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Variations in transcription profiles induced by herbivore feeding in cassava (Manihot esculenta Crantz)

Molemi Rauwane: Agricultural resrach Council-Wits University

<div>Cassava mealybug (<em>Phenacoccus manihoti</em>) was introduced into Africa in the 1970s and can cause yield losses of up to 80%, threatening the food security of over 750 million people. Although biological control of mealybug using the parasitoid wasp: <em>Apoanagyrus (Epidinocarsis) lopezi</em> has been practiced with some success, growing resistant cultivars remains an important means by which to manage the pests. A comparison of differentially expressed genes of two cassava genotypes (AR23.1 and P40/1) in response to mealybug infestation was monitored. The transcriptional responses of the two genotypes differed in time as illustrated by the variations in their expression patterns at 24 and 72 hours of mealybug infestation compared to mock infested. We observed mixed responses depending on the genotypes although there was overall suppression of transcripts and less induction, suggesting suppression of the plant’s immune response by the pest. Biological pathway analysis using KEGG revealed significant enrichment of plant hormonal signal transduction for up-regulated DEGs, while plant-pathogen interactions was over-represented in down-regulated DEGs for both genotypes. Stress-associated genes such as 2-oxogluterate (2OG) and the HSP20-like chaperones superfamily proteins were induced in the AR23.1 genotype, and were further validated by real-time RT-qPCR. The study revealed a significantly different response to mealybug infestation in the two genotypes studied, with the resistant genotype (AR23.1) showing a higher proportion of differentially expressed transcripts post infestation. Candidate defence-related genes that were overexpressed in the AR23.1 genotype post infestation will be useful in future functional studies towards the control of mealybugs.</div>