Cassava mosaic disease impairs photosynthesis and sugar metabolism: varietal susceptibility and key metabolic disruptions

Cassava mosaic disease (CMD) is a major threat to cassava production, causing significant disruptions in photosynthesis, carbohydrate metabolism, and leaf structure, severely reducing crop productivity. This study investigates CMD's physiological, biochemical, and structural impacts across five cassava genotypes, revealing substantial differences in CMD susceptibility. Genotypes such as Sree Visakham and Sree Vijaya exhibited greater tolerance, maintaining higher chlorophyll content, enhanced non-photochemical quenching, and less severe structural alterations, suggesting tolerance mechanisms against CMD. In contrast, Sree Athulya showed rapid viral accumulation and steep declines in photosynthetic efficiency, stomatal function, and carbohydrate synthesis. The study highlights CMD's disruption of source-sink dynamics, with significant reductions in starch content and altered sugar accumulation in susceptible varieties, indicating impaired carbon allocation. Confocal and scanning electron microscopy analyses provided direct evidence of CMD-induced chloroplast damage and distortions in the epidermal structure, further compounding the physiological stress. These findings emphasize the need for breeding strategies incorporating CMD tolerance traits, such as enhanced photosynthetic efficiency and structural resilience, to develop resistant cassava varieties. Such efforts are critical for ensuring food security in regions dependent on cassava as a staple crop.