Occurrence of fungal seed-borne pathogens of rice and effect of postharvest handling methods on seed quality in Uganda

Studies aimed at determining the occurence of seed-borne fungi and bacteria of rice in Uganda and effect pf postharvest processing practices on the quality of rice seed were conducted at Makerere University. A total of seventy seed samples from three districts of Uganda namely Bugiri, Pallisa, and Lira were examined by the blotter method for fungal infection. Twenty different seed-borne fungi were identified and their incidence and infection levels varied significantly (P<0.01) with respect to location and within districts. Bipolaris oryzae was the most prevalent pathogen with an infection range of 3-94%. Phoma oryzae, Phyricularia oryzae, Alternaria padwickii, Fusarium moniliforme, Curvularia lunnata, Nigrospora oryzae, Verticilium cinabarium and Alternaria alternate were also present in all the districts. However, some pathogens were localized for example, Exerohilium rostratum and Curvularia eragrostidis were only encountered in Lira and Bugiri districts, respectively. Pallisa district had the least number of fungal species while Bugiri registered diversity. Mean infections were low in Pallisa as opposed to Bugiri and Lira districts. Nine categories of seddlings with decay in shoot and root were encountered most frequently. Bipolaris oryzae Phoma oryzae, Pyricularia oryzae, Alternaria padwickii, Fusarium moniliforme, Curvilaria lunnata, Melanosopora zaminae and Alternaria alternate were found associated with 100%, 55.6%, 44.4%, 66.7%, 77.8%, 11.1% and 11.1% of the different abnormalities, respectively. The results of the study have shown that threshing, drying and storage methods used by farmers significantly affect the quality of the seed and their effects are addictive. Threshing by ‘’beating’’ significantly reduced the quality of the seed while drying on cemented floors and polythene sheets reduced he germination % of the seed but maintained good physical purity of the seed. On the hand, storing seed in polythene bags resulted in seeds of high quality. The study demonstrated that a wide range of seed-borne fungi are prevalent in the rice growing area of Uganda and are associated with different seedling abnormalities and seed decay during rice germination; thus control measures should be sought to avert the would be economic losses, and b) the post production operations need to be considered as a systems approach in order to minimize quality losses.