Pathogenicity and molecular characterization of coffee bacterial blight (Pseudomonas syringae pv. garcae van Hall) isolates from Sidama and Gedeo Zones, SNNP Regional State, Ethiopia.

Abstract

Bacterial blight of coffee (BBC) caused by the phytopathogenic bacterium, Pseudomonas syringae pv. garcae van Hall is an important disease of Arabica coffee in Ethiopia due to its increasing incidence and severity. There is no information on the current status, pathogenicity and molecular characterization of the pathogen in this study area in Ethiopia. Therefore, this study was carried out to assess the disease intensity, pathogenicity and molecular characterization of BBC isolates from Sidama and Gedeo zones, SNNP Regional State, Ethiopia. A total 204 coffee trees, 96 coffee fields or peasant associations in 6 districts and in 2 coffee producing zones in SNNP Region was surveyed during the study time. The frequency and intensity of BBC disease was varied between the zones and districts of coffee producing surveyed areas. The percentage of disease incidence (70.0, 56.1, 44.6, 39.3%) and the severity (29.9, 15.7, 13.7, 12.5%) were recorded in Wensho, Dara, Aletachuko, Aletawondo districts of Sidama zone and the incidence (72.2 and 47%) and severity (21.6 and 13.1 %) were recorded in Dilla and Wonago areas of Gedeo zone, respectively. The prevalence of BBC disease was recorded in both Sidama and Gedeo zones, 87.5 and 93.8%, respectively while the mean BBC disease prevalence was 90.7%. Symptomatic of 204 diseased samples were initially isolated and purified on nutrient agar (NA) and nutrient broth (NB) slants. Among 204 isolates, 37 BBC isolates were selected for biochemical tests based on similar morphological and in growth characteristics on selective media. The pathogenicity test response was conducted on coffee leaves in which all the isolates induced the hypersensitive reaction and confirmed. Out of 37 isolates, 8 isolates were analysed for the molecular characterization through RAPD analysis. Out of five primers, OPAC 04 (5’- ACG GGA CCTG-3’) primer revealed more number of RAPD patterns and polymorphism and hence differentiating all the isolates. The amplified fragments / bands ranged from 100 bp to above 1100 bp. Out of 8 isolates, the highest number of bands were observed in isolate 8 Gordahama FII T2. In other 6 isolates, the number of bands was ranged from 100 bp to above 950 bp and also uniform number of bands was noticed. The number of common bands was observed to be present in almost six isolates and the molecular weights of these ranged from 100 bp to 550 bp. This is clearly indicated that the genetic diversity of as Pseudomonas syringae pv garcae. The morphological and microscopic characters, β-glucosidase activity, biochemical nature and RAPD analysis of the test isolates confirmed the organism identity as Pseudomonas syringae pv. garcae. The present study provided first information on molecular epidemiological about BBC isolates from Sidama and Gedeo zones in Ethiopia. The coffee production in Gedeo and Sidama zones is threatened by BBC at present, appropriate measures new to be developed to solve this problem, otherwise, the country will be lost foreign currency as a result, the life standard of farmers will be collapsed and leading to lost foreign income.