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. 2024 Sep 15;16(9):1469.
doi: 10.3390/v16091469.

Occurrence and Distribution of Major Cassava Pests and Diseases in Cultivated Cassava Varieties in Western Kenya

Everlyne N Wosula  1 , Rudolph R Shirima  1 , Massoud Amour  1 , Vincent W Woyengo  2 , Bonface M Otunga  2 , James P Legg  1
Affiliations

Occurrence and Distribution of Major Cassava Pests and Diseases in Cultivated Cassava Varieties in Western Kenya

Everlyne N Wosula et al. Viruses. .

Abstract

Cassava is an important food crop in western Kenya, yet its production is challenged by pests and diseases that require routine monitoring to guide development and deployment of control strategies. Field surveys were conducted in 2022 and 2023 to determine the prevalence, incidence and severity of cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), whitefly numbers and incidence of cassava green mite (CGM) in six counties of western Kenya. Details of the encountered cassava varieties were carefully recorded to determine the adoption of improved varieties. A total of 29 varieties were recorded, out of which 13 were improved, although the improved varieties were predominant in 60% of fields and the most widely grown variety was MM96/4271. The CMD incidence was higher in 2022 (26.4%) compared to 2023 (10.1%), although the proportion of CMD attributable to whitefly infection was greater (50.6%) in 2023 than in 2022 (18.0%). The CBSD incidence in 2022 was 6.4%, while in 2023 it was 4.1%. The CMD incidence was significantly lower (5.9%) for the improved varieties than it was for the local varieties (35.9%), although the CBSD incidence did not differ significantly between the improved (2.3%) and local varieties (9.7%). Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) were both detected. Most infections were single CBSV infections (82.9%), followed by single UCBSV (34.3%) and coinfection with both viruses (16.7%). Whiteflies were more abundant in 2023, in which 28% of the fields had super-abundant populations of >100/plant, compared to 5% in 2022. KASP SNP genotyping designated 92.8% of the specimens as SSA-ECA for 2022, while it was 94.4% for 2023. The cassava green mite incidence was 65.4% in 2022 compared to 79.9% in 2023. This study demonstrates that cassava viruses, whiteflies and cassava green mites continue to be important constraints to cassava production in western Kenya, although the widespread cultivation of improved varieties is reducing the impact of cassava viruses. The more widespread application of high-quality seed delivery mechanisms could further enhance the management of these pests/diseases, coupled with wider application of IPM measures for whiteflies and mites.

Keywords: Bemisia tabaci; cassava brown streak disease; cassava green mite; cassava mosaic disease; whitefly.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Geographic distribution of the top five cassava varieties cultivated in 2022 and 2023 in six counties of western Kenya.
Figure 2
Figure 2
Geographic distribution of cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) in 2022 (A,B) and 2023 (C,D) in relation to the Bemisia tabaci whitefly abundance across six counties in western Kenya.
Figure 3
Figure 3
Geographic distribution of cassava-colonizing Bemisia tabaci whiteflies in counties surveyed in western Kenya based on mtCOI sequencing (2017 (A), 2022 (B) and 2023 (C) and KASP SNP genotyping 2017 (D)).
Figure 4
Figure 4
Geographic distribution of the cassava green mite (CGM) incidence in 2022 (A) and 2023 (B) across six counties in western Kenya.
See this image and copyright information in PMC

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