PREVALENCE AND CHARACTERIZATION OF Xanthomonas campestris pv. musacearum AND EVALUATION OF BANANA GENOTYPES FOR RESISTANCE TO BANANA WILT IN THARAKA NITHI COUNTY, KENYA

Abstract

Banana (Musa spp.) is one of the most grown food crops in the world, and is rich in carbohydrates, vitamins and minerals. A major constraints to banana production in Tharaka Nithi County is banana Xanthomonas wilt (BXW) caused by Xanthomonas campestris p.v musacearum. The pathogen attacks photosynthetic leaves and young fruits reducing palatability and marketability. Currently, there is limited information on severity and prevalence of BXW in Tharaka Nithi County. Different strategies are used in the region to curb the wilt, including use of chemicals, as well as cutting and uprooting infected plants, although effective management of BXW is yet to be achieved. In other parts of the world, an integration of resistant cultivars with other control methods has been the most effective method for BXW management. However, data on banana varieties that are resistant to BXW in Nithi region is still limited. The objective of this study was to determine the prevalence of BXW in Nithi region, isolate and characterize the pathogen using morphological and biochemical tests and to assess local banana genotypes for resistance to BXW. The prevalence of BXW was assessed on-farm by symptoms inspection and a survey design using structured questionnaires to banana farmers in five villages (Kiang’ondu, Marima, Mitheru, Gibumbu and Giampampo). Laboratory isolation and characterization of BXW pathogen at Chuka University was arranged in Completely Randomized Design based on site of sample origin, with three replicates. Susceptibility tests were conducted under controlled green-house conditions arranged in a Randomized Complete Block Design (RCBD) with five banana varieties and one pathogen, replicated five times. Prevalence data from the questionnaire was analysed on SAS version 9.4 version using chi square t-test of association, while data on genotype susceptibility data was analysed using a general linear model on SAS version 9.4 and significant means separated using Least Significance Difference at α = 0.05. Study revealed that percentage prevalence of BXW in the studied villages was not significantly different (p > 0.05), with the highest value of 21.14% at Giampampo while Mitheru had the least value of 11.24%. Majority of the farmers (92%) were unaware of existence of BXW in the region. Morphological and biochemical tests (Catalase test, Starch hydrolysis test, Gelatine liquefaction test, Ammonia production test) revealed the banana wilt pathogen is Xanthomonas campestris pv. musaceaerum. Susceptibility of five banana varieties to Xanthomonas wilt pathogen isolate was statistically significant (p < 0.05), with Gasukari variety having the mean of 70.37% followed by Kiganda (60.74%) while Muraru had the lowest susceptibility mean of 45.19%. In terms of resistance, Muraru variety may be a good source of breeding material due to its relative resistance to BXW and is recommended for farmers in the region. This study broadens the understanding BXW prevalence in Nithi region and provides opportunities for selection of resistant banana varieties for better yields and improved food and nutritional security in the region.