| Papaya（Carica Papaya）was a perennial succulent herb,tropical evergreen fruit tree.The papaya fruit had high nutrient content,juicy and sweet taste,and was deeply loved by the public.Papaya was a climacteric fruit.In the post-ripening process,the latent infecting pathogens became active and rapidly develop,causing the fruit to rot,and then the quality of the fruit was severely damaged.Especially anthracnose had a long incubation period and the classification is complicated.The disease can damage the entire fruit.It was one of the most serious postharvest diseases of papaya.Carvol(C10H14O)which had select antifungal activity was the main component of oregano essential oil.It had the characteristics of non-toxic,no residue,friendly with environment and its extensive antifungal effect.And it was an important spice and preservative that was currently widely used.In this study,the identification of the postharvest fungal of papaya in Hainan Province were carried out,the antifungal activities of carvacrol and oregano essential oil were determined and showed the possible mechanism of carvacrol against Colletotrichum okinawense.This study is expected to provide reference for future research on plant active ingredients to prevent and control papaya diseases after harvest.Main results for this study are as follows:1.Identification of the postharvest fungal of papaya in Hainan ProvinceThere were 6 pathogens of papaya postharvest diseases identified in this paper:C.okinawense,C.siamense,C.tropicale,Fusarium solani,L.theobromae and D.cf.heveae.Among them,C.okinawense was first reported on papaya in mainland China,and C.tropicale and D.cf.heveae were first reported on papaya.2.Antifungal activities of carvacrol and oregano essential oilThe indoor virulence test result showed that both carvacrol and oregano essential oil had good antifungal effects with 6 pathogens of papaya postharvest diseases.The EC50values of carvacrol for 6 pathogens with an average EC50value of 0.041μL/m L;the EC50values of oregano essential oil for 6 pathogens,with an average EC50value of 0.111μL/m L.The maximum EC50value of carvatrol for tested pathogens is only 0.077μL/m L,the average EC50value of carvacrol was lower than the average EC50value of oregano essential oil for the tested pathogens.The antifungal effect of carvacrol is better than oregano essential oil.3.Antifungal mechanism of carvacrol against C.okinawense3.1 The effect of carvacrol treatment on the growth and development of C.okinawense.Under the carvacrol treatment at 0.057μL/m L(EC50value),compared with the control,the spore germination rate was reduced by 50%and the mycelial growth was reduced by 79.26%.The scanning electron microscope（SEM）observation result showed the mycelia were severely deformed,shriveled,shrunken and broken;the conidia shrunken and deformed and lost the ability to continue growth and development.3.2 The effect of carvacrol treatment on the cell wall and cell membrane of C.okinawense.Under the carvacrol treatment at 0.057μL/m L(EC50value),transmission electron microscopy（TEM）observation result showed that the cell wall became uneven and thickness,the boundary between cell wall and cell membrane is blurred,much of vacuoles in the cell,and the organelles cannot be identified.The chitinase activity in the mycelia was enhanced,the cell wall was digested,the cell membrane permeability became larger,and soluble protein,soluble reducing sugar and soluble total sugar were all leaked.3.3 The effect of carvacrol treatment on the respiration and energy metabolism of C.okinawense.Under the carvacrol treatment at 0.057μL/m L（EC50 value）,the mycelia respiration rate decreased.The ATPase activity in mycelia was decreased,intracellular Na+K+-ATPase and Ca++Mg++-ATPase activities continued decrease.The ATP content continued decrease,and it decrease continuously over time.With the extension of treatment time,SDH and MDH which were two key enzymes in the TCA cycle,continued decrease. |
