Nematodes in Grapes Introduction Nematodes account for an estimated 14% of all worldwide plant losses, which translates into almost $100 billion dollars annually. Nematodes are translucent, microscopic roundworms, typically measuring 0.25 to 1 mm in length and only about 0.1 to 0.2 mm in diameter. Most nematodes in soil are beneficial components of the soil ecosystem, where they feed on bacteria, fungi and other micro- invertebrates, stimulating and regulating the turnover of nutrients. Their abundance ranges from about 1000 per liter of degraded or infertile soil, up to 50,000 per liter of highly fertile soil. Root knot nematode invading plant roots Courtesy: End Next

Symptoms of damage Plant-parasitic nematodes use hollow spear-like mouthparts called “stylets” to feed. Nematodes feed on root cells and disturb the uptake and movement of nutrients and water from the soil into the plant. The main symptoms of nematode damage are stunted growth, poor vigour and yellow leaves. These symptoms can be confused with nutrient deficiencies or moisture stress. Most species cause direct damage, including gall-like malformations that impair root function (root-knot nematodes) or dieback of root tips and formation of lesions on the roots (e.g root-lesion nematodes). EndPrevious Next

Symptoms of damage A few nematode species do not cause much direct damage on their own, but can transmit viruses while they are feeding (e.g., dagger nematodes). When nematode population densities are large, root systems will be sparse, there will be few fine roots, and the damaged roots will appear reddish, brown or black rather than a healthy white colour. If root-knot nematodes are present, it may be possible to see characteristic swellings or galls on feeder roots. Vines severely damaged by plant-parasitic nematodes are stunted and have reduced yields. EndPrevious Next

Life cycle The reproduction is by meiotic parthenogenesis. Males are very rare. Female lay 500 to 1000 eggs outside her body in a gelatinous sac, in late summer. The larvae develop into first stage juveniles in the egg sac, and root feeding occurs after emergence of the second stage juvenile (J2). Maturation and sexual reproduction occurs at the adult stage. Feeding larvae and adults are active throughout the growing season. Egg masses of M. incognita (R. Gapasin). Newly hatched Meloidogyne J2. Photo: David McK. Bird EndPrevious Next

Nematode Species The most common genera of nematodes are detected in soils from vineyards are listed below: 1.Citrus nematode, Tylenchulus semipenetrans 2.Lesion nematode, Pratylenchus penetrans 3.Root knot nematode, Meloidogyne sp. 4.Reniform Nematode, Rotylenchulus reniformis 5.Dagger nematode, Xiphinema index EndPrevious Next

Citrus nematode Tylenchulus semipenetrans Females are swollen, sac like, remain attached to roots with head region buried in tissues. Damage results in Drying of apical leaves, buds, twigs downward. Vines show reduced vigour, gradual reduction in yield. Nematodes make cavities and tunnels by destroying the cells. Thin and dense fibrous roots are the characteristic symptoms of stubby root nematodes. Root lesion nematodes Pratylenchus penetrans Females of Tylenchus sp. Courtesy: nemweb.ucdavis.edu EndPrevious Next

Root-knot Nematode Meloidogyne sp. : The affected roots exhibit severe galling. Galling is the result of the proliferation of cells of the affected roots. In severe attack, the vines get defoliated. As a result of feeding, infested roots show Knot-like galls on roots. Stunted plants with chlorotic leaves. Reniform Nematode Rotylenchulus reniformis: The nematodes mostly damage the secondary and the feeder roots. The affected roots show Brownish discoloration. The affected portions rot and get sloughed off. As a result the nutrient uptake is affected and the vine appears sick. Females and egg mass of R. reniformis Courtesy: plpnemweb.ucdavis.edu Root galls EndPrevious Next

Dagger Nematode, Xiphinema index (Nematode- borne or nepo virus) Xiphinema index, plant parasitic dagger nematode transmits grape fanleaf virus (GFLV). Spread of virus occurs by two principal modes: grapevine-to- grapevine spread in the vineyard by the nematode vector; and, long distance spread via distribution of propagation material from infected grapevines. The disease can cripple infected grapevine with misshapen leaves, short internodes, and poor berry set. All cultivars of wine grapes are susceptible to the disease and severe economic damage with yield losses up to 80 percent have been recorded in many sensitive cultivars. EndPrevious Next

Typical symptoms of grapevine fanleaf viral disease fan-shaped leaves mimicking the “lady’s fan” (and hence the name of the disease) with toothed margins, vein-banding and yellow mosaic symptoms infected grapevines produced small clusters with poor fruit set, irregular ripening and shot berries Courtesy: EndPrevious Next

Management Nematodes are best managed before planting. Selection of planting material from nematode free nurseries. Application of neem or castor cake. Application of carbofuran 50 g / vine and watering. Preplant soil fumigation with DD mixture and using clean nursery stocks. In infested orchards, soil drenching with DBCP (Dibromo chloro propane) is found to be effective. Crop rotation with Non-host crops or resistant crops can be planted when nematode population is high. Use of trap crops and antagonistic crops. Planting Tagetes erecta (African marigold)and Crotolaria spectabilis in nematode infested soil is effective against the root-knot nematode. EndPrevious Next

Let’s sum up: Nematodes account for an estimated 14% of all worldwide plant losses, which translates into almost $100 billion dollars annually. Nematodes are translucent, microscopic roundworms, typically measuring 0.25 to 1 mm in length and only about 0.1 to 0.2 mm in diameter. The main symptoms of nematode damage are stunted growth, poor vigour and yellow leaves. Nematodes are best managed before planting. Generally, nematode infestations result in areas of the vineyard with vines that lack vigour and have restricted growth and reduced yields. Manures and other soil amendments can improve vine vigour and frequently reduce the effect of nematode infestation. EndPrevious Next