Importance of seed-borne inoculum level on the development of common bean bacterial blight disease and associated yield loss of common bean in the central rift valley of Ethiopia

Abstract

Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap) is one of the major constraints to common bean production worldwide, with up to 40% yield loss. Xap is a seed-borne pathogen, and the worldwide distribution of the disease it causes can be attributed to transport on or within the seed. However, the relationships between seed inoculum level and disease developed in the field and associated yield loss have not been investigated so far in Ethiopia. Therefore this study aimed to determine the relationships of seed inoculum level with seedling infection, disease intensity and yield loss. The experiment was carried out during the 2015 main growing season at two sites of Malkassa Agricultural Research Center trial site. The experimental design was a split-plot, with the seed infection type as the main plot and the infection level as a subplot. Treatments were sown onto 2m * 2m (4m2) plots and each treatment was replicated three times. Germination and seedling infection were recorded 10 and 21 days after sowing respectively. After that, disease incidence and severity records were taken at 35, 49, 63 and 77 days after planting. At harvest, yield component and yield data were recorded from the net plot. All the data were subjected to ANOVA using SAS and treatment means were separated using the LSD test. The results of the study revealed significant differences among seed infection-type treatments for most of the parameters measured. Seed infection levels were also significantly different for all disease and yield and yield component parameters at both locations. From the results, it can be concluded that infected seeds were effective sources of initial inocula for common bacterial blight disease development in the field. Hence the production and use of disease-free seeds can be implemented as effective disease management strategies where environmental conditions permit common blight outbreaks.