities of kiwifruit during storage at different temperature were also investigated. The main results are as following:1 Symptoms of two kind of main kiwifruit post-harvest diseases and the pathogens isolation and identificationSymptom of kiwifruit soft rot disease:at the beginning, a brown spot appeared, a clear watery, dark green boundary appeared later, firmness of the whole fruit dramatically dropped, white mycelium scattered out from inner which lead to the peel broken and exudation of tissue fluid was observed when the fruit decayed severely. The pathogen is Botryosphaeria parva.Symptom of kiwifruit anthracnose:at the beginning, a brown spot appeared, expanded gradually along with colour deepen and dehydration, some orange clay was observed on the rot spot, which is conidia of the pathogen. The pathogen is Colletorichum acutatum2 The biological characteristics and indoor fungicides screening, host range investigation of B.parva and C.acutatum.For mycelium growth and sporulation of C.acutatum, the optimum temperature were 25℃and 20℃respectively; the optimum pH value was 6 respectively; lethal temperature of spore was 49℃,15min or 50℃,5min. For mycelium growth of B.parva, the optimum temperature were 30℃; the optimum pH value was 6; lethal temperature of mycelium was 42℃,10min or 43℃,5min. Both of two pathogens prefer monosaccharide and disaccharides than polysaccharide, prefer organic nitrogen than inorganic nitrogen. No remarkable effect of light on mycelium growth and sporulation of two pathogens.Both of B.parva and C.acutatum could infect 7 kinds of fruit trough mechanical wound, they could also infect hosts though lenticel which is lager than normal one is, such as mongo. The carbendazim exhibited the best inhibitory effect, followed by triadimefon, mancozeb and chlorothalonil showed the least inhibitory effect. 3 Effect of B.parva and C.acutatum on qualities and physiology of kiwifruitAt 25℃, inoculation of both B.parva and C.acutatum could increased the loss of firmness, TSS and total sugar content and Vc content. By contrast, the decrease proportion of TA was inhibited by the pathogens, nevertheless, the change was not significant. No evidence showed that pathogens ascended the respiration rate and ethylene production submit value, but they induced the submit occurred approximately 1d ahead of time compared with control group. After inoculating post-harvest kiwifruit with B.parva and C.acutatum, the activities of peroxidase(POD), polyphenol oxidase(PPO), phenylalanine ammonia lyase(PAL), and chitinase were significantly induced, the maximum of them appeared around second day and fifth day after inoculating respectively,which is about 2-3 times of control. The activities of these enzymes markedly rised with increase of the time course of infection and the disease expansion. Activities of the cell wall degrading enzymes (CWDEs) PG and Cx produced by these two pathogens were induced, the peaks of PG and Cx activity appeared on the second day and sixth day respectively after inoculation. When the diameter of lesion was 1 cm, from the lesion to the edge of healthy flesh, the activities of all enzyme reduced gradually except chitinase. 4 Preservation technology of ozoneFor kiwifruit inoculated with pathogens, ozone treatment(200mg/m3,20min) could only delay the process of decay but had no significant influence on decay rate.Kiwifruit were regularly treated by ozone (200mg/m3,20min) during storage at room temperature (20±3℃) and low temperature (0±1℃,5±1℃). Deal kwifruit with ozone every 3 days at 200mg/m3,20min, can could significantly reduce the decay rate at room temperature,until 4 weeks later,which decay rate was only 22% compared with 100% in CK group.However, similar effect have not been observed at low temperature.