Occurrence, effects and control of Seedborne pathogenic fungi of cotton (Gossypium hirsutum l.) seeds using plant extracts in Simiyu region, Tanzania

Dissertation

This study was carried out to assess the presence and effect of seed-borne pathogenic fungi on cotton seeds collected from different ginneries and seed processor in Simiyu region and the potential of developing control measures using plant extracts. A total of 30 cotton seed samples were collected from four cotton ginneries and one cotton seed processor in Simiyu region. The samples were then analyzed for seed-borne fungi and germination using standard procedures. Twelve fungal species in eight genera were detected in the 30 seed samples tested for seed-borne fungi. The detected fungal species were: Aspergillus flavus, Fusarium moniliforme, A. niger, F. equiseti, Penicillium spp, F. oxysporum, F. pallidoroseum, Cladosporium herbarum, Phoma exigua, Stagonospora nodorum, Bipolaris spicifera and Rhizopus spp. Aspergillus flavus and F. moniliforme were the most predominant species. They infected 58.9% and 13% of the tested seeds respectively, from 83% of the collected seed samples. The least frequent seed borne fungal species was Bipolaris spicifera which infected 0.3% of seeds from 3% of the seed samples. Seed germination, roots and shoots lengths and seedling vigour were significantly reduced (P≤0.05) by the tested isolated pathogenic fungi: Fusarium oxysporum, Phoma exigua, F. equiseti, F. moniliforme, F. pallidoroseum and Stagonospora nodorum. Seedling girth was only significantly affected by Fusarium moniliforme. Fusarium oxysporum and Stagonospora nodorum reduced the tested percentage germination, seedling vigour, seedling girth, seedling shoot and root length to the highest and lowest extent, respectively implying that F. oxysporum is the most pathogenic while Stagonospora nodorum is the least. In a separate study, the efficacy of leaf and seed extracts of Neem and Moringa were evaluated for the management of seed-borne fungi of cotton seeds. The results showed that Neem and Moringa leaf extracts are effective in managing Phoma exigua, F. moniliforme, F. equiseti and F. oxysporum in cotton seeds at a concentration of 25% (v/v) while Moringa seed extract was effective in managing all the seed-borne fungal pathogens at the same concentration except F. moniliforme. All the tested plant extracts were superior to Cruiser extra except Moringa seed extract which was inferior in managing F. moniliforme but significantly effective in managing F. oxysporum. Soaking of fungi inoculated seeds for six and 12 hours in plant extracts significantly reduced seedling mortality and increased population of health seedlings than soaking for one hour. With the exception of soaking time, there were significant differences in respect of the 3-way interactive effects and 2-way interactive effects between plant extracts, concentration and soaking period for all other parameters studied for Phoma exigua. For Fusarium moniliforme there were significant differences in respect of the 2 and 3 way interactive effects for all parameters. This was similar with Fusarium equiseti except that for F. equiseti there was no significant effect of soaking time and plant extract concentration in reducing death of seedlings and increasing the population of heath seedlings. For F. oxysporum the three way interactive effects of plant extracts, concentration and soaking period and two way interactive effects between plant extracts and concentration and between plant extracts and soaking period were not significant (P >0.05) for the percentage seeds with fungal infection. Also the interaction between soaking time and plant extract concentration was not significant for the percentage seed germination. Therefore for the management of seed-borne pathogenic fungi in cotton seeds, priority should be given to Moringa oleifera leaf extract followed by Azadirachta indica leaf extracts as they were superior to Cruiser extra in increasing seedling vigour, reducing death of seedlings and ensuring maximum population of health seedlings. All tested plant leaf extracts should be used at 25% concentration and seeds should be soaked in the plant extracts for six hours before sowing.

Town Director of Bariadi Town Council, Tanzania Cotton Board, Quton (T) Ltd, Alliance Ginneries Ltd, NGS Investment Co. Ltd, Kahama Oil Mills Co. Ltd, BioRE