Maize (Zea mays L) is the most important food grain in sub-Saharan Africa and is mostly grown by small-scale farmers under rainfed conditions. Aluminum toxicity caused by low pH is one of the abiotic factors limiting maize production among smallholder farmers. Therefore, breeding maize hybrids that are tolerant to aluminum toxicity will sustain and increase maize production in these areas. Hence this study was undertaken to assess the genotypic variation for aluminum toxicity in maize inbred lines. Fourteen maize inbred lines of historical importance that are used in maize hybrid breeding in Zambia were studied for seedling root variation under different aluminum concentrations using hydroponic conditions. The aluminum tolerance membership index based on three traits (actual root length, relative root length and root length response) classified genotypes L3233 and L1214 as highly tolerant, L5527 and ZM421 as tolerant, and L12, L3234, and ZM521 as intermediate. The high PCV, GCV, and heritability observed for the root traits indicate that opportunities for selection and breeding for aluminum tolerance among Zambian inbred lines exist. Furthermore, the study indicated that a higher genetic gain would be expected from net root growth followed by shoot length response as selection traits, thus supporting the use of root traits for aluminum tolerance screening. OPEN ACCESSAgronomy 2015, 5 201

Aluminum toxicity in acidic soils is a major constraint to common bean (Phaseolus vulgaris L.) production. The objective of this study was to identify quantitative trait loci (QTL) for Al resistance in a population of 150 F 4:8 recombinant inbred lines (RILs) derived from parents Solwezi and AO-1012-29-3-3A, which contrasted in resistance to Al. The RILs and their parents were evaluated for Al resistance in a hydroponic system that had two nutrient solutions with either 0 μM (control solution) or 15 μM Al concentration (Al stress solution). Primary traits including root length (RL), root dry weight (RDW), and shoot dry weight (SDW) were measured. Percentage reductions in RL, RDW, and SDW were calculated from their respective primary traits. The RILs were genotyped with 5,398 single nucleotide polymorphisms and QTL identified using composite interval mapping. A total of eight QTL for Al resistance were identified on chromosomes Pv02, Pv04, Pv06, Pv07, Pv09, and Pv10. Variation in Al resistance explained by individual QTL ranged from 7.6 to 14.7%. Aluminum resistance QTL RL10.1 on Pv10 explained 10% of the genetic variation in RL. The QTL RL10.1 overlapped with QTL RDW10.1 identified for RDW in Al stress solution. Another Al resistance QTL RL6.1, which explained 10% of Al resistance variation, was identified on Pv06. The QTL on Pv02 and Pv07 appear to overlap with previously reported QTL for Al resistance. A candidate gene Phvul.007G025900 encoding an Al-activated malate transporter was identified within the QTL RL7.1 The genetic architecture of Al resistance in the Solwezi and AO-1012-29-3-3A population is polygenic with additive action.Abbreviations: LOD, logarithm of odds; QTL, quantitative trait locus/loci; RDW, root dry weight; RIL, recombinant inbred line; RL, root length; SDW, shoot dry weight; SNP, single nucleotide polymorphism.

The objective of this study was to evaluate the performances of three cassava genotypes on yield, physiology and morphological traits under different fertilization regimes. A field experiment was conducted in a split-plot design for two consecutive seasons in the Mansa district of the Luapula Province of Northern Zambia in the highly weathered Chromi-haplic Acrisol soils. Four fertilization regimes, control-M3, lime-M1, NPK fertilizer-M4 and NPK fertilizer + lime-M2 were the main plots, while three varieties (Mweru-V1, Bangweulu-V2 and Katobamputa (local)-V3) were subplots. Periodic measurements of leaf area index, light interception, yield and yield components from 75 days after planting (DAP) up to 410 DAP and daily weather measurements of data were recorded. Fertilization significantly increased the radiation use efficiency (RUE) and light extinction coefficient (K) in two seasons compared to the control. Significant fertilization regimes and varietal effects were observed for seasonal LAI, stem yield, root yield, biomass, harvest index (HI), tuber number, root diameter, plant height and SPAD (chlorophyll index). A significant year’s effects on root yield, yield components and physiological performances were observed while significant fertilization × variety interaction was observed on seasonal LAI, tuber number, root diameter, plant height and SPAD. Significant fertilization × year interaction effects were observed on root yield, yield components and physiological performances. Variety × year interaction was significant for seasonal LAI, stem yield, harvest index and plant height and no three-way interactions were observed on all the traits. NPK fertilizer + lime and NPK fertilizer treatments may be adopted to increase the response of cassava varietal yield, physiology and morphological traits in low soil nutrient conditions under high rain-fed conditions.

Nitrogen is a major plant nutrient which is most limiting in the soil due to soil losses of mineral nitrogen (N) form. To ensure availability of nitrogen in the soil, the study was conducted to screen four cowpea genotypes for Biological Nitrogen Fixation (BNF) and their contribution to maize yield in maize- cowpea rotation. The cowpea genotypes used were mutants LT11-3-3-12 (LT) and BB14-16-2-2 (BB) and their parental varieties Lutembwe (LTPRT) and Bubebe (BBPRT) respectively. Trials were established at two sites (Chisamba and Batoka) of different soil types. The Randomized Complete Block Design (RCBD) with three replications was used. Labelled 15N urea was applied at 20kgNha-1 on the four cowpea genotypes during 2015/16 growing season. Cowpea plant parts were dried and milled for 15N isotopic analysis. The data collected included Nitrogen content and atom % 15N excess in the fixing cowpea genotypes and non-nitrogen fixing pearl millet to determine total nitrogen derived from the atmosphere (TNdfa) and total nitrogen (TN) in plant parts which were further used to compute Biological Nitrogen Fixation (BNF). The results showed that BNF by cowpea genotypes at Chisamba was 63.9 kg ha-1 and was significantly (P<0.001) more than BNF of 6.6 kgha-1 at Batoka. The LT mutant fixed significantly (P<0.001) higher nitrogen of 86.1 kgha-1 and 16.5kg ha-1 at Chisamba and Batoka respectively than other genotypes. However, both BB and LT mutants significantly fixed more nitrogen than their parents and have demonstrated to increase maize grain yields up-to 12 tha-1 in the maize – cowpea rotation.

in rotation with maize and soybeans rnZambia. Can. J. Soil Wheat (Triticum aestivum L.) was grown in rotation with maize (Zea mays L.) and soybeans (Glycine max L) as first crops at the National Irrigation Research Station, Nanga, Zambia. Two nodulating soybean cultivars used in the first season of the rotation were compared for their ability to support symbiotic N, fixation by B,radyrhizobium japonicum using a nonnodulating cultivar as a reference crop and the t)N isotope dilution technique. All first crops received two levels of P (0 or 30 kg P ha-'). The legumes received a blanket application of 20 kg N ha-t, whereas maize received two rates ofN (20 and 60 kg N ha 1). There were no benefits ofresidual P from the first crops to the succeeding wheat. However, the yields of wheat grown on plots where fixing legumes had been grown the previous season were significantly higher than those where maize had preceded. The superior wheat yield in the soybean-wheat rotation over the maize-wheat rotation was attributed to residual N from biological N, fixation by the preceding legume crop. The .To assess the benefit of including legumes into rotation with wheat, a soybean-wheat rotation was compared to a maize-wheat rotation. Although the main focus of this study was to identifu whether wheat would benefit from biologically fixed N by soybeans grown instead of maize, the P nutrition of these two latter crops also differs. Hence The experiment was arranged in a randomized complete block design with six replications.