Effect Of Pineapple Endophyte Fungus Spergillus Niger On Pineapple Storability

China is the third largest pineapple producer in the world,and the pineapple industry is the pillar of C hina's tropical and subtropical agriculture industry.Black heartis one of the major diseases that cause loss of fresh pineapple fruit during postharveststorage and transportation,which severely limits the transport and marketing of the fruit.Research of this laboratory shows that treatment with abscisic acid(ABA)is the most effective way to control pineapple blackheart,but it causes withering of the crown.To seek for a more effective and way to enhance storability of pineapple,the cultivar‘Comte de Paris' was used for isolation of endophytes and investigation of the efficacy and mechanism of endophytes application in reducing blackheart and keeping the crown fresh.The main results were as follows:1.A strain endophyte fungus was isolated from flesh of pineapple and designated P1,its ITS-r DNA sequence was amplified.The endophyte P1 was identified as Aspergillus nigerbased on the sequence,which shared 99 % identity with that of Aspergillus niger strain SICAU SDT35,and the morphological character of the fungus.2.Treating harvested pineapple with the spore suspension A.nigereffectively control blackheart and crown withering.A.niger spore suspensiontreatment at three different concentrations.Three different concentrations ofcontro lled pineapple blackheart and crown withering to different extents,with the concentration of 5 x 107 cfu·m L-1being most effective concentration.This concentration was used in a repeated experiment.The results showed that the internal browning incidence and crown withering index of the treated fruit were 48.84 % and 55.17 %,respectively,of that of the control.3.A.niger treatment had certain influence on pineapple quality.A.niger treatmentreduced TSS,increased TA,delayed degradation of As A inpineapplefruit,suggesting it slightly enhanced the acidity,but maintain the nutritional quality to a certain extent.4.A.niger treatmentenhanced antioxidant defense capacity of harvested pineapple and inhibited oxidation of phenolic compounds.A.niger treatment decreased H2O2 content,increased ascorbic acidcontent,and enhanced activities of SOD and POD,suggesting it activated antioxidant defense system in pineapple.A.niger treatmentreduced content of phenolic compounds and lowered the activity of PPO suggesting that it could decrease accumulation and oxidation of phenolics.5.A.niger treatmentregulated the ratio of endogenous hormones in harvested pineapple.A.niger treatmentreduced the content of gibberellic acid(GA1 and GA4),and increased the content of ABA and IAA.6.Exogenous application of A.niger directly led to increased abundance of A.niger within tissue of pineapple.Following 9 d ofstorage,DNA of A.niger was only detected in pulp of untreated fruit,while it was detected in both pulp and core of treated fruit,and abundance was significantly higher than the control.Moreover,no matter in the control or the treatment,A.niger was not detected in peels of pineapple.These suggest that the exogenous application of endophyte A.niger on the pineapple can through penetrate the peel to get into pulp and core,and multiply there in large quantity.In conclusion,exogenous application of endophyte A.niger can enterinto pineapple fruit,and,after mass multiplication,can effectively control blackheart development and crown withering.The mechanism of A.nigerin preserving pineapple fruit involves elevated antioxidant enzyme activities,reduced reactive oxygen,decreased accumulation and oxidation of phenolics,and regulation of the homeostasis of endogenous hormones such as GAs,ABA and IAA.