Cardamom Mosaic Virus
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Cardamom mosaic virus (CdMV) is a
mosaic virus A mosaic virus is any virus that causes infected plant foliage to have a mottled appearance. Such viruses come from a variety of unrelated lineages and consequently there is no taxon that unites all mosaic viruses. Examples Virus species tha ...
that affects the production of green
cardamom Cardamom (), sometimes cardamon or cardamum, is a spice made from the seeds of several plants in the genus (biology), genera ''Elettaria'' and ''Amomum'' in the family Zingiberaceae. Both genera are native to the Indian subcontinent and Indon ...
( ''E. cardamomum''). It is a member of the genus ''
Macluravirus ''Macluravirus'' is a genus of viruses, in the family ''Potyviridae''. Plants serve as natural hosts. There are 11 species in this genus. Description ''Macluravirus'' is characterised by its flexuous filamentous particles, inclusion bodies ...
'' (recognized under the family ''
Potyviridae ''Potyviridae'' is a family of positive-strand RNA viruses that encompasses more than 30% of known plant viruses, many of which are of great agricultural significance. The family contains 13 genera that contain 259 species. Structure Potyviri ...
'' by ICTV in 1988), and is transmitted through
aphid Aphids are small sap-sucking insects in the Taxonomic rank, family Aphididae. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white Eriosomatinae, woolly ...
s (''P.'' ''caladii'') and infected
rhizome In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...
s, the former in a non-persistent manner.


Host and symptoms

Green cardamom is one of the world's very ancient spices. Known as the “queen of spices”, because of their aroma and flavor, it is one of the most exotic and highly priced spices. It is the world's third most expensive spice after
vanilla Vanilla is a spice derived from orchids of the genus ''Vanilla (genus), Vanilla'', primarily obtained from pods of the flat-leaved vanilla (''Vanilla planifolia, V. planifolia''). ''Vanilla'' is not Autogamy, autogamous, so pollination ...
and
saffron Saffron () is a spice derived from the flower of '' Crocus sativus'', commonly known as the "saffron crocus". The vivid crimson stigma and styles, called threads, are collected and dried for use mainly as a seasoning and colouring agent ...
. Although
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
is the top producer of the spice, producing 31.1% of the world's cardamom followed by
Guatemala Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...
and
Nepal Nepal, officially the Federal Democratic Republic of Nepal, is a landlocked country in South Asia. It is mainly situated in the Himalayas, but also includes parts of the Indo-Gangetic Plain. It borders the Tibet Autonomous Region of China Ch ...
, Guatemala is the top exporter (exporting 43.6% of the world's cardamom) followed by Nepal and India. Cardamom suffers from several oomycetous, fungal, viral, nematode-induced diseases and pests that affect the productivity and the industry as a whole. Among them, "mosaic disease" or "katte disease" is one of the major diseases in cardamom that has resulted in a reduction in its production. The virus was reported at first in southern India in the 1900s by Mollison and it has also highly affected Guatemala and Sri Lanka. The disease is widely distributed among cardamom-cultivating regions. The cardamom production industry in some parts of Guatemala started showing symptoms of the disease, after which all nearby plantations of the southern-pacific coastal region (producing 60% of the total cardamom) were infected with the disease. Recent surveys conducted in cardamom-producing areas of India for CdMV have revealed its prevalence in most of the cardamom plantations in
Karnataka Karnataka ( ) is a States and union territories of India, state in the southwestern region of India. It was Unification of Karnataka, formed as Mysore State on 1 November 1956, with the passage of the States Reorganisation Act, 1956, States Re ...
. It has been reported that based on the time and stage of infection, there is a variation in yield loss due to CdMV. It has been reported that early infection at a young stage leads to almost 100%, whereas higher crop loss ranges from 38 to 68.7% from first to the third year for monocultured cardamom, leading to declining of the infected plants occurring within 3 to 5 years (the economic cycle of a healthy cardamom plant starts from the third year and can last up to 8–10 years). Chemical management practices, breeding for resistance and cross-protection show limited success against CdMV. Early detection of the virus, use of virus-free seedlings, and eradication of the
vector Vector most often refers to: * Euclidean vector, a quantity with a magnitude and a direction * Disease vector, an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematics a ...
and infected clumps are a few methods of CdMV disease management.


Causal agent and its genome characterization

Virions of the genus ''Macluravirus'' are non-enveloped, flexuous, and filamentous, measuring 650-660 nm lengthwise with a 10-12 nm diameter and pinwheel-type
inclusion bodies Inclusion bodies are aggregates of specific types of protein found in neurons, and a number of tissue (biology), tissue cells including red blood cells, bacteria, viruses, and plants. Inclusion bodies of aggregations of multiple proteins are also ...
relating it to the family of potyviruses. The CdMV genomes are single-stranded linear
positive-sense In molecular biology and genetics, the sense of a nucleic acid molecule, particularly of a strand of DNA or RNA, refers to the nature of the roles of the strand and its complement in specifying a sequence of amino acids. Depending on the context, ...
RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...
as reported by Jacob and Usha (2001). As a result of amplification, cloning, sequencing and gene expression, it can be reported that CdMV contains ~8.5kb of genomes, presence coding regions for partial Cytoplasmic Inclusion, CdMV encoded proteins: complete Nuclear Inclusion b (NIb) gene in the genome which is the
RNA-dependent RNA polymerase RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the self-replication, replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand Complementarity (molecular biology), compleme ...
(RdRp), Nuclear Inclusion a (NIa)
Protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products ...
(Nia 1 protease) and a complete 6K2 genome-linked viral protein. The coat protein of potyvirus is a suitable carrier to display the
epitope An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that binds to the epitope is called a paratope. Although e ...
s of the pathogens. The sequencing of coat proteins and 3’ UTR regions of different isolated strains of CdMV from different cardamom-growing geographical regions in India revealed that there are three different CdMV strains causing disease on the basis of severity of symptoms on young and matured leaves, transmission efficiency, effect on plant height and leaf area. The strains varied in the N-terminal region of coat protein in their sequence.


Host range

There is a long association between the infection of Macluravirus and spice crops. They have a narrow host range infecting families
Amaranthaceae Amaranthaceae ( ) is a family of flowering plants commonly known as the amaranth family, in reference to its type genus '' Amaranthus''. It includes the former goosefoot family Chenopodiaceae and contains about 165 genera and 2,040 species, maki ...
,
Asteraceae Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...
,
Iridaceae Iridaceae () is a family of plants in order Asparagales, taking its name from the Iris (plant), irises. It has a nearly global distribution, with 69 accepted genera with a total of about 2500 species. It includes a number of economically importan ...
,
Dioscoreaceae Dioscoreaceae () is a family of monocotyledonous flowering plants, with about 715 known species in nine genera. The best-known member of the family is the yam (some species of ''Dioscorea''). The APG system (1998) and APG II system (2003) both ...
,
Amaryllidaceae The Amaryllidaceae are a family of herbaceous, mainly perennial and bulbous (rarely rhizomatous) flowering plants in the monocot order Asparagales. The family takes its name from the genus '' Amaryllis'' and is commonly known as the amaryl ...
,
Moraceae Moraceae is a family of flowering plants comprising about 48 genera and over 1100 species, and is commonly known as the mulberry or fig family. Most are widespread in tropical and subtropical regions, less so in temperate climates; however, their ...
,
Aizoaceae The Aizoaceae (), or fig-marigold family, is a large family of dicotyledonous flowering plants containing 135 genera and about 1,800 species. Several genera are commonly known as 'ice plants' or 'carpet weeds'. The Aizoaceae are also referred to a ...
,
Ranunculaceae Ranunculaceae (, buttercup or crowfoot family; Latin "little frog", from "frog") is a family (biology), family of over 2,000 known species of flowering plants in 43 genera, distributed worldwide. The largest genera are ''Ranunculus'' (600 spec ...
and
Zingiberaceae Zingiberaceae () or the ginger family is a family of flowering plants made up of about 50 genera with a total of about 1600 known species of aromatic perennial herbs with creeping horizontal or tuberous rhizomes distributed throughout tropical ...
. For CdMV, the natural hosts are small cardamom (
Elettaria cardamomum ''Elettaria cardamomum'', commonly known as green cardamom or true cardamom, is a herbaceous plant, herbaceous, perennial plant in the Zingiberaceae, ginger family, native to southern India. It is the most common of the species whose seeds are u ...
) along with their other hosts that belong to the family Zingiberaceae-''Amomum connecarpum, A. invollucraltum, A. microstephanum, A. muricatum, A. pterocarpum, A. subulatum, Alpinia neutans, Alpinia mutica, Curcuma neilgherrensis, Hedychium flavescens, Zingiber cernuum,'' and ''Maranta arundinacea'' of family Marantaceae


Symptoms

The expression of symptoms associated with the disease varies according to the varieties grown, growing region and strain variations; these include mild to severe mosaic, overall
chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...
, chlorotic flecks and necrotic and ring spots. The virus infection is systemic in nature that gradually spreads to all tillers in a clump and can infect plants of all stages. The first visible symptom of the disease is seen on the youngest leaves of the affected tiller that appear as spindle shaped slender chlorotic flecks (2–5 mm in length). The flecks later develop into pale green discontinuous stripes that run parallel to the vein form the midrib to leaf margin. The mosaic symptoms are masked as the leaves mature. The next emerging leaves of the infected plant will show the characteristic mosaic symptoms over the entire lamina. The mosaic type mottling is often seen on the leaf sheaths and young shoots. The mature leaves formed before infection do not develop symptoms. As the disease advances, the size of the leaves eventually creating a negative effect in the plant's vigor and causing stunting of the clump with a few slender tillers and shorter panicles. The plants infected by mosaic or Katte can survive for many years and act as the source of inoculum. Virus Transmission and Spread The virus is transmitted through the aphid vector '' Pentalonia caladii'' (formerly ''P. nigronervosa'' f. ''caladii''). They are also transmitted by infected rhizomes, infected clones, seedlings raised in the vicinity of infected plantations, volunteer plants, and a few of the infected zingiberacae.Naidu, R., & Venugopal, M. N. (2007). Epidemiology of'Katte'virus disease of small cardamom-II: Foci of primary disease entry, patterns and gradients of disease entry and spread. Along with ''P. caladii'', various other species of aphid have been reported to transmit the virus. The virus can be transmitted by both the nymphal and the adult stages, but efficiency increases with age of the vector; alate and apterous form are the most efficient. In plantations, aphids are prevalent throughout the year, although a decline occurs during monsoon season. The migrating population was found to be the maximum during January–February, while the populations of alate vectors were found higher during November to May. The primary spread in the plantation occurs due to active viruliferous alate forms of the vector at random with a radius of 400–600 m from the virus source. The secondary spread is internal with low rate of spread and as the apterate adults become active, there comes a centrifugal influx of the primary source. The secondary spread was found to be gradient within 40m radius from the initial source in India while in Guatemala, the rate of disease spread was very fast (83% within 6 months of plantation). In the field, CdMV incubated from 20 to 114 days at different months; their expression is influenced by growth of the plants. When the plants are in active phase of growth (May–November) the symptoms start expressing and develop on young seedlings (3-4 leaves stage) within 15–20 days of incubation, while, the expression is slowed due to prolonged incubation period (December – March) and it expressed in the adults only after 30–40 days of incubation during active times (90–120 days during winter months). Although the aphid population increased during November to May in the field and decreased during the monsoon, they were found throughout the year.


Control / management

For successful management of any disease, an integrated disease management strategy needs to be developed. The following are some disease management strategies for CdMV: * Use of healthy plant material for further cultivation * Early detection using the methods mentioned above and accurate identification of the virus involved. * Regular monitoring, tracing out, rouging and elimination of infected clumps of cardamom, remnants of infected plants. * Use of virus free seedlings for large scale multiplication and planting. * The nurseries where the nucleus planting materials are grown should be kept in isolated locations and it should be obtained from disease-free plants. * Monitoring of the collateral hosts that may serve as the breeding sites of the vectors. * For aphids transmitting virus in non- or semi-persistent manner, chemical control measures are not considered effective for managing the viral disease. However, spraying recommended dose of insecticides after eliminating the infected hosts and also oil spraying the plants does increase the efficiency in controlling the vector. * The vector can also be controlled by spreading their predators or entomopathogens like ''Beauveria bassiana'', ''Verticillium chlamydosporium'' and ''Paecilomyces lilacinus'' that feed on the aphids. * Resistance breeding in cardamom against CdMV has been in the process. For example, the lines NKE 9 and NKE 12 that are resistant to CdMV has been released for breeding in different parts of cardamom growing areas in India 1 However, it is a lengthy, expensive and cumbersome process. Therefore, there are researches are still in progress to develop transgenic cardamom resistant to CdMV.


References

{{Taxonbar, from=Q18974817 Potyviridae Viral plant pathogens and diseases