The Effect Of Preharvest UV-C On The Fruit Quality And Plant Disease Resistance Of Strawberry

Strawberry is rich in nutrition but as a soft fruit it has fast senescence and decay rate in postharvest storage.UV-C radiation as a new environment-friendly approach had been widely reported to enhance the quality and increase the storage period of fruit in postharvest stage.However,the research on the preharvest application of UV-C is rare and the mechanism is far from clear.In this study,we applied the UV-C radiation to strawberry plants from the plant blossom to fruit harvest,and the effect of preharvest UV-C on the fruit yield,quality and plant disease resistance were investigated systematically.The obtained results were as follows,1.Preharvest UV-C treatment was applied on strawberry plants during the fruiting period with a dose of 0.6 kJ m^-2 every day,every two days or every three days?high,middle or low dose group?.All three UV-C treatment models didn‘t cause negative effect on fruit yield,size,firmness,and color.At the same time,the fruit in low and middle groups had higher flavonoids and ellagic acid content,25%to75%higher,with higher antioxidant capacity.Preharvest UV-C increased accumulation of abscisic acid?ABA?and the expression of the upstream genes of flavonoid pathways,including FaCHS1,FaCHI,FaFHT,and FaDFR.2.The shelf life of the preharvest UV-C treated fruit at room temperature was extended for 1day.After 72 h storage at room temperature,the fruit senescence of the treated group was significantly lower than control and had higher sugar and organic acid content.On the other hand,during the storage period,the expression of miR159 and miR398 were down-regulated by preharvest UV-C,while their target genes,FaPOX1,FaPOX2,and FaCSD were up-regulated.The lipid peroxidation and ROS accumulation of treated group were significantly lower than control.However,the depletion of esters,flavonoids,and ABA titers,as well as the drop in FaPYR1,SnRK2,and FaASR expression,suggested that the effect of preharvest UV-C on the postharvest quality of the fruit declined with time.3.Preharvest UV-C radiation with dark period primed the physiological metabolisms in plant-pathogen interaction pathways.The pathogen-related genes,including FaPAL,BG2-3,FaPR1,and FaChi3,were up-regulated and the activity of PAL,CHI,POD and G-POD were increased in UV-C treated leaves.At the same time,the level of the signal molecule,O^2?-,ABA and salicylic acid?SA?,were higher in treated leaves,and the expression of FaPYR1 and FaEDS1 were significantly up-regulated.4.The inoculation experiment of M.fragariae suggested that preharvest UV-C treated leaf had higher disease resistance.Compared to the inoculated untreated plants?control+?,the plants with UV-C treatment?UVC+?had higher pathogen related enzyme activates and PR related genes expression after pathogen inoculation.After 4 days after inoculation?DAI?,UVC+group had higher contents of H₂O₂,total phenolic compounds,and volatile terpenes than control+.At the same time,UVC+had higher ABA and SA level at the early stage of disease development while JA was higher after the disease spot appearing.The expression of FaPYR1,FaEDS1,FaPAD4 and FaAOS was up-regulated synchronously.Correlation analysis suggested that ROS,plant hormones and volatile terpenes interacted with each other in the regulation of UV-C on plant disease resistance of strawberry.In summary,as a abiotic stress,low preharvest UV-C radiation had no negative effect on the fruit ripening and yield,enhanced the fruit quality and storable characters,and also activated the disease defense system of plants,increasing plant disease resistance.ROS molecules,plant hormones,and volatiles terpenes played key roles in the regulation of UV-C on the physiological mechanisms of strawberry.