Response to Cassava Brown Streak Disease Infections in Local and Improved Cassava Genotypes under Field and Greenhouse Assays in Lower Eastern Kenya

Abstract

Cassava brown streak disease (CBSD) is caused by two cassava brown streak viruses (CBSVs) transmitted by whiteflies (Bemisia tabaci). CBSD significantly inhibits cassava production in Kenya through losses of up to 100% in farmer-preferred but susceptible varieties. As a management strategy, the present study evaluated the effect of CBSD on two local varieties (Thika-5 & Serere) and 15 improved genotypes in lower Eastern Kenya. Between October 2016 and June 2017, the genotypes were infected with CBSVs through whitefly transmission under field experiment at SEKU research farm (1.31ºS, 37.75ºE) and chip-bud grafting at KALRO-Katumani (1.35ºS, 37.14ºS) greenhouse conditions. RCBD and CRD experimental designs were respectively applied in field and greenhouse assays. CBSD symptoms were quantified through disease incidence (DIC) and severity (DSY) every 3 months for the field experiment and weekly for greenhouse assay. At harvest, storage root necrosis (SRN) was scored and non-necrotic roots weighed as marketable root yield (MRY). Molecular diagnostics was accomplished through duplex RT-PCR. Results revealed significantly (P≤0.01) higher foliar field DIC (81-100%) and SRN (2.3 -5.0) recorded in 2 Thika-5 and Serere compared to all the improved genotypes that were foliarly asymptomatic (0% DIC and mean SRN of 1.0). Concomitantly and substantially lower (P≤0.01) MRY (1.99 -2.16 t/ha) were bulked by Thika-5 and Serere compared to 10 improved genotypes that bulked 5.81 -9.21 t/ha MRY. Upon chip-bud graft infection, Thika-5 and Serere showed higher DIC of 81 -90% compared to four improved genotypes with 20 -35% DIC. Correlations between MRY, DIC and SRN were inverse and significant (P≤0.01). RT-PCR detected pre-dominantly CBSV. In conclusion, the natural whitefly-based transmission of CBSVs was ineffective compared to chipbud grafting. The inverse correlations between CBSD symptoms and yield corroborated the deleterious impact of CBSD on cassava production. The ten improved, high yielding and asymptomatic genotypes identified in the current study could potentially be used to confer resistance against CBSD into farmer-preferred but often sensitive varieties.

Cassava begomovirus species diversity changes during plant vegetative cycles

“…There were also differences in the EACMV-like species found in the western (EACMKV and EACMV-Ug) and the coastal areas (EACMZV). The viruses detected in the field-collected samples are consistent with other field studies in Kenya (Bull et al, 2006;Mwatuni et al, 2015;Ombiro, 2016;Koima et al, 2018;Were et al, 2021). After 3 years of maintaining the plants by vegetative cutting in a greenhouse, EACMV-like viruses became prominent in all plants, with EACMKV and EACMV in western samples and EACMV and EACMZV in coastal samples.…”

“…The distributions of CMBs across different regions of sub-Saharan Africa have been characterized using field survey data (Ntawuruhunga et al, 2007 ; Chikoti et al, 2015 ; Harimalala et al, 2015 ; Tajebe et al, 2015 ; Doungous et al, 2022 ). Multiple studies have characterized the distribution of CMB species in Kenya during and after the pandemic (Sseruwagi et al, 2004 ; Mwatuni et al, 2015 ; Koima et al, 2018 ). Field studies provide important snapshot information, but they do not show how propagation affects viral species over time.…”

Influence of Compost and Farmyard Manure on Cassava Growth, Yield and Dry Matter Partitioning at Mvomero and Masasi Districts

“…The average cassava yield in Tanzania is 8 t ha -1 compared to the potential of 20 t ha -1 [7]. Among the factors accounting for the low productivity of cassava are diseases, mostly, Cassava Mosaic Disease (CMD) and Cassava Brown Streak Disease (CBSD) that account for cassava yield losses of about 70 to 100% if left unmanaged [5,8]. Furthermore, low soil fertility levels contribute to reduced land productivity exacerbated by continuous farming without the use of fertilizers [9,10] and lack/inadequate purchasing power for inputs including fertilizers by smallholder farmers [10,11,12,13].…”