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Taro (Colocasia esculenta) and tannia (Xanthosoma sp.) plants growing in 25 districts across Ethiopia, Kenya, Tanzania and Uganda were surveyed for four RNA viruses. Leaf samples from 392 plants were tested for cucumber mosaic virus (CMV), dasheen mosaic virus (DsMV), taro vein chlorosis virus (TaVCV) and Colocasia bobone disease-associated virus (CBDaV) by RT-PCR. No samples tested positive for TaVCV or CBDaV, while CMV was only detected in three tannia samples with mosaic symptoms from Uganda. DsMV was detected in 40 samples, including 36 out of 171 from Ethiopia, one out of 94 from Uganda and three out of 41 from Tanzania, while none of the 86 samples from Kenya tested positive for any of the four viruses. The complete genomes of nine DsMV isolates from East Africa were cloned and sequenced. Phylogenetic analyses based on the amino acid sequence of the DsMV CP-coding region revealed two distinct clades. Isolates from Ethiopia were distributed in both clades, while samples from Uganda and Tanzania belong to different clades. Seven possible recombination events were identified from the analysis carried out on the available 15 full-length DsMV isolates. Nucleotide substitution ratio analysis revealed that all the DsMV genes are under strong negative selection pressure.

We have characterized the complete genome sequence of an Australian isolate of banana streak CA virus (BSCAV). A greater-than-full-length, cloned copy of the virus genome was assembled and agroinoculated into five tissue-cultured plants of nine different Musa acuminata banana accessions. BSCAV was highly infectious in all nine accessions. All five inoculated plants from eight accessions developed symptoms by 28 weeks post-inoculation, while all five plants of M. acuminata AA subsp. zebrina remained symptomless. Symptoms were mild in six accessions but were severe in Khae Phrae (M. acuminata subsp. siamea) and the East African Highland banana accession Igisahira Gisanzwe. This is the first full-length BSCAV genome sequence reported from Australia and the first report of the infectivity of an infectious clone of banana streak virus.

Yam is an important food staple in many Pacific Island countries, but its production is limited by several factors including virus infection. The presence of viruses also hinders the exploitation of the crop by restricting the international dissemination of yam germplasm due to quarantine concerns. In this study, a total of 224 yam accessions present in the Pacific germplasm collection at SPC-CePaCT, Fiji, were tested for the presence of badnaviruses using a combination of rolling circle amplification (RCA) and sequencing. Of these, 35 tested positive for either Dioscorea bacilliform AL virus (DBALV) or Dioscorea bacilliform AL virus 2 (DBALV2). DBALV was only detected in samples from Vanuatu and Tonga, while DBALV2 was restricted to Papua New Guinean samples. Ten complete genome sequences of DBALV and DBALV2 were obtained and pairwise comparison of the partial reverse transcriptase/ribonuclease H (RT/RNase H)-coding sequence revealed identities ranging from 89% to 100% and 92% to 100%, respectively. The results suggest that DBALV and DBALV2 are the prevalent badnavirus species infecting yams in the Pacific region.

PR, IFPRI3; ISI; HarvestPlus; CRP4; B Promoting healthy food systems; DCA, HarvestPlus; A4NH, CGIAR Research Program on Agriculture for Nutrition and Health (A4NH)

Several key issues need to be resolved before an efficient and reproducible Agrobacterium-mediated sugarcane transformation method can be developed for a wider range of sugarcane cultivars. These include loss of morphogenetic potential in sugarcane cells after Agrobacterium-mediated transformation, effect of exposure to abiotic stresses during in vitro selection, and most importantly the hypersensitive cell death response of sugarcane (and other nonhost plants) to Agrobacterium tumefaciens. Eight sugarcane cultivars (Q117, Q151, Q177, Q200, Q208, KQ228, QS94-2329, and QS94-2174) were evaluated for loss of morphogenetic potential in response to the age of the culture, exposure to Agrobacterium strains, and exposure to abiotic stresses during selection. Corresponding changes in the polyamine profiles of these cultures were also assessed. Strategies were then designed to minimize the negative effects of these factors on the cell survival and callus proliferation following Agrobacterium-mediated transformation. Some of these strategies, including the use of cell death protector genes and regulation of intracellular polyamine levels, will be discussed.

We have mapped the mRNA transcripts of banana bunchy top virus (BBTV) DNA-1. Northern hybridization and 3' RACE analysis identified two polyadenylated RNAs associated with BBTV DNA-1. Previously, one major ORF in the virion sense of DNA-1 had been identified, which encoded a putative replication protein (Rep). An mRNA was identified in BBTV infected bananas that was clearly transcribed from this Rep ORF. Further, a second transcript was identified which mapped to an ORF completely within the Rep ORF. This encoded a putative 5 kDa protein of unknown function. Both these transcripts were also identified in a tobacco plant that had been transformed with Agrobacterium tumefaciens harbouring a binary construct containing the Rep ORF from BBTV DNA-1. This Rep ORF was inserted 3' of a cauliflower mosaic virus 35S promoter and 5' of a vegetable storage protein terminator. The transcripts mapped from these tobacco plants were identical at the 3' end to the transcripts from BBTV infected banana plants. The site of polyadenylation for the Rep ORF was at base 963 immediately 3' of the translational stop codon confirming that the polyadenylation signals for this transcript were all within the ORF. However, the internal ORF had a large untranslated region of 272 bases with its site of polyadenylation at nucleotide 803 and a polyadenylation signal 3' of the translational stop codon. A possible upstream termination signal (A/TTGTAA) was identified and was conserved within BBTV DNA-1 sequences from different international isolates.