Endophytic fungi associated with core rot of apples in South Africa, with specific reference to Alternaria species

Apple fruits were sampled at five stages of development for endophytic colonisation by fungi associated with core rot, a major post-harvest disease. In addition, isolations were made from diseased core tissues of apples after 8 months of cold storage. The cultivars Top Red (susceptible to core rot) and Granny Smith (resistant to core rot) were sampled in orchards during the 1995/6 growing season. Of the 40 different fungal taxa encountered, 19 had a relative importance (RI) value of more than 10%. In general, more fungal isolates were obtained from Top Red than from Granny Smith apples, but no tissue specificity was detected. As found in previous studies, the Alternaria complex was the most dominant, representing 57% of the total number of 1602 isolates. On the basis of sporulation patterns and spore morphology, this complex could be divided into two different groups in the Alternaria alternata, two in the Alternaria infectoria, and one in the Alternaria tenuissima complexes. A further group was identified which may represent an additional Alternaria species. This study has further shown that the Alternaria spp. are present as endophytes already at the bud development stage, which has serious implications for any programme using fungicides for disease control.