Effects Of Tea Tree Oil And Its Main Compound Terpinen-4-ol On The Quality And Disease Resistance Of Postharvest Strawberry

Strawberry(Fragaria × ananassa)fruit is very susceptible to mechanical damage and pathogen infection after harvest,which makes storage and transportation of strawberry fruit difficult.The use of natural substances such as essential oils to extend the fresh-keeping period of fruits and vegetables has attracted people's interest and attention.Our previous research found that tea tree oil(TTO)showed good antifungal effects in vivo and in vitro,and could reduce the incidence of postharvest disease in strawberry fruit.But it is not clear whether TTO and its components can induce the fruit disease resistance to affect the shelf life.Terpinen-4-ol is the most important characteristic component of TTO.In this paper,TTO,terpinen-4-ol and other components of TTO were used for fumigation of strawberry(cv.‘Hongyan')to explore the effects on fruit quality,antioxidant capacity,and disease resistance.Terpinen-4-ol was used to investigate the mechanism on inducing strawberry disease resistance,providing theoretical basis and a new method for strawberry fruit storage and preservation.The specific research results are as follows:1.The strawberry fruit were fumigated with 0.9g/L TTO,terpinen-4-ol and other components of TTO(?-terpinene,?-terpinene and 1,8-cineole)for 3 h,and then stored at 20? to simulate shelf temperature.Results showed that the terpinen-4-ol treatment group had the lowest decay index of natural disease,the lowest weight loss rate,and maintained high fruit firmness and anthocyanin content.Terpinen-4-ol can increase the activity of superoxide dismutase,catalase,ascorbate peroxidase and glutathione reductase and the expression of corresponding genes,thereby reducing the accumulation of hydrogen peroxide and enhancing the antioxidant capacity of the fruit.Since the effect of terpinen-4-ol treatment is better than that of TTO,we conclude that terpinen-4-ol is the main reason for TTO to help delay the senescence of strawberry fruit,maintain fruit quality,and improve the antioxidant capacity of fruit.2.The strawberry fruit were fumigated with 0.9g/L TTO,terpinen-4-ol and other components of TTO(?-terpinene,?-terpinene and 1,8-cineole)for 3h,and then artificially inoculated Botrytis cinerea(inoculation after fumigation treatment),to observe the disease development at 20°C.The results showed that terpinen-4-ol significantly improved the disease resistance of strawberry fruit,and was the most effective component in controlling the occurrence and development of inoculation diseases among four main components of TTO.Strawberry fruit treated with terpinen-4-ol can increase the activity and gene expression of pathogenesis-related proteins(chitinase and ?-1,3-glucanase),the activity of phenylpropane metabolic pathway-related enzymes(phenylalanine ammonialyase,cinnamate-4-hydroxylase and 4-coumarate-CoA ligase)and expression of FaPAL within 24h,and significantly increased the peroxidase and polyphenol oxidase activities and the expression of FaPPO within 12h,which increased the accumulation of total phenol,lignin and other phenylpropane metabolites.These results indicate that terpinen-4-ol can improve the disease resistance of strawberry fruit by rapidly inducing the activity of disease-resistant enzymes within24 h,and the effect is significantly better than TTO treatment.3.Metabolomics analysis of strawberry fruit at 12h after terpinen-4-ol and TTO treatment revealed that compared with control group,31 and 34 differential metabolites were found in the terpinen-4-ol and TTO treatment groups,respectively.These differential metabolites were mainly concentrated in phenylpropane,flavones,and flavonols biosynthetic pathways,leading to the accumulation of phenolic acids and flavonoid metabolites such as coumarin,cinnamaldehyde,conifer aldehyde,naringenin,taxifolin,quercetin and quercetin.Combined with the changes in enzyme activity and genes related to the phenylpropane metabolic pathway,it has been comprehensively demonstrated that TTO mainly promotes disease resistance of strawberry fruit by promoting the phenylpropane metabolism pathway through the main characteristic component terpinen-4-ol.