Diagnosis and Detection of Plant Virus and Viroid Diseases

Abstract

Diagnosis / detection of virus and viroid diseases at the early stage of infection helps in further prevention of spread of the disease and also helps in routine screening. The use of one or more of the tests will help to detect infections before they become major problem. The diagnostic methods for plant virus and viroid diseases are being continuously improved. Virus diagnosis by bioassay on indicator hosts to prove the pathogenicity is well established but tedious and requires long time for symptom expression. Almost 50 years back outcherlony double diffusion technique was widely used for virus detection. In the recent years the most common detection method for viruses is ELISA which uses virus specific antibodies and is quite sensitive, reliable and quick. ELISA cannot be used for viroid disease detection since they lack specific encoded proteins. Therefore, viroid detection must rely on bioassays or by direct detection of the genomic viroid RNA. The most common method of molecular hybridization is the dot-blot hybridization technique and is being used widely in virus diagnosis in horticultural crops. Polymerase chain reaction (PCR) is universally practiced technology which is highly rapid, versatile, specific and sensitive molecular method that uses the nucleic acid of virus or viroid. DNA viruses use standard PCR and reverse transcriptase - PCR is for RNA viruses and viroids. Many forms of PCR viz., RT-PCR, Multiplex PCR, Taqman PCR, quantitative PCR, Immunocapture PCR, Competitive flourescence PCR etc., have been developed depending on virus-host combination. In 21st century DNA microarray technology is used for virus nucleic acid identification. Recently biosensors, rolling circle amplification, metagenomics and deep sequencing are also used for virus diagnosis. These advanced molecular tests for plant virus and viroid disease diagnosis would be highly useful at quarantine stations and also at disease diagnostic centers (DDCs). The application of recombinant DNA technology in plant virology has permitted using diagnostic methods based on the nucleotide sequences of the genome component of viruses. Among them molecular hybridization and polymerase chain reaction are used for virus and viroid diagnosis in field, lab and also in certification schemes.