Studies on fungi causing post-harvest rotting of pawpaw (carica papaya l.) and banana (musa sapientum l.) fruits in Tanzania

A study on fungi associated with post-harvest rotting of pawpaw (Carica papaya) and banana (Musa sapientum) fruits in Dar Es Salaam, Tanzania was conducted. Khizopus sp. was found to be pathogenic on wounded and non-wounded pawpaw fruits, while Alternaria tenuissima and Curvularia geniculata were found to be pathogenic on wounded fruits only. Colletotrichum gloeosporoides was found to be pathogenic on wounded and non-wounded banana fruits, while Alternaria tenuissima and Curvularia sp. were pathogenic on wounded banana fruits only. Using the culture plate technique, Rhizopus sp. was the only fungus among the pathogenic ones which was found to have its spores present in the air at the Dar es Salaam Kariakoo market. When the dilution plate technique was used, all the above mentioned pathogenic fungi were found to have their spores present on the surface of their respective healthy fruit hosts. Colletotrichum sp. was the only fungus which was found to be present on its host fruit at some farms. This suggests that the fruits were probably getting the initial inoculum while they were on transit to the market and that infection began either at the market or while the fruits were being transported to the market. Culture media having extracts of the host fruits supported better growth of the pathogenic fungi than the other growth media tested. Optimum temperature for mycelial growth, spore production and spore germination for all the pathogenic fungi was 26 C. Experiments on spore germination using liquid water and different levels of air moisture showed that, free liquid water was necessary for spore germination. Crude extracts of root-bark of Iloringa oleifera which had showed antifungal activity in preliminary tests, were tested on fungi pathogenic on pawpaw and banana fruits. Growth of the pathogenic fungi on the fruits and in culture media was inhibited by the extract for the entire period of the experiment (9days). This indicated that the extracts of M. oleifera have good potential for controlling fruit ret caused by fungi. It is therefore recommended that further/ more refined studies be conducted on the chemical components of the crude extract which have the antifungal activity. This may lead to identification of a chemical which can be obtained locally to solve problems caused by fungi. It may even prove that refining the crude extract is not necessary for certain uses.