Efficacy Of Blackheart Control Of Harvested Pineapple By Combination Treatment Of ABA And Aspergillus Niger

Pineapple is one of the four most famous tropical fruits that have a unique flavor and are loved by consumers.‘Comte de paris’pineapple is the main variety in China,accounting for more than 80%of the pineapple cultivation area.However,’Comte de paris’pineapple is susceptible to blackheart.The problem of pineapple blackheart has become a limiting factor for the further development of the pineapple industry.Therefore,the development of pineapple blackheart control technology has important practical significance.Aspergillus niger,a endophyte isolated from pineapple in our laboratory’s preliminary work,has displayed some effect in reducing pineapple blackheart.Based on the study of the effect of ABA on the vitality of Aspergillus niger,this study explored the effect of various combinations of Aspergillus niger and ABA on the control of pineapple blackheart,aiming to optimize the method for control of pineapple blackheart.The main findings are as follows:1.The spore germination rate and germtube growth rate of Aspergillus niger vary with the colony age of Aspergillus niger.For the Aspergillus niger colony age of 7-23 d,the spore germination rate and germtube growth rate showed a peak-shaped curve with colony age,indicating that the viability of the spores was the highest when the colony age of Aspergillus niger was 17 d old.Additing 200 mg?L^-1 ABA in the spore suspension significantly increased the spore germination rate and germtube growth rate of Aspergillus niger,and greatest increase in viability occurred at 17 d,indicating that the stronger the viability of Aspergillus niger,the more significant effect of ABA.2.The spore germination rate and the germtube growth rate formed a peak-shaped curve with storage time,which reached to the peak at 72 h and droped to the lowest levels at 120 h.The addition of ABA to the spore suspension did not affect the dynamic change of spore germination rate and germtube growth rate,but significantly increased the spore germination rate of 72 h.It indicated that the Aspergillus niger could be preserved for 3-4 d,and the suspension of Aspergillus niger with ABA solution could maintain high spore activity.3.The efficacy of combining ABA with spore suspension to control pineapple blackheart is better than application of either Aspergillus niger or ABA,However,the effect of ABA combine Aspergillus niger on the on control of blackheart is varies with the order of application.The effect of applying spore suspension first is better than that of spraying ABA solution first.4.The spore suspension was sprayed with 8 days and 16 days old Aspergillus niger spores to spray pineapple.After 3 days,50 mg?L^-1ABA was sprayed.The latter controlled pineapple blackheart better.5.Following application of the Aspergillus niger spore suspension,the pineapple fruit was stored at 20℃or 25℃for evaluating the effect of blackheart control.It was found that when the pineapple was stored at 25℃,the blackheart index and incidence increased compared with those stored at 20℃,indicating that when the storage temperature was high,it was not conducive for Aspergillus niger spores to control blackheart.6.Preparation of a suspension mixture containing 2×10⁶ cfu?m L^-1spores from 16 d old colony and 200 mg?L^-1 ABA,which was then preserved either 0 d or 3 d before being diluted for applying to pineapple fruit(After dilution,the concentration of ABA is less than 10 mg?L^-1).The results showed that preservation of the suspension for 3 d enhanced efficacy in control of pineapple blackheart compared with treatment on 0 d（apply immediately after preparation）.The effects of these two treatments in controlling blackheart were better than those of 50 mg?L^-1 ABA alone,suggesting that the preparation containing appropriate concentration of Aspergillus niger spores and lower concentration of ABA could effectively control pineapple blackheart.7.Adding 200 mg?L^-1 GA₄₊₇to the spore suspension significantly increased the germination rate and growth rate of the Aspergillus niger spores.The efficacy of the Aspergillus niger spore suspension formulated with GA₄₊₇ on pineapple blackheart was slightly higher than that of GA₄₊₇ alone,but slightly lower than the spore suspension fomulated with ABA.As exogenous application of GA is the main cause of pineapple blackheart,this result indicates that the effect of endophytic spores in controlling blackheart could be compromised by GA.