First report of Cassava brown streak viruses on wild plant species in Mozambique

Jamisse J.G Amisse,Joseph Ndunguru,Fred Tairo,Laura M Boykin,Monica A Kehoe,Nurbibi Cossa,Elijah Ateka,Chrissie Rey,Peter Sseruwagi

doi:10.1016/j.pmpp.2018.10.005

Abstract

Cassava brown streak disease (CBSD) caused by Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) is the main constraint to cassava (Manihot esculenta Crantz) production in Mozambique. Using RT-PCR to amplify partial coat protein nucleotide sequences, we detected for the first time the occurrence of CBSV in two non-cassava perennial wild plant species: Zanha africana (Radlk.) Exell. and Trichodesma zeylanicum (Burm.f.) R.Br., that occur widely within and near cassava fields in Nampula, Zambezia, Niassa and Cabo Delgado provinces. In addition, we also detected CBSV and UCBSV in Manihot carthaginensis subsp. glaziovii (Müell-Arg.) Allem., a wild cassava relative. These findings were verified in biological assays through mechanical inoculation of CBSV to T. zeylanicum, albeit at low rates of infection. Phylogenetic analysis clustered the CBSV isolates from the non-cassava plant species with those from cultivated cassava, with high sequence homology among CBSV (91.0–99.6%) and with UCBSV (84–92%) isolates. These results provide definitive evidence of a wider host range for CBSV and UCBSV in Mozambique, indicating that these viruses are not restricted to cultivated cassava. Our findings are key to understanding the epidemiology of CBSD and will aid in the development of sustainable management strategies for the disease.

Highlights

Cassava (Manihot esculenta Crantz, family Euphorbiaceae) is the second most important crop after maize in Mozambique [1]
The cassava relative M. carthaginensis subsp. glaziovii (Müell-Arg.) Allem had typical severe chlorosis with severity scale of 4, on the 1–5 severity scale described by Refs. [21] and [22] on the leaves and necrosis on the stems (Fig. 1C and D)
For the first time, the occurrence of Cassava brown streak virus (CBSV) in two non-cassava perennial wild plant species, Velvet-fruited zanha (Z. africana (Radlk.) Exell) and Camel bush (T. zeylanicum (Burm.f.) R.Br.), and Ugandan cassava brown streak virus (UCBSV) in M. carthaginensis subsp. glaziovii (Müell-Arg.) Allem., a wild cassava relative in Mozambique, based on results obtained in PCR using virus species-specific primers [12] and phylogenetic analyses of the partial coat protein (CP) sequences of the isolates

Summary

Introduction

Cassava (Manihot esculenta Crantz, family Euphorbiaceae) is the second most important crop after maize in Mozambique [1]. More than 80% of cassava production in Mozambique occurs in the north and central regions. Production in these regions is severely constrained by two cassava brown streak viruses, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) [2,3,4], which cause Cassava brown streak disease (CBSD) [2,5]. The disease was first reported to be transmitted with very low efficiency by whitefly, Bemisia tabaci (Gennadius) [6,7], but [8] recently confirmed generally moderate rate of transmission of CBSV, ranging from 30 to 53% using 20 to 100 whiteflies.

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