IMPORTANT NEMATODE

DISEASES, SYMPTOMS

AND

DIAGNOSIS

SYMPTOMS OF DAMAGE

•Nematodes feed on root cells and disturb the uptake and movement of nutrients and water from the soil into the plant.

• The above ground main symptoms of nematode damage are reduced growth, severe stunting, poor vigour, yellowing of foliage and wilting of leaves. These symptoms can be confused with nutrient deficiencies or moisture stress.

•Most species cause direct root damage, including gall-like structures that impair root function; also includes swelling, shriveling, splitting and cracking; brown necrotic lesions and stubby or broken rootlets.

•Nematodes cause reduced quantity and poor quality produce.

IMPORTANT DISEASES OF NEMATODES

Root-knot disease - Meloidogyne spp. Ear cockle disease - Anguina tritici Potato disease - Globodera spp. Dry rot disease - Ditylenchus spp. Lesion disease - Pratylenchus spp. Slow decline disease - Tylenchulus semipenetrans Spreading decline disease - Radopholus similis Red ring disease - Rhadinaphelenchus cocophilus Molya disease - Heterodera avenae Ufra disease - Ditylenchus angustus White tip disease - Apelenchoides besseyi Pine wilt disease - Bursaphelenchus xylophilus Reniform nematode - Rotylenchulus reniformis

ROOT-KNOT NEMATODES (MELOIDOGYNE SPP.) Root-knot nematodes (RKN) are the most important

wide spread and economically important plant parasitic nematodes that cause great damage to agricultural productions all over the world.

Root -knot nematodes are endoparasites, invading the root tips and establishing permanent feeding sites inside the root.

Root-knot nematodes greatly modify roots to form small knots or galls. Meloidogyne have been commonly found associated with over 2000 different species of cereals, vegetables ornamental, medicinal and fruits crops causing serious losses globally.

In Pakistan vegetable crops are found highly susceptible to these nematodes with overall 50-60 % incidence of the disease.

Among the four common RKN species M. incognita are pre-dominant than M. javanica.

SYMPTOMS OF RKN ON DIFFERENT CROPS

Infected carrot roots Infected sweet potatoes

Infected potato tubers

SYMPTOMS OF RKN ON DIFFERENT CROPS

Infected turnip roots

Tomato plants showing yellowing and wilting symptoms of RKN infection

SYMPTOMS OF RKN ON TOMATO

Tomato roots showing galling

Cyst nematodes are endoparasites, feed on the root cortex.

Cysts range in colour from light brown, dark brown or reddish brown.

Females on the root surface have a whitish, pearled, brown or golden colour according to genus and cyst maturity.

Females are swollen, lemon, round or pyroid shaped, white or pearly white in appearance.

Cysts have the ability to persist for many years in the soil in the absence of a host.

CYST NEMATODES (HETERODERA/ GLOBODERASPP.)

Healthy plant Infected plant

POTATO CYST NEMATODE (GLOBODERA ROSTOCHIENSIS)

Infected potato roots with PCN

RENIFORM NEMATODE (ROTYLENCHULUS RENIFORMIS)

Reniform nematodes are semi-endoparasites.

Reniform 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 plants appears sick.

Purpling of cotton leaves by Rotylenchulus reniformis

RENIFORM NEMATODE (ROTYLENCHULUS RENIFORMIS)

CITRUS NEMATODES (TYLENCHULUS SEMIPENETRANS)

Citrus nematodes are semi-endoparasites and cause slow decline disease in citrus.

They bury into the root cortex with their anterior end while the posterior end remains outside the root.

Roots have a dirty and enlarged look, because soil adheres to the gelatinous matrix that protects the eggs.

The surface of infected roots appears rough and irregular.

Feeder roots shorten and slowly disappear.

CITRUS NEMATODE (TYLENCHULUS SEMIPENETRANS)

“Slow decline” disease of citrus caused by Tylenchulus semipenetrans

“Spreading decline disease” by R. similis 

BURROWING NEMATODES (RADOPHOLUS SIMILIS)

• Radopholus similis, burrowing nematode is also a citrus damaging nematode which causes a severe “spreading decline” disease of citrus.

• The roots develop cavities and necrotic lesions and show retarded growth.

• The other symptoms include yellowing of leaves and reduction in size of fruits.

• The diseased trees may topple over in severe cases of infection causing heavy losses.

ROOT LESION NEMATODES (PRATYLENCHUS SPP.)

• Root lesion nematodes are migratory endoparasites.

• They invade and move within roots.

• Their feeding destroys root cells, causing lesions to form along the root.

• Lesions are usually narrow and dark and are often invaded by rot-causing pathogens.

• When there is too much feeding damage to the root, lesion nematodes leave and continue feeding on non invaded roots

STUBBY-ROOT NEMATODE TRICHODORUS SPP.

• Stubby root nematodes are migratory ectoparasites of perennial and woody plant roots.

• The infected plants produce short, stunted, stubby and necrotic roots.

• Leaves become chlorotic and yellow.

• Several Trichodorus species are capable to transmit plant viruses.

Anguina tritici was the first plant parasitic nematode to be described in the literature in 1743 by Needham.

It causes a disease in wheat and rye called “ear-cockle” or seed gall.

Symptoms are basal swelling of stem, wrinkling, curling, twisting of leaves, stunted growth; and formation of galls instead of grains.

Infected grains are black, round, hard and short sized as seen.

From a single gall, up to 90,000 nematodes have been counted.

Threshold of 10,000 juveniles/kg soil develop disease.

WHEAT-GALL NEMATODES (ANGUINA TRITICI)

Infected seeds Healthy seeds

Symptoms of D. destructor

POTATO ROT NEMATODE (DITYLENCHUS DESTRUCTOR)

• Potato rot nematode is a major pest of potato and mainly damage tubers.

• Potato rot or potato tuber nematode (Ditylenchus destructor) cause severe damage to potatoes.

RED RING NEMATODE (RHADINAPHELENCHUS COCOPHILUS)

“Red ring” disease by R. cocophilus

• Rhadinaphalenchus cocphilus causes red ring disease of coconut and other palms by the infestation of roots, trunks and leaves.

• Nematode is transmitted by palmweevil, Rhyncophorus palmarum.

• Characteristic symptoms is the red ring of diseased tissue full of R. cocphilus, 2-5 cm beneath the trunk surface.