An Original Investigation into the Molecular Mechanisms of Cassava Response to Cassava Brown Streak Virus in Nigerian Accessions

Cassava brown streak virus disease (CBSD) is advancing northward across the African continent and poses an existential threat to Nigerian cassava production if it becomes established, yet the molecular mechanisms of host resistance and susceptibility in Nigerian cassava accessions have not been characterised, representing a critical knowledge gap for resistance breeding. This study conducted an original investigation into the molecular mechanisms of cassava response to CBSD infection in Nigerian cassava accessions. A multi-level molecular phenotyping methodology was employed, combining virus inoculation experiments on 16 Nigerian accessions (8 improved IITA varieties and 8 landraces), transcriptome profiling of resistant and susceptible accessions using RNA-Seq at 14 and 28 days post-inoculation, candidate gene validation through qRT-PCR, and protein-protein interaction network analysis. CBSD symptoms were absent in 5 accessions and severe in 6, with the remainder showing intermediate response. Transcriptome analysis identified 2,847 differentially expressed genes in the resistant versus susceptible comparison at 14 dpi. Pathway enrichment analysis revealed that the jasmonate signalling pathway, WRKY transcription factors, and cell wall reinforcement processes were most strongly upregulated in resistant accessions. Suppression of SA-mediated defence was significantly higher in susceptible accessions. Three novel WRKY candidates (MeWRKY47, MeWRKY83, and MeWRKY115) showed expression patterns highly correlated with resistance phenotype. The study constitutes an original contribution to CBSD molecular biology in Nigerian germplasm and recommends MeWRKY83 as a priority target for functional validation and marker development.

Keywords: cassava brown streak virus, molecular resistance, transcriptome, WRKY transcription factors, Nigeria