Evaluation of fusarium sp. (Abu Haraz isolate) as a biocontrol agent for striga hermonthica (Del.) benth. on sorghum bicolor (L)

Fusarium sp. was isolated from diseased S. hermonthica plants growing on a field of sorghum at Abu Haraz in the premises of the Faculty of Agriculture and Natural Resources, University Of Gezira (U. of G). Greenhouse, field and laboratory experiments were undertaken to a) study the efficacy of the fungus on S. hermonthica on sorghum under greenhouse and field conditions, b) reaction of major crops viz cotton, sesame, groundnut, sunflower and wheat to the fungus c) effects of Fusarium spores and culture filtrate on S. hermonthica seeds germination during conditioning and d) influence of temperatures on fungal growth. Soil incorporation, in pots, of Fusarium sp., propagated on autoclabed sorghum grain, henceforth referred to as fungus culture, at 5, 10, and 15g kg-1 soil prior to sorghum sowing, reduced Striga parasitism by 43-86% in comparison to Striga infested and infested autoclabed grain sorghum controls, respectively. In unsterilized soil, the fungus culture was less effective in reducing Striga infestation and growth than that in sterilized soils. Striga biomass was significantly reduced. Sorghum shoot and root growth and dry weight were concurrently increased. In field experiments Fusarium propagated on autoclaved sorghum grain, at 5, 10 and 15g hole-1 incorporated in the same hole as sorghum seed reduced Striga parasitism by 44-64 and by 22-46% in season 2000-2001 and 2001-2002, respectively. Fusarium culture in combination with urea at 190 kg ha-1 reduced Striga parasitism by 42-67 and 56-68% in both seasons, respectively. Striga biomass in both seasons was reduced significantly and sorghum biomass and grain yield were increased significantly. Striga hermonthica seeds conditioned in Fusarium spore suspension exhibited no germination, irrespective of the conditioning period or strigol concentration in the terminal solution. Seeds conditioned in Fusarium culture filtrate for 3 days displayed poor germination. However, germination increased on further extension of the conditioning period and on increasing strigol concentration in the ternal solution. Striga seeds conditioned in Fusarium culture filtrate for 12 days showed similar germination to those conditioned in distilled water. The Fusarium sp. displayed maximum germination at 25-30 deg C, above and below this range growth of the fungus declined significantly. At 40 deg C, the fungus exhibited negligible growth. Host specificity of Fusarium studied revealed that the crops wheat, sunflower, sesame, groundnuts and cotton did not show disease symptoms related to the fungus. However, the fungus was isolated from the roots of these crops. The fungal isolated from S. hermonthica were Aspergillus flavous, A. niger, A. terreus, Rhizopus sp., Curvularia sp., Phoma sp. and the bacteria Bacillus subtilis. The findings indicate that Fusarium sp. designated in the thesis as Abu Haraz isolate, is a potential biocontrol agent for S. hermonthica. Work should continue to develop easy and inexpensive methods of application, identify the fungus and the active metabolites it produces, Identification of the metabolites is important as they may provide lead compounds for future research. However, safety of the Fusarium sp. to animals and humans should be ensured