Seed Transmission and Epidemics of Colletotrichum lindemuthianum in the Major Common Bean Growing Areas of Ethiopia

Abstract

The seed-borne nature, mechanism of transmission and disease development of Colletotrichum lindemuthianum in the field was studied in three major common bean growing areas including Arssinegelle, Ambo and Bako in Ethiopia. The relationship between level of seed infection by Colletotrichum lindemuthianum, and its transmission to the seedlings in the field and greenhouse was studied. Multiple regression analysis showed positive and linear relationship with high coefficient of determination (R² =0. 98, 0.91, 0.86) between seed infection and early seedling infection at Bako, Ambo and Arssinegelle respectively. During germination of the infected seeds, the pathogen was transferred from seed coat, by colonizing the cotyledons, radicle and plumule of the emerging seeds. Pre- and postemergence seedling mortalities were very common both in the field and greenhouse. Sporulation of C. lindemuthianum from acervuli was observed on the cotyledons of un-germinated seed. Moreover, sporulation of C. lindemuthianum on the growing seedling was common at Bako and Ambo where there was frequent rainfall during the crop season. Anthracnose inoculum in the field transferred to the young pods, consequently enabled the pathogen to grow through the entire pod surface, showing sunken anthracnose lesions, and infected the seed coats of the newly formed seed. Seedling infection and disease epidemic in the field varied between different bean growing locations. Seed infection by C. lindemuthianum played the major role as the main source of primary inoculum of bean anthracnose and further disease epidemic in the field.