Authors: Gitanjali Devi and Jisna George
Department of Nematology,Assam Agricultural University
India is the 'home of spices' with an array of spices originated and cultivated. Ginger is one of the earliest known oriental spices and is being cultivated in India for both as fresh vegetable and as a dried spice. Ginger is obtained from the rhizomes of Zingiber officinale. India is the largest producer of ginger in the world with an estimated 7,99,860 tonnes from an area of 153450 ha in 2015-16. Ginger faces a variety of production constraints. Plant parasitic nematodes are recognised as serious constraint to crop productivity in India. Among the various plant - parasitic nematode species, root-knot nematode (Meloidogyne spp.), burrowing nematode (Radopholus similis), lesion nematode (Pratylenchus coffeae) and reniform nematode ( Rotylenchulus reniformis ) are important.
Root-knot nematode (Meloidogyne hapla, M. incognita, M. javanica, and M. arenaria).
Symptoms of damage:
- Root-knot nematode feed on tender rhizomes, roots and base of pseudostem. Infested plants show stunting and chlorosis and marginal necrosis of leaves.
- Roots and underground rhizomes exhibit galling and rotting.
- The infested rhizomes have brown, water-soaked areas in the outer tissues especially in angles between shoots.
Â· Nematode infestation aggravates rhizome rot disease.Losses: Root-knot nematode infestation is reported to cause yield loss from 46.4% in India. An initial inoculum level of 10,000 nematodes per plant causes 74% reduction in rhizome weight over a period of six months under potted conditions. At an inoculum level of two infective juveniles per g soil, the fibrous roots are reduced.
The incidence of rhizome rot in ginger caused by the fungus P. aphanidermatum is reported to be severe when rhizomes are infested with M. incognita .
Survival and spread:
- Nematodes survive in soil and infected rhizomes as primary inoculum.
- Therefore, tissues from infected crops remaining in the field serve as a reservoir of the fungus.
- It spreads from infected plants or through soil.
- Use of nematode free seed rhizomes.
- Solarization of ginger beds for 40 days.
- Application of carbofuran or phorate at 1 kg a.i. / ha suppresses M. incognita infestations in ginger.
- Soil application of carbofuran at 3 kg a.i./ha three weeks after planting of the ginger crop was found to decrease yield losses due to the infestation of M. incognita.
Â· Application of phenamiphos @ 3 kg a.i. per ha in fields reduces infestation of M.incognita.
- Pre planting application of neem (Azadirachta indica) cake at 1 t/ha followed by post planting application of carbofuran at 1 kg a.i./ha 45 days after is recommended to control M. incognita infestation .
Â· Application of well decomposed cattle manure or compost @ 25-30 tonnes per ha, neem cake @ 2 tonnes per ha and mulching with green leaves @ 10-12 tonnes per ha at planting and mulching again during the growth period help in reducing M. incognita population.
Â· IISR- Mahima, a ginger selection is resistant to M. incognita. The high-yielding varieties PCT-8, PCT-10, Suguna, and Sudharshana are generally free from M. incognita infestation.
Â· Paddy, forage sorghum, potato, lablab and mustard should be grown in rotation.
- The nematodes can be controlled by treating infested rhizomes with hot water (50Â°C-55Â°C) for 10 minutes.
- Pochonia chlamydosporia , a nematode biocontrol agent can be incorporated in ginger beds (20 g/bed at 106 cfu/g) at the time of sowing.
Burrowing nematode (Radopholus similis): Symptoms of damage: Infected plants exhibits stunting, reduced vigour and tillering. The topmost leaves become chlorotic with scorched tips. Affected plants tend to mature and dry out faster than healthy plants. Infected rhizomes have small, shallow, sunken, water-soaked lesions. The nematode penetrates through cell walls and is found coiled within a single cell and then penetrate the tissues intracellularly. Due to infection large channels or galleries are found within the rhizomes. Secondary organisms eventually rot the entire rhizome.
The perpetuation and dissemination of the nematode take place through infested rhizomes used for planting.
Losses: An initial inoculums level of 10,000 nematodes per plant causes 73.6 % reduction in rhizome weight. The plant exhibited signs of death due to severe rotting of rhizomes and roots. Even an initial inoculum level of 10 nematodes per plant reduced shoot weight, root weight and rhizome weight by 43, 56 and 40 % , respectively , in a pot experiment.
Management: Rotation with taro and cassava, applying large quantities of poultry manure as fertiliser, dipping seed in hot water 510C for 10 min before planting, have been suggested for management of Radopholus similis.
Lesion nematodes (Pratylenchus spp.)
The lesion nematodes cause severe damage to roots and rhizomes of ginger. This nematode is a migratory endoparasite and occurs throughout tropical and warm temperate regions, mainly because of man-made dispersal through infested plant materials. They have a wide host range and cause extensive damage to root cortical tissues, but contamination by microorganisms leads to root decay. Several species of Pratylenchus, namelyP.brachyurus, P. coffeae, P.indicus, P.pratensis and P. zeae, are reported on ginger. P. coffeae is reported to cause 'ginger yellows' disease and is more prevalent in Himachal Pradesh. The nematode infestation causes yellowing of leaves and dry rot symptoms on rhizomes. Dark, brown necrotic lesions can be observed within the infected rhizomes. Also cause rotting of mature rhizomes of ginger. The fingers are more severely affected. Infected rhizomes show dark brown necrotic lesions. The incidence of rhizome rot in ginger caused by the fungus P. aphanidermatum is reported to be severe when rhizomes are also infested with nematodes, such as infestation by P. coffeae .
Survival and spread: Spread and distribution of the nematodes are mostly through infested seed rhizomes.
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