Sorghum mosaic

The virus survives the winter in perennial grass hosts and crop debris. When conditions become favorable in the spring, it is transmitted to newly emerged seedlings by insect vectors.

Transmission occurs primarily through an aphid-borne, non-persistent mode. Common vectors include Schizaphis graminum (greenbug) and Rhopalosiphum maidis (corn leaf aphid), which acquire the virus while probing healthy plants.

Mechanical transmission can occur in experimental conditions or through intense agricultural activity, though it plays a minor role in large-scale field dissemination compared to insect vectors.

Reliable identification of the pathogen usually involves laboratory-based diagnostic tests, such as ELISA (Enzyme-Linked Immunosorbent Assay) or RT-PCR, to distinguish it from other viral or nutritional disorders.

Sorghum mosaic primarily affects various sorghum species, including grain, sweet, and forage types, as well as Sudan grass, causing substantial reductions in both yield and quality.

Maize and sugarcane are also susceptible hosts, often serving as reservoirs for the virus in regions where these crops are grown in proximity to sorghum fields.

The infection disrupts fundamental metabolic pathways, leading to stunted growth, reduced biomass production, and poor grain fill, which directly impacts the farmer's bottom line.

In sweet sorghum, the virus significantly inhibits sugar accumulation, reducing the total fermentable sugar content and lowering the overall efficiency of processing for bioethanol or syrup production.

Early-season infection is particularly devastating, as it can result in stand loss or severely weakened plants that fail to produce marketable grain heads or healthy forage.

The disease spread is closely linked to the migratory activity of aphids. These populations typically peak during late spring and early summer, coinciding with the rapid vegetative growth stages of sorghum.

Environmental factors, such as moderate temperatures and optimal humidity, promote rapid aphid colonization of new fields, leading to the establishment of disease hotspots.

Plants are most vulnerable during the seedling stage and early tillering phase; infections occurring during these times usually result in the most severe symptoms and yield losses.

As the growing season progresses into late summer and maturity, the susceptibility of the crop decreases, and the activity of primary insect vectors often declines as plants harden.

Weather patterns that support multi-generational aphid cycles can trigger recurring waves of infection, complicating management efforts throughout the season.

Symptoms of Sorghum mosaic usually manifest on the younger leaves as the infection spreads systemically from the point of inoculation.

• Mosaic patterns featuring alternating light and dark green, or yellow-green, streaking on leaves.
• Severe chlorosis or whitening of the foliage in highly susceptible varieties.
• Stunted plant height and reduced internode length, creating a characteristic "dwarfing" effect.
• Poor head exertion and reduced inflorescence development.
• Necrotic lesions or leaf tip death in extreme cases where environmental stress is high.

While some varieties may show distinct symptoms, others may be asymptomatic carriers, which makes visual scouting alone insufficient for disease management.

Visual signs may be masked by nutrient deficiencies or herbicide damage, requiring careful observation of the spatial distribution of symptoms within the field.

The most effective strategy is the planting of resistant or tolerant sorghum hybrids, which have been specifically bred to limit viral replication and symptom severity.

Sanitation practices, such as the destruction of wild grasses and weed hosts surrounding fields, are crucial for reducing the source of primary viral inoculum.

Targeted insecticide applications to control aphid populations during the early seedling stage can help slow the spread of the virus within and between neighboring fields.

Effective crop rotation schemes and maintaining appropriate planting distances from older maize or sugarcane fields can significantly lower the risk of early-season infection.

Adjusting planting dates to avoid synchronizing the most vulnerable seedling stages with peak aphid migration periods is a vital cultural control measure.