Evaluation of enset (Ensete ventricosum) clones for resistance reaction against pathogenic Xanthomonas compestris pv. musacearum isolates from Southwestern Ethiopia

Enset (Ensete ventricosum) bacterial wilt (EBW) incited by Xanthomonas campestris pv. musacearum (Xcm) is threatening enset production in southwestern Ethiopia. The objectives of this study were to determine the pathogenicity of Xcm isolates and select enset clones resistant to pathogenic Xcm isolates in the study areas. A total of 30 Xcm isolates were subjected to pathogenicity tests on a susceptible enset clone Yeko and all were found pathogenic. Out of 30 pathogenic isolates, three isolates representing three altitude groups [lowland (1470 m.a.s.l), midland (1938 m.a.s.l) and highland (2360 m.a.s.l)] were used for enset clonal evaluation trials. In the clone evaluation trial, 15 enset clones (13 local and a tolerant and susceptible check) were evaluated for 2 years (2017 and 2018) under screen house conditions at Tepi National Spice Research Center, southwestern Ethiopia. The experiments were factorially arranged in a completely randomized design with three replications. An aliquot of 10 ml of the bacterial cell suspension with a concentration of 1 x 10(8) cfu/ml was inoculated into the second innermost leaf petiole of enset using a sterile hypodermic syringe. Starting from 15 days after inoculation (DAI), data were collected on incubation period (IP), disease incidence (DI), percentage severity index (PSI), days to complete wilting/death (DD), area under disease progress curve (AUDPC) and disease progress rate. Analysis of variance for IP, DI, DD and AUDPC revealed significant differences (P < 0.05) among tested enset clones, while for PSI significant differences (P < 0.05) existed among the interaction effect of enset clones x bacterial isolates. Disease incidence recorded ranges from 0% to 90% and IP ranges from 0 to 23 days. Similarly, the days to complete wilting of susceptible clone reaches up to 63 days, while the calculated AUDPC values ranged from 0 (Gudiro, Maziya and Nobo) to 3190%-days (Arkia, Ataro, Yeko, Chikaro and Ogisso). Disease progress rates also ranged from -0.00165 to 0.04398 units day(-1). Clones Gudiro, Maziya and Nobo showed a resistant/ tolerant reaction to EBW, while clones Arkia, Ataro, Yeko, Chikaro and Ogisso were the most susceptible enset clones. Based on the results, it is recommended that more clones be evaluated across different agro-ecological areas to select enset clones with stable resistance against the disease. In addition, clone selection should also be given due attention to adaptability as well as quantitative and qualitative yield traits to improve adoption.