Sugarcane Grassy Shoot Disease - AbsoluteAstronomy.com

Sugarcane grassy shoot disease (SCGS), caused by small, parasitic bacteria, contributes to losses of 5% to 20% in the main crop of sugarcane

Sugarcane

Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...

, and these losses are higher in the ratoon crop. A higher incidence of SCGS has been recorded in some parts of Southeast Asia

Southeast Asia

Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

and India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, resulting in 100% loss in cane yield and sugar

Sugar

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

production.

Causal organism

SCGS disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

is caused by a phytoplasma
Phytoplasma
Phytoplasma are specialised bacteria that are obligate parasites of plant phloem tissue and transmitting insects . They were first discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be cultured in vitro in cell-free media...

(Candidatus phytoplasma), which is one of the destructive pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

s of sugarcane
Sugarcane
Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...

(Saccharum officinarum L). In India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, SCGS phytoplasmas are spreading at an alarming rate, adversely affecting yield of the sugarcane crop.

Phytoplasmas, formerly called mycoplasma
Mycoplasma
Mycoplasma refers to a genus of bacteria that lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic. Several species are pathogenic in humans,...

-like organisms (MLOs), are a large group of obligate, intracellular, cell wallless parasites classified within the class Mollicutes.
Phytoplasmas are associated with plant diseases and are known to cause more than 600 diseases in several hundred plant species, including gramineous
Poaceae
The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...

weed
Weed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...

s and cereals. The symptoms shown by infected plants include: whitening or yellowing of the leaves
Leaves
-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...

, shortening of the internodes
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

(leading to stunted growth), smaller leaves and excessive proliferation of shoots, resulting in a broom phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

and loss of apical
Apical dominance
In plant physiology, apical dominance is the phenomenon whereby the main central stem of the plant is dominant over other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets....

dominance.

Transmission

Sugarcane is a vegetatively propagated

Vegetative reproduction

Vegetative reproduction is a form of asexual reproduction in plants. It is a process by which new individuals arise without production of seeds or spores...

crop, so the pathogen is transmitted via seed

Seed

A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...

material and by phloem

Phloem

In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...

-feeding leafhopper

Leafhopper

Leafhopper is a common name applied to any species from the family Cicadellidae. Leafhoppers, colloquially known as hoppers, are minute plant-feeding insects in the superfamily Membracoidea in the order Hemiptera...

vectors. Saccharosydne saccharivora
Leafhopper
Leafhopper is a common name applied to any species from the family Cicadellidae. Leafhoppers, colloquially known as hoppers, are minute plant-feeding insects in the superfamily Membracoidea in the order Hemiptera...

, Matsumuratettix hiroglyphicus, Deltocephalus vulgaris and Yamatotettix flavovittatus have been confirmed as vectors for phytoplasma transmission in sugarcane. Unconfirmed reports also suggest a spread through the steel blades (machete

Machete

The machete is a large cleaver-like cutting tool. The blade is typically long and usually under thick. In the English language, an equivalent term is matchet, though it is less commonly known...

s) used for sugarcane harvesting.

SCGS disease symptoms

Phytoplasma-infected sugarcane plants show a proliferation of tillers, which give it typical grassy appearance, hence the name grassy shoot disease. The leaves of infected plants do not produce chlorophyll

Chlorophyll

Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...

, and therefore appear white or creamy yellow. The leaf veins turn white first as the phytoplasma resides in leaf phloem tissue. Symptoms at the early stage of the plant life cycle include leaf chlorosis, mainly at the central leaf whorl. Infected plants do not have the capacity to produce food in the absence of chlorophyll

Chlorophyll

, which results into no cane formation. These symptoms can be seen prominently in the stubble crop

Ratooning

Ratooning is a method which leaves the lower parts of the plant along with the root uncut at the time of harvesting to give the ratoon or the stubble crop. The main benefit of ratooning is that the crop matures earlier in the season...

. The eye or lateral buds sprout before the normal time on growing cane. A survey of various fields of western Maharashtra

Maharashtra

Maharashtra is a state located in India. It is the second most populous after Uttar Pradesh and third largest state by area in India...

showed grassy shoot with chlorotic or creamy white leaves was the most prevalent phenotype in sugarcane plants infected with SCGS.

SCGS and sugarcane iron deficiency

Symptoms of iron deficiency

Iron deficiency (plant disorder)

Iron deficiency is a plant disorder also known as "lime-induced chlorosis". It can be confused with manganese deficiency. A deficiency in the soil is rare but iron can be unavailable for absorption if soil pH is not between about 5 and 6.5. A common problem is when the soil is too alkaline...

(interveinal chlorosis) are very similar to those of SCGS. It shows creamy leaves, but no chlorosis occurs in leaf veins, and they remain green. In the case of severe iron deficiency, veins may lose chlorophyll in the absence of iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

and appear similar to SCGS disease.
Iron deficiency is caused by a lack of iron

Iron

nutrients in the soil; therefore, one may observe several plants showing symptoms of iron deficiency in localized patches in a field. Phytoplasma-infected plants, though, may occur anywhere in the field in a more random distribution. Treatment with 0.1% ferrous sulfate, either by spraying or supplying it through fertilizer

Fertilizer

Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...

cures iron deficiency, but phytoplasma-infected sugarcane does not respond to any treatment. Phytoplasma-infected plants growing in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

show sensitivity to tetracycline.

Detection methods

Based on symptoms

Phytoplasma-infected sugarcane can be recognized by visual symptoms, but there are limitations.

Visual symptoms occur only after considerable growth, normally two to three weeks after planting.
If not observed keenly, confusion may occur on differences between symptoms of SCGS disease and iron deficiency.
In addition to above points, the poor relationship between symptoms and phytoplasma presence has been confirmed by earlier findings that symptoms alone are not reliable indicators of infection or identity. This highlights the importance of employing tests, such as the molecular tests, to verify associations between phytoplasma and putative disease symptoms. Also it suggests the inability to recognize a symptomless sugarcane harboring a phytoplasma could result in inadvertent exposure of sugarcane to a potential disease source.
Precise diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...

is therefore necessary for effective disease identification and control. Though reliable, DNA hybridization, electron microscopy and PCR techniques require specialized equipment and trained human resources. Among these, PCR is an accurate, economical and convenient method, which allows analysis of samples in a short time.

Polymerase chain reaction

In recent years, regions of the rRNA operon

Operon

In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create...

of the prokaryotic and eukaryotic organisms have been sequenced and are being used to develop PCR-based detection assays. These sequences are highly specific to the infecting organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

The ribosomal DNA
Ribosomal DNA
Ribosomal DNA codes for ribosomal RNA. The ribosome is an intracellular macromolecule that produces proteins or polypeptide chains. The ribosome itself consists of a composite of proteins and RNA. As shown in the figure, rDNA consists of a tandem repeat of a unit segment, an operon, composed of...

contains one transcriptional unit with a cluster of genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...

coding for the 18S, 5.8S and 28S rRNAs and two internal transcribed spacer regions, ITS1
Internal transcribed spacer
ITS refers to a piece of non-functional RNA situated between structural ribosomal RNAs on a common precursor transcript. Read from 5' to 3', this polycistronic rRNA precursor transcript contains the 5' external transcribed sequence , 18S rRNA, ITS1, 5.8S rRNA, ITS2, 28S rRNA and finally the 3'ETS...

and ITS2 in eukaryotes, and for 16S
16S ribosomal RNA
16S ribosomal RNA is a component of the 30S subunit of prokaryotic ribosomes. It is approximately 1.5kb in length...

, 5S
5S ribosomal RNA
5S ribosomal RNA is a component of the large ribosomal subunit in both prokaryotes and eukaryotes .Eukaryotic 5S rRNA is synthesised by RNA polymerase III, whereas most other eukaroytic rRNAs are cleaved from a 45S precursor transcribed by RNA polymerase I...

and 23S in prokaryotes . Previous studies have demonstrated the complex ITS regions are useful in measuring close genealogical relationships, because they exhibit greater interspecies differences than the smaller and larger subunits of rRNA genes.
The use of specific probes as selective PCR primers offers an impressive approach for the rapid identification of a large number of phytoplasma isolates
Isolates
Isolates is a term used in developmental psychology and family studies, to describe members of a study group, usually child through young adult, who do not actively participate in cliques or friendship groups...

.
The agarose gel electrophoresis image beside shows amplification of partial, 1.2kb long, 16S rDNA] of Candidatus phytoplasma, where total genomic DNA from a suspected sugarcane plant has been used as template DNA.

ELISA

Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...

has been used as a diagnostic tool in medicine and plant pathology. Serological detection using a specific antiserum

Antiserum

Antiserum is blood serum containing polyclonal antibodies. Antiserum is used to pass on passive immunity to many diseases. Passive antibody transfusion from a previous human survivor is the only known effective treatment for Ebola infection .The most common use of antiserum in humans is as...

is an economical and convenient method that allows for both analysis of many samples in a short time and immunohistological observation of infected tissues.

A phytoplasma-specific antibody
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

can be prepared using the following steps:

Cloning
Cloning
Cloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...

of the phytoplasma
Phytoplasma
Phytoplasma are specialised bacteria that are obligate parasites of plant phloem tissue and transmitting insects . They were first discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be cultured in vitro in cell-free media...

gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

fragment into an Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

expression vector
Expression vector
An expression vector, otherwise known as an expression construct, is generally a plasmid that is used to introduce a specific gene into a target cell. Once the expression vector is inside the cell, the protein that is encoded by the gene is produced by the cellular-transcription and translation...

;
Expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

in E. coli and purification of the protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

; and
Preparation of antibodies in rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...

s.
- This technique has been used to develop antibodies to the immunodominant membrane protein of several phytoplasmas. These antibodies represent important tools in the detection, localization, and purification of phytoplasmas and the target antigen
  Antigen
  An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
  
  .

Control

In SCGS disease, the primary concern is to prevent the disease rather than treat it. Large numbers of phytoplasma-infected seed sets used by the farmers usually cause fast SCGS disease spread. Healthy, certified 'disease free' sugarcane sets are suggested as planting material. If disease symptoms are visible within two weeks after planting, such plants can be replaced by healthy plants. Uprooted infected sugarcane plants need to disposed of by burning them.

Moist hot air treatment of sets is suggested to control infection before planting. This reduces percentage of disease incidence, but causes a reduction in the percentage of bud sprouting.

Reports that the disease spreads through steel blades used for sugarcane harvesting are unconfirmed, but treating the knives using a disinfectant (Lysol

Lysol

Lysol is a trade name for common household cleanersLysol may also refer to:* Lysol , a 1992 album by The Melvins* Lysol , Actor muMs da Schemer played Lysol in The Mad Real World skit on Chappelle's Show....

) or by dipping them in boiling water for some time is suggested as a precaution.

Phytoplasma infection also spreads through insect vectors; it is therefore important to control them.

General field observation reports the ratoon crop
Ratooning
Ratooning is a method which leaves the lower parts of the plant along with the root uncut at the time of harvesting to give the ratoon or the stubble crop. The main benefit of ratooning is that the crop matures earlier in the season...

has higher percentage of disease incidence than the initial planted (main) crop. When the disease incidence is more than 20%, it is suggested to discontinue that crop cycle.
It is always wise to purchase the certified planting material from authorized seed growers, which assures disease-free planting material.