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Soybean yellow mosaic virus (MYMV / MYMIV)

Yellow mosaic disease (YMD) of soybean is caused by begomoviruses of the geminivirus family — primarily Mungbean Yellow Mosaic India Virus (MYMIV) in central and northern India and Mungbean Yellow Mosaic Virus (MYMV) in southern India. It is the most economically important viral disease of soybean in the Indian central plateau and is the principal reason for the gradual replacement of the iconic but susceptible JS-335 with newer resistant lines.

Identification and symptoms

Symptoms first appear 20-30 days after sowing as small bright-yellow chlorotic patches scattered on young leaves. Patches enlarge and merge into a bright-yellow mosaic with green islands, giving the typical "yellow-green mottle" appearance. Severely infected plants are stunted, with crinkled puckered leaves, small distorted trifoliates, sparse flowering, fewer pods and small shrivelled seed. Plants infected before flowering may bear no pods. Late-infected plants show patchy yellowing on upper canopy only.

Pathogen and vector

The causal agents — MYMIV and MYMV — are bipartite begomoviruses with single-stranded DNA genomes packaged in twinned (geminate) particles. They are transmitted by the whitefly Bemisia tabaci in a persistent, circulative manner; the virus is not mechanically sap-transmissible and is not seed-borne in soybean. The minimum acquisition feeding period is 15-30 minutes; once acquired, the vector can transmit for the rest of its life (10-15 days). Alternative hosts include mungbean, urdbean, cowpea, French bean and several Fabaceae weeds, which carry the virus between soybean seasons.

Hosts and epidemiology

In Madhya Pradesh, Maharashtra (Vidarbha, Marathwada), Rajasthan (Kota-Jhalawar), Karnataka (Belagavi-Dharwad) and Telangana, YMD outbreaks coincide with high whitefly populations from late August onwards. Hot dry spells in the early kharif (40-50 days after sowing) accelerate vector build-up; rain events with intermittent dry days are the highest-risk pattern. Infection levels of 60-80 percent in JS-335 fields have been recorded in epidemic years (2007, 2010, 2015, 2019, 2021).

Economic impact

National yield loss estimates from AICRP-Soybean place average annual losses at 8-15 percent on susceptible varieties, with 60-90 percent losses in localised epidemic years. The 2007 outbreak in Madhya Pradesh caused estimated losses of more than ₹1,200 crore. Oil content and seed quality are also reduced.

Management

  • Resistant varieties: the principal long-term defence — JS 20-69, JS 20-29, NRC 37 (Ahilya 4), NRC 86, NRC 130, NRC 132, JS 20-34, JS 20-98 and Phule Sangam (KDS-726) carry resistance to MYMIV/MYMV; see Soybean Js 335 Kharif.
  • Cultural: timely sowing (last week of June – first week of July) to avoid late-sown crops coinciding with peak vector populations; rogue out infected plants in the first 30 DAS; avoid mungbean/urdbean as a preceding crop; maintain 45 cm row spacing and remove weed hosts.
  • Seed treatment: imidacloprid 600 FS at 1 ml/kg seed or thiamethoxam 30 FS at 10 ml/kg seed gives 25-35 days of whitefly suppression and reduces early infection.
  • Foliar sprays: at 25-30 DAS, foliar spray of thiamethoxam 25 WG at 0.2 g/L or acetamiprid 20 SP at 0.2 g/L for vector management. Spray neem oil 1500 ppm at 3-4 ml/L in alternation to delay insecticide resistance.
  • Field hygiene: deep summer ploughing, removal of volunteer plants, and balanced fertilisation reduce vector pressure.

See also: Soybean JS-335, Soybean MSP procurement, NMOOP.

Sources

  1. Yellow Mosaic Disease of Soybean. ICAR-Indian Institute of Soybean Research, Indore.
  2. Mungbean Yellow Mosaic Virus datasheet. CABI Compendium.
  3. AICRP-Soybean Disease Management Bulletin. ICAR-IISR, Indore.