Virus-indexing technology for production of quality banana planting material: a boon to the tissue-culture industry and banana growers in India

Banana and plantain (Musa spp.) are the most important fruit crop in India and play a major role in the livelihood of millions of resource-poor small farmers. Use of quality planting material is very important for increasing productivity. Though conventional suckers are still the primary planting material, use of tissueculture plants has increased because of their advantages, like more uniform bunches with even maturity and increased yield. However, banana viral pathogens, which are economically important in India, can be inadvertently spread through tissue-culture plants. In order to control the spread of the viruses, virus-indexing techniques were developed at the National Research Centre for Banana, Tiruchirapalli for early detection in mother plants and tissue-culture plants used for mass propagation. Polymerase chain reaction (PCR), reverse transcriptase PCR (RT-PCR), nonradioactive probe-based nucleic acid spot hybridisation (NASH) and enzyme-linked immune-sorbent assay (ELISA) based techniques were developed and validated for routine testing. PCR and NASH tests are being done for detection of Banana bunchy top virus (BBTV) and Banana streak Mysore virus (BSMysV). RT-PCR and ELISA tests are being done for the detection of Banana bract mosaic virus (BBrMV) and Cucumber mosaic virus (CMV). Based on the work done at the centre, the Department of Biotechnology (DBT), Government of India, has accredited the Molecular Virology lab for testing for banana viruses in the country. In total, 15,850 tissue-culture and mother-plant samples were tested against viruses. The percentage of positive plants for BBTV, BSMysV, CMV and BBrMV were 3.83, 2.85, 17.3 and 0.95% respectively. Indexing was done mostly for the cultivars ‘Grande Naine’ (AAA, Cavendish subgroup), ‘Robusta’ (AAA, Cavendish subgroup) and ‘Hill Banana’ (syn. ‘Virupakshi’, AAB, Pome subgroup). Around 25 tissue-culture banana commercial laboratories are undertaking the services of virus testing. Our laboratory has also developed polyclonal antisera for CMV and BBrMV through recombinant DNA technology, which is currently being validated for ELISA-based testing. INTRODUCTION Banana is one of the most important staple food and fruit crops in the world. In India, it ranks first in production with 19.1 million tonnes produced annually from an area of 0.69 million ha. There are four important viral diseases affecting banana in India. Banana bunchy top virus (BBTV) of the genus Babuvirus in the family Nanoviridae is considered to cause the most serious viral disease of bananas worldwide (Dale, 1987). In India, it has almost wiped out the famous ‘Hill Banana’ (syn. ‘Virupakshi’, AAB, Pome), causing huge economic loss to the growers. It spreads primarily through infected planting materials, such as corms, bits or suckers or tissue culture-propagated plantlets and secondarily through banana black aphid, Pentalonia nigronervosa. Banana streak Mysore virus (BSMysV), a plant pararetrovirus, causes banana streak disease in ‘Poovan’ (AAB, Mysore). This important, widely-grown cultivar is almost 100% infected. BSV particles are non-enveloped, bacilliform shaped, 130-150×30 nm sized with a doublestranded Proc. Int’l ISHS-ProMusa Symp. on Global Perspectives