Field evaluation of selected cassava genotypes for cassava brown streak disease based on symptom expression and virus load

Abstract

BackgroundProduction of cassava (Manihot esculenta Crantz), a food security crop in sub-Saharan Africa, is threatened by the spread of cassava brown streak disease (CBSD) which manifests in part as a corky necrosis in the storage root. It is caused by either of two virus species, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), resulting in up to 100% yield loss in susceptible varieties.MethodsThis study characterized the response of 11 cassava varieties according to CBSD symptom expression and relative CBSV and UCBSV load in a field trial in Uganda. Relative viral load was measured using quantitative RT-PCR using COX as an internal housekeeping gene.ResultsA complex situation was revealed with indications of different resistance mechanisms that restrict virus accumulation and symptom expression. Four response categories were defined. Symptom expression was not always positively correlated with virus load. Substantially different levels of the virus species were found in many genotypes suggesting either resistance to one virus species or the other, or some form of interaction, antagonism or competition between virus species.ConclusionsA substantial amount of research still needs to be undertaken to fully understand the mechanism and genetic bases of resistance. This information will be useful in informing breeding strategies and restricting virus spread.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-014-0216-x) contains supplementary material, which is available to authorized users.

Eleven years of breeding efforts to combat cassava brown streak disease

“…In all these trials: seedling trials (2011), unreplicated clonal trial at single site (2012) and replicated clonal trials at two sites (2013), entries were evaluated for CBSD root necrosis as described by Kaweesi et al (2014).…”

Crop losses in Brazilian cassava varieties induced by the Cassava common mosaic virus

“…In current highly competitive cassava production systems, relative losses in root yield caused by CsCMV in magnitudes of 30 % are unacceptably high. Among other cassava viruses, only Cassava mosaic disease (CMD) and CBSD cause great reduction in root yield, eventually reaching 80 % (Moses et al, 2007) and 100 % (Kaweesi et al, 2014), respectively.…”

Occurrence and estimated losses caused by cassava viruses in Migori County, Kenya

“…CBSD resistance studies have revealed variations of symptoms in different genotypes (Pariyo et al, 2015;Kaweesi et al, 2014). Kaweesi et al (2014) screened for CBSD resistance by quantitative PCR and reported four disease reactions including: -Restricted disease symptoms and virus quantities which is a characteristic of resistant varieties that is, Kaleso, -Restricted virus quantities with high disease symptoms (tolerant varieties), -Restricted disease symptoms with high virus quantities (tolerant varieties) and, -Accumulation of high virus quantities and very severe symptoms which is a characteristic of susceptible varieties that is, Albert. Different disease reactions prompt the need to consider breeding of genotypes with different disease reactions in order to achieve durable resistance.…”