Cassava brown streak disease (CBSD) has occurred in the Indian Ocean coastal lowlands and some areas of Malawi in East Africa for decades, and makes the storage roots of cassava unsuitable for consumption. CBSD is associated with Cassava brown streak virus (CBSV) and the recently described Ugandan cassava brown streak virus (UCBSV) [picorna-like (+)ssRNA viruses; genus Ipomovirus; family Potyviridae]. This study reports the first comprehensive analysis on how evolution is shaping the populations of CBSV and UCBSV. The complete genomes of CBSV and UCBSV (four and eight isolates, respectively) were 69.0-70.3 and 73.6-74.4 % identical at the nucleotide and polyprotein amino acid sequence levels, respectively. They contained predictable sites of homologous recombination, mostly in the 39-proximal part (NIbHAM1h-CP-39-UTR) of the genome, but no evidence of recombination between the two viruses was found. The CP-encoding sequences of 22 and 45 isolates of CBSV and UCBSV analysed, respectively, were mainly under purifying selection; however, several sites in the central part of CBSV CP were subjected to positive selection. HAM1h (putative nucleoside triphosphate pyrophosphatase) was the least similar protein between CBSV and UCBSV (aa identity approx. 55 %). Both termini of HAM1h contained sites under positive selection in UCBSV. The data imply an on-going but somewhat different evolution of CBSV and UCBSV, which is congruent with the recent widespread outbreak of UCBSV in cassava crops in the highland areas (.1000 m above sea level) of East Africa where CBSD has not caused significant problems in the past.

Baobab (Adansonia digitata L) belonging to Bombacaceae family, is one of the most widely used indigenous priority tree species in sub-Saharan Africa, valued in the cosmetic industry for its seed oil, and powdery fruit pulp for juice making. Baobab has high potential for domestication in southern Africa, therefore understanding its genetic diversity and population structuring is warranted. The study investigated the level of genetic diversity and Mantel's test showed a weak positive insignificant correlation (Z=0.12; P=0.64) between genetic distance among populations and actual distance on the ground implying that geneflow was not directly influenced by isolation by distance. The results suggest that seed distribution and tree improvement should recognise the presence of ecotypes and conservation measures should protect all the populations due to existence of private alleles which are of adaptive importance.

A study was conducted to investigate genetic diversity and population structure among populations of Nile tilapia Oreochromis niloticus (Cichlidae) in the Volta Lake of Ghana using microsatellite markers. Four hundred (400) fish specimens were obtained from nine naturally occurring subpopulations and one selectively bred strain, 'Akosombo strain'. These were characterized using 15 microsatellite loci. Twelve of the loci were multi-allelic, producing 2 to 11 alleles per locus while the effective number of expected alleles (Ne) ranged from 2.030 to 2.855. The observed heterozygosity (Ho) and expected heterozygosity (

Cassava brown streak disease (CBSD) has emerged as a major threat to cassava (Manihot esculenta) in eastern and southern Africa. CBSD was first reported in Malawi in the 1950s, but little data on the distribution and epidemiology of the disease are available. A diagnostic survey was therefore conducted in Malawi to determine the distribution, incidence and diversity of viruses causing the disease, and to characterize its effects on local cassava cultivars. Diagnostic tests confirmed the presence of cassava brown streak viruses (CBSVs) in 90% of leaf samples from symptomatic plants. Average CBSD foliar severity was 2.5, although this varied significantly between districts. Both Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) (genus Ipomovirus, family Potyviridae) were detected from sampled plants. UCBSV was widespread, whereas CBSV was detected only in the two most northerly districts. The average abundance of the whitefly vector (Bemisia tabaci) was 0.4 per plant, a low value that was partly attributable to the fact that the survey was conducted during the cool part of the year known to be unfavourable for B. tabaci whiteflies. Spearman's correlation analyses showed a positive correlation between CBSD foliar incidence and CBSD severity and between CBSD severity and CBSD stem incidence. Of the 31 cassava varieties encountered, 20-20 was most severely affected, whilst Mtutumusi was completely unaffected. Although data from this study do not indicate a significant CBSD deterioration in Malawi, strengthened management efforts are required to reduce the current impact of the disease.

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Understanding the levels and associated ecological risk caused by heavy metals is important for the sustainable management and utilization of Lake Chilwa catchment, an important ecosystem in Malawi providing fertile lands for agriculture and a designated wetland ratified by the Ramsar convention in 1997. Concentrations of chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), arsenic (As), mercury (Hg) and cadmium (Cd) were analyzed from 22 soil sampling locations. Extraction and quantification were achieved by microwave digestion and Inductively Coupled Plasma Optical Emission Spectrometer, respectively. Mean values were detected in the following order; Zn > Cr > Ni > Cu > Pb > As. Strong correlations were observed between As and Pb (r = 0.85), Cr and Ni (r = 0.82), Cu and Ni (r = 0.81), Cr and Cu (r = 0.8), and Pb and Zn (r = 0.73) suggesting similar sources of input. Principal component analysis revealed that Cu, Pb, Zn and As originate from anthropogenic activities, while Cr and Ni were geogenic. The ecological risk caused by these metals, calculated by the Ecological Risk Index (RI) method, showed a low to moderate ecological risk. The wetland areas had higher overall concentrations and RI values compared to the rest of the catchment. It is therefore important to enforce measures to manage and control these levels to avoid their damaging effects.

Sweet potato (Ipomoea batatas [L.] Lam) is an important root crop in Malawi and Sub-Saharan Africawhere micronutrient deficiency is an eminent health problem. Using 15 sweet potato genotypes grown in a randomized complete block design at Bvumbwe Research Station, a study was undertaken to determine the extent of variability of selected micronutrients in the genotypes as influenced by storage root age and peeling. Analysis of variance (ANOVA) showed significant (p≤ 0.01) variability among genotypes for dry mater, β-carotene, ascorbic acid levels and reduction of β-carotene due to peeling across all ages. Significant (p ≤ 0.05) variations in zinc, iron and copper were also observed among all genotypes. Peeling reduced β-carotene, ascorbic acid levels, iron, zinc and copper content while late harvesting resulted in low iron, zinc and copper. Therefore, 5 months after planting (MAP) and 4 MAP are recommended for high levels of β-carotene and ascorbic acid and iron, zinc and copper, respectively. Ten genotypes exhibited acceptable levels of dry mater of ≥30%. Zondeni (10.9 mg/100 g, WW) and Babache (23.84 mg/100 g, WW) had highest levels of β-carotene and ascorbic acid, respectively. Mzungu displayed the highest levels of Iron (0.67 mg/100 g, DW) and zinc (0.63 mg/100 g, DW) while Yoyera (0.61 mg/100 g, DW) had the highest levels of copper. Variations of various traits entail potential to breed for higher levels of micronutrients.Key words: Sweet potato, genotypes, β-carotene, ascorbic acid, iron, zinc, copper, peeling, storage root age. INTRODUCTIONApproximately one billion (795 million) people from developing countries suffer from hunger, malnutrition and poverty (FAO, 2015). Various reasons including climate change, environmental degradation, dwindling of natural resources and an ever increasing population have been implicated. In 2015, global population was estimated at 7.3 billion and was expected to climb up to about 9.7 billion in 2050 when nearly 90% of the population will be in resource poor developing countries of Asia, Africa and Latin America (James, 2015). The UN population projection shows that the trend will continue until the end of this century when the global population will reach 10.8 billion or more (UN DESA, 2015). Such increases in global population will result in ever increasing number of food in-secure people, who by definition are people with no physical and economic access to enough safe and nutritious food which meets their dietary needs at all times (FAO, 1996). However, over 3 billion people suffer from a different, sneakier form of hunger than the simple lack of sufficient quantities of foodstuffs referred to as micronutrient malnutrition or "hidden hunger" which is caused by a lack of food of sufficient dietary quality (Kennedy et al., 2003; FAO, 2013). Monotonous diets which are a hallmark of Sub-Saharan countries, based on cereals and other starchy staple foods frequently fail to deliver sufficient quantities of essential minerals and vitamins like Iodine, Iron, Zinc and Vitamin A (D...

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