Studies On Latent Infection And Biological Characteristics Of Mango Stem End Rot Pathogens

The latent infection of the mango stem end rot pathogens wasinvestigated by isolating the pothgens from the shoots prior to flowering, infloresence, ftuitlet, ripeless fruits and ripening fruit of two varieties, Shihaomang and Zihuamang , in mango orchard of Guangxi University. The result of investigation indicated that some stem end rot pathogengs were found to occur endophytically in the shoot prior to flowering. There were 42 isolates causing mango fruit rot that obtained from the period prior to flowering to store. Except nine isolates (D-l, D-2, D-3, D-4, D-5, D-6, D-7, D-8, D-9) produced conidia, all of the others didn't produce conidia after induction. After identifying, D-l, D-2, D-3, D-4, D-5, D-6, D-7, D-8, D-9 respectively were Dothiorella dominicana Pet.et Cif. , Botryodiplodia (heobromae Pat., Pestalotiopsis sp., Colletotrichum gloeosporioides (Penz.) Sacc., Diplodina sp., Phomopsis mangiferae Ahmad, Cladosporium sp., Penicillium sp. and Aspergillus sp. .D-1, D-2, D-3 latently infected the shoots perior to flowering ; D-4 stared to infecting the tissue of infloresence during flowering ; D-5 invaded fruitlets and made ripe fruits rotten after latent period; D-6, D-7, D-8 latently infected ripeless fruits before harvest; while D-9 only could be isolated from fallen and rotten fruits during storing. Among these pathogens, D-l, D-2, D-5 were the main pathogens that caused mango stem end rot in the orchard; while D-3, D-6 were the minor one; the others could cause the symptom of stem end rot only in certain conditions. There were no correspondent reports on mango stem end rot caused by Diplodina sp. in the world. So D-5 was identified to be a new pathogen of mango stem end rot.The study on biological characteristics of D-5 isolate (Diplodina sp.) indicated: The range of growth tempreture was 10-37 C, while the optimum growth tempreture was 25-28 C. It could growth between pH 4.0-9.0, while pH 5.5 wae it's optimum pH. Fluoresent light was the best light to it's growth, while black light was the best light to it's production of stroma. The best carbon and nitrogen source to it's growth was lactose and L-glutamic acid respectively. There were 7 fungicides showing control effects on it among the tested 11, and the control effects of the 7 fungicides from strong to weak successively were Tilt, Spoetak, Tecto, Carbendazim, Score, Indar, Diniconazole.The study on the activities of peroxidase (POD), polyphenoloxidase (PPOD) and phenylalanine ammonialyase (PAL) in mango peel after inoculation by Dothiorella dominicana, Botryodiplodia theobromae andDiplodina sp. indicated: The activities of POD after inoculation by pathogens were all higher than CK, furthermore, the activities of POD increased while the disease of mango became more serious, it meant that the pathogen with more strong pothogenicity could induce mango fruit producted more POD than that less pathogenicity or that the activities of POD higher and higher with the time of stem rot prolong. The change of the activities of PPOD was somewhate similar to POD. The activities of PAL had some differences between different combination of mango varietise and pathogen strains. The activities of PAL of combination of Dolhiorella dominicana, Botiyodiplodia theobromae and Sihaomang in mango peel were all higher than CK ,which aparted from disease spot 1 cm; while the activities of PAL in mango peel were all lower than CK, which aparted from disease spot 2 and 3 cm. The activities of PAL of combination of Diplodina sp. and Zihuamang in mango peel were all lower than CK too.