and the high spatial variability of N 2 O flux across the field are shown to be linked to the distribution of waste from grazing animals and the resultant reactive nitrogen compounds in the soil which are made available for microbiological processes. Features within the field such as shaded areas and manure heaps contained significantly higher available nitrogen than the rest of the field. Although these features only represented 1.1 % of the area of the field, they contributed to over 55 % of the total estimated daily N 2 O flux.

Background Improvement of tuber yield and tolerance to viruses are priority objectives in white Guinea yam breeding programs. However, phenotypic selection for these traits is quite challenging due to phenotypic plasticity and cumbersome screening of phenotypic-induced variations. This study assessed quantitative trait nucleotides (QTNs) and the underlying candidate genes related to tuber yield per plant (TYP) and yam mosaic virus (YMV) tolerance in a panel of 406 white Guinea yam (Dioscorea rotundata) breeding lines using a genome-wide association study (GWAS). Results Population structure analysis using 5,581 SNPs differentiated the 406 genotypes into seven distinct sub-groups based delta K. Marker-trait association (MTA) analysis using the multi-locus linear model (mrMLM) identified seventeen QTN regions significant for TYP and five for YMV with various effects. The seveteen QTNs were detected on nine chromosomes, while the five QTNs were identified on five chromosomes. We identified variants responsible for predicting higher yield and low virus severity scores in the breeding panel through the marker-effect prediction. Gene annotation for the significant SNP loci identified several essential putative genes associated with the growth and development of tuber yield and those that code for tolerance to mosaic virus. Conclusion Application of different multi-locus models of GWAS identified 22 QTNs. Our results provide valuable insight for marker validation and deployment for tuber yield and mosaic virus tolerance in white yam breeding. The information on SNP variants and genes from the present study would fast-track the application of genomics-informed selection decisions in breeding white Guinea yam for rapid introgression of the targeted traits through markers validation.

Dearth of information on extent of genetic variability in cassava limits the genetic improvement of cassava genotypes in Sierra Leone. The aim of this study was to assess the genetic diversity and relationships within 102 cassava genotypes using agro-morphological and single nucleotide polymorphism markers. Morphological classification based on qualitative traits categorized the germplasm into five different groups, whereas the quantitative trait set had four groups. The SNP markers classified the germplasm into three main cluster groups. A total of seven principal components (PCs) in the qualitative and four PCs in the quantitative trait sets accounted for 79.03% and 72.30% of the total genetic variation, respectively. Significant and positive correlations were observed between average yield per plant and harvest index (r = 0.76***), number of storage roots per plant and harvest index (r = 0.33*), height at first branching and harvest index (0.26*), number of storage roots per plant and average yield per plant (r = 0.58*), height at first branching and average yield per plant (r = 0.24*), length of leaf lobe and petiole length (r = 0.38*), number of leaf lobe and petiole length (r = 0.31*), width of leaf lobe and length of leaf lobe (r = 0.36*), number of leaf lobe and length of leaf lobe (r = 0.43*), starch content and dry matter content (r = 0.99***), number of leaf lobe and root dry matter (r = 0.30*), number of leaf lobe and starch content (r = 0.28*), and height at first branching and plant height (r = 0.45**). Findings are useful for conservation, management, short term recommendation for release and genetic improvement of the crop.

White Guinea yam is mostly a dioecious outcrossing crop with male and female flowers produced on distinct plants. Fertile parents produce high fruit set in an open pollination polycross block, which is a cost-effective and convenient way of generating variability in yam breeding. However, the pollen parent of progeny from polycross mating is usually unknown. This study aimed to determine paternity in white Guinea yam half-sib progenies from polycross mating design. A total of 394 half-sib progenies from random open pollination involving nine female and three male parents was genotyped with 6602 SNP markers from DArTSeq platform to recover full pedigree. A higher proportion of expected heterozygosity, allelic richness, and evenness were observed in the half-sib progenies. A complete pedigree was established for all progenies from two families (TDr1685 and TDr1688) with 100% accuracy, while in the remaining families, paternity was assigned successfully only for 56 to 98% of the progenies. Our results indicated unequal paternal contribution under natural open pollination in yam, suggesting unequal pollen migrations or gene flow among the crossing parents. A total of 3.8% of progenies lacking paternal identity due to foreign pollen contamination outside the polycross block was observed. This study established the efficient determination of parental reconstruction and allelic contributions in the white Guinea yam half-sib progenies generated from open pollination polycross using SNP markers. Findings are useful for parental reconstruction, accurate dissection of the genetic effects, and selection in white Guinea yam breeding program utilizing polycross mating design.

Abstract. One hundred N2O flux measurements were made from an area of intensively managed grazed grassland in central Scotland using a high resolution dynamic chamber method. The field contained a variety of features from which N2O fluxes were measured including a manure heap, patches of decaying grass silage, and areas of increased sheep activity. Individual fluxes varied significantly across the field varying from 2 to 79 000 μg N2O-N m−2 h−1. Soil samples were collected at 55 locations to investigate relationships between soil properties and N2O flux. Fluxes of N2O correlated strongly with soil NO3− concentrations. Distribution of NO3− and the high spatial variability of N2O flux across the field are shown to be linked to the distribution of waste from grazing animals and the resultant reactive nitrogen compounds in the soil which are made available for microbiological processes. Features within the field such as shaded areas and manure heaps contained significantly higher available nitrogen than the rest of the field. Although these features only represented 1.1% of the area of the field, they contributed to over 55% of the total estimated daily N2O flux.

Choosing superior parents with complementary trait values for hybridization and selecting variants with desired product profiles to release as a new cultivar are important breeding activities to progress genetic improvement in crops. This study assessed the genetic potential of 36 parental lines of white Guinea yam (Dioscorea rotundata) genotypes using multi-trait index-based factor analysis and ideotype design (FAI-BLUP). The experiment utilized 36 white yam genotypes laid out in a 6 × 6 triple lattice design with three replications and phenotyped for 18 agronomic and food quality traits. Findings showed significant differences among genotypes for all assessed traits. Fifteen traits had desired genetic gains, whereas stem diameter (−1.34%), and two starch property traits ((holding strength (−26.31%) and final paste viscosity (−3.33%)) had undesired selection gain. The FAI-BLUP index provided total genetic gains of 148.91% for traits desired for increase and –29.26% for those desired for decrease. Genotypes TDr08-21-2, TDr9518544, TDr9501932, TDr8902665 and Pampars were identified as top best candidate for simultaneous improvement of the measured traits in white yam breeding. The findings indicate the effectiveness of the FAI-BLUP index in identifying and selecting genotypes.

An experiment was conducted to investigate the effect of chicken manure on the growth, yield and profitability of maize at the School of Agriculture Experimental Site, Njala University, during 2014 and 2015 cropping seasons. A total of eight treatment combinations comprising two plant densities (26,666 and 53,333 plants.ha -1 ) and four chicken manure levels (0, 2, 4 and 8 t.ha -1 ) were established in split plot design with three replicates. Results revealed that plant height, stem diameter, leaf area index (LAI) and chlorophyll content of leaves significantly increased with time and increasing chicken manure (CM) rate. Seed yield and yield attributes of populations one and two significantly increased with increasing CM rates. Application of CM at 2.0 t.ha -1 increased yields by more than 100% in the second and third seasons; and in populations one compared to the control. Findings of the economic analysis revealed that the 2.0 t.ha -1 CM point application is the most profitable maize production system for populations 1 and 2 in the upland and IVS ecologies. Results suggest that optimum application and adequate supply of plant nutrient from chicken manure is important for the success of conservation and sustainable farming systems. Findings in this study could be used as guide for improving nutrient use efficiency of CM in crop management rotation systems and commercial production of the crop.

Cassava (Manihotes culenta Crantz) is among major food and income security crops in sub-Saharan Africa. However, high seed dormancy and delayed germination limit seed propagation. Using traditional stem cutting causes loss of superior genotypes and decreases productivity as a result of low multiplication ratio (1:10) and viral and bacterial diseases.Thus, the aim of this study was to optimize and screen efficient in vitro protocols for rapid multiplication and production of disease-free cassava planting materials through nodal culture technique. The experiment was laid out in a 5 x 5 factorial arrangement in Completely Randomized Design with five cassava genotypes (Warima, Munafa, SLICASS 6, Coco cassada and SLICASS 7) and five BAP supplemented MS medium (0, 0.02, 0.1, 1.0 and 2.0 mg/L), replicated three times. Results revealed that, BAP supplement significantly (p<0.001) influenced numbers of leaves and shoots compared to plantlet height growth traits of nodal cassava explants in culture. Virus indexing of infected plants from screen house using species specific primer pairs, OjaRep/EACVMRep and OjaRep/ACMVRep, confirmed the presence of East Africa Cassava Mosaic Virus (EACMV) and the African Cassava Mosaic Virus (ACMV) at an amplicon of approximately 650bp and 400bp, respectively. The study demonstrated the effectiveness of cytokinin supplemented MS medium in enhancing growth of cassava; and the adequacy and effectiveness of the PCR technique in identifying ACMV and EACMV using nodal cuttings. Future studies will involve molecular characterization of the EACMV strain(s) existing in the country.