Banana


Nematode Pests of Fruit Crops and their Management - Banana

Fruits are the major source of vitamins and minerals with high nutritional status and are grown in all parts of the world. Though, they suffer heavy damage due to nematode pests, yet the information available on their nematode status is scanty and localized barring a few fruits like banana, citrus and grapes.

I. BANANA
Banana is the most popular fruit of the tropics and subtropics. Production of the crop is affected by as many as 71 species belonging to 33 genera of plant parasitic nematodes in association with banana roots. The most important and widespread among them are Radopholus similis, followed by Helicotylenchus multicinctus. A few other nematodes of significance in banana arePratylenchus coffeae, Heterodera oryzae, Meloidogyne spp. and Rotylenchulus reniformis

a. Burrowing nematode (Radopholus similis)

Causal organism: Black head toppling disease/Banana rot/Black head/Banana decline/Radopholus root rot

Distribution
The nematode occurs in all the tropical and sub-tropical areas of the globe. In India, it is distributed in all the banana growing states viz.,Tamilnadu, Kerala, Karnataka Goa, Maharashtra, Gujarat, Madhya Pradesh, Assam and Tripura.

Host range
Though, the nematode has a very wide host range, it causes serious problem in crops like banana, pepper, coconut, arecanut, coffee, tea, cocoa, sugarcane, turmeric and ginger.
     
Biology
  • The life cycle of the burrowing nematodes consists of an egg stage, four juvenile stages and adult stage.
  • Juveniles and females penetrate roots and parasitize host tissues. Males are free living.
  • More than one generation can occur inside the root but after deterioration of roots, the nematodes migrate to the soil.
  • Females lay 4-5 eggs per day.
  • The egg to egg cycle is completed in 20-25 days at 24-32o C temperature in which eggs hatch at 10-12 days and juveniles mature within 10-13 days.
  • Nematodes can survive in corms until they remain succulent.
Nature of Damage:
  • These are migratory endoparasitic nematodes which live in inter cellular spaces in cortical parenchyma from where they penetrate the nearby cells, suck their cell sap and destroy them by forming cavities.
  • After destroying one site, the nematode moves to another site for feeding.
  • These cavities coalesce with one another and produce characteristic reddish brown lesions throughout the cortex.
Symptoms:
  • The above ground symptoms are characterized by dwarfing, leaf chlorosis, thin pseudostem, small bunches and premature lodging of plants.
  • Root symptoms appear in form of dark red lesions on cortical or outer part of the root.
  • Heavily infected roots show numerous depressed and open lesions which cause root to break.
  • Infested plants with short necrotic roots cannot support the weight of the bunch or the stress of heavy winds and are thus dislodged or uprooted giving the name to the disease as ‘black-head toppling disease’ of banana.
  • The nematode also helps in causing the ‘Panama wilt’, caused by the fungus Fusarium oxysporum f. sp. cubense. The fungus cannot invade healthy tissue unless there are wounds caused by nematodes.
13.1
Toppling of banana plantations due to Radopholus root rot and Longitudinal section of cord roots of banana to show cortical lesions

b. Banana Spiral Nematodes (Helicotylenchus multicinctus)

Distribution
Helicotylenchus multicinctus, especially important as a pest of banana, is widely distributed in almost all tropical and warm temperate banana growing countries including India. In tropical soils, this nematode often occurs along with R. similis but in cooler dry soils H. multicinctus alone is prevalent.
     
Host Range
Crops susceptible to H. multicinctus include banana, cocoa, sweet potato, citrus, sugar cane, coffee, rubber, oil palm, tea, rice grapevines etc.

Nature of Damage
  • Though, most of the 200 described species of Helicotylenchus are ectoparasitic, H. multicinctus is an endoparasite of outer layers of cortical tissue.
  • Movement inside the root tissue has not been observed.
  • The nematode reproduces through amphimixis.
Symptoms:
  • Infested plants remain stunted, take longer to mature, yield smaller bunches and degenerate faster than uninfested plants.
  • Extensive, discrete, superficial necrotic brown lesions on root surface which may even coleasce.
  • The thin secondary and tertiary roots are also attacked and necrosis is more pronounced which eventually leads to debility of entire plant.
  • The nematode also penetrates the corms, causing red lesions.
  • Infested plants remain stunted, take longer to mature, yield smaller bunches and degenerate faster than uninfested plants.
13.2
Damage caused by H. multicinctus on banana roots

c. Lesion nematode (Pratylenchus coffeae)

Out of several species of lesion nematodes found to be associated with banana, the most important is Pratylenchus coffeae.
Distribution
Widely distributed in most of the tropical regions of Asia (India, Japan, Thailand), Africa, Australia and America.

Life cycle
  • The life cycle and feeding behaviour of the lesion nematodes is similar to that of the burrowing nematodes except that in Pratylenchus, males of are also infective.
  • The egg-to-egg cycle is completed in about 27 days at 26-320C.
Symptoms
  • The symptoms caused by P. coffeae are very similar to the burrowing nematodes.
  • Unlike R. similis, this nematode causes root decay also.
d. Root-knot nematode (Meloidogyne spp.)

The most common species that attack banana are M. arenaria, M. incognita and M. javanica. These species have a global distribution; confined to the tropics and subtropics.

Symptoms:
  • The infested plants are stunted and chlorotic.
  • The roots are heavily galled. The galls vary in size and occur at the tips as well as in other areas along the root.
  • Such roots cease to grow and sometimes develop secondary roots above the gall.
  • Necrosis is never associated with root-knot infection unless secondary organisms like fungi enter the root.
e. Reniform nematodes (Rotylenchulus reniformis)

The reniform nematode probably occurs in all tropical and subtropical areas of the world feeding as sedentary semi-endoparasite on the secondary or tertiary roots of banana

Biology:
  • Only the immature female of this nematode is parasitic.
  • Eggs are laid in a mass covered by gelatinous substance. An egg masse may contain 45 to 66 eggs.
  • After hatching, juveniles(J2s) migrate in the soil and undergo three molts in quick succession without feeding.
  • After the last moult, the female infects roots by penetrating the tissue with its head and leaving rest of the body outside the host tissue. At the same time the body enlarges and takes a kidney shape.
  • Nurse cells are formed as a prerequisite of feeding.
  • The egg to egg cycle is about 24-29 days at 28-31o C.
Symptoms:
  • Necrotic lesions are produced in the areas where females are attached to the roots. The posterior part of the female body and egg mass are protruded outside the host.
  • High population of the nematodes causes severe necrosis and destruction of feeder roots.
Management
Management tactics include cultural, physical, chemical, biology methods, host resistance and integrated management.

Cultural methods include summer ploughing, organic manuring, crop rotation and destruction of infected crop residues.
  • Ideally, uninfested banana suckers should be planted to uninfested land.
  • Heavy mulching of organic matter minimizes the population of H. multicinctus. Propping up of the fruiting stems helps to prevent premature toppling.
  • Intercropping with Crotalaria is known to reduce the R. similis population in root and increase plant growth.
  • Crop rotation with sugarcane, sorghum, tobacco, cassava and grape fruit increased the yield of banana significantly with control of R. similis. Rice or green gram grown after the crop reduces the population of P. coffeae, H. multicinctus and R. similis and increases plant growth.
Physical methods include removal of infested tissues by paring and disinfecting them in hot water at 550 C for 20 minutes before planting. In Kerala, the practice of ‘sun drying’ the rhizome before planting has been found effective in control of nematodes.

Chemical control
  • Carbofuran and phorate at 2 g a.i./plant at planting are the most effective and popular granular nematicides used against banana nematodes. Ethoprop at 2-3g a.i./plant or carbofuran at 1.2 g a.i./ plant reduce the nematodes population with high cost benefit ratio.
  • Pre planting treatment of banana suckers decreases or eliminates infestation. Paring of the corms i.e. removal of the infected portion followed by dipping in carbofuran (3%), aldoxycarb (3%) or oxamyl (1%) eliminated both R. similis and H. multicinctus.
  • Application of 4 g carbofuran, fensulfothion or oxamyl per plant, applied to the soil at planting followed by repeated treatment four months later decreased nematode population and increased the yield.
  • The best way of management of nematode population is obtained by paring (removal of infected part of the suckers) and pralinaging (coating of suckers with some nematicide) with carbofuran or fensulphothion at 42 and 17 g per sucker, respectively before planting.
Biocontrol: The promising biological agents include the fungus, Paecilomyces lilacinus, VAM, and bacterium, Pasteuria penetrans.
Resistance: A few germplasms like Kadali, Kunnan, Pisang seribu and Ayiranka Poovan are known to support low nematode populations.
Integrated: Integrations of paring of suckers and hot water dipping at 55o C for 20 min., neem cake 400 g per plant and carbofuran 20 g per plant before planting significantly reduce the nematode population and improve the plant growth.
Last modified: Thursday, 31 May 2012, 5:43 AM