Molecular characterization of Morogoro maize-associated virus, a nucleorhabdovirus detected in maize (Zea mays) in Tanzania.

RNAtag-seq of maize samples collected in Tanzania revealed the presence of a previously undescribed nucleorhabdovirus, tentatively named "Morogoro maize-associated virus" (MMaV), in three samples. The MMaV genome is 12,185-12,187 nucleotides long and shares a 69-70% nucleotide sequence identity with taro vein chlorosis virus. Annotation of the genomes showed a typical nucleorhabdovirus gene organization. PCR was unable to detect the same virus in the remaining 35 samples collected in the region.

Diversity and distribution of Maize-associated totivirus strains from Tanzania.

Typically associated with fungal species, members of the viral family Totiviridae have recently been shown to be associated with plants, including important crop species, such as Carica papaya (papaya) and Zea mays (maize). Maize-associated totivirus (MATV) was first described in China and more recently in Ecuador, where it has been found to co-occur with other viruses known to elicit maize lethal necrosis disease (MLND). In a survey for maize-associated viruses, 35 samples were selected for Illumina HiSeq sequencing, from the Tanzanian maize producing regions of Mara, Arusha, Manyara, Kilimanjaro, Morogoro and Pwani. Libraries were prepared using an RNA-tag-seq methodology. Taxonomic classification of the resulting datasets showed that 6 of the 35 samples from the regions of Arusha, Kilimanjaro, Morogoro and Mara, contained reads that were assigned to MATV reference sequences. This was confirmed with PCR and Sanger sequencing. Read assembly of the six MATV-associated datasets yielded partial MATV genomes, two of which were selected for further characterization, using RACE. This yielded two full-length MATV genomes, one of which is divergent from other available MATV genomes.

Grain-yield stability among tropical maize hybrids derived from doubled-haploid inbred lines under random drought stress and optimum moisture conditions.

Drought is a devastating environmental stress in agriculture and hence a common target of plant breeding. A review of breeding progress on drought tolerance shows that, to a certain extent, selection for high yield in stress-free conditions indirectly improves yield in water-limiting conditions. The objectives of this study were to (i) assess the genotype × environment (GE) interaction for grain yield (GY) and other agronomic traits for maize (Zea mays L.) across East African agro-ecologies; and (ii) evaluate agronomic performance and stability in Uganda and Tanzania under optimum and random drought conditions. Data were recorded for major agronomic traits. Genotype main effect plus GE (GGE) biplot analysis was used to assess the stability of varieties within various environments and across environments. Combined analysis of variance across optimum moisture and random drought environments indicated that locations, mean-squares for genotypes and GE were significant for most measured traits. The best hybrids, CKDHH1097 and CKDHH1090, gave GY advantages of 23% and 43%, respectively, over the commercial hybrid varieties under both optimum-moisture and random-drought conditions. Across environments, genotypic variance was less than the GE variance for GY. The hybrids derived from doubled-haploid inbred lines produced higher GY and possessed acceptable agronomic traits compared with the commercial hybrids. Hybrid CKDHH1098 ranked second-best under optimum-moisture and drought-stress environments and was the most stable with broad adaptation to both environments. Use of the best doubled-haploids lines in testcross hybrids make-up, well targeted to the production environments, could boost maize production among farmers in East Africa.

Unravelling the genetic diversity of the three main viruses involved in Sweet Potato Virus Disease (SPVD), and its practical implications.

SUMMARY Sweetpotato (Ipomoea batatas) is a widely grown food crop, in which the most important diseases are caused by viruses. Genetic variability of three widely distributed sweetpotato viruses was analysed using data from 46 isolates of Sweet potato feathery mottle virus (SPFMV), 16 isolates of Sweet potato mild mottle virus (SPMMV) and 25 isolates of Sweet potato chlorotic stunt virus (SPCSV), of which 19, seven and six isolates, respectively, are newly characterized. Division of SPFMV into four genetic groups (strains) according to phylogenetic analysis of coat protein (CP) encoding sequences revealed that strain EA contained the East African isolates of SPFMV but none from elsewhere. In contrast, strain RC contained ten isolates from Australia, Africa, Asia and North America. Strain O contained six heterogeneous isolates from Africa, Asia and South America. The seven strain C isolates from Australia, Africa, Asia, and North and South America formed a group that was genetically distant from the other SPFMV strains. SPMMV isolates showed a high level of variability with no discrete strain groupings. SPCSV isolates from East Africa were phylogenetically distant to SPCSV isolates from elsewhere. Only from East Africa were adequate data available for different isolates of the three viruses to estimate the genetic variability of their local populations. The implications of the current sequence information and the need for more such information from most sweetpotato-growing regions of the world are discussed in relation to virus diagnostics and breeding for virus resistance.

Incidence of Viruses Infecting Sweetpotato in Tanzania.

A survey for incidence of sweetpotato viruses was carried out in the three sweetpotato-producing districts (Bukoba, Misungwi, and Tarime) in the Lake Victoria basin and in the Indian Ocean coastal zone (Bagamoya on the mainland and Unguja on Zanzibar Island) in Tanzania in March and April 2003. A total of 170 plants from 43 sweetpotato fields were collected, established in an insect-proof screenhouse, and tested for viruses by nitrocellulose membrane enzyme-linked immunosorbent assay (NCM-ELISA). Scions from symptomless plants were grafted onto Ipomoea setosa, a nearly universal indicator plant for sweetpotato viruses, and leaves were tested by NCM-ELISA. Results were confirmed in several seropositive plants by cloning and partial sequencing of the viruses. Sweet potato feathery mottle virus (SPMFV), Sweet potato mild mottle virus, Sweet potato chlorotic stunt virus (SPCSV), and Sweet potato chlorotic fleck virus were detected serologically in single or mixed infections. Frequencies of occurrence of these viruses as determined by serological detection showed SPMFV to be the most prevalent virus in all the surveyed districts. Our study revealed a higher incidence and diversity of viruses in the Lake Victoria basin compared with the Indian Ocean coastal area. These results represent the first survey for sweetpotato viruses in Tanzania using accurate detection methods.