Screening And Optimization Of Control Technology Of Chestnut Postharvest Disease

Chestnut is a kind of a delicious and nutritious nut fruit which is famous as its high edible value.However,due to its high moisture content and strong respiration during postharvest storage,chestnut is extremely vulnerable to the postharvest diseases causing by the infection of pathogenic microorganisms during the process of storage,transportation and marketing.These issues have caused the rot and deterioration of chestnut and consequentially,countless economic losses to chestnut industry.Because of the unique physiological characteristics of chestnut and the complexity of disease pathogenesis,it is quite difficult to make the prevention and control of postharvest diseases.Based on the results of previous screening experiment,this study focused on the control effects of 6 kinds of fresh-keeping treatments on postharvest diseases of chestnut.In the next stage,the control effects of the composite treatment of carvacrol and poplar bud extract on chestnut postharvest diseases and the fresh-keeping effects of chestnut during storage were further studied.The main results are as follows（1）The control effects of hot air treatment,UV treatment,carvacrol treatment,PBE treatment,carvacrol/chitosan coating and PBE/chitosan coating on chestnut postharvest diseases were screened via“in vitro”antifungal experiment,challenge inoculation experiment and natural storage experiment.The resuilt of“in vitro”antifungal experiment indicated that hot air treatment and UV-A irradiation had few or no antifungal effect on Fusarium asiatica and Neofusicoccum parvum,but UV-C irradiation treatment had certain antifungal effect on these two pathogenic fungus.Prominent antifungal effects on Fusarium asiatica and Neofusicoccum parvum from the treatments both by carvacrol and PBE were found:The EC₉₀of carvacrol on Fusarium asiatica and Neofusicoccum parvum were respectively 24.43 and 11.78μL/L,and the EC₉₀of PBE on Fusarium asiatica and Neofusicoccum parvum were1832.65 and 3639.05 mg/L,respectively.The further challenge inoculation experiments showed that carvacrol treatment and PBE treatment could significantly reduce the disease index of artificially inoculated chestnut.Finally,according to the natural storage experiment,the effects of 6 kinds of postharvest treatments on chestnut decay rate were compared.It was found that the effect of hot air and UV treatment on the decay rate of chestnut was the worst one,whose decay inhibition rate was failed to matched 20%.The antifungal effect of carvacrol fumigation treatment was better than that carvacrol/chitosan composite coating,and the effect of PBE/chitosan composite coating with 1%PBE was the most effective one.（2）The synergistic antifungal effect of carvacrol and PBE was evaluated by the combined antifungal susceptibility experiment using filter paper diffusion method and agar checkerboard dilution method.The results showed that the FIC index of carvacrol and PBE against Fusarium asiatica and Neofusicoccum parvum were 0.375and 0.5（≤0.5）,respectively.The effects of the combined treatment of carvacrol and PBE on the micro surface morphology,cell wall,cell membrane and respiration of pathogenic fungus were further researched.Compared with the separate treatment,the combined treatment had greater effects on the growth and development morphology,cell wall/cell membrane barrier and active oxygen metabolism of pathogenic fungi.（3）Carvacrol and PBE were respectively applied to the treatment of chestnut in the form of fumigated and composite coating.The natural storage experiment’s results illustrated that the combined treatment of carvacrol/PBE was effective in controlling the decay of chestnut.And the decay inhibition rate reached 39.22%and 50.72%,respectively,which was not far apart the positive control group treated with prochloraz（38.85%and 64.59%,respectively）.（4）The effects of carvacrol/PBE composite treatment on the quality,physiological,and disease resistance indicators of chestnut were determined.The results illustrated that the composite treatment had no adverse effect on the quality indicators of chestnut,including weight loss,brightness,reducing sugar,starch,soluble protein,and titratable acids,but positive effects on the inhibition of respiratory strength,MDA producing and damage of the cell membrane.In addition,the composite treatment increased the total phenol and flavonoid contents of chestnut,kept the activities of peroxidase,catalase and phenylalaninammo.In summary,after screening,carvacrol treatment and PBE/chitosan composite coating showed the best effect on controlling postharvest diseases of chestnut.Carvacrol and PBE showed a synergistic antifungal effect on the two dominant pathogens.The combined treatment of carvacrol/PBE significantly reduced the decay rate of chestnut,kept the storage quality,delayed the senescence of chestnut,boosted the disease resistance of chestnut.