The Effects of Auxins and Cytokinin on Growth and Development of (<i>Musa</i>sp.) Var. “Yangambi” Explants in Tissue Culture

The aim of this study was to investigate the effects of concentration of different growth regulators (auxins and cytokinins) on growth and development of banana shoot tips cultured in vitro. Explants were taken from young suckers of field grown plants of var. “Yangambi”. The shoot tips were cultured on MS media supplemented with different concentrations of BAP (0, 2, 4, 6 and 8 mg/l) with or without IAA at concentration of 0.34 mg/l. At the rooting phase, the media was supplemented with different concentrations of IBA (0.1, 0.5, 1.0, 1.5 and 2.0 mg/l) with or without BAP at concentration of 0.2 mg/l. The results indicated that 6.0 mg/l BAP significantly increased the number of shoots formed and the interaction of 6 mg/l BAP with 0.35 mg/l IAA significantly increased the fresh weight. For rooting, 2.0 mg/l IBA was more efficient in number and length of roots produced than all other treatments.

Effects of Light on Sweet Potato （Ipomoea Batatas L.）, Cowpea （Vigna Unguiculata L.） and Pineapple （Ananas Comosus L.）

An experiment was carried out at Mkuranga Research Station of National Coconut Development Programme （NCDP） to study the effect of light regimes on three different crops which are sweet potato, cowpea and pineapple between 1995 and 1996. Four light intensities with nominal values of light transmission namely L0 = 100%, L 1 = 75%, L2 = 50%, L3 = 25% were provided by nylon netting materials which filtered sunlight to varying light percentages. The experiment was a split-plot on randomized complete block design, replicated four times. Growth measurements and yield were recorded at a regular interval in all crops. Leaf morphological characteristics were carried out only on sweet potato. Result on the leaf morphological characteristics showed light intensity strongly influenced growth and development of sweet potato. Specific leaf area values in full light were smaller than those in under heavy shade. The light intensity increased the cowpea seed yield significantly （P 〈 0.01） and the interaction between seasons （year） x light regimes was significant （P 〈 0.01）. In low intensity, pineapple flowered earlier and yielded more than in high intensity. These results have provided useful information in planning intercropping models in coconut based-farming systems in Tanzania.

Effects of Ascorbic Acid in Controlling Lethal Browning in <i>in Vitro</i>Culture of <i>Brahylaena huillensis</i>Using Nodal Segments

Brachylaena huillensis (Asteraceae) is a threatened resourceful timber tree species. B. huillensis regenerates only through seeds. However, the seeds have poor germination rate and are also not obtainable. Developing tissue culture techniques for B. huillensis will permit the application of biotechnology to its propagation and provide alternative method for its regeneration. The current study was conducted to investigate the effect of antioxidant ascorbic acid in controlling lethal browning caused by oxidized phenols in in vitro culture of Brachylaena huillensis using nodal segments. The treatments included four levels of ascorbic acid (0, 50, 100, 150, 200, & 250 mg/litre) supplied into basal woody plant medium supplemented with Benzylaminopurine (BAP). The results of the current study revealed that production of phenolic compounds of explants was significantly controlled by incorporating higher levels of ascorbic acid into the medium. The best control was achieved by supplying 200-250 mg/litre of ascorbic acid in the woody plant medium supplemented with BAP.

The <i>in Vitro</i>Propagation Techniques for Producing Banana Using Shoot Tip Cultures

Banana is an important food crop and the second most important fruit crop. Despite the significant commercial value of the crop, the main production constrain is the availability of reliable and safe planting material. The planting materials obtained through conventional methods (suckers) do not meet the increasing demand for planting and they are of poor quality. Tissue culture is the approach which can solve these problems. Micro propagation of the crop is also faced with challenges which need to be addressed in order to improve its production. Some of the problems which hinder the success of the crop include oxidative browning of the wounded tissues and low number of shoots produce per explant. This review highlights the challenges encountered in tissue culture of banana and explores the in vitro propagation techniques by using shoot tip cultures of banana as the possibilities to overcome these problems.

Development of Sanitation Protocol for Leaf Explants of <i>B. huillensis</i>for <i>in Vitro</i>Culture

Brachylaena huillensis (Silver Oak) is a multipurpose timber tree species in the family of Asteraceae. There has been a very high demand for B. huillensis wood and its products leading to overexploitation. B. huillensis regenerates through seedlings. However, it produces seeds with poor germination. Seeds are also difficult to be collected because of small size. Many are eaten by insects and currently there is a lack of seed bank. The facts that have hindered and rendered the natural regeneration of the tree species were uncertain. The present investigation was carried out to develop sanitation protocol of B. huillensis using leaves as explants. Juvenile leaves from the tips of B. huillensis naturally growing seedlings were collected from Bombo West Forest Reserve in Tanzania. The leaves were washed and immersed in NaOCL containing various concentrations levels and two drops of tween 20. There was significant difference between the concentrations levels employed. However, the best results were obtained when leaf explants were immersed in 1.5% v/v NaOCL for ten minutes and later in ethanol for ten seconds and cultured on woody plant media medium containing antifungal (cefotaxime). Genuinely, the protocol is vital and so opens up the way for other subsequent stages for in vitro propagation of B. huillensis.

Genetic Diversity and Structure of East African Tall Coconuts in Tanzania Using RAPD Markers

RAPD markers were used to estimate levels of genetic diversity and structure among twelve East African Tall (EAT) coconut (Cocos nucifera L.) accessions that are maintained at Chambezi station. Ten primers were used in the analysis of 120 accessions. Cluster analysis was performed based on Jaccard’s coefficient and Nei genetic distances. Further analyses included principal coordinate analysis (PCA) and finally bootstrap analysis. The cluster analysis revealed two main clusters. One cluster contained provenances from Lindi and Mtwara regions (south) and those from Coast and Dar es Salaam regions (central);the second had provenances from Tanga region, which is the northern part of the coastal belt. A similar distribution of provenances was shown by the results of the principal coordinate analysis, whose first three coordinates explained 56% of the total variation. The results were able to discriminate between the different provenances and provide evidence of the different origins for the coconut palms in the northern and southern parts of coastal coconut-growing belt. The two major clusters concur well with the history and distribution of coconuts in the coastal belt of Tanzania.

A Transaction Cost Analysis on the Acquisition of Rice Seed by Small-Scale Farmers in ECA Region： Generating Empirical Evidence in Tanzania

The present study is an attempt to develop empirical evidence of transaction costs that rice farmers incur in production and other factors that affect farmers＇ demand for seed and estimating the proportion of costs accounted for by transaction costs due to quality seed in the formal and informal sectors, and analyze how these costs affect sourcing decision. An agricultural household model was developed from the study area. To test the model, information was collected in a survey of 387 households. There is now empirical evidence that transaction cost in rice seed acquisition in Tanzanian agriculture is an added cost to the farmer in the process of purchasing seed. Descriptive analysis shows that about 18% of the total seed cost is accounted for transaction cost, which is 2% of the total variable cost in farmers＇ rice farming. Econometric model was fitted to the household data to determine the factors hindering farmers to use purchased quality seed. Factors that were significant in influencing transaction cost include information search, seed source, farmers＇ seed arrangements, trust, and distance from farmers＇ homestead to the seed source, location and age of the farmer. We recommend that, policy amendments inclined towards reduction of the transaction costs can improve the profitability of the rice enterprise by increasing the demand for inputs.

Whole-genome single nucleotide polymorphism and mating compatibility studies reveal the presence of distinct species in sub-Saharan Africa Bemisia tabaci whiteflies

In sub-Saharan Africa cassava growing areas,two members of the Bemisia tabaci species complex termed sub-Saharan Africa 1(SSA1)and SSA2 have been reported as the prevalent whiteflies associated with the spread of viruses that cause cassava mosaic disease(CMD)and cassava brown streak disease(CBSD)pandemics.At the peak of CMD pandemic in the late 1990s,SSA2 was the prevalent whitefly,although its numbers have diminished over the last two decades with the resurgence of SSA1 whiteflies.Three SSA1 subgroups(SGI to SG3)are the predominant whiteflies in East Africa and vary in distribution and biological properties.Mating compatibility between SSA1 subgroups and SSA2 whiteflies was reported as the possible driver for the resurgence of SSA 1 whiteflies.In this study,a combination of both phylogenomic methods and reciprocal crossing experiments were applied to determine species status of SSA1 subgroups and SSA2 white-fly populations.Phylogenomic analyses conducted with 26548205 bp whole genome single nucleotide polymorphisms(SNPs)and the full mitogenomes clustered SSA1 subgroups together and separate from SSA2 species.Mating incompatibility between SSA1 subgroups and SSA2 further demonstrated their distinctiveness from each other.Phylogenomic analyses conducted with SNPs and mitogenomes also revealed different genetic relationships among SSA1 subgroups.The former clustered SSA 1-SGI and SSA1-SG2 to-gether but separate from SSA1-SG3,while the latter clustered SSA1-SG2 and SSA1-SG3 together but separate from SSA 1-SG1.Mating compatibility was observed between SSA 1-SGI and SSA1-SG2,while incompatibility occurred between SSA 1-SGI and SSA1-SG3,and SSA 1-SG2 and SSA 1-SG3.Mating results among SSA 1 subgroups were coherent with phylogenomics results based on SNPs but not the full mitogenomes.Furthermore,this study revealed that the secondary endosymbiont--did not mediate reproductive success in the crossing assays carried out.Overall,using genome wide SNPs together with reciprocal crossings assays,this study established accurate genetic relationships among cassava-colonizing populations,illustrating that SSA1 and SSA2 are distinct species while at least two species occur within SSA1 species.