Study On Disease Resistance Of Postharvest Jiashi And 86-1 Muskmelon Infected With Alternaria Alternata

Muskmelon is one of the most famous fruits in Xinjiang.However,it is easily infected until decay by pathogenic microorganism in the postharvest,causing enormous economic losses and affecting the sustainable and stable development of muskmelon industry in Xinjiang.Jiashi and 86-1 muskmelon are Xinjiang characteristic muskmelon,the former is a late maturing variety which is resistant to storage and transportation;the latter is medium and late maturing variety,and its resistance to storage is general.There is a great difference in structure and tissue between the pericarp and the sarcocarp of the muskmelon.In this paper,the fruits of Jiashi and 86-1 muskmelon were used as experimental materials,the differences of resistance ability to A.alternata disease between different muskmelon variety and tissue were compared to find out the reasons of Jiashi muskmelon’s storage tolerance,which provided theoretical basis for the control of postharvest disease and disease resistance prediction of muskmelon.The main findings are as follows:（1）Jiashi muskmelon was took as the experimental materials,the depth of 3 mm（pericarp）、5 mm（pericarp and sarcocarp at the junction）and 10 mm（sarcocarp）were inoculated with A.alternata,and stored at 7℃cold storage,the lesion diameter of pericarp and sarcocarp,the contents of total phenols and flavonoids in antibacterial substances,and the activities of PPO,POD,SOD and CAT were determined every 4 days.The results revealed that pericarp lesion diameter was significantly smaller than the sarcocarp during the storage.the disease resistance of pericarp was greater than sarcocarp;the contents of antibacterial substances and reactive oxygen metabolism related enzymes in the 3,5 and 10 mm inoculated groups were significantly higher than those in the control groups,the fruit of 3 mm inoculation group had higher resistance to disease.In conclusion,both pericarp and sarcocarp of the muskmelon could resist the infection of A.alternata,pericarp exerted a greater resistance to disease.（2）Jiashi and 86-1 muskmelon were inoculated with A.alternata,and stored at 7℃cold storage,the lesion diameter and active oxygen metabolism related substances and enzyme activities were determined.The results indicated that the lesion diameter of 86-1 muskmelon’s pericarp and sarcocarp was larger than that of Jiashi muskmelon,and the lesion diameter of both muskmelon’s sarcocarp was bigger than that of pericarp.After A.alternata infecting the fruit,early induction of H₂O₂and O₂^-·were rapidly accumulated,and the activities of PPO,POD,SOD and CAT were promoted,and the content of MDA was reduced.The levels of ROS accumulation and enzyme activities in Jiashi muskmelon’s pericarp and sarcocarp were higher than the corresponding 86-1 muskmelon;moreover,the accumulation of ROS and enzyme activities of both muskmelon pericarp were higher than those of sarcocarp,but the content of MDA was opposite.In conclusion,the postharvest disease resistance of muskmelon was closely related to the metabolism of ROS;Jiashi muskmelon’s disease resistance was stronger than 86-1 muskmelon and pericarp’s disease resistance ability was stronger than sarcocarp.（3）Jiashi and 86-1 muskmelon were inoculated with A.alternata,and stored at 7℃cold storage,the lesion diameter and phenylpropane metabolite substances content and related enzyme activities and pathogen-associated protein activities were determined.The results indicated that during the storage,86-1muskmelon’s lesion diameter was greater than Jiashi muskmelon,and the lesion diameter in sarcocarp was greater than that in pericarp.After inoculated with the A.alternata,the contents of flavone and total phenol and the activity of PAL,C4H,4CL,CHT and GLU were increased.The content of antibacterial substance and enzyme activity of Jiashi muskmelon were higher than those of 86-1 muskmelon,the content and enzyme activity of pericarp were higher than those of sarcocarp.In conclusion,Jiashi muskmelon showed strong resistance to A.alternata,and the disease resistance ability in pericarp was stronger than that in sarcocarp.