Distribution of Cassava Bacterial Blight and Reaction of Selected Cassava Genotypes to the Disease in Kenya

Hilda M Odongo ,W M Muiru ,Agnes W Mwang’ombe ,John W Kimenju ,Douglas W Miano

doi:10.7176/jnsr/9-4-05

Abstract

Cassava bacterial blight (CBB) disease is an important bacterial disease of cassava. A study was carried out to determine the distribution of CBB in Kenya and to evaluate selected cassava genotypes for reaction to the disease. A survey was conducted in all the cassava growing regions within the country where cassava leaves showing symptoms of CBB were collected and isolated for biochemical characterization and PCR detection of the causal agent. The isolates were then used to determine the reaction of seven cassava genotypes to the disease. The disease was present in 17 out of the 21 counties surveyed. The bacteria extracted from the leaf samples conformed to all the biochemical and physiological tests specific to Xanthomonas axonopodis pv manihotis and to xanthomonads in general. Polymerase chain reaction amplified the expected 500 base pairs fragment. Disease prevalence was highest in Kwale County at 100% Kilifi County recorded the highest incidence at 64%. All the genotypes evaluated in the greenhouse had area under disease progress curve (AUDPC) values higher than 52 which grouped them as susceptible. The study confirms the wide distribution of CBB in Kenya and the presence of the disease in the coast region, which was previously considered CBB free. The study also shows that some of the cassava genotypes being targeted for improvement by other projects are susceptible to the disease, and therefore the need consider resistance to CBB in developing improved cassava genotypes. Keywords: Cassava bacterial blight, Distribution, Resistance DOI : 10.7176/JNSR/9-4-05

Highlights

Cassava (Manihot esculenta) is ranked the fourth most important food crop in the world after rice, wheat and maize, and is an important source of carbohydrates for over 500 million people in the tropics (Rowan et al 2010)
Cassava production in Africa is hindered by various biotic and abiotic factors including bacterial blight (CBB) disease caused by Xanthomonas axonopodis pv. manihotis (Xam) (Trujilo et al 2014)
Methods of identifying and detecting Xam have for a long time been dependent on isolating the bacteria, carrying out biochemical and serological tests such as enzyme linked immunosorbent assays (ELISA) (Ojeda and Verdier, 2000)

Summary

Introduction

Cassava (Manihot esculenta) is ranked the fourth most important food crop in the world after rice, wheat and maize, and is an important source of carbohydrates for over 500 million people in the tropics (Rowan et al 2010). Methods of identifying and detecting Xam have for a long time been dependent on isolating the bacteria, carrying out biochemical and serological tests such as enzyme linked immunosorbent assays (ELISA) (Ojeda and Verdier, 2000). These methods are not very accurate as they are not entirely specific because of cross reactions (Ojeda & Verdier 2000). Molecular techniques such as polymerase chain reaction (PCR) are highly effective in the detection of plant pathogenic bacteria such as Xanthomonas axonopodis pv. In this study, selected cassava genotypes that were identified for improvement by other cassava projects were inoculated with CBB strains from various geographic origins within the country and their reaction evaluated

Materials and Methods

DNA extraction and PCR amplification

Results

Discussion

Findings

Conclusion