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Articles by O.M. Olanya
Total Records ( 3 ) for O.M. Olanya
  M. Osiru , E. Adipala , O.M. Olanya , B. Lemaga and R. Kapinga
  Assessment of disease occurrence in relation to agro-ecological and cropping variables is essential for effective Alternaria leaf petiole and stem blight disease control. The occurrence and distribution of the disease was investigated in a systematic survey of the major sweetpotato producing districts in Uganda during two cropping seasons. The composition of the Alternaria sp. was determined from a random sample of diseased leaf tissues. Farmers’ practices and perceptions on disease management were also investigated. A survey of the 35 districts in both years showed that Alternaria disease was widespread throughout Uganda. The predominant species observed were A. bataticola (55% of isolates) and A. alternata (40% of isolates). The severity of Alternaria disease was very low, however, the range in disease incidences were from 0 to 49.2%. The disease was more prevalent in the Lake Crescent Region than in the less humid regions of eastern and northern Uganda. No significant correlations were detected between altitude at which sweetpotato cultivars were grown and disease severity or yield. Among the sweetpotato cultivars surveyed, the lowest incidence of Alternaria disease was detected on cultivars Dimbuca and Silk. The study also noted that perception of farmers and disease practices were contributing factors to disease spread. These studies suggest that selective deployment of cultivars and cultural practices can limit the spread and damage attributed to Alternaria leaf petiole and stem blight disease of sweetpotato. This is the first record of A. bataticola on sweetpotato in Uganda.
  M.O. Osiru , E. Adipala , O.M. Olanya , P. Kelly , B. Lemaga and R. Kapinga
  Not available
  O.M. Olanya , G.A. Porter , D.H. Lambert , R.P. Lakin and G.C. Starr
  The aim of this research was to evaluate the effects of irrigation and soil management on potato tuber diseases. Supplemental irrigation, soil amendment and crop rotation can improve potato growth and tuber yield under drought stress conditions, but may also increase potato tuber diseases. The effects of irrigation, soil amendment and crop rotation on the incidence of tuber diseases were quantified from 1994 to 1997 in potato plots. Surface sprinkler irrigation was applied each year, based on tensiometer or moisture block readings deployed in field plots. Black scurf (Rhizoctonia solani), black dot (Colletotricchum coccodes), silver scurf (Helminthosporium solani) and common scab (Streptomyces scabei) diseases were quantified on potato tubers randomly sampled at harvest and kept at storage temperature of 7.2°C before visual disease assessment. The incidence of tuber diseases varied among irrigation treatments, crop rotations and soil amendments. The mean incidence of black scurf, silver scurf and black dot ranged from 3-18, 2-33 and 4-7%, in best, un-irrigated and reduced irrigation, respectively. The incidence of back scurf, silver scurf and black dot diseases ranged from 2.4-10, 0.8-21 and 1-31% on potato tubers grown in plots under green manure rotation crop (peas/vetch). Disease incidences on tubers were 1-28, 0-35 and 2-16% for black scurf, silver scurf and black dot, respectively; when potato plants were grown under small-grain rotation. Soil amendments had significant (p<0.05) effects on the incidences of silver scurf disease in 1997 and black dot disease in 1996 and 1997. The interactions of soil amendment with irrigation resulted in significant effects on black scurf incidence in 1994. This research implied that water application may lead to increases in some potato tuber diseases, however; crop rotation and soil amendment may reduce the incidences of selective potato tuber diseases, depending on the type, duration or frequency of supplemental irrigation.
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