Tobacco

Nematode Management


Root-Knot : Meloidogyne species

  • Root-knot, a disease caused by nematodes, is prevalent in all types of tobacco grown in lighter soils.
  • Its incidence is reported from Gujarat, Karnataka and light sandy soils of Andhra Pradesh where tobacco nurseries are raised on commercial scale, although stray incidence of root-knot was observed in other tobacco-growing tracts of Bihar and Tamil Nadu.
  • Root-knot menace is increasing every year especially in tobacco nurseries, which are abandoned under severe infestation and new sites are taken up for raising seedlings.
  • Infection at early stage results in heavy loss in yield and quality of leaf.
  • So far no systematic survey of root-knot disease has been undertaken in India but damage to the extent of 60% has been noticed in individual plots.
  • Losses from root-knot are generally heavy and in combination with other pathogens the disease has become disastrous.

Symptoms

  • In nurseries, the disease can be identified by the sickly appearance of the seedlings. Affected seedlings are pale and stunted. When such seedlings are pulled out, characteristic symptoms of galls are seen on the roots.
  • These galls vary in size from a pinhead to many times the thickness of the root on which they grow. They are round to irregular in shape.
  • In the field, the disease can be identified by the stunting and yellowing of plants which in severe cases of infection wilt and die.
  • Such plants when pulled out show enormous galls on the roots. In severe infection, individual galls coalesce to form multiple elongated, thick galls.
  • In the case of light infection, minute pinhead sized galls are seen on the roots, such plants do not show any external symptoms and are able to make normal growth.

Life Cycle

  • Eggs of the nematodes remain in soil and under favourable soil moisture and temperature, these hatch into pre-parasitic larvae, which migrate till they reach host roots. The larvae penetrate the roots and stimulate the gall formation. The females lay about 400-500 eggs in mass which hatch into larvae within the knots.
  • Often the cortical tissue of the root is broken and eggs are pressed out. After the crop is harvested, the knots containing eggs and larvae are left behind which can remain dormant for a longer time in cultivated soil under favourable conditions.
  • Meloidogyne species has a very wide host range and infect crop plants as well as weeds.
  • Under favourable soil temperature conditions (22 – 31° C) the nematodes complete their life cycle in less than 20 days, thus producing more generations in a season resulting in heavy gall formation.
  • At temperature below 8 or above 32° C the females do not mature. Soil moisture influence on nematodes is relatively less but the nematodes are noticed to be more active after irrigation. With 40-80% moisture-holding capacity of soil, little difference is noticed on root-knot development.

Control

  • Basis of root-knot control is to reduce the nematode populations to a minimum and to prevent the spread and development of existing nematode species to a damaging level.
  • Nematodes are obligate parasites, hence keeping the tobacco nurseries and fields free from weeds and other vegetation specially during off-season will starve them.
  • Immediate uprooting of harvested plants for the roots to dessiccate thereby killing the nematodes inside them, and deep ploughing and turning over the soil during hot summer months, will result in dessication and death of the egg masses and larvae.
  • Use of gall-free seedlings will prevent spread of nematodes to the planted fields.
  • Half the battle against nematodes can be won if they are checked in the nurseries which are the source of infection.
  • Rabbing the seedbeds by burning paddy husk or dried material before sowing effectively reduced the disease.

Root knot nematode

  • Root knot nematode controlled by application of carbofuran 3 G (or) Aldicarb 10 G in planting holes at 0.4 kg a.i/acre.
  • Avoid irrigation water from infested fields to the non-infested ones.
  • Use of non-host crops in rotation with tobacco is next best solution against nematodes. But rotation for at least 3 years is essential for effective reduction of nematode populations.
  • Six crop plants, viz. Arachis hypogaea
  • Sesamum indicum
  • Cajanus cajan
  • Gossypium hirsutum, Capsicum annuum and Cuminum cyminum were found non-host to M. javanica and these can be used as rotation crop against root-knot.

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