Screenhouse Screening of Ten Cassava (Manihot esculenta Crantz) Varieties for Resistance to Cassava Mosaic Disease via Graft Inoculation in Sudan Savannah, Nigeria.

Abstract

Cassava mosaic disease (CMD) is the most important viral constraint to cassava production in Africa. This study aimed to rigorously assess the phenotypic responses of ten cassava varieties, eight improved genotypes (IBA30572, OBASANJO 2, GAME CHANGER, IBA 164773, IBA 154810, IBA 961632, BABA 70, IBA 0505) and two local landraces (DANGWAMNATI and BAHAUSHE) to CMD under controlled graft inoculation, providing a benchmark for genotype selection under uniform high pathogen pressure. The experiment was laid out in a completely randomized design (CRD) with six replicates to ensure statistical robustness and to enable reliable discrimination among resistance phenotypes. Healthy rootstocks were graft-inoculated with scions from CMD-infected plants and monitored for disease incidence and severity at 2, 4, 6, 8, 10, and 12 weeks after inoculation (WAI). Data were analyzed using descriptive statistics (mean incidence and severity percentages), with no inferential statistical tests applied; this descriptive-only approach was chosen to characterize phenotypic patterns rather than test treatment differences, and its limitation lies in the absence of formal hypothesis testing or variance partitioning. Results revealed four distinct resistance phenotypes. Highly resistant varieties (OBASANJO 2, GAME CHANGER, BABA 70, IBA 0505) maintained 0% incidence and 0% severity throughout, demonstrating true immunity characteristic of CMD2 gene-mediated resistance. Tolerant varieties (IBA 30572, IBA 154810) showed 16.67% incidence but remarkably low severity (4.17%), indicating ability to contain infection and limit symptom expression. IBA 164773 exhibited partial resistance with 33.34% incidence and 8.33% severity. Susceptible varieties showed progressive disease development: IBA 961632 reached 66.67% incidence and 29.17% severity, while local landraces DANGWAMNATI and BAHAUSHE showed complete susceptibility (100% incidence by 6 WAI) with devastating severity (83.33% and 87.50%, respectively). Symptom expression in susceptible genotypes included severe mosaic, leaf distortion, and stunting, while resistant plants remained symptomless. These findings provide detailed information on resistance phenotypes under uniform high-pressure inoculation, revealing true genetic potential that may not be fully expressed under field conditions.