Screening for Resistance in Farmer-Preferred Cassava Cultivars from Ghana to a Mixed Infection of CBSV and UCBSV.

Wilfred Elegba,Hervé Vanderschuren,Wilhelm Gruissem

doi:10.3390/plants9081026

Abstract

Cassava brown streak disease (CBSD) caused by the Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) is a threat to cassava production in Africa. The potential spread of CBSD into West Africa is a cause for concern, therefore screening for resistance in farmer-preferred genotypes is crucial for effective control and management. We multiplied a selection of eleven cassava cultivars grown by farmers in Ghana to test their response to a mixed infection of CBSV (TAZ-DES-01) and UCBSV (TAZ-DES-02) isolates using a stringent top-cleft graft inoculation method. Virus titers were quantified in the inoculated scions and cuttings propagated from the inoculated scions to assess virus accumulation and recovery. All cultivars were susceptible to the mixed infection although their response and symptom development varied. In the propagated infected scions, CBSV accumulated at higher titers in leaves of eight of the eleven cultivars. Visual scoring of storage roots from six-month-old virus-inoculated plants revealed the absence of CBSD-associated necrosis symptoms and detectable titers of CBSVs in the cultivar, IFAD. Although all eleven cultivars supported the replication of CBSV and UCBSV in their leaves, the absence of virus replication and CBSD-associated symptoms in the roots of some cultivars could be used as criteria to rapidly advance durable CBSD tolerance using breeding and genetic engineering approaches.

Highlights

In tropical and semi-tropical regions of the world, cassava (Manihot esculenta Crantz) is an important source of carbohydrate in the diets of nearly 800 million people, one-third of whom live in sub-SaharanAfrica (SSA) [1,2]
Leaf samples of the cultivars from the Biotechnology and Nuclear Agriculture Research Institute (BNARI) germplasm collection were screened for cassava mosaic geminiviruses (CMGs) (Figure S4) with two commonly-used generic primer pairs [36,37]
High cassava brown streak disease (CBSD) incidence has been observed in most of the cassava mosaic disease (CMD)-resistant cultivars deployed over the last decade [39], our results suggest that Afisiafi could be classified as tolerant to CBSD based on its ability to restrict symptom expression and severity under the top-graft inoculation of mixed Cassava brown streak virus (CBSV) (TAZ-DES-01) and Ugandan cassava brown streak virus (UCBSV) (TAZ-DES-02) infection [25]

Summary

Introduction

In tropical and semi-tropical regions of the world, cassava (Manihot esculenta Crantz) is an important source of carbohydrate in the diets of nearly 800 million people, one-third of whom live in sub-SaharanAfrica (SSA) [1,2]. CMD is widespread across all cassava-growing regions in SSA while CBSD is prevalent in low- to mid-altitude regions of Eastern and Central Africa [3,4,5,6]. Estimated annual yield losses attributable to both CMD and CBSD has been reported to exceed USD 1 billion [2,3]. Both viral diseases reduce root yield in susceptible varieties, necrotic lesions caused by CBSD further exacerbate economic losses as they make storage roots unfit for consumption and processing [7,8,9].

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Results

Discussion

Conclusion