The Banana bunchy top virus

Banana bunchy top virus (BBTV) spread into 11 countries in the sub-Saharan Africa region reducing yields of  bananas and plantains (Musa spp.) crops. Nucleotide sequences of DNA-S and DNA-R of BBTV isolates from these countries are genetically identical to the 'South Pacific' phylogroup which include Australia, Egypt, South Asia and South Pacific.  [1]

Kumar et al 2011 deduce from these data that transferring vegetative propagules  together with virus spread by the banana aphid vector, Pentalonia nigronervosa, are the reason of  the rapid expansion of  of the virus, and phytosanitary programs are suggested for the management of the virus and their vector.
Yu et al 2011 isolated, cloned and sequenced a banana bunchy top virus sample. It is  a single stranded DNA virus (ssDNA) banana bunchy top virus (BBTV), family Nanaviridae, genus Babuvirus  which represents a satellite DNA component with 12 DNA sequences motifs. [2]

The disease is extremely difficult to eradicate or manage. The virus leads to dark green stripes on leaf stem, followed by stunted growth and the decay of the fruit production No cure for the virus has yet been discovered. Some control can be achieved by killing the aphids which spread the virus.
The banana aphid, which acquires the virus feeding on an infected plant in 4 to t8 hours, retaining the virus through its adult life.

Control of banana bunchy top is achieved by killing the banana aphids and destroying all infected material. Infected banana plants can be first sprayed with an insecticide like Sevin, or simply soapy water.  Sevin, the trademark of Carbaryl (1-naphthyl methylcarbamate) is a chemical in the carbamate family used chiefly as an insecticide.

Cucumber Mosaic Cucumovirus (CMV)
The cucumber mosaic cucumovirus is also spread by the banana aphid, though it does not spread as rapidly as BBTV, nor does it cause significant damage to banana fruit. Symptoms include flower mottling and streaking. [3]

Anhalt and Almeida 2008 found  that adult aphids transmitted BBTV more efficiently at 25 and 30 degrees C than at 20 degrees C than third instar nymphs which, however were not influenced by temeprature variation. Both BBTV acquisition and inoculation efficiencies peaked after 18 h of plant access period and requires a latent period [4]

Niu et al 2009 report that B3 and B4, encoded by DNA3 and DNA4 of banana bunchy top virus (BBTV), exhibit RNA silencing suppression activity to achieve infection of banana plant. B3 and B4 are the RNA silencing suppressors of banana bunchy top virus,  increasing the pathogenicity of the virus and act at different steps in the RNA silencing pathways of the plant. [5]

Amin et al 2011 report that major pathogenicity determinants of BBTV pathogenicity are movement protein (MP) and cell-cycle link protein (Clink) as suppressors of RNA silencing of plant which is being invaded. [6]

The genome of Banana bunchy top virus (BBTV) consists of six segments of single-stranded DNA of approximately 1 kb in length. Yu et al 2012  sequenced the complete genomes of two BBTV isolates from Haikou, Hainan, China. BBTV could be grouped into two large groups, the Southeast Asian group and the Pacific-Indian Oceans group. Both the Haikou-2 and Haikou-4 isolates belong to the newly proposed Southeast Asian group. [7]

Recombination in the banana bunchy top virus genome
Stainton et al 2012 report that DNA-U3 components of the banana bunchy top virus (BBTV) present inter- and intra-component recombination, but all of the South Pacific DNA-R components have a common intra-component recombinant origin. The DNA-U3 and DNA-M components display a greater degree of inter-component recombination than the DNA-R, -S, -C and -M components. [8]

Intergenomic recombination in DNA-U3 among the isolates of two sub-groups of BBTV indicates that such intragenomic recombination may have importance in the evolutionary process of  BBTV genome. Hyder et al. 2011 stress that intragenomic recombination generate genetic diversity in the  ssDNA viruses. [9]

[1] Kumar PL, Hanna R, Alabi OJ, Soko MM, Oben TT, Vangu GH, Naidu RA: Banana bunchy top virus in sub-Saharan Africa: investigations on virus distribution and diversity. Virus Res. 2011 Aug;159(2):171-82.
http://www.ncbi.nlm.nih.gov/pubmed/21549775

[2] Yu NT, Feng TC, Zhang YL, Wang JH, Liu ZX: Bioinformatic analysis of BBTV satellite DNA in Hainan.Virol Sin. 2011 Aug;26(4):279-84
http://www.ncbi.nlm.nih.gov/pubmed/21847760

[3] Have you seen Banana Bunchy Top Virus? Hawaii Early Detection Pest. Hawaii Biodiversity Information Network.
http://www.pbin.org/reportapest/pestlist/bbtv.htm

[4] Anhalt MD, Almeida RP: Effect of temperature, vector life stage, and plant access period on transmission of banana bunchy top virus to banana.Phytopathology. 2008 Jun;98(6):743-8.
http://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO-98-6-0743

[5] Niu S, Wang B, Guo X, Yu J, Wang X, Xu K, Zhai Y, Wang J, Liu Z: Identification of two RNA silencing suppressors from banana bunchy top virus. Arch Virol. 2009;154(11):1775-83.
http://www.ncbi.nlm.nih.gov/pubmed/19816653

[6] Amin I, Ilyas M, Qazi J, Bashir R, Yadav JS, Mansoor S, Fauquet CM, Briddon RW: Identification of a major pathogenicity determinant and suppressors of RNA silencing encoded by a South Pacific isolate of Banana bunchy top virus originating from Pakistan.Virus Genes. 2011 Apr;42(2):272-81.
http://www.ncbi.nlm.nih.gov/pubmed/21161359

[7] Yu NT, Zhang YL, Feng TC, Wang JH, Kulye M, Yang WJ, Lin ZS, Xiong Z, Liu ZX: Cloning and sequence analysis of two banana bunchy top virus genomes in Hainan. Virus Genes. 2012 Jan 28.
http://www.ncbi.nlm.nih.gov/pubmed/22286609

[8] Stainton D, Kraberger S, Walters M, Wiltshire EJ, Rosario K, Halafihi M, Lolohea S, Katoa I, Faitua TH, Aholelei W, Taufa L, Thomas JE, Collings DA, Martin DP, Varsani A: Evidence of inter-component recombination, intra-component recombination and reassortment in Banana bunchy top virus. J Gen Virol. 2012 Jan 25.
http://www.ncbi.nlm.nih.gov/pubmed/22278830

[9] Hyder MZ, Shah SH, Hameed S, Naqvi SM: Evidence of recombination in the Banana bunchy top virus genome. Infect Genet Evol. 2011 Aug;11(6):1293-300.
http://www.ncbi.nlm.nih.gov/pubmed/21539936