Development of a molecular-based detection tool for sweet potato leaf curl viruses and determination of their incidence levels in Tanzania

Sweet potato (Ipomoea batatas L.) is an important food security crop in sub-Saharan Africa, where its production is constrained by devastating diseases; including those caused by sweet potato leaf curl viruses (SPLCVs; Begomovirus; Geminiviridae). The objective of this study was to develop a molecular-based diagnostic detection tool for SPLCVs, as well as to generate information on their geographical distribution and incidence in Tanzania. A comprehensive survey of SPLCVs was done in all major sweet potato growing areas in Tanzania. Incidences of SPLCVs and their causative diseases were determined visually and by polymerase chain reaction (PCR), using primers designed, optimised and validated. DNA was extracted from 4166 sweet potato leaf samples and detection of SPLCVs was done. Visual incidence of disease symptoms ranged from 0 to 100%; while PCR-based incidence of SPLCVs ranged from 0 to 60%. The highest mean PCR-based incidence of SPLCVs was 32%. SPLCVs occurred in all sweet potato growing areas. There was a negative correlation between the visually assessed incidence of disease symptoms and PCR-based incidence of SPCLVs (r = -0.122 and R2 = 0.012). A weak positive correlation between altitude and PCR-based incidence of SPLCVs was also found. In ten-fold serially diluted sweet potato DNA samples, using our new primer pair d1-SPLCVF/d1-SPLCVR, the detection limit of SPLCVs was at the dilution of 10-3. The youngest fully expanded leaf of the sweet potato plant was the best for PCR detection of SPLCVs. These findings will be useful for strategic deployment of planting material and conducting sweet potato breeding experiments for resistance against SPLCVs. &nbsp

Comparison of Parametric and Nonparametric Methods for Analyzing the Bias of a Numerical Model

Numerical models are presently applied in many fields for simulation and prediction, operation, or research. The output from these models normally has both systematic and random errors. The study compared January 2015 temperature data for Uganda as simulated using the Weather Research and Forecast model with actual observed station temperature data to analyze the bias using parametric (the root mean square error (RMSE), the mean absolute error (MAE), mean error (ME), skewness, and the bias easy estimate (BES)) and nonparametric (the sign test, STM) methods. The RMSE normally overestimates the error compared to MAE. The RMSE and MAE are not sensitive to direction of bias. The ME gives both direction and magnitude of bias but can be distorted by extreme values while the BES is insensitive to extreme values. The STM is robust for giving the direction of bias; it is not sensitive to extreme values but it does not give the magnitude of bias. The graphical tools (such as time series and cumulative curves) show the performance of the model with time. It is recommended to integrate parametric and nonparametric methods along with graphical methods for a comprehensive analysis of bias of a numerical model

Multiple Trypanosoma infections are common amongst Glossina species in the new farming areas of Rufiji district, Tanzania

<p>Abstract</p> <p>Background</p> <p>Tsetse flies and trypanosomiasis are among several factors that constrain livestock development in Tanzania. Over the years Rufiji District was excluded from livestock production owing to tsetse fly infestation, however, a few years ago there was an influx of livestock following evictions aimed at conserving the Usangu wetlands.</p> <p>Methods</p> <p>A study was conducted to determine the efficiency of available traps for catching tsetse flies, <it>Glossina </it>species infesting the area, their infection rates and <it>Trypanosoma </it>species circulating in the area. Trapping was conducted during the semi dry season for a total of 30 days (ten days each month) during the onset of the dry season of May - July 2009. Harvested flies after every 24 hours were dissected and examined under a light microscope for trypanosome infections and whole fly DNA was extracted from 82 flies and analyzed for trypanosomes by polymerase chain reaction (PCR) using different sets of primers.</p> <p>Results</p> <p>The proportions of total tsetse catches per trap were in the following decreasing order S3 (33%), H-Trap (27%), Pyramidal (19%), sticky panel (11%) and biconical trap (10%). Of the 1200 trapped flies, 75.6% were identified as <it>Glossina pallidipes</it>, 11.7% <it>as G. brevipalpis</it>, 9.6% as <it>G. austeni </it>and 3.0% <it>G. morsitans morsitans</it>. Dissections revealed the overall infection rate of 6.6% (13/197). Whole DNA was extracted from 82 tsetse flies and the prevalence of trypanosomes circulating in the area in descending order was 92.7% (76/82) for <it>T. simiae</it>; 70.7% (58/82) for <it>T. brucei </it>types; 48.8% (40/82) for the <it>T. vivax </it>types and 32.9% (27/82) for the <it>T. congolense </it>types as determined by PCR. All trypanosome types were found in all tsetse species analysed except for the <it>T. congolense </it>types, which were absent in <it>G. m. morsitans</it>. None of the <it>T. brucei </it>positive samples contained human infective trypanosomes by SRA - PCR test</p> <p>Conclusion</p> <p>All tsetse species found in Rufiji are biologically important in the transmission of animal trypanosomiasis and the absence of <it>T. congolense </it>in <it>G. m. morsitans </it>could be a matter of chance only. Therefore, plans for control should consider all tsetse species.</p

Lablab purpureus—A Crop Lost for Africa?

In recent years, so-called ‘lost crops’ have been appraised in a number of reviews, among them Lablab purpureus in the context of African vegetable species. This crop cannot truly be considered ‘lost’ because worldwide more than 150 common names are applied to it. Based on a comprehensive literature review, this paper aims to put forward four theses, (i) Lablab is one of the most diverse domesticated legume species and has multiple uses. Although its largest agro-morphological diversity occurs in South Asia, its origin appears to be Africa. (ii) Crop improvement in South Asia is based on limited genetic diversity. (iii) The restricted research and development performed in Africa focuses either on improving forage or soil properties mostly through one popular cultivar, Rongai, while the available diversity of lablab in Africa might be under threat of genetic erosion. (iv) Lablab is better adapted to drought than common beans (Phaseolus vulgaris) or cowpea (Vigna unguiculata), both of which have been preferred to lablab in African agricultural production systems. Lablab might offer comparable opportunities for African agriculture in the view of global change. Its wide potential for adaptation throughout eastern and southern Africa is shown with a GIS (geographic information systems) approach

Learning from Wasukuma ethnopedology: an indigenous well-established system for transfer of agro-technology in Tanzania

This study was initiated by the fact that the language of the largest ethnic group in Tanzania – called Wasukuma, contains a very rich nomenclature which generally describes soils and their properties in relation to management and productivity. (54) randomly selected farmers from three different villages (namely Shishiyu, Mwanhegele and Bukangilija) participated in the study. A questionnaire was designed for the purpose of interviewing farmers. Farmers provided information on major local soils they could identify and describe. According to farmers, transient and permanent characteristics that influence the plough layer were most discriminating. These soil surface characteristics include colour, texture and workability as related to consistence. Another characteristic that farmers used to differentiate soils was the ability of a particular soil to support growth of certain crops. This study underscores the fact that local knowledge can be fully exploited in resourceassessment studies. Keywords: Indigenous knowledge, local soil classification, local soil nomenclature. Indilinga Vol. 6 (1) 2007 pp. 64-7

Effects of Phosphate Rock on Phosphorus Availability for Vegetable Crops in Cropping Sequence

This study was conducted to investigate the effects of cropping sequence and Minjingu Phosphate Rock (MPR) on soil phosphorus (P) availability and yield of selected vegetable crops. The study involved a researcher managed on farm field experiment conducted in Mbeya, Tanzania using a split plot design with three replications. Crop sequence (i) Cabbage - tomato - maize (ii) Maize - tomato -cabbage (iii) Cabbage - cabbage - maize (iv) Maize - tomato – maize, constituted the main plots. The P sources (i) control (no fertilizer), (ii) MPR, (iii) compost + MPR, (iv) crotalaria green manure + MPR (v) NPK (standard), were sub plots. The experiment was repeated three times on the same plots. In the fourth season, bean was planted in all plots without fertilizer to capture residual nutrients. Results indicated more percent increase in soil available P in plots where cabbage was included in the sequence (207.9%) as compared to when it was ommited (85.39%). Compost + MPR treatment significantly increased soil pH from 5.8 to 6.33 while in NPK treated plots it decreased to 5.49. After three seasons there was higher residual P in MPR treated plots (33.33 mg/kg) as compared with NPK (27.65mg/kg). Plots treated with NPK produced the highest maize yield while plots treated with MPR alone or combined with compost or crotalaria produced significantly (P ≤ .01) higher cabbage and tomato yield especially during the first and second seasons. Bean pod yield was higher in MPR treated plots. Therefore, the use of PR and including cabbage in crop rotations should be encouraged in organic vegetable farming systems to restore P on phosphorus deficient soils

Discriminant analysis in small and large dimensions

We study the distributional properties of the linear discriminant function under the assumption of normality by comparing two groups with the same covariance matrix but different mean vectors. A stochastic representation for the discriminant function coefficients is derived, which is then used to obtain their asymptotic distribution under the high-dimensional asymptotic regime. We investigate the performance of the classification analysis based on the discriminant function in both small and large dimensions. A stochastic representation is established, which allows one to compute the error rate in an efficient way. We further compare the calculated error rate with the optimal one obtained under the assumption that the covariance matrix and the two mean vectors are known. Finally, we present an analytical expression of the error rate calculated in the high-dimensional asymptotic regime. The finite-sample properties of the derived theoretical results are assessed via an extensive Monte Carlo study.AMS version of the paper (together with DOI) appears approximately a year laterStatistic

Effectiveness of Phosphate Rock Application Methods and Frequencies on Soil Available P and Uptake by the Leafy Vegetable Amaranth

Low solubility of phosphate rock (PR) limits its direct application to leafy vegetables. However the low solubility and slow P releasing characteristics contribute to higher residual effect than water soluble P fertilizers. A pot experiment was conducted over three crop cycles at the Agricultural Research Institute Uyole (ARI Uyole) in Tanzania to determine the most appropriate PR application method and frequency for amaranth, a nutritious leafy vegetable. The experiment was laid out in a split plot design with three replications. Frequency of Minjingu phosphate rock (MPR) application constituted the main plots while the application methods were the sub plots. The methods were (i) control (no fertilizer material added), (ii) direct application of MPR, (iii) compost + MPR, (iv) crotalaria green manure + MPR, and (v) NPK (Nitrogen –Phosphorus-Potassium fertilizer) as standard. Frequencies were (i) once in the first crop cycle, (ii) during the first and third crop cycle, and (iii) during each crop cycle. Compost + MPR gave significantly higher fresh weight and dry matter amaranth yield than did other treatments. During the third crop cycle there was significant (P ≤ 0.01) interaction between frequency and method of MPR application on P uptake, plant P content, fresh weight and dry matter yield. There was positive and highly significant (P ≤ 0.01) correlation between soil available P, P uptake, concentration and amaranth yield. The results indicate that application of MPR once during three crop cycles especially when combined with manure could supply adequate levels of phosphorus thus replace the use of soluble P fertilizers in production of short season leafy vegetables such as amaranth. &nbsp

Patterns of Dekadal Rainfall Variation Over a Selected Region in Lake Victoria Basin, Uganda

Understanding variations in rainfall in tropical regions is important due to its impacts on water resources, health and agriculture. This study assessed the dekadal rainfall patterns and rain days to determine intra-seasonal rainfall variability during the March–May season using the Mann–Kendall ( M K ) trend test and simple linear regression ( S L R ) over the period 2000–2015. Results showed an increasing trend of both dekadal rainfall amount and rain days (third and seventh dekads). The light rain days ( S L R = 0.181; M K = 0.350) and wet days ( S L R = 0.092; M K = 0.118) also depict an increasing trend. The rate of increase of light rain days and wet days during the third dekad (light rain days: S L R = 0.020; M K = 0.279 and wet days: S L R = 0.146; M K = 0.376) was slightly greater than during the seventh dekad (light rain days: S L R = 0.014; M K = 0.018 and wet days: S L R = 0.061; M K = 0.315) dekad. Seventy-four percent accounted for 2–4 consecutive dry days, but no significant trend was detected. The extreme rainfall was increasing over the third ( M K = 0.363) and seventh ( M K = 0.429) dekads. The rainfall amount and rain days were highly correlated (r: 0.43–0.72)