Yellow Vein Mosaic of Okra
Symptoms
Yellow vein mosaic disease of okra (Abelmoschus esculentus) is characterized by distinct foliar symptoms that significantly impact plant productivity. The disease manifests as conspicuous yellowing of veins and veinlets on young leaves, creating a network-like pattern. As the infection progresses, interveinal chlorosis develops, and leaves become smaller, thickened, and distorted. Severely affected plants exhibit stunted growth with shortened internodes, leading to a bushy appearance. Flowering is drastically reduced or completely suppressed, and any fruits that develop are small, deformed, and unmarketable. The disease is most severe when plants are infected at the seedling stage, often resulting in complete crop failure.
Etiology
Yellow vein mosaic disease is caused by Bhendi yellow vein mosaic virus (BYVMV), a member of the genus Begomovirus in the family Geminiviridae. The virus possesses bipartite, single-stranded circular DNA genome components (DNA-A and DNA-B) and is often associated with satellite DNA molecules (betasatellites) that modulate symptom severity. BYVMV exists as a complex of closely related viral strains with varying degrees of virulence. The virus particles are geminate (twinned) in morphology, approximately 18-20 nm in diameter, and specifically infect plants in the Malvaceae family, with okra being the primary host.
Disease Cycle
The disease cycle of yellow vein mosaic is entirely dependent on its vector, the whitefly Bemisia tabaci. The virus is transmitted in a persistent circulative manner, meaning the whitefly must feed on infected plants for an acquisition access period of 15-30 minutes to acquire the virus. After acquisition, the virus circulates through the insect's hemolymph, crosses the gut barrier, and reaches the salivary glands within 8-24 hours (latent period). Once established, adult whiteflies remain viruliferous for life and transmit the virus while feeding on healthy plants. The virus does not pass through the egg to progeny (non-transovarial transmission). Primary inoculum sources include infected okra plants from previous seasons, alternative weed hosts such as Ageratum conyzoides, and volunteer okra plants. Disease incidence peaks during warm, humid conditions (25-30°C) that favor whitefly population buildup. The disease spreads rapidly when susceptible cultivars are grown in areas with high whitefly populations.
Management
Cultural Control: Implement crop rotation with non-host crops such as cereals or legumes. Remove and destroy infected plants immediately, along with alternative weed hosts around field margins. Avoid planting okra near previous season's fields or in areas with high whitefly pressure. Use of barrier crops like maize or sorghum around okra fields can reduce whitefly migration.
Host Resistance: Plant resistant or tolerant varieties such as Arka Anamika, Arka Abhay, Parbhani Kranti, or Kashi Pragati. These varieties carry resistance genes that limit viral replication or reduce symptom expression and represent the most economical and environmentally sustainable management strategy.
Vector Control: Apply neem-based products (azadirachtin 1500 ppm) at 3 ml/L as a biopesticide during early growth stages. When whitefly populations exceed economic threshold levels (5-10 adults per leaf), use selective insecticides such as imidacloprid (0.3 ml/L), thiamethoxam (0.2 g/L), or spiromesifen (1 ml/L) as foliar sprays. Spray in the evening when whiteflies are less active. Install yellow sticky traps at 15-20 traps per acre to monitor and mass trap adult whiteflies.
Preventive Measures: Raise seedlings in whitefly-proof net houses before transplanting to the main field. Apply systemic insecticides as soil drenching or seed treatment to protect young plants during the most vulnerable stage. Practice early sowing to allow plants to establish before peak whitefly season. Maintain field sanitation and avoid water stress, as stressed plants are more susceptible to severe infection.
An integrated approach combining resistant varieties, cultural practices, and judicious use of insecticides provides the most effective and sustainable management of yellow vein mosaic disease in okra.
