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~y,~IIGA1A .....' ~ ~ ~ , reAR ia#r()~ !61 - 2011 ~ [HfI'!]"!iiiil" Technical Bulletin

C. N. Biju and A. I. Bhat

IISR, Cardamom Research Centre Appangala, Madikeri Viral diseases of cardamom

Authors C. N. Biju' and A.I. Bhae 'Indian Institute of Spices Research, Cardamom Research Centre, Appangala, Heravanadu Post, Madikeri 571201, Ka rnataka, India

l Division of Crop Protection, Indian Institute of Spices Research, Marikunnu P.O., Kozhikode - 673012, Kerala, India

Editors R. Dinesh B. Sasikumar T. E. Sheeja Indian Institute of Spices Research, Marikunnu P.O., Kozhikode - 673012, Kerala, India

Published by Director Indian Institute of Spices Research, Marikunnu P.O., Kozhikode - 673012, Kerala, India

December 2012

Cover design A.Sudhakaran

Printed at GKPRINTERS Azad Buil ding, Azad Road, Kaloor, Kochi - 17 Phone - 0484 2340013. E-mail : [email protected] mall cardamom (Elettaria cardamomum Maton) is a perennial, shade Sloving, herbaceous monocot, which belongs to the rhizomatous fam­ ily, Zingiberaceae. Aptly sobriquetted as th e 'Queen of Spices', this spice has its origin in the biodiversity rich evergreen forests of Western Ghats ofSouth India. In India, cardamom is cultivated in an area of 7 \, 170 ha, with a pro­ duction of 11 ,000 tonnes. Among the cardamom cultivating states, Kerala has the maximum production of 8,545 tonnes from an area of 41 ,362 ha, while the contribution of Karnataka and Tamil Nadu are 1,725 and 965 tonnes, re­ spectively. India, the 'land of spices' once occupied a premier position in the global spice market, especially in cardamom trading. However, widespread incidence of pests and diseases adversely affected the cardamom industry and resulted in a substantial reduction in total production and productiv­ ity. Among the diseases, katte/marble/ mosaic disease incited by Cardamom mosaic virus (CdMV) is considered as a major production constraint en­ countered by the cardamom industry. Besides this dreadful disease, chlorotic treak caused by a strain of Banana bract mosaic virus (BBrMV) is an emerg­ ing ci i ea e of recent origin, which could po ibly pose a threat to the car­ damom industry in future. Another viral disease, kokke kandu has become a threat to cardamom cultivation in a few endemic po ket viz., Kodagu, Hassan. hickmagalur, Shimoga and Uttara Kannada districts of Karnataka.

Katte/ Marble/ Mosaic disease Distribution, incidence and yield loss

In India. especially in the ollthern states viz.> Karnataka, Kerala and Tamil Nadu, the di ea e is widely distributed in all the cardamom grow­ ing tracts wi.t h an in idence ranging from 0.0 1-99%. Recent surveys under­ taken to tudy the d istribution and incidence ofkatte disea e revealed that the incidenc of viral dl easewa higher in Karnataka compared to Kerala. Ofthe 84 plantation in 44 1 cations urveyed, incidence of the di ease ranged from 0- 5%. In Karnataka> of the 25 fields bel nging to 13 10 ations surveyed. dis­ ease incidence ranged from 2-85%. In Kerala, the incidence of kalte was less Viral dJ:"eases ofcardamom il .. and spread was restricted with an incidence ranging between 2-12%. Besides India, the disease is also reported to be widespread in Guatemala.

Crop losses due to the disease depend on the growth stage at the time of infection. When the plants are. infected at early stages of growth. the loss will be almost total while. late infection results in a gradual decline in productivity. In monocrop conditions, reduction in the yield to a tune of 38. 62 and 68.7% was observed for first. second and third year of infection. re­ spectively. Under cardamom - areca mixed cropping conditions. crop los e ' of 10-60, 26-91 and 82-92% was reported in the first. second and third year of production, respectively. In general. total decline in both producti n d productivity of the affected plantations occurs within a time span of3·5 after the occurrence of disease.

Symptoms

The disease makes it's appearance on the youngest leaf 06 the affe ed tiller as slender chlorotic flecks (Figs. 1-3). These flecks later develo'p.iJltO pale green discontinuous stripes, which run parallel to the veins from midrib to the leaf margins. The newly emerged leaves also exhibit mosaic symptoms characterized with evenly distributed green tissue over the entire lamina (Fig. 4). Mosaic type mottling is often manifested on leaf sheaths and young shoots (Fig. 5). On artificially inoculated plants. the symptoms initially appear as chlorotic flecks in the fourth leaf formed after the inoculated leaf, which later turns into granular mosaic followed by clear mosaic. Eventually, size of the leaves gets reduced; the plant loses its vigour and becomes stullted. The dis­ ease gradually spreads to all tillers in the clump. In the advanced stages of disease progression. the affected plants produce shorter and slender tillers with a few short panicles. Young plants when infected rarely produce fruits.

Symptoms associated with the disease varied significantly in dif­ ferent cardamom growing tracts. These included, mild to severe mosaic. yel­ lowing, chlorotic flecks and necrotic and ring spots. The symptom expression is also influenced by the varieties grown in the respective re.gions and strain variation.

Causal virus - Characterization and Transmission

Earlier, by employing butanol clarification method, a tlexuous rod shaped virus with dimensions 650 nm to 10-12 nm resembling the genus Potyvirus was reported as the causal agent of katte disease. The concentra­ tion of virus particles were found to be higher in the preparations of sam­ ples infected with the severe strain viz.• CKV-18 (CPCRI, 1984). Similarly in Guatemala, flexuous rod shaped virus particles were found to be associated Viral diseases of'CardaIlJOJ1] with mosaic afFected plants. Further, presence of pinwheel type of inclusion bodies in the cytoplasm of infected plants suggested the possible association of a Potyvirus with this disease. Serological studies have indicated that. the virus is related to Zucchini yellow mosaic virus, Papaya ring spot virus, Cow­ pea aphid borne mosaic virus and Bean common mosaic virus. Analyses of nucleic acid sequences of coat proteil1 (CP) and 3' untranslated regions (3' UTR) of an isolate originating from Sakleshpur in Karnataka revealed that the causal agent of katte disease belongs to the genus Macluravirus of the family Potyviridae. Cloning and sequencing of the coat protein al1d 3' UTR region was reported. Further, sequencing coat protein and 3' UTR regions of different biologically distinct isolates of CdMV frolll diverse geographical locations of Karnataka and Kerala revealed the existence of difFerent strains of the virus. The sequence of strains varied mainly at the N-terminal region ofcoat protein.

Sequence analysis of coat protein gene of six geographically dis­ tinct isolalc!s originating frolll Karnataka, Kerala and Tamil Nadu revealed the existence of high diversity among the isolates. The sequence identity be­ tween the isolate5 varied frolll 75.3-96.9 % and 82.4-98.1 % at nucleotide and ino acid levels, respectively. Among the distinct species of Macluravirus, C'dM wa. found to be closer to Alpinia mosaic virus. TIle deduced amino acid sequences ofcoat protein gene showed a high level of identity in the core and C- terminus regions, whereas the first 39 amino acids of the N- terminus end exhibited considerable variations. Further, three groups were elucidated based on percent identity among the isolates, in which .111 Karnat.lka isolates (except Sirsi) belonged to one group and all the isolates belonging to Kerala and one frolll Tamil Nadu were clustered into .Inother group. Phylogenetic relationship studies revealed that the isolates originating from Karnataka were more divergent compared to those from Kerala and Tamil Nadu.

Recently, CdMV-related sequences have been found in cardamom plant genome (cv. Njallani Green Gold). Integrated DNA was sequenced and found identical to 3' end of Nib, the RNA dependent RNA polymerase gene ofCdMY. These CdMV-related integrated DNA sequences were also detected in a few other plant genomes.

Based on the criteria such as symptom expression on cardamom, transmission through the aphid vector Penta/onia ca/adii (formerly P. nigron­ ervosa f. caladii) and reaction on a set of differentials belonging to Zingib­ eraceae such as E. cardamoll1unl (Malabar type). A/pillia lIlutica, Amomllll1 microstephanllm, A. canneacarpulI1, several strains of the virus has been iden­ tified. Among 31 katte isolates collected from varied agro-c1imatic condi­ tions' six strains were identified based on severity ofsymptoms on young and matured leaves, transmission efficiency, effect on plant height and leaf area in

3 ,." Viral diseases ofcardamom ii r the cultivar CL-37 (Clone -37). Among the isolates, CKV-24 collected from Nelliampathy hills appeared to be the mild type and subsequently used for cross protection studies. The strain K IV was mild on cardamom and pro­ duced severe reaction on A. microstepillmum and Alpinia malaccensis while, the severe strain K I wa mild on A. microstephanum and A. canneacarpum.

lhe vim ot transmitted through seed, soil, root to root contact and t\rough cultural operations. issemination of the virus is mainly medi­ ated by aphid vector. P. caJadil(Fig. 6) and also through the use of infected pJanti erials. The first experimental transmission of katte disease was obtained ~ • nIgrollervosa, the banana aphid. So far, about 13 species of aphids viz.. civora, A. gossypii. A. nqrii. A.rumicis. Brachycaudlls helidtrysi. GreertldiQ tI1tocarpi, Ma~ iphum pi ". tf. rosaefarmis. M. sanehi. ~phi c)'peri, P. nigronervas ica. P. I ogrollervasa f. caladii were re­ ported to trans 'r the vi rus. It w earlier reporled that the aphids associated with cardamom banana are simila r. However, detailed studies indicated that, P. nigronervosa f. t)"pica breeds on Musa and related genera while. P. lIi­ gronervosa f. caladii breeds on cardamom. colocasia and caladium. Recently ba ed on DNA sequences of mitochondrial cytochrome oxidase subunit ­ I and nuclear elongation factor 1 a as well as morphometric differences, P. nigronervosa f. caladii has been restored to full species status as P. ealadii. The virus-vector relatton:.hip is of non-persistent type and both nymphal and adult stages of the vector are capable of tran mitting the disease. However. efficiency of transmission increased with age of the vector and adult; alate and apterous forms were most efficient transmitters. A single aphid is capa­ ble of transmitting the disease. However. higher percentage of transmission was obtained when 15-20 aphids were released per plant. In plantations. the aphid population is prevalent through the year, although a drastic decline in the population occurs during monsoon season. The migrating population of vector was found to be the maximum during January-February, while the populations of alate vectors were more during November-May. The primary sources of inoculum include infected plants and volunteers in disease affected plantations. Under laboratory conditions, successful colonization of aphids was observed on detached young leaves of Musa, followed by Curcuma langa and cardamom.

In plantations, primary spread of the disease occurs randomly due to the activity of viruliferous alate forms of vector, while secondary spread is mainly internal with a very low rate, concentrated within 40 m radius. It is observed that, the rate of spread is higher in cardamom-areca mixed crop­ ping areas of South India. In the infected plants, incubation period of the vi­ rus varies from 20-114 days and expression ofsymptoms is greatly influenced by growth of the plants. Variations in the climatic factors also have profound

4 Viral diseases ofcardamom effects on the incubation period. Early expression of the symptoms is ob­ served during active growth phase of the crop (May to November) while, dur­ ing the months of December to March, the incubation period is prolonged. Symptoms manifests on young seedlings (3-4 leaf stage) within 15-20 days of inoculation while, adult plants require 30-40 days for the expression ofsymp­ toms. Seed transmission studies ofCdMV in the cultivar Njallani Green Gold indicated that though presence of the virus could be detected in immature capsules, immature and mature seeds, seedlings raised from the seeds were asymptomatic and absence of the virus in the seedlings was subsequently confirmed by performing reverse transcription- polymerase chain reaction (RT-PCR). This suggested that though the virus is seed-borne it is not seed transmitted.

Several plants belonging to the Zingiberaceae family viz. , Anwmul1I call11eaCarpum, A. illvoluctrum, A. subulatum. Alpinia lIe1/talls. A. mutica. Curcuma l1eilgilerresnis. Zillgiber cemaUlI1I! were reported to be susceptible hosts under artificial inoculation tests. Among the different plant parts tested to identify the ideal source of inoculum. actively growing symptomatic leaves and pseudostems and symptomless intlorescens as well as capsules appeared to serve as potential sources ofinoculum. Highest percentage of transmission was recorded with symptomatic young leaves and lowest transmission was effected with inflorescens. However. partially dried pseudostem and ripened capsules did not serve as sources of inoculum. Detection and Diagnosis Enzyme Linked Immunosorbent Assay (ELISA)

Procedures for purification of CdMV particles from cardamom. production of polyclonal antiserum and development of direct antigen coat­ ed and double antibody sandwich ELISA (DAC - ELISA) systems were de­ veloped for the detection of virus in plants. Expression ofcoat protein gene of CdMV in E. coli. production of polyclonal antiserum against expressed coat protein gene and development of ELISA for detection of the virus in plants have also been reported.

RT-PCR

Protocols for the isolation of total RNA from katte affected samples and reverse transcription PCR using virus specific primers designed to con­ served region of coat protein gene for the detection of CdMV in plants was developed. The method was validated by testing more than 50 field samples collected from different geographical regions of the Karnataka and Kerala.

5 Viral diseases ofcardamom ii ..

Real-time RT-PCR

A procedure for SYBR green based real-time RT-PCR using total RNA isolated from infected plant and primers designed to coat protein region of the virus was developed. The specificity of the method was confirmed by melt curve analysis and by gel electrophoresis of real-time RT-PCR product. The optimum template volume and annealing temperature needed for suc­ cessful amplification were determined.

Figs 1-3: Chlorotic flecks on young feat; Fig 4: Mosaic symptoms on leilVes; Fig 5: Mosaic mottling on leafshe.7th and shoots; Fig 6: Aphid vector - Pen­ talonia caladii Chlorotic Streak Disease Distribution, incidence and yield loss

During surveys under taken in the cardamom plantations of Kar­ nataka, Kerala and Tamil Nadu, a new kind of viral disease characterized with chlorotic streak symptoms on veins \ ' re noticed in certain plantation. Based on symptoms, the disease was nam d as chlorotic streak. Of the 77

6 Viral diseases ofcardamom plantations in 49 locations surveyed, incidence of the disease ranged from 0-15%. In Kerala, the disease incidence ranged from 0- 15%, with highest in­ cidence in Vythiri Taluk ofWayanad District. In Karnataka, incidence ranged from 0-5% with the highest incidence (5%) in Sirsi, Siddapur and Yellappur Taluks of Vttara Kannada Districts. However, in Tamil Nadu chlorotic streak disease was not noticed in any of the plantations surveyed. Symptoms

The disease is characterized by the formation of continuous or dis­ continuous spindle shaped yellow or light green intravenous streaks along the veins and midrib (Fig. 7). These streaks later coalesce together and impart yellow or light green colour to the veins. Discontinuous spindle shaped mot­ tling are also noticed on ps€udostem and petioles (Fig. 8). In severe cases, till­ ering in infected plant is suppressed to a greater extent (Fig. 9). Distinguish­ ing feature of the disease is the formation of intravenous chlorotic streaks; hence the disease was named as chlorotic streak. Causal virus- characterization

The plants infected with chlorotic streak disease tested negative in RT-PCR for CdMV. Leaf dip electron microscopy of these samples revealed the presence of flexuous virions resembling Potyvirus (Fig. J0). In view of this, total RNA extracted from these plants was subjected to RT-PCR using primers targeting the conserved regions ['WCIEN' and Poly (A)l specific to Potyvirus genus. Sequencing of this product showed Banana bract mosaic virus (BBrMV) as the closest one. Hence, primers were designed to amplify the coat protein (CP) gene of BBrMV using forward and reverse primers de­ signed to the conserved region identified based on multiple sequence align­ ment of coat protein gene and 3' untranslated region (VTR) of all available BBr rv equences from GenBank database.

The ,p gene sequences of six isolates of BBrMV from cardamom ere compared am ong themselves and with corresponding CP gene sequenc­ es of aU avail

Si.;, banana isolates of 13BrMV from India showed high identity towards to BBrMV cardamom isulates (97-99%) while, BBrMV banana iso­ lates from Philippines, Thailand, Vietnam, Western Samoa along with two Indian isolate ; howed identity of 94-96,8% with cardamom isolates. BLAST analysis showed Sugarcane mosaic virus (SCMV) as the closest species to the present virus. Multiple sequence alignment of CP gene deduced amino acid revealed a slig tly variable N-terminal region that had maximum sequence heterogeneity W lile the core and C-terminus was found to be highly con­

7 '" Viral diseases of' cardamom Ii .. served. Analysis of the sequence revealed, several motifs commonly found in potyviral coat proteins including a DAG amino acid triplet, a WCIEN box in the core region and an RQ, AFDF and QMKAA. Phylogenetic analyses of the BBrMV isolates revealed two major clusters, one with all cardamom along with six banana isolates from India while the other cluster consisted of banana isolates from the Philippines, Thailand, Vietnam, Western Samoa and two from India.

Real-time RT- peR

A procedure for SYBR green based real-time RT-PCR using total RNA isolated from infected plant and primers designed to coat protein region of the virus was developed. TIle specificity of the method was confirmed by melt curve analysis and gel electrophoresis of real-time RT-PCR product. The optimum template volume and al1Jlcaling temperature needed for successful amplification were determined.

Pig. 7: Spjndle shaped yeJ/ow or light green jntravenous streaks along the vejns ilnd Jllidrjb; Fig. 8: MottJjng on pselldostem; Fjg. 9: BBrMV jnfected plant whh reduced tjfle6ng; Fjg. /0: Electron Jlljcrograph ot' BBrMV

Cardamom Vein Clearing or Kokke Kandu Disease Distribution, incidence and yield loss

This disease has become a threat to cardamom cultivation in few endemic pockets of Karnataka. The disease which is reported from Kodagu, Hassan, Chickmagalur, Shimoga and North Canara districts of Karnataka may occur either Singly or mixed infections with katte. Unlike katte disease, the plants affected with this disease decline rapidly with yield reduction upto :t:I VjraJ diseases of'cardamom

62-84% in the first year of peak crop. The affected plants become stunted and perish within 1-2 years of infection. Several thousands of hectares of car­ damom plantations in the Hongadahalla zone of Hassan and North Canara districts of Karnataka have become uneconomical due to the kokke kandu infection Symptoms

The first visible symptoms of the disease include continuous or dis­ continuous clearing of the veins (Fig. II). Later rosetting, loosening of leaf sheath and shredding of leaves were manifested on the affected plants. Newly emerging leaves get entangled in the older leaves (Fig. 12) and form hook-like tiller and hence the name kokke kandu (Fig. 13). Leaf sheaths of the infected plants exhibit mottling symptoms (Fig. 14). Light green patches with shallow grooves are also seen on the immature capsules (Fig. 15). Cracking of fruits and partial sterility ofseeds are other associated deformities. Causal virus- characterization, transmission

The exact etiology of the disease is not yet established. Diseased cardamom samples showed positive serological relationship with potyviruses such as Peanut mottle virus, Sugarcane stripe virus and Indian and Guate­ malan mosaic virus isolates indicating the possible involvement of a virus belonging to the genus, Potyvirus. Immunosorbent electron microscopic (ISEM) observations using crude and clarified sap revealed the presence of flexuous particles with dimension 710-740 x 12 nm. However, consistent as­ sociation of the particles was not observed with the diseased samples. Two protocols for purifying the causal agent of kokke kandll were tried with two isolates of kokke kandu. However, no virus pnrticles were observed in the protocol tried for potyvirus and a few isometric particles were observed in the purified preparations ofJeaf sheath of infected cardamom (Sirsi isolate).

The virus is not transmitted through seed, soil or sap. It is also dif­ ficult to transmit the disease mechanically. The disease is transmitted through cardamom aphid, P. caladii in a semi persistent manner. The vector could re­ tain the virus for more than 8 hours after post-acquisition period. Incubntion period for the virus within the plant ranges from 22-128 days.

Potential sources of virus inoculum that facilitnte disease spread includes nearby affected plantations, voluntary seedlings, nurseries raised in the vicinity of virus sources and sprouted discards of infected suckers. Pri­ mary spread in a new plantation occurs due to the activity of incoming alate viruliferous vectors. Random spread was reported in new plantations located lip to 2000 111 nWJy from infected plantations. Secondary spread within the plantations is through alate forms of aphid. Rate of pread varied [rom 1.3­ 8.5% year.

9 Viral diseases ii ..

The disease \Va. fir l repor Nilgiris, Tamil Nadu. The dis­ ease was prevalent only in :l fe w p cket ofTam il Nadu and Kerala. Intensity of the disease wa s found to be les than 1% in al l the affected plantations.

Figs. 11 a and b: Continuous or discontinuous clearing ofthe vein .: Fig. 1:!: Newly emelged leafenlangled in older leaves; Fig. 13: Hook-like tiller; Fig. 14: Mottling symptoms on leafsheath; Fig. 15: Light green patches with shal­ low grooves on immature capsules

Symptoms

The sympto m ~ as.·oci ated with the di sease include irregular yel­ low patches on younger leaves (F ig. 16) which later developed into necr()ti patches (Fig. 17). Tillering in the affected plants is reduced, resulting in stun t­ ed appearance (Fig. 18).

\0 Viral diseases ofcardamom

Causal virus- characterization, transmission

Preliminary studies based on leaf dip electron microscopy indicat­ ed the association of flexuous rod shaped virus particles measuring 570-700 nm x 10-12 nm in the infected leaf tissues and it belongs to genus, Carlavirus.

The disease was mainly observed adjacent to tea plantations. The disease spread in a centrifugal fashion and the involvement ofan aerial vector is suspected. However, the cardamom aphid failed to transmit the disease.

Multiplex RT-PCR (mRT-PCR)

Multiplex RT-PCR based procedure for the simultaneous detection of CdMV and BBrMV was also standardized. With this procedure, two bands of expected size (650 bp for BBrMV and 850 bp for CdMV) were generated in a single reaction.

Fig. 16: Irregular yellowish patches on younger lea ves; Fig. 17: Necrotic patches on the leaves; Fig. 18: Stunted appearance ofNilgiri necrosis affected plant Management ofviral diseases

Viral diseases are responsible for decline in the production potential of plantations and pose constant threat for sustainable production of carda­ mom. Use of healthy planting material and exact identification of pathogens re indispensable components in an integrated disease management pack­ age. A succe' ful d isease management strategy depends on an early detection of the causal organL m in the plants at the incubation stage. Cardamom is P )p

Production and use of virus -free planting material

, ursery lie: The nurseries should be raised in isolated locations to produce

11 viml diseases ofcardamom ii .. disease free healthy seedlings. The incubation period of viral diseases varies and hence, it is not recommended to use the clones obtained from affected plantations. It is recommended to index the mother stock with sensitive tools like ELISA or PCR to ascertain the virus- free status.

Avoidance of volunteers: Volunteers formed from the remnants of infected plants coul.d be potential primary sources of infection and might facilitate further spread of disease within the plantations. Rouging of the infected vol­ unteers and its total avoidance in the vicinity of primary nurseries, especially in the hot spots are pre-requisites fm producing virus-free planting materials.

Removal of sources o.f virus: 1he viruses survive in the principal or collateral hosts which might acts as primary sources of inoculum. Regular tracing of infected plants and subsequent destruction, removal and destruction of vol­ unteers and collateral hosts are indispensable in managing viral diseases of cardamom.

Early detectioll of the viruses: Early detection of the viruses using reliable and sensitive techniques like PCR would enable to identify disease-free healthy plants from which stickers can be obtained for subsequent propagation.

Management ofvector

Chemical control: Chemical control measures are considered to be less effec­ tive in managing viral diseases owing to the non-persistent and semi-persis­ tent modes of transmission of viruses by the vectors. Spraying recommended insectides after undertaking trashing operation increases the efficacy of ap­ plication and manages the vector to a greater extent. In an insecticidal trial, katte disease incidence was found to be significantly higher in the treatments where ph orate, dimethoate, phosphamidon, carbofuran and quinalphos were applied, than the unsprayed treatments indicating that insecticidal applica­ tion may not be effective in preventing spread of the disease, if source of in­ oculum in maintained in the plantation.

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

Biopesticides: Extracts from several plant species were found to adversely af­ fect the breeding potential of aphids. Neem products at O.l % concentration were found to reduce the population of aphids on cardamom and were lethal to the aphid at higher concentrations. Aqueous extracts of Acorus calamus (dried rhizome), Annona squamosa (seeds) and Lawsonia inermis (leaves) were also found to reduce the setting percentage of aphids on cardamom

12 "" Viral diseases ofcardamom leaves. Essential oil of turmeric acted as repellent against the aphid. Ento­ mogenous fungi like Beauveria bassiana, Verticil/hun chlamydosporillm and Paceilamyees lilacinus were reported to be promising in suppressing aphid population without cJlIsing hyperactivity.

Resistant sources

Efforts were made to produce katte immune seedlings through gamma irradiation (CPCRI, 1978). The seedlings grown from the irradiated seeds which did not take lip infection were field planted in contiguous with katte affected plants. Though the plants were free from disease up to two years after planting, all the plants contracted the disease when inoculated artifi­ cially (CPCRI, 1979). On artificial inoculation, Alpinia galollga, Hedychium coronarium, H. flaveseens, Zingiber zerumbet and Afmmomum melegueta were found to be immune and A. mutica was found to be selectively immune to katte disease.

Natural katte escape (NKE) 12 which exhibited immune reaction to katte disease even after repeated inoculations was released as IISR Vijetha and recommended for cultivation in hot spots of katte disease.

Future strategies

Cardamom suffers from the attack of various pathogenic fungi and viruses both in nurseries as well as in plantations. Among the viral diseases, katte is widespread across the cardamom growing tracts while the incidence and distribution of chlorotic streak disease is restricted to certain pockets. Since cardamom is cultivated under diverse cropping systems encompass­ ing a wide variety of other crops, it is speculated that this close association would facilitate other pathogens; espeCially viruses would transmigrate to cardamom apart from its natural host (s) as it was established in the case of BBrMV. Under such circumstances, this association could lead to the emer­ gence of new diseases or could devastate the crop due to synergistic action with other viruses. Future thrust should focus on development of resistant varieties to each of the viruses. Epidemiology, strain variation and emergence of new viruses need to be looked into. Focus should also be given to the iden­ tification and subsequent development of diagnostics for the viruses causing kokke kandu and Nilgiri necrosis diseases. Development of a certification system for the production of virus-free planting material and creating aware­ ness on the importance of use of certified material among all stake holders including farmers, nursery men, extension functionaries and policy makers are also needed.

13 IISR, Cardamom Research Centre Appangala, Madikeri