Major Viral Diseases Affecting Sugarcane Production In India, SBI

I

.* rIt/;

ti'

AJOR ,y IRAL DISEASES F F E C ~ I N GSUGARCANE PRODUCTION IN~INDIA

Indian Council of Agricultural Resear1 Coimbatore - 641 007

MAJOR VI

JGARCANE r K U U U b I IUN IN INUlH

Viruses cause diseases such as mosaic, streak mosaic, streak, red mottle, yellow leaf (syndrome) and Fiji disease in sugarcane. In.addition, infection of sugarcane bacilliform virus, sugarcane mild mottle virus etc are also common in some regions. The viruses infect the plant systemically and practically most of the varieties are infected with mosaic, streak mosaic and yellow leaf disease although the susceptibility may vary from one another. This bulletin summarizes symptoms, detection and management of these three important viral diseases of sugarcane.

rn

a Isease problem Insugarcane

All the three viral diseases are important as they occur in almost all the sugarcane growing regions and varieties under cultivation show different levels of Infection. Although the viruses do not cause appreciable symptomsllosses in the new varieties, slowly the viruses cause decline in their performance.

Symptoms

-

Sugarcane mosaic is caused by sugarcane mosaic virus (SCMV). The virus causes a mosaic pattern of contrasting shades of dark green and light green patches on the leaves. This is due to varied concentration of chlorophyl on the leaf tissues (Fig. 1). The chlorotic areas are most easily seen in young, rapidly growing leaves, particularly near the basal portion of the leaf. The symptoms become still prominent when the young suspected leaf is held against bright light. The light green or yellow and chlorotic areas usually have diffused margins, but the response of some cultivars to the virus may result in sharply defined chlorotic areas accompanied by reddening or necrosis. The proportion of the leaf that is covered by the chlorotic areas may vary from scattered, short yellowish stripes to chlorotic areas that predominate over the leaf with islands of normal green. Prominent yellow blotches that spanned tothe entire length of the leaves are also observed in some varieties (Fig. 2). On older leaves, the symptoms tend to fade and recovery of symptoms is seen. Some varieties exhibit systemic yellowing where entire foliage remains yellow from grand growth phase. In general, the symptoms due to this virus vary with the growing cond~tions,varieties and strains of the virus.

The sugarcane. streak mosaic virus (SCSMV) is the causative agent of the disease. Itisa new memberofTritimovirusgenusofthefamily Potyviridae.This is a recently reported virus in India and elsewhere. The symptoms of the disease do not vary much from sugarcane mosaic. However closer examination of the symptoms would show the presence of numerous small stripes/discontinuous streaks running parallel toveins which coalesce to form discontinuous streaks on young leaves (Fig. 3). Later the discontinuous streaks merge together to form continuous streaks resulting similar to the mosaic symptoms caused by sugarcane mosaic virus. In somevarieties, thestreak pattern remains discontinuous.

Fig- 1.Mosaic infecled sugarcane Fig-2. Mosaic affected sugarcane showing showing shades of light and dark green severe yellowing and drying of leaves patches in Ihe leaves

Fig- 3. Sugarcane leaf showing characteristicstreak mosaic symptoms

ta% *+-

cilsrase (syndmm)

This is also a recently reported viral disease in India and other countries. This disease is caused by sugarcane yellow leaf virus belonging to Luteovirus. The symptoms appear initially on third to fifth leavesfrom top in a maturing plant or ratoon crop. The symptoms will be very clear after 5 to 6 months of crop growth.

On the leaves, the symptom appears as yellowish midrib on the lower surface.

The yellowing may be confined to midrib region or the yellow discolouration may spread laterally to adjoining laminar region parallel to midrib up to a distance of 2.0 cm (Fig. 4 ) . Reddish discoloration of midrib and laminar region is also noticed in certain varieties. In most susceptible varieties, typical yellowing of midribs and laminar region is noticed on upper surface of the leaves. Finally symptoms of necrosis of discolored laminar region from leaf tip to bottom and subsequent drying of entire leaf or noticed in severely affected plants. In ratoon crop the intensity of the disease will be much higher than in plant crop. The disease incidence in sugarcane is found aggravated by poor maintenance of thecrop in the field.

Under field conditions it is very common to see mixed infections of sugarcane varieties with mosaic, streak mosaic and yellow leaf viruses. In such situation foliage turn pale yellow aftercaneformation from intensestreakslblotches. Our studies have clearly established that infection of these viruses reduces cane growth (Fig. 5).photosynthesis, brixand sucrose levels and cane yield. Varietal degeneration in sugarcane is largely attributed to these viruses which slowly buildup their titre in the canes over the years owing to the vegetative pro~aaation.

.

-*, .

Since the viral diseases do not cause diaqnosable symptoms on the seed ca;le

&OslsOf

sugarcanevlral d i s a ~ e s

.,I-

- 4

'

I

and also the expression in the field is inflienced by different factors we need to follow certain diagnostic techniques based on serblogy or molecular biology to detect suaarcaneviruses in the seed cane in the field.

This is a commonly used serological assay in microplates, very effectively applied for the detection and assay of plant viruses. Due to reasonably high sensitivity, reliability, specificity and amenability to automationi ELISA has become the most popular and useful technique particularly when large numbers of tests are needed. Its sensitivity is as low as l-IOnglmL. In this technique, presence of the virus is assessed based on colour development in the microalate wells (Fia. 6)or the colour intensitv is assessed in a micro~late reader. ~ i r e cantigen t coating (DAC)-ELISA, double antibody sandwich (DAS)ELISA. triale anfibodv sandwich (TASbELISA. etc. are the different tvaes of , ., E L I S A ~ can ~ ~beekployedaccording C ~ to need and purpose.

. " ,

.

9

iase chain reactlon(PCR)

Polvmerase chain reaction develo~edin the earlv 1980's has revolutionized themolecular biology research in different fields. f h i s is also used to diagnose plant pathogens present in very low levelslasymptomatic plants. PCR allows

I

L

Fia- 4. Yellow leaf disease infected canes showing yellowing ol mid nb and adioinino , " laminar realon in the lop leaves"

-

Flo- 5.lmoact of viruses on cane Fla- 6. Detection of suoarcane mosaic visus gmkh in sugarcane in the suspecrei sugarcane by vanetv CoC 671 Left-Cmo ELISA. Yellow colour develooment h the raised imm mosalc free seed plate wells indicates that tie particular cane Right - Cmp raised from mosaic samples are posilive to the disease. infecled seed cane

-

,,,,,,

-

Fig 7. Detectionof sugarcane mosaic virus in sugarcane varieties in agarose gel electrophoresis afler PCR amplification

M - DNA molecular weight marker 1,2 - Virus infected sugarcane samples

massive amplification of a specific DNAsequence, starting from a single DNA fragment; one can obtain overa billion copies of that specific piece of DNAin a few hours. The PCR process requires a repetitive series of three fundamental steps that defines one PCR cycle: denaturation, annealing and extension. The amplified nucleotide product is separated on agarose gels and detected after staining (Fig. 7). PCR technique is used to detect viruses with genomic DNA. Since most of the plant viruses have RNAas their genome, an additional step of reverse-transcription to convert RNA to cDNA is done before PCR. This a ~ ~ r o a is ch called as RT-PCR. F

c acid based probes

In placeof PCR, nucleicacid based probes are used if large number of samples are to be processed. In this approach the target genome is labeled with radioactive or non radioactive isotopes. This probe is later hybridized to membrane having blotted nucleic acids from different samples. The presence of the virus is assessed based on hybridized bands or dots using enzyme substrates.

-

m e r-n e n t

/

Since primary transmission of the disease takes place through infected setts planting of disease free materials is required to prevent disease introduction in the field. Seed cane plots are needed to be monitored periodically for the disease at regular intervals and seed canes should be selected from such fields. Alternatively, going for tissue culture seedlings derived through meristem cultureensures virus free planting materials.

Yellow leaf virus disease is aggravated by many biotic and abiotic factors.

Biotic factors such as infestation of internode borer or Striga favours disease manifestation and partial wilt infection induces disease expression.

Additionally water logging and drought predispose the plant in expressing the disease. Since many of these biotic and abiotic factors predispose the crop in disease build up, adequate care should be taken to minimize them.

Movement of seed materials from one place to another facilitates introduction of new virus and viral strains. The new viruslviral strain may become more virulent in the new environment or on other varieties. Hence care should be aken while transporting the cane material for research or commercial use.

Extension Publication No. 124 (2007) Script by

: Dr. R. Viswanathan Dr. M. Balamurali krishnan and Dr. P. Malathi Dr. R. Thiagaragan Dr. Rajula Chandranand Dr. D Puthira Prathap

.

Dr. N. Vijayan Nair, Director, Sugarcane Breeding Institute Coimbatore 641 007 Print-Rite, Coimbatore