Cassava brown streak disease in Rwanda, the associated viruses and disease phenotypes

Abstract

Cassava brown streak disease (CBSD) was first observed on cassava (Manihot esculenta) in Rwanda in 2009. In 2014 eight major cassava‐growing districts in the country were surveyed to determine the distribution and variability of symptom phenotypes associated with CBSD, and the genetic diversity of cassava brown streak viruses. Distribution of the CBSD symptom phenotypes and their combinations varied greatly between districts, cultivars and their associated viruses. The symptoms on leaf alone recorded the highest (32.2%) incidence, followed by roots (25.7%), leaf + stem (20.3%), leaf + root (10.4%), leaf + stem + root (5.2%), stem + root (3.7%), and stem (2.5%) symptoms. Analysis by RT‐PCR showed that single infections of Ugandan cassava brown streak virus (UCBSV) were most common (74.2% of total infections) and associated with all the seven phenotypes studied. Single infections of Cassava brown streak virus (CBSV) were predominant (15.3% of total infections) in CBSD‐affected plants showing symptoms on stems alone. Mixed infections (CBSV + UCBSV) comprised 10.5% of total infections and predominated in the combinations of leaf + stem + root phenotypes. Phylogenetic analysis and the estimates of evolutionary divergence, using partial sequences (210 nt) of the coat protein gene, revealed that in Rwanda there is one type of CBSV and an indication of diverse UCBSV. This study is the first to report the occurrence and distribution of both CBSV and UCBSV based on molecular techniques in Rwanda.

Distinct strains of the re‐emergent Cassava common mosaic virus (genus: Potexvirus) infecting cassava in Argentina

“…It is known that mixed viral infections can interact in unexpected ways, including synergisms and antagonisms (Syller, ; Adams et al ., ). Naturally occurring mixed infections have been reported associated with severe cases of cassava mosaic and cassava brown streak diseases in Africa (Legg et al ., , ; Munganyinka et al ., ) and cassava frogskin disease in South America (Carvajal‐Yepes et al ., ), where the cumulative effect of each pathogen leads to an increasing effect on yield losses. Furthermore, mixed infections among distinct strains of the same virus species can facilitate the generation of recombination variants showing novel biological features, e.g.…”

Alternative Approaches for Assessing Cassava Brown Streak Root Necrosis to Guide Resistance Breeding and Selection

“…Cassava brown streak disease (CBSD) caused by two ssRNA virus species, Uganda cassava brown streak virus (UCBSV) and cassava brown streak virus (CBSV), have both viruses, been restricted to southern and eastern Africa for the past 90 years (Ndunguru et al, 2015; Alicai et al, 2016; Munganyinka et al, 2018), with no presence in Latin America, the center of origin of cassava and/or in west Africa. The negative impact of CBSD on both the quality and quantity of marketable cassava roots makes it an acute factor limiting aspirations of cassava commercialization in eastern and southern Africa.…”

Computational models to improve surveillance for cassava brown streak disease and minimize yield loss

“…We simulated two different types of management interventions, those that depend on farmer education (roguing and preferential selection), and those that rely on external inputs (clean seed and pesticide coating). Current guidelines for cassava recommend selecting healthy plants mid-season and roguing diseased plants [25,26]. However, previous studies show that farmers in regions with CBSD are unaware of the disease and that training from extension agents is required for farmers to be able to recognize infected plants in their fields [8,27].…”