Analysis of microbial quality of common bean (Phaseolus vulgaris l.) seeds from five bean producing districts in Uganda

Abstract

Being a basic and an affordable source of protein, common bean (Phaseolus vulgaris L.) is grown widely in Uganda and the world at large. The quality of bean seeds has gained little attention yet remains a significant aspect of the value chain of production and consumption in Uganda. The aim of this study was to assess the microbial quality of common beans from five bean producing districts of Uganda. One hundred bean samples were collected from farmers and traders purposively selected from five bean producing districts of Uganda (Arua, Oyam, Hoima, Nakaseke, and Sironko districts). Three replicates of twenty samples of bean seeds randomly obtained from each district were subjected to microbial quality analysis using whole seed and agar plate standard protocols under laboratory conditions. The modified blotter method was used to test germinability and health of bean seeds in the laboratory. Standard seedling symptom tests were conducted in screen house experiments using a completely randomized design to assess germination and health of bean seedlings. Seed health tests revealed that 85% of the bean samples were contaminated with seed borne fungi. Five seed borne fungal genera were isolated from the seed samples, with Aspergillus (42.8 %) and Fusarium (37.1 %) being the most common fungi followed by Penicillium (18.9 %) while Colletotrichum (12.2 %) and Rhizopus (6.2%) were the least occurring fungi. Xanthomonas sp. was the only bacteria isolated from 15% of the samples tested. In the laboratory, bean seeds exhibited relatively poor germination (58.2%), with 30.9% of seeds having fungal outgrowths. While in the screen house, only 63.2% of seeds germinated, with 23.9% of ungerminated seeds being rotten. Disease assessment in the screen house revealed that, 25.1% of seedlings were diseased with various symptoms. Six seed borne diseases were recorded including; Fusarium wilt, Angular leaf spot (ALS), Ascochyta blight, Anthracnose, Common Bacterial Blight (CBB) and Bean common mosaic virus (BCMV). Determinately, the beans available in Uganda are of low/poor quality. Poor quality seeds contaminated with seed borne pathogens may result in poor germination rates, poor health of seedlings and reduced crop stand and yield. Therefore, improving access to clean and healthy seed for farmers is inevitable. Farmers are urged to embrace good bean production practices especially disease management in the field and post-harvest handling practices in order to improve production of safe and quality beans.