Biology and control of stem end rot pathogens of mango

Abstract

Extensive sampling of mangoes from several sites in northern Australia, and incubation of the fruit at 230C for 3 w, revealed the presence of stem end rots (SER) that yielded pure cultures of several fungi (mostly one species per lesion), whose pathogenicity was confirmed on detached fruit. The pathogens recorded included Dothiorella dominicana, D. mangiferae, D. 'long', D. aromatica, Lasiodiplodia theobromae (all of which are considered to be anamorphs of Botryosphaeria spp.), as well as Phomopsis mangiferae, Pestalotiopsis mangiferae and Cytosphaera mangiferae. As well, Colletotrichum gloeosporioides caused stem end anthracnose and Aspergillus niger caused aspergillus rot at the stem end. On unharvested, developing mango fruit, D. dominicana was shown to form quiescent infections that subsequently developed into lesions on harvested, mature fruit during ripening. D. dominicana also caused small, superficial, discrete, dendritic spots on the sides of ripe mangoes.In the survey, SER lesions yielded D. dominicana most frequently, in contrast to the reports from many tropical countries where generally, the disease has been attributed to L. theobromae. L. theobromae and Phomopsis mangiferae were isolated from a considerable proportion of the SER lesions on fruit from only a few sites. In most cases, individual lesions yielded only one fungus. When co-inoculated onto detached fruit, D. dominicana predominated over D. mangiferae, D. 'long', Phomopsis mangiferae and Alternaria altemata as the cause of SER during storage at either 13 or 220C, and was generally reisolated exclusively. Similarly, when co-inoculated onto detached fruit, D. dominicana predominated over L. theobromae as the cause of SER during storage at 13, 18 and 250C however, L. theobromae was the major cause of SER losses in co-inoculated fruit held at 300C. Although D. dominicana predominated over C. gloeosporioides as the cause of stem end lesions on the majority of detached mangoes that were co-inoculated with the two fungi and held at 13 or 180C, stem end anthracnose (caused by Colletotrichum gloeosporioides) developed instead of SER in more than one-quarter of the fruit. This result indicates that in some circumstances, the development of stem end anthracnose on naturally infected fruit could prevent the development of SER, despite the presence of quiescent infections of D. dominicana.The SER fungi (D. dominicana, Phomopsis mangiferae, C. mangiferae and Pestalotiopsis mangiferae) were associated also with necrotic twigs, tree litter (Botryosphaeria dothidea) and old foliar anthracnose lesions (L. theobromae).The taxonomy of the fungi causing SER of mango and avocado and fruit rot of kiwifruit has been reviewed and the fungi have been described. Suggestions have been made for possible revisions to the taxonomy to alleviate the current anomaly whereby anamorphs of Botryosphaeria spp. of similar morphology have been classified in either Dothiorella or Fusicoccum, vis. (a) D. dominicana should probably be reduced to synonymy with Fusicoccum aesculi, the anamorph of Botryosphaeria dothidea; (b) isolates of D. mangiferae appeared conspecific with some isolates of Fusicoccum parvum (the anamorph of Botryosphaeria parva), a cause of SER of avocado and fruit rot of kiwifruit. Although Dothiorella mangiferae was reduced to synonymy with Nattrassia mangiferae by Sutton and Dyko (1989), further studies may justify their reduction (along with F. parvum) to synonymy under the new combination, Fusicoccum mangiferae. Hendersonia creberrima which causes soft brown rot of mangoes in South Africa also appeared to be indistinguishable from D. mangiferae (confirming of Sutton and Dyko (1989)); (c) D. aromotica and Fusicoccum luteum (another cause of SER of avocado and fruit rot of kiwifruit) appeared to be conspecific. Further studies may justify their reduction to synonymy under the new combination, Fusicoccum aromotica; (d) D. 'long' appeared to be an undescribed species, with affinity to Fusicoccum cajani.