DISTRIBUTION, CHARACTERIZATION AND MANAGEMENT OF SORGHUM ANTHRACNOSE (Colletotrichum sublineolum) IN EASTERN ETHIOPIA

Abstract

Sorghum is a major food crop in Ethiopia. However, it adversely affected by biotic and abiotic constraints, of which sorghum anthracnose, caused by Colletotrichum sublineolum, is one of the most important diseases, which cause significant yield and quality losses. This study was conducted with the following objectives to: 1) determine the distribution and importance of sorghum anthracnose in major sorghum-growing areas of eastern Ethiopia; 2) examine association of sorghum anthracnose intensity with biophysical factors in the study areas; 3) assess the cultural and morphological characteristics of C. sublineolum isolates infecting sorghum in eastern Ethiopia; 4) evaluate the reaction of sorghum genotypes against sorghum anthracnose under field conditions; and 5) evaluate the extent of genetic variability among Ethiopian sorghum genotypes and the relationships among various traits. A field survey was carried out in 2017 main cropping season and a total of 125 fields were assessed in five major sorghum-growing districts of eastern Ethiopia. In addition, a laboratory experiment was conducted to examine the cultural and morphological characteristics of C. sublineolum isolates. Further, field experiments were conducted at Hirna during 2017 and 2018 cropping seasons. Forty-nine sorghum genotypes were tested and the treatments were arranged in triple lattice square design. The results of the survey revealed that all the inspected sorghum farms were infected with sorghum anthracnose. However, significant variations existed in anthracnose intensity across the districts with mean incidence ranging from 74 to 97.2%, while severity varied from 44.5 to 86.8%. Anthracnose incidence and severity were the lowest in Babile and the highest in Girawa district. District, sowing date, residue management, growth stage, cropping system, weed management and preceding cropping practices were significantly associated with disease intensity in a multiple-variable model. C. sublineolum isolates showed variations in cultural characteristics, conidial morphology and they were pathogenic to sorghum. Isolates of C. sublineolum showed significant variations in culture growth and ranged from 15 to 44 mm at eight-days after incubation. The length and width of conidia also varied from 10.01 to 27.75 µm xv and 2.97 to 6.01 µm, respectively. The evaluated sorghum genotypes had significantly different responses to anthracnose in both experimental years. In the year 2017 and 2018, the mean anthracnose severity varied from 35 to 91% and 38 to 93%, respectively. AUDPC varied from 1744 to 3865 %-days and from 2354 to 4908 %-days in 2017 and 2018 cropping seasons, respectively. Overall, anthracnose severity in 2018 cropping year was higher than in 2017. Highly significant variations were observed among genotypes for phenology, growth, yield and yield component traits in both cropping years. In 2017 and 2018 cropping years, the computed genotypic coefficients variation ranged from 6.70 to 21.09% and from 4.16 to 21.30%, and phenotypic coefficients variation varied from 7.10 to 27.35%, and from 5.07 to 26.36%, respectively. Sorghum yield showed positive and significant associations with all leaf traits, all panicle characters and thousand seed weight at the genotypic and phenotypic levels. Howevere, it showed very strong negative associations with anthracnose traits regardless of experimental years. Since sorghum is a staple cereal crop in eastern Ethiopia and anthracnose is a major problem in the studied districts, giving due attention in developing effective management option is crucial. Because the genotypes ETSL 100335, ETSL 100395, ETSL 101474, ETSL 100523, ETSL 100498, ETSL 100989, ETSL 100597 and ETSL 101000 consistently had lower disease level in the two experimental years, they recommended as alternative source of resistant gene for anthracnose resistant breeding and for their vigorous growth and good grain yield to the farmers. Removal of crop residues, crop rotatoin and weed management can also serve as important options in minimizing anthracnose.