Banana Bunchy Top Virus

Abstract

Banana bunchy top virus (BBTV, genus Babuvirus, family Nanoviridae) causes the most destructive viral disease of banana worldwide, but is restricted to some countries in Africa and the Asia-Pacific region. Hosts of the virus are found only in the plant family Musaceae, and it is transmitted through vegetative planting material and in a circulative, nonpropagative manner by its sole vector the banana aphid (Pentalonia nigronervosa). In banana, disease symptoms include stunting, leaf chlorosis, and rosetting, and a cessation of fruiting, and no natural source of immunity is known. Histological effects and virus replication are restricted to the phloem tissue. The virus has isometric virions, 18–20 nm in diameter, separately encapsidating each of the six integral circular single-stranded DNA (ssDNA) genome components. All components are monocistronic, except for DNA-R, which encodes the master replication initiation protein, and a smaller internal open reading frame (ORF) of unknown function. Replication is via a rolling-circle mechanism, and the genome components share two conserved areas in their respective untranslated regions; the stem loop common region that contains the origin of replication and the major common region which binds a heterogeneous population of DNA primers, around 80 nt in length, that prime complementary strand synthesis.