VIRAL DISEASES –

UNRELENTING MALADIES IN CARDAMOM PLANTATIONS

Biju C.N and Praveena R

Indian Institute of Spices Research,
Cardamom Research Centre,
Appangala, Heravanadu Post,
Madikeri 571 201, Karnataka.

A. I. Bhat

Division of Crop Protection,
Indian Institute of Spices Research,
Marikunnu, Calicut673 012, Kerala

Small cardamom (Elettaria cardamomum Maton) is a perennial, herbaceous monocot, which belongs to the rhizomatous family, Zingiberaceae. In India, cultivation of cardamom spreads in an area of 71,170 hectares with a production of 11, 000 tonnes. Among the cardamom cultivating states, Kerala has the maximum production of 8,545 tonnes, while the contribution of Karnataka and Tamil Nadu are 1,725 and 965 tonnes, respectively. Though India is blessed with favourable agro-climatic conditions for cultivation of cardamom, it is paradoxical that the productivity is no way near to the world average. Rampant incidence of diseases, especially the viral diseases has immensely contributed to a rapid decrease of production over years and still remains as one of the bottleneck encountered by the cardamom industry in achieving sustainable production levels. Among the viral diseases, mosaic/katte/marble disease incited by Cardamom mosaic virus (CdMV) is considered as a major production constraint. Besides this dreadful disease, chlorotic streak caused by a strain of Banana bract mosaic virus (BBrMV) is an emerging disease of recent origin. Other viral diseases such as kokke kandu, Nilgiri necrosis and infectious chlorosis are confined only to certain endemic areas of cardamom growing tracts.

 

MOSAIC DISEASE

 Mosaic disease, also known as katte/ marble is the most widespread and destructive among the viral diseases of cardamom. The disease is prevalent throughout all the cardamom growing regions of South India, with an incidence ranging from 0.01 to 99 per cent. Crop losses due to the disease depend on the growth stage of cardamom plants at the time of infection. Infection in the early stages of development results in total loss of the crop while, late infection results in a gradual decline in productivity. Due to katte infection, under monocropping and mixed cropping conditions in areca gardens, yield reduction to the extent of 38, 62 and 68.7 per cent is observed during first, second and third year of infection, respectively. In general, total decline in both production and productivity of the affected plantations occurs within a period of thre to five years after initial establishment of the disease.  

The disease initially manifests on youngest leaf of the affected plants as slender chlorotic flecks. These flecks eventually develop into pale green discontinuous stripes, which run parallel to the veins from midrib to the leaf margins. Later, mottling develops on the leaf sheath as well as on the pseudostems. Young plants when infected rarely become productive.  

Cardamom mosaic virus(CdMV), the causal agent of kattedisease belongs to the genus Macluravirus of the family Potyviridae. The virus is not transmitted through seed, soil, root to root contact and through cultural operations. Dissemination of the virus is mainly mediated by the aphid vector and also through the use of infected planting materials. About 13 species of aphids are reported to transmit the virus of which, Pentalonia caladii which breeds on cardamom, Colocasia and Caladium is the principal vector.  

In plantations, primary spread of the disease occurs randomly due to the activity of viruliferous winged forms of the vector. Generally, early expression of the symptoms occurs during the active growth phase of the plant i.e., May to November while, during the months of December to March, expression of the symptoms is delayed. Apart from cardamom, several plants belonging to the Zingiberaceae family viz., Amomum canneacarpum,A. involuctrum, A. subulatum, Alpinia neutans, A. mutica, Curcuma neilgherresnis, Zingiber cernauum are also found to be susceptible hosts to the virus.  

CHLOROTIC STREAK DISEASE 

Chlorotic streak is a newly reported viral disease of cardamom. The disease is reported from the cardamom growing zones of Karnataka and Kerala. In Kerala, the disease incidence ranged from 0 – 15 per cent, with the highest incidence in Vythiri Taluk of Wayanad district and in Karnataka, incidence ranged from 0-5 per cent with the highest incidence (five per cent) in Uttara Kannada districts. 

The disease is characterized with continuous or discontinuous spindle shaped yellow or light green streaks intravenously and along the midrib, which later coalesce together and impart yellow or light green colour to the veins. Formation of discontinuous spindle shaped mottling along the pseudostem and petiolesare also observed. In the advanced stages of disease progression, size of the leaves gets reduced and production of new tillers is suppressed. 

The incitant of chlorotic streak disease is a strain of Banana bract mosaic virus (BBrMV).Transmission of BBrMV infecting cardamom is not yet established using aphids, sap or seed.The disease mainly spreads through infected planting materials.

CARDAMOM VEIN CLEARING ORKOKKE KANDU DISEASE 

Cardamom vein clearing disease is restricted only to a few endemic pockets in Karnataka. The disease is reported from Kodagu, Hassan, Chickmagalur, Shimoga and North Canara districts of Karnataka. The affected plants decline rapidly with a yield reduction upto 62-84 per cent in the first year of the crop. The affected plants become stunted and perish within one to two years after taking infection.  

The disease manifests on the leaves as continuous or discontinuous clearing of the veins. Subsequently, rosetting, loosening of leaf sheath and shredding of leaves are also noticed. Newly emerging leaves get enmeshed in the older leaves. Subsequently, the tiller assumes a ‘hook-like’ appearance and hence the name kokke kandu. Mottling symptoms develops on the leaf sheaths and the immature capsules exhibit shallow grooves on the outer rind. Cracking of fruits and partial sterility of seeds are also associated with the disease.  

The exact etiology of the disease is not yet established. However, infected cardamom samples showed positive serological relationship with potyviruses, indicating the possible involvement of a virus belonging to the genus, Potyvirus. The virus is not transmitted through seed, soil, root, sap, mechanical contact and farm implements. The disease is transmitted mainly through cardamom aphid, P. caladii. Primary sources of inoculum includes, infected planting materials obtained from disease affected plantations. Primary spread to a new plantation mainly occurs due to the activity of incoming alate viruliferous vectors.  

CARDAMOM NECROSIS DISEASE (NILGIRI NECROSIS DISEASE)

Cardamom necrosis disease was first noticed in severe form in Nilgiris district of Tamil Nadu and hence commonly known as Nilgiri necrosis disease. The symptoms are manifested on the young leaves as whitish to yellowish continuous or broken streaks proceeding from the midrib to the leaf margins. In the advanced stages of infection, these streaks turn reddish brown leading to shredding of the leaves. The leaves are reduced in size with distorted margins. Early infected plants produce few panicles and capsules and in the advanced stages of infection, tillers are highly stunted and fail to bear panicles and capsules. 

The virus causing Nilgiri necrosis disease belongs to Carlavirus group. Seed, soil, sap, insects and mechanical means do not transmit the disease. The disease spreads mainly through infected planting material. The pattern of spread of this disease is also similar to katte disease; however, rate of spread is comparatively low in the plantations.  

INFECTIOUS VARIEGATION DISEASE 

This disease was first noticed in Vandiperiyar region of Kerala with an incidence of 15 per cent. Later it was also reported from Kodagu, Hassan and North Canaradistricts of Karnataka. Infected plants exhibit typical variegated symptoms on the leaves with characteristic slender to broader radiating stripes of light and dark green on the lamina. Distortion of leaves, tillers and stunting are other associated symptoms. The infected plants become unproductive within the same year of infection.

MANAGEMENT OF VIRAL DISEASES 

Cardamom is propagated mainly by vegetative means and the viruses infecting cardamom primarily spreads through the planting material. Systemic nature of viral diseases further aggravates the problem, as it would be difficult to obtain healthy, virus-free planting materials from infected mother stock. Prevention is better than cure is the thumb rule to manage viral diseases, effectively and economically. In view of this, combinations of strategies need to be formulated and adopted for management of viral diseases.  

PRODUCTION AND USE OF VIRUS – FREE PLANTING MATERIAL 

Primary, secondary/ polybag nurseries as well as clonal nurseries should be raised in isolated locations, away from the main plantations.

 
The clones obtained from affected plantations should be strictly avoided for establishing new plantations and for undertaking replanting in the existing plantations. 

If tissue culture raised plants are used, it is obligatory to check presence of virus in the mother plant. If the mother plant is infected, the plantlets derived from this also will harbour and facilitates subsequent spread of the virus.  

Volunteer plants that grow from the remnants of infected plants are potential primary sources of inoculum and makes further spread of disease within the plantations easier. Removal and destruction of the infected volunteers and its total avoidance in the vicinity of nursery sites are highly essential for checking the spread of viral diseases.  

Regular monitoring, tracing, removal and subsequent destruction of infected plants and collateral hosts are indispensable for managing viral diseases. The removed plants should be either burnt or buried deep in the soil. 

As visual inspections for symptoms may not be always sufficient to confirm the virus-free status of the planting material, use of sensitive diagnostic tools based on serology [enzyme linked immunosorbent assay (ELISA) or electro-blot immunoassay] or nucleic acid [polymerase chain reaction (PCR)] is essentially recommended. Indian Institute of Spices Research (IISR), Kozhikode has developed PCR based diagnostic kits for the detection of both CdMV and BBrMV in the cardamom plants.  

VECTOR MANAGEMENT  

The insect vectors whenever noticed on the plants should be controlled by adopting insecticidal sprays. Insecticides like dimethoate or monocrotophos @0.05 per cent can be used to control aphids and other sucking insects.  

Spraying neem based products at 0.1 per cent concentration were also found to reduce population build up of the aphids on cardamom.  

Spraying recommended insecticides after undertaking trashing operation further enhances efficacy of the application.

Periodical removal of senile old parts, which are the breeding sites for aphids and other collateral hosts like Colocasia and Caladium, effectively reduces the aphid population and check subsequent spread of viral diseases.  

RESISTANT SOURCES  

IISR Vijetha, the mosaic disease resistant variety is recommended for cultivation in katte prone areas