Occurrence of Banana bract mosaic virus on cardamom

Abstract

During a survey for mosaic disease caused by Cardamom mosaic virus (CdMV) in cardamom plantations, a new kind of viral disease showing chlorotic streak on veins was observed in some plantations. Based on the type of symptom, the disease was named ‘chlorotic streak’. In a survey of 77 cardamom plantations at 49 locations in the states of Kerala, Karnataka and Tamil Nadu in India, incidence of the disease ranged from zero to 15%. The plants infected with chlorotic streak tested negative in reverse transcription polymerase chain reaction (RT-PCR) for CdMV. Leaf dip electron microscopy of these samples showed the presence of flexuous virions resembling Potyvirus. Total RNA extracted from these plants when subjected to RT-PCR using primers targeted to conserved region in Potyvirus resulted in an amplicon size of ~700 bp. Sequencing and BLAST analysis of this amplicon showed Banana bract mosaic virus (BBrMV) as the closest virus. Using primers specific for BBrMV, the coat protein gene from five different geographical isolates of the virus was cloned and sequenced. Sequence analysis of the coat protein gene showed an identity of >94% with BBrMV isolates while identity with other distinct potyvirus species was <60%, indicating that the causal virus is a strain of BBrMV. Multiple sequence alignment and phylogenetic analyses showed high sequence conservation and close clustering of cardamom isolates along with a few banana isolates from India. This is the first report of the occurrence of BBrMV in cardamom. A reliable RT-PCR-based method was also developed for detection of the virus in cardamom plants.