Effect Of Hot Water Combined With Fungicides On Fruit Postharvest Physiology And Storage Of ’Newhall’ Navel Orange

Pathogen infection is the key cause of citrus fruit postharvest decay. Chemotherapy and heat treatment are the main control methods at present while these treatments may easily lead to fruit physical harm or pesticide residues, etc. In this study, ?Newhall? Navel Orange was used as test material and the main postharvest pathogens were isolated, purified and confirmed based on Koch’s postulates. The toxicities of different new fungicides on these pathogens were tested by using the methods of Oxford Cup and the mycelial growth rate in order to select effective fungicides. In addition, the effects of hot water treatment, chemotherapy and hot water combined with fungicides on citrus fruits postharvest physiology changes and pesticide residues. The results showed as follows:1. Isolation and purification of ?Newhall? Navel orange postharvest pathogens were conducted. The pathogens isolated and purified from diseased fruits with typical symptoms were identified as Penicillium..italicum, Penicillium.penicillium, Colletotrichum gloeosprioides, Alternaria citri, Geotrichum citri-aurantii and Diplodia natalensis according to colony and conidial morphology, cultural characteristic and pathogenicity.2. Toxicity tests of fungicides against the main postharvest pathogens in the laboratory were carried out. They were tested against P.italicum and P.penicillium by using Oxford Cup while against C.gloeosprioides, A.citri and G.citri-aurantii by the mycelial growth rate. The toxicith test showed that 95% carbendazim、500g/L probenazole and 95% trifloxystrobin had the best effect on P.italicum,P.penicillium and G.citri-aurantii with Ec50 value of 0.2758 mg/L, 3.0966 mg/L and 0.0385mg/L respectively. 95% difenoconazole showed the strongest inhibitory activity against C.gloeosprioides with Ec50 value of 0.0026 mg/L and the best fungicide against G.citri-aurantii was 95% pyraclostrobin whose Ec50 value was 1.1504 mg/L.3. Effect of hot water combined with fungicides on fruit postharvest physiology and storage of ?Newhall? navel orange. The results showed that compared with the single hot water treatment or fungicide treatment, hot water combined with fungicides reduced decay rate and weight loss rate. Besides, it also delayed the decline of total sugars, Vc and titratable acidity.Furthmore, it induced the activity of defensive enzymes including POD, SOD, PAL, GUN and CHT of fruit storage more effectively.4. It was analyzed of pesticide residues of navel orange fruit postharvest treated with hot water combined with fungicides. HPLC-MS and GC-MS were respectively used to detect the residuces of probenazole(carbendazim) and chlorothalonil(metabolite of carbendazim). Results were as followes:(1) probenazole was not found when treated by 100mg/L probenazole while 100mg/L probenazole HWD led to 0.0033mg/kg probenazole(National Standards: 10mg/kg);(2) 100mg/L carbendazim caused 0.0133mg/kg carbendazim and 0.0803mg/kg metabolite of carbendazim; 0.0683mg/kg carbendazim and 0.2625 mg/kg metabolite of carbendazim were detected in the flesh treated with 100mg/L carbendazim HWD(National Standards: 5mg/kg);(3) 100mg/L chlorothalonil HWD did not cause the residuces of chlorothalonil(National Standards: 1mg/kg). The above implied that hot water combined with fungicides could increase the fruit storage but not to cause excessive pesticide residues.