Comprehensive Surveys of Bean common mosaic virus and Bean common mosaic necrosis virus and Molecular Evidence for Occurrence of Other Phaseolus vulgaris Viruses in Tanzania.

Susan Nchimbi-Msolla,Deogratius Mark,Beatrice Mwaipopo,Deusdedith R. Mbanzibwa,Paul J. R. Njau

doi:10.1094/pdis-01-18-0198-re

Abstract

Virus diseases are among the main biotic factors constraining common bean (Phaseolus vulgaris L.) production in Tanzania. Disease management requires information on types, distribution, incidence, and genetic variation of the causal viruses, which is currently limited. Thus, a countrywide comprehensive survey was conducted. Use of a next-generation sequencing technique enabled simultaneous detection of 15 viruses belonging to 11 genera. De novo assembly resulted in many contigs, including complete or nearly complete sequences of Bean common mosaic virus (BCMV), Bean common mosaic necrosis virus (BCMNV), and Southern bean mosaic virus (SBMV). Some viruses (for example, SBMV and Tomato leaf curl Uganda virus-related begomovirus) were detected for the first time in common bean in Tanzania. Visually assessed virus-like disease incidence ranged from 0 to 98% but reverse-transcription polymerase chain reaction-based incidence of BCMV and BCMNV (7,756 samples) was mostly less than 40%. The Sanger-based nucleotide sequences encoding coat proteins of BCMV and BCMNV isolates were 90.2 to 100% and 97.1 to 100% identical to each other, respectively. Phylogenetic analysis showed that BCMV isolates were more diverse than BCMNV isolates. The information generated in this study will contribute to the development of molecular diagnostic tools and strategies for management of virus diseases nationally and internationally.

Highlights

Tanzania is the largest producer (>1,000,000 tons annually) of common bean (Phaseolus vulgaris L.) in sub-Saharan Africa (FAO 2014)
De novo assembly resulted in many contigs, including complete or nearly complete sequences of Bean common mosaic virus (BCMV), Bean common mosaic necrosis virus (BCMNV), and Southern bean mosaic virus (SBMV)
We detected 15 viruses belonging to 11 genera in the common bean samples collected from all over Tanzania

Summary

Introduction

Tanzania is the largest producer (>1,000,000 tons annually) of common bean (Phaseolus vulgaris L.) in sub-Saharan Africa (FAO 2014). The annual quantity of bean produced in Tanzania is associated with the large cultivated area rather than high yield per unit area (FAO 2014). Many viruses are known to infect and cause diseases in common bean plants and can cause yield losses as high as 100% (Hagedorn and Inglis 1986). Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) are considered the most important of these viruses (Grogan and Walker 1948) These viruses cause mosaic symptoms on common bean plants but BCMNV causes systemic vascular necrosis, the disease known as black

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