MANGO STEM END ROT PATHOGENS - FRUIT INFECTION BY ENDOPHYTIC COLONIZATION OF THE INFLORESCENCE AND PEDICEL

The stem end rot pathogens of mango (Mangifera indica), (Dothiorella dominicana, Dothiorella mangiferae, Lasiodiplodia theobromae (Syn. Diplodia natalensis Phomopsis mangiferae, Cytosphaera mangiferae, Pestalotiopsis sp. and Dothiorella 'long'), as well as other fungi (including Alternaria alternata), were found to occur endophytically in the stem tissue of mango trees prior to inflorescence emergence. On samples from trees with a record of low stem end rot levels, colonisation did not extend into the most recently produced flush of stem tissue. At a site with a history of high stem end rot levels, sequential monitoring of inflorescence tissue between flowering and harvest by plating out small (c. 8 mm3) tissue pieces revealed, that at least some of the pathogens - Dothiorella spp., P. mangiferae, Pestalotiopsis sp. and C. mangiferae gradually colonised the inflorescence, reaching the pedicel tissue of young fruit - 8 wk after flowering. Subsequently, detection frequency of the pathogens in inflorescence tissue declined, possibly because of interference from copper residues (from field sprays) accumulating on tissue samples. The detection frequency of A. alternata also increased as Dothiorella spp. declined, however these changes could not be attributed to antagonistic interactions between the two fungi. Using larger tissue pieces (1-2 mm thick transverse sections, or a square of tissue 25 mm2 x 3 mm thick) in isolations, endophytic colonisation by Dothiorella spp. and P. mangiferae was detected in stem, inflorescence and pedicel tissues of mature-fruit-specimens from two different sites, one unsprayed, and the other regularly sprayed with copper. The fungi were detected more frequently in the samples from unsprayed trees. Fruit from the sprayed orchard subsequently developed a high level of stem end rot caused by D. dominicana, while a lower level of stem end rot developed in unsprayed fruit, possibly because the latter fruit were also extensively diseased by anthracnose (Colletotrichum gloeosporioides Penz.). Endophytic colonisation of inflorescence and pedicel tissue was found to be a primary route of infection for fruit which develop stem end rot during ripening.