Yam (Dioscorea spp.) is a nutritional and medicinal staple tuber crop grown in the tropics and sub-tropics. Among the food yam species, water yam (Dioscorea alata L.) is the most widely distributed and cultivated species worldwide. Tuber dry matter content (DMC) and oxidative browning (OxB) are important quality attributes that determine cultivar acceptability in water yam. This study used a single nucleotide polymorphism (SNP) assay from a diversity arrays technology (DArT) platform for a genome-wide association study (GWAS) of the two quality traits in a panel of 100 water yam clones grown in three environments. The marker–trait association analysis identified significant SNPs associated with tuber DMC on chromosomes 6 and 19 and with OxB on chromosome 5. The significant SNPs cumulatively explained 45.87 and 12.74% of the total phenotypic variation for the tuber DMC and OxB, respectively. Gene annotation for the significant SNP loci identified important genes associated in the process of the proteolytic modification of carbohydrates in the dry matter accumulation pathway as well as fatty acid β-oxidation in peroxisome for enzymatic oxidation. Additional putative genes were also identified in the peak SNP sites for both tuber dry matter and enzymatic oxidation with unknown functions. The results of this study provide valuable insight for further dissection of the genetic architecture of tuber dry matter and enzymatic oxidation in water yam. They also highlight SNP variants and genes useful for genomics-informed selection decisions in the breeding process for improving food quality traits in water yam.

Purple witchweed [Striga hermonthica (Del.) Benth.], here called just striga, parasitizes cereal crops in the savanna zone of sub‐Saharan Africa. The objectives of this study were to investigate the expressions of a tolerant and a susceptible cultivar of maize (Zea mays L.) to striga as affected by timing (0, 2, 4, and 6 wk after maize planting) and rates (60 and 120 kg N ha−1) of N application under striga infestation. The experiment was designed as a split‐split plot with four replications. Timing of N application and N rates significantly affected striga emergence, host‐plant damage scores, agronomic traits, and grain yield. Nitrogen rate x application time interaction was highly significant for striga emergence. Time of N application was more important than N rate in suppressing striga emergence and host‐plant damage. Nitrogen application at 2 wk after planting and 120 kg N ha−1 gave the best result in terms of maize performance and reduction of striga emergence. Host‐plant damage symptoms were more useful in differentiating response of host genotypes to striga than striga emergence values. The tolerant cultivar (hybrid 8322‐13) produced 188% higher grain yield than the susceptible cultivar (hybrid 8338‐1) across all treatments. Grain yield of the tolerant cultivar at 60 kg N ha−1 was 88% higher than that of the susceptible cultivar at 120 kg N ha−1. The tolerant cultivar produced an average 157% more ears at 60 kg N ha−1 and 51% more ears at 120 kg N ha−1 than the susceptible cultivar. Among all the factors studied, the most important component for striga management was genetic tolerance, the ability of a host plant to withstand the parasite.

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An experiment was conducted from 1997 to 2000 on an acid soil in Cameroon to assess the effectiveness of cultivating acid tolerant maize (Zea mays L.) cultivar and the use of organic and inorganic fertilizers as options for the management of soil acidity. The factors investigated were: phosphorus (0 and 60 kg ha )1 ), dolomitic lime (0 and 2 t ha )1 ), organic manure (no manure, 4 t ha )1 poultry manure, and 4 t ha )1 of leaves of Senna spectabilis), and maize cultivars (ATP-SR-Y -an acid soil-tolerant, and Tuxpen˜o sequiaan acid susceptible).On acid soil, maize grain yield of ATP-SR-Y was 61% higher than the grain yield of Tuxpen˜o sequia. Continuous maize cultivation on acid soil further increased soil acidity, which was manifested by a decrease in pH (0.23 unit), exchangeable Ca (31%) and Mg (36%) and by an increase in exchangeable Al (20%). Yearly application of 60 kg ha )1 of P for 3 years increased soil acidity through increases in exchangeable Al (8%) and H (16%) and a decrease in exchangeable Ca (30%), Mg (11%) and pH (0.07 unit). Lime application increased grain yield of the tolerant (82%) and susceptible (208%) cultivars. The grain yield increases were associated with a mean decrease of 43% in exchangeable Al, and 51% in H, a mean increase of 0.27 unit in pH, 5% in CEC, 154% in exchangeable Ca, and 481% in Mg contents of the soil. Poultry manure was more efficient than leaves of Senna producing 38% higher grain yield. This yield was associated with increases in pH, Ca, Mg and P, and a decrease in Al. The highest mean grain yields were obtained with lime added to poultry manure (4.70 t ha )1 ) or leaves of Senna (4.72 t ha )1 ).Grain yield increase was more related to the decrease in exchangeable Al (r=)0.86 to )0.95, P<0.01) and increase in Ca (r=0.78-0.94, P<0.01), than to pH (r=)0.57 (non-significant) to )0.58 (P<0.05)). Exchangeable Al was the main factor determining pH (r=)0.88 to )0.92, P<0.01).The yield advantage of the acid tolerant cultivar was evident even after correcting for soil acidity. Acid soil-tolerant cultivars are capable of bringing unproductive acid soils into cultivation on the short run. The integration of soil amendments together with acid soil-tolerant cultivar offers a sustainable and comprehensive strategy for the management of acid soils in the tropics.

Striga hermonthica causes significant yield loss in maize (Zea mays L.) and other cereals. Limited studies have been conducted to determine the relationship between marker‐based genetic distance among maize inbred lines expressing varying levels of field resistance to S. hermonthica and the reaction patterns of the resulting crosses to S. hermonthica. Forty‐five diallel crosses of 10 parental lines were evaluated with and without S. hermonthica infestation at two locations each in Benin Republic and Nigeria for 3 yr. Canonical discriminant analysis using nine traits separated the crosses into three distinct groups in each country depending on doses of resistance obtained from their parental lines. Hybrids formed from two resistant parents had the highest levels of resistance, while those formed from two susceptible parents exhibited the lowest levels of resistance to S. hermonthica Crosses that involved one resistant line as a parent showed intermediate levels of field resistance to S. hermonthica Assessment of genetic divergence among the 10 parental lines using 18 amplified fragment length polymorphism (AFLP) primer combinations generated a total of 1176 polymorphic AFLP fragments. The genetic distance (GD) estimates among all pairs of parental lines varied from 0.44 to 0.93, with an average of 0.63 ±0.023. The correlation between the AFLP‐based GD estimates of parental lines and the means observed in diallel crosses under S. hermonthica infestation were not significant for grain yield and other traits. Some hybrids formed from inbred lines with GD estimates both below and above 0.50 exhibited good performance under S. hermonthica infestation. The observed broad range of genetic divergence detected with AFLP markers indicates the presence of a significant reservoir of diversity among resistant lines that can be exploited in breeding.