Studies on fungal storage rot and seed-borne pathogens of onion and their management

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Surveys of fungi associated with postharvest deterioration of onion bulbs in four major markets in Kumasi Metropolis were conducted. Rotten onion bulbs obtained from the four markets: Abinchi, Anloga, Kwadaso and Central markets were infected by five fungal species: Aspergillus niger, Aspergillus flavus, Penicillium sp., Rhizopus stolonifer and Fusarium oxysporum. Of these, Aspergillus niger and Penicillium sp. were the most frequently isolated fungi. Aspergillus flavus was the least encountered fungus. Rhizopus stolonifer and Aspergillus niger were the most pathogenic. Black mould, Blue mould, Soft rot, Neck rot and Basal plate rot were the major postharvest diseases identified in a dry season survey in the markets. Incidences of these postharvest diseases were high in the wet season. Black mould enjoyed the highest incidence in all the markets. The lowest incidence was recorded for Blue mould. Seed-borne mycoflora of 37 samples of farmer-saved onion seeds from Bawku in the Upper East Region of Ghana were studied. Nine different fungal species were identified and isolated from the seeds. The most frequently encountered fungi species were Aspergillus niger, Rhizopus stolonifer, Aspergillus flavus, Penicillium sp. and Fusarium verticilloides with percentage occurrence of 33.3, 32.5, 25.8, 3.1 and 3.0 %, respectively. Efficacy of aqueous leaf extracts of Pawpaw (Carica papaya), Neem (Azadirachta indica), Moringa (Moringa oleifera), Cassia (Cassia alata) and Tobacco (Nicotiana tabacum) in managing seed-borne fungi of Bawku Red were studied in vitro and in vivo. All the aqueous leaf extracts significantly (P < 0.05) inhibited the radial mycelial growth of the test fungi (Aspergillus niger, Aspergillus flavus, Rhizopus stolonifer, Botrytis sp. and Fusarium oxysporum) in vitro. The highest percentage growth inhibition was achieved with aqueous Pawpaw leaf extract. In the in vivo test, all aqueous leaf extracts significantly (P < 0.05) reduced all the seed-borne fungi. Lastly, three fungicide/insecticide chemical seed dressants: Seed Power, Seedrex and Seed Star were evaluated for effectiveness in the management of seed-borne pathogens of onion. Seedrex was identified as the most effective seed dressant. However, seed germination was not significantly enhanced.  
Dissertation presented to the School of Graduate Studies Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirement for the award of MSc. Crop Protection (Plant Pathology) degree