The Improvement On Techniques Of Pineapple Blackheart Control By Application Of ABA

The pineapple is one of the most important fruits for export from south China.Blackheart is the major disease that causes losses of fresh pineapple fruit during storage and transportation.The previous research in this laboratory shows that postharvest application of ABA to pineapple can effectively control the occurrence of black heart,but it causes severe withering of the pineapple crown.In order to develop a new technology that can achieve the dual goal of controlling the postharvest pineapple blackheart and maintaining the freshness of the pineapple crown,we designed a series of experiments to study the effects of different methods of pineapple preservation,such as combining potassium,6-BA,KT and IAA with ABA,respectively,in postharvest treatment,applying ABA to different parts of pineapple fruit,soaking the pineapple fruit stem in ABA solutions,preharvest spray of mixture of ABA and IAA on the pineapple crown,and other methods.The main results were as follows:1.Postharvest combination of potassium and ABA treatment decrease the efficacy of blackheart control and aggravated crown withering.Compared with application of ABA alone,the combination of potassium at different concentrations and ABA increased the internal browning（IB）index and incidence,the degree of the crown withering,as well as the weight loss rate and the relative electrical conductivity.2.Postharvest application of ABA by soaking the stem end effectively control blackheart,but enhanced crown withering.Postharvest immersion of the pineapple fruit stem in ABA solutions lowered the pineapple IB index and incidence,but to a certain degree promoted the crown withering,and,soaking resulted in decay of the fruit stem-end.Adding Ca C l2 and Sportak（SPK）to the soaking solution also cannot mitigate the decay of fruit stem cut.3.Postharvest application of ABA in combination with different plant growth regulator alleviated crown withering,but reduced blackheart control effect.Whether it is sprayed to the crown or the whole pineapple（crown + fruit）,whether mixed solutions are used or not,and regardless of the spraying order,the postharvest treatment with ABA combined with 6-BA,KT and IAA,compared with application of ABA alone,significantly alleviated the degree of pineapple crown withering,but increased the IB index and incidence.4.Application of ABA to crown of harvested pineapple showed the same effects in blackheart control as that to the whole fruit.Postharvest application of exogenous ABA to the crown was as effective as to the whole pineapple in reducing pineapple IB index and incidence,while the effect of application of ABA to the fruit only was poorer.Application of ABA to the crown only and that to the whole pineapple reduced polyphenol oxidase（PPO）,phenylalanine ammonia lyase（PAL）activities,and total phenolic contents.They increased the activity of catalase（CAT）and peroxidase（POD）,and reduced the content of H₂O₂.The results suggested that the crown has important influences on the synthesis and oxidation of phenolic compounds and antioxidant capacity.Application of ABA to the crown only and that to the whole pineapple both reduced the content of endogenous gibberellins（GA1 and GA4）,and increased the content of endogenous ABA,which indicated that ABA was absorbed by the crown and could regulate the balance between endogenous hormones in the fruit.These results suggested that the crown plays a major role in regulating pineapple blackheart.5.Pre-harvest application of mixture of ABA and IAA to crown showed good effects in controlling blackheart and keeping crown fresh.Pre-harvest application of ABA and IAA mixture to the pineapple crown obviously reduced the postharvest pineapples IB index and incidence,maintained the freshness of crown,increased the activity of PAL enzyme and the content of phenolic compounds,reduced the activity of polyphenol oxidase,and increased the activity of POD and C AT as well as the H₂O₂ level.In conclusion,neither postharvest application of ABA with potassium,nor with growth regulators,nor different ways of applying ABA helped achieve the dual goal of keeping the crown fresh and controlling blackheart.Postharvest application of ABA to the crown only was as effective as that to the whole pineapple in reducing the occurrence rate of blackheart.Preharvest application of ABA in combination with IAA to the pineapple crown can effectively control the occurrence of blackheart,and also keep the crown fresh.Therefore,this technology has a good prospect to be applied to pineapple industry.