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1.
Two tropical maize composites were subjected to four cycles of reciprocal recurrent selection to develop divergent inbred lines with good combining ability. This study was conducted to examine the extent of genetic diversity, changes in allele composition and genetic structure, of 100 randomly selected S1 lines each from the original (C0) and advanced (C4) selection cycles of TZL COMP3 and TZL COMP4, genotyped using single nucleotide polymorphism (SNP) markers. Results revealed that the proportion of alleles at both low and high frequencies decreased from C0 to C4, whereas those at intermediate frequencies increased at C4 in the two composites. More unique and other alleles were lost at C4 in TZL COMP3 relative to those in TZL COMP4. The changes in different measures of genetic diversity were either small or negligible with selection in the two composites. The proportion of markers departing from Hardy–Weinberg equilibrium (HWE) decreased with selection, whereas the total number of pairs of markers in linkage disequilibrium increased with selection in the two composites. Examination of changes in population structures using a model‐based approach as well as cluster and multivariate analyses found a high degree of concordance in stratifying the 400 S1 lines into four non‐overlapping groups corresponding to the two selection cycles each within the reciprocal composites. The observed molecular‐based divergence between cycles within the same composite and the clear differentiation between the complementary composites highlight the importance of reciprocal recurrent selection for preserving genetic diversity for long‐term selection. This increases the potential of the advanced selection cycles to sustain genetic gain in productivity of hybrids adapted to the savannas in West and Central Africa.  相似文献   
2.
Among the Phytophthora species that cause black pod of cacao, P. megakarya is the most virulent, posing a serious threat to cacao production in Africa. Correct identification of the species causing the black pod and understanding the virulence factors involved are important for developing sustainable disease management strategies. A simple PCR‐based species identification method was developed using the species‐specific sequences in the ITS regions of the rRNA gene. A phylogenetic tree generated for 119 Phytophthora isolates, based on the 60S ribosomal protein L10 gene and rDNA sequence, verified the PCR‐based identification assay and showed high interspecific variation among the species causing black pod. Phytophthora megakarya isolates were uniformly virulent in an assay using susceptible cacao pod husks inoculated with zoospores, while the P. palmivora isolates showed greater divergence in virulence. The virulence of P. megakarya was associated with earlier production of sporangia and an accelerated induction of necrosis. While zoospore germ tubes of both species penetrated pods through stomata, only P. megakarya produced significant numbers of appressoria. A hypersensitive‐like response was observed when attached SCA‐6 pods were inoculated with P. palmivora. SCA‐6 pods became vulnerable to P. palmivora when wounded prior to zoospore inoculation. Phytophthora megakarya was more aggressive than P. palmivora on attached SCA‐6 pods, causing expanding necrotic lesions with or without wounding. Phytophthora megakarya is predominant in the Volta region of Ghana and it remains to be seen whether it can displace P. palmivora from cacao plantations of Ghana as it has in Nigeria and Cameroon.  相似文献   
3.
Field experiments were conducted at the Teaching and Research Farm, Ladoke Akintola University of Technology, Ogbomoso, Nigeria in 2007 and 2008 to determine the effects of phosphorus fertilizer application on performance of intercropped maize and soybean. The experiments, arranged as a split plot in a randomized complete block design, replicated four times. A cropping system with sole maize, sole soybean and maize/soybean intercrop formed the main plot treatments while P rates with 0, 15 and 30 kg P2O5 ha?1 were the subplot treatments. For both years, neither P fertilizer application nor cropping systems had a significant effect on maize grain yield. However, soybean grain yield was significantly higher (92.3% in 2007 and 44.5% in 2008) under sole cropping than under maize/soybean intercropping. On average, N fixed by soybean increased with the increase in P rate (from 51.8% without P to 60.5% with 30 P), but there was no significant difference in N fixed by sole soybean and soybean/maize intercrop. However, the interaction effect on N fixed between cropping systems and P rates was significant (P ≤ 0.05). N, P and K contents in maize grain were significantly higher (>100%) in intercropped maize than in sole maize. The cropping systems had no significant effect on post-harvest soil chemical characteristics. The land equivalent ratio was 1.52 in 2007 and 1.78 in 2008. The result shows that in utilizing legumes for N enrichment, the alleviation of P deficiency can enhance N2-fixation by legumes. Furthermore, P replenishment in a maize/soybean intercrop may improve maize grain quality even though yield is not increased.  相似文献   
4.
The effects of cultivating and incorporating residues of previous tropical kudzu (Pueraria phaseoloides) and soybean (Glycine max) with application of NPK fertilizer on yam performance were evaluated at the teaching and research farm, LAUTECH, Nigeria. There were nine treatments: incorporation of legume residues (5 t DM ha?1), application of recommended fertilizer rate for yam (90–50–75 kg NPK ha?1) in the zone or 50% of recommended rate (45–25–37.5 kg NPK ha?1), alone and in combination with residues and a control without residues or fertilizer in a randomized complete block design. Cultivation of previous legumes reduced soil nematode population (>200%) compared with no legumes. For both years, application of Pueraria residues improved tuber yield by an average of 15.8% compared with control. Fertilizer application enhanced arbuscular mycorrhizal (AM) colonization of yam roots but AM colonization was lower (～50%) in plots where Pueraria residues were incorporated compared with other plots. Combined application of plant residues with fertilizer improved soil organic carbon, total N, exchangeable Ca and Mg compared with application of NPK fertilizer. From these results, it is concluded that half of the recommended NPK rate may be adequate and incorporation of residues with reduced NPK fertilizer application may be a sustainable soil fertility management option for continuous yam production.  相似文献   
5.
This study evaluated physical properties of selected soil series and their implications on the soil compaction and erosion in Abeokuta, southwestern Nigeria. Daily rainfall data (1999–2007) were collected to estimate the rainfall erosivity. Seven soil series (Iwo, Iseyin, Ekiti, Jago, Okemesi, Apomu, and Egbeda) were sampled from 0–15, 15–30, and 30–50 cm depths for particle size distribution, organic carbon, pH, upper plastic limit, and compactibility (Proctor test). Microtopographical changes along and across toposequences of two farmers’ fields cleared mechanically and manually, respectively, were monitored using the erosion pin method. Mean annual erosivity (EI30) was high (7646 MJ mm ha?1 hr?1). Particle size, organic carbon, and pH were similar (p ≥ 0.05), while upper plastic moisture was ≤?2% among different soil series. Soil-moisture density curves indicated a maximum bulk density of 1.77–1.99 g cm?3 for a moisture range of 7.6–14%; while the soils were prone to compaction at low moisture content. Microtopographic changes were found between –2 and 0 cm and –8 and –2 cm on mechanically and manually cleared farmland, respectively. Spatial dependence showed that the soil erosion could be predicted within 5–8 m distance. To avoid erosion and compaction, soil water content should be less than 7.6% before the introduction of mechanical tillage.  相似文献   
6.
Abstract

A pot experiment was conducted to determine most limiting nutrients for maize performance using nutrient omission treatments in three soil types of southwestern Nigeria. There were six treatments; full nutrient [120?kg nitrogen (N)/ha, 40?kg phosphorus (P)/ha, 80?kg potassium (K)/ha, 10?kg molybdenum (Mo)/ha, and 5?kg zinc (Zn)/ha]; full nutrient minus N, P, K, Mo, and Zn including control was replicated thrice. Treatments were arranged as split plot in a complete randomized design. Data were collected on growth parameters, shoot, root dry weights, and NPK uptakes. Data were subjected to analysis of variance and means separated using LSD0.05. Majeroku and Egbeda soils and full nutrient supported better maize growth and NPK uptakes. Shoot weight was higher in Egbeda while root weight was higher in Itagunmodi soil. Phosphorus was the most limiting in Egbeda and Itagunmodi soils, and nitrogen in Majeroku soil. In conclusion, maize growth, nutrient uptake and most limiting nutrient varied with soil types.  相似文献   
7.
Two pot experiments were conducted, one to evaluate the levels of tolerance of fifteen cowpea [Vigna unguiculata (L.) Walp] lines to aluminum (Al) application, and the second to determine the effect of phosphorus (P) addition on the performance of Al‐tolerant lines (IT 91K‐93–10, IT 93K‐2046–1, and IT 90K‐2 77–2) and Al‐sensitive lines (IT 86D‐719, IT 90K‐284–2, and IT 89KD‐349) in an Alfisol with Al amendment. Fourteen of the fifteen lines tested showed decreased root biomass (between 19 to 81% reduction) with Al addition, but this effect was significant for eight of them. Fewer lines showed decreased shoot biomass and grain yield with Al application. Despite little change in nodule number following Al application, there was a significant decrease in nodule weight (between 24 and 53% reduction) for nearly all lines. Phosphorus fertilization increased shoot and root biomass, grain yield, nodule number, and weight, and nitrogen (N) and P content of nearly all lines. Al‐tolerant lines showed higher response in shoot and root biomass and nodulation to P fertilization than Al‐sensitive lines, with the highest response from IT 90K‐277–2. Increase in shoot dry weight as a result of P fertilization was from 64 to 107% for Al‐tolerant lines and from 44 to 48% for the Al‐sensitive lines, and increase in root dry weight was from 46 to 86% for the Al‐tolerant lines and from 7 to 42% for the Al‐sensitive lines. Results of these trials indicated that lines IT 91K‐93–10, IT 93K‐2046–1, and IT 90K‐277–2 have potential for good performance in soil with Al toxicity problems, and that cowpea lines with inherent genetic tolerance to Al will give higher response to P fertilization when grown in soil with Al toxicity problems.  相似文献   
8.
Forty-eight rabbits used to investigate the response of growing rabbits to diets containing differently processed cassava peel meals were divided into four groups balanced for sex and weight. These groups were then assigned at random to the experimental treatments. Four diets were formulated such that the diets contained 200 g/kg of the experimental feedstuffs, sun-dried cassava peel meal (S), ensiled cassava peel meal (E) and retted cassava peel meal (R), and the control did not contain any cassava peels. Hydrogen cyanide (HCN) concentration in the processed cassava peel meal was lower relative to the unprocessed meal. It was, however, lowest in R and highest in E. With the exception of S, fibre fractions were lower in the processed meal compared to the unprocessed meal. The E depressed (p < 0.05) feed and digestible nutrient intakes, weight gain, nutrient digestibility, digestible protein (DP), digestible energy (DE) and DP/DE ratio but increased protein intake to gain and feed to gain ratios compared to other diets. Intake of HCN decreased (p < 0.05) successively in this order: R, S and E. The results indicate that retting and sun-drying are more effective in cassava peel detoxification than ensiling, and dietary HCN concentration and intake of 56 and 4 mg/kg BW, respectively, were not toxic under the conditions of the experiment.  相似文献   
9.
The effect of three smoking durations (60, 90, and 120 min) and two smoking temperatures (60°C and 70°C) on proximate composition and quality of brackish cultured milkfish steaks of 3 cm size was studied. No significant difference was observed in the sensory properties across all the samples, except in the overall acceptability of sample smoked at 60°C for 60 min. There was significant difference in the values obtained for the textures of all the samples. The L*a*b* values showed a significant difference in the raw and smoked samples. The moisture content showed significant difference in all six samples. Naphthalene, fluorine, and anthracene were detected in the raw sample and in all the smoked samples with significant difference, except for naphthalene. The effect of smoking on the sensory properties and the moisture content of a smoked fish sample are dependent on the smoking time and temperature. Polycyclic aromatic hydrocarbon (PAH) concentration in smoked fish can be a factor, based on both water pollution and the smoking procedure. Benzo-a-pyrene and PAH4, which are acceptable indicators of total PAH presence in smoked foods, were not detected in all the smoked samples, thereby indicating the products to be safe for consumption.  相似文献   
10.
Insect glutathione transferases have been implicated in insecticides and herbicides metabolism. In this study, glutathione transferase was purified to apparent homogeneity from cowpea storage bruchid (Callosobruchusmaculatus) by anion exchange chromatography of DEAE-Sephacel and affinity chromatography of glutathione-Sepharose 4B. The purified enzyme is slightly acidic, pI 5.5, with a molecular weight of 48.5 ± 4 kDa and is composed of subunit molecular weight of 25 kDa. It exhibited an optimum pH and temperature of 8.0 and 40 °C, respectively. Kinetic data gathered from substrate specificity using 1-chloro-2,4-dintrobenzene,7-chloro-4-nitrobenzene-2-oxa-1,3-diazole, p-nitrophenyl acetate, ethacrynic acid, 1,2-dichloro-4-nitrobenzene and paranitrophenychloride and inhibition studies (cibacron blue, bromosulphophthalein, hematin, oxidized glutathione and S-hexylglutathione) of the enzyme showed that is of sigma class. The GST poorly conjugates 4-hyroxylnonenal, a product of lipid peroxidation, and cumene hydroperoxide and may not be involved in oxidative stress protection. Steady state kinetics and product inhibition studies were consistent with a random sequential detoxification mechanism. The interaction between the GST and the insecticides, Fenvalerate and Cypermethrin, was investigated by inhibition studies, circular dichroism and competitive inhibition spectroscopy. It demonstrated that enzyme was inhibited at a concentration that induced some minor changes in the secondary and tertiary structures of the enzyme consequently decrease the detoxification ability and enzyme stability but might not unfold it.  相似文献   
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