Yam Breeding Research Articles

Trends in genetic gain for yam in the IITA breeding program

AbstractMonitoring genetic gain is crucial to ensure breeding programs' effectiveness and identify potential challenges and areas for their improvement. Our study provides a first overview of the trends in genetic gain for tuber yield and disease resistance traits in the IITA's (International Institute of Tropical Agriculture) yam breeding program. We used historical data (2010–2022) from multiple generations of past breeding cycles evaluated at 31 sites in the white Guinea yam (Dioscorea rotundata Poir) breeding pipeline and 28 sites in the water yam (Dioscorea alata L.) breeding pipeline of IITA and its national partners in West Africa. Our result shows positive genetic trends in fresh tuber yield while recording a gain of 1.38% or 99.17 kg ha−1 per year in the white Guinea yam and 2.18% or 252.41 kg ha−1 per year in the water yam breeding pipelines. Genetic trends for virus and anthracnose resistance were in the desired direction but negligible in white Guinea yam, while significant for virus and nonsignificant for anthracnose resistance in water yam. Our findings indicate that while the breeding program has succeeded in enhancing tuber yield, post‐harvest tuber dry matter content and disease resistance (yam mosaic virus and anthracnose) did not follow a similar trend in the material being developed. This implies that the yam breeding program needs to strike a balance between various traits, ensuring that increased yield does not come at a cost to food quality or disease resistance. Our results highlight the importance of continually monitoring and assessing the performance of a breeding program and making informed decisions about which traits to focus on for future improvement.

Farming practices, varietal preferences, and land suitability analyses for yam production in Eastern D.R. Congo: implications for breeding initiatives and food sovereignty

Yam (Dioscorea spp.) is a key tuber crop in sub-Saharan Africa (SSA) with huge potential for poverty alleviation, food sovereignty, and nutrition security. Exploiting its full potential requires that factors holding it down are understood and mitigated. This study, conducted between May and July 2022 and 2023, assessed yam farming practices, varietal preferences, and land suitability in the Eastern Democratic Republic of Congo (DRC). We interviewed 765 smallholder farmers within four agro-ecological zones (AEZ) to assess the sociocultural, agronomic, varietal, and biophysical factors affecting yam production. Land suitability analyses were conducted using the Analytic Hierarchy Process (AHP) to identify areas suitable to extensive yam production and to cluster environments that could optimize yam varietal selection and testing. Results showed that yam is mainly cultivated by women in eastern DRC (70%). The seed delivery system is informal, relying primarily on farmer-saved seeds and farmer-seed exchanges (74.9%). Soil depletion (68.3%), limited access to high-quality seeds (54.5%), youth disengagement in yam value chain (50.3%), insect pests (17.9%), and short tuber shelf-life (65.8%) were, respectively, the main ecological, agronomic, sociocultural, biological, and tuber quality factors hindering yam production in eastern DRC. However, the perceived importance of most factors significantly varied with farmer gender and age categories. A multitude of varietal traits was used to assess yam varieties in eastern DRC, of which the tuber taste (59%) was the most valued trait regardless of gender and age categories, though it had highest scores among middle-aged adult women. Land suitability analyses discriminated five clusters; the most significant part of the region falling under suitable (27%), highly suitable (24%), and very highly suitable classes (37%). We further discussed how breeding initiatives for delivering yam varieties, suiting local producers’ and end-users’ needs, could unlock the crop’s potential for enhancing food security and wealth creation in eastern DRC. The land suitability map from this study is a valuable decision-making tool in defining priority areas for extensive yam production and varietal selection and testing. This study provided valuable insights on factors affecting yam production and suggested yam breeding as a backbone of a holistic approach seeking to address challenges faced in unlocking the potential for yam production in eastern DRC.

Identification of diagnostic KASP‐SNP markers for routine breeding activities in yam (Dioscorea spp.)

AbstractMaintaining genetic purity and true‐to‐type clone identification are important action steps in breeding programs. This study aimed to develop a universal set of kompetitive allele‐specific polymerase chain reaction (KASP)‐based single nucleotide polymorphism (SNP) markers for routine breeding activities. Ultra‐low‐density SNP markers were created using an initial set of 173,675 SNPs that were obtained from whole‐genome resequencing of 333 diverse white Guinea yam (Dioscorea rotundata Poir) genotypes. From whole‐genome resequencing data, 99 putative SNP markers were found and successfully converted to high‐throughput KASP genotyping assays. The markers set was validated on 374 genotypes representing six yam species. Out of the 99 markers, 50 were highly polymorphic across the species and could distinguish different yam species and pedigree origins. The selected SNP markers classified the validation population based on the different yam species and identified potential duplicates within yam species. Through penalized analysis, the male parent of progenies involved in polycrosses was successfully predicted and validated. Our research was a trailblazer in validating KASP‐based SNP assays for species identification, parental fingerprinting, and quality control (QC) and quality assurance (QA) in yam breeding programs.

Molecular and phenotypic profiling of white Guinea yam (Dioscorea rotundata) breeding lines

Phenotypic and genotypic profiling helps identify genotypes with suitable and complementary traits for genetic improvement in crops. A total of 32 traits were assessed in 36 genotypes of white Guinea yam established in a 6 × 6 triple lattice design. The objective was to evaluate an array of plant traits that define the genetic merits of breeding lines for yam improvement. Different analytical tools were used to identify and prioritize relevant traits defining the genetic merits of breeding lines in the yam improvement program. Out of the 32 traits measured, the linear combination of 14 traits that minimize within-group variance and maximize between-group variance for discriminating the genetic values of yam breeding lines were identified. When best linear unbiased prediction with genomic relationship matrix (GBLUP) was used, the accuracies of genomic breeding values were higher (r=0.87 to 0.97) for the seven traits (dry matter content, intensity of flesh oxidization of shredded tuber, pasting temperature, pasting time, tuber flesh colour, yam mosaic virus and fresh tuber yield) with high broad-sense heritability values (H2m>0.6). While, for the remaining seven traits with low (H2m<0.3) to medium (H2m=0.3 to 0.54) broad-sense heritability values, the accuracies of genomic estimated breeding values (GEBV) were low (r<0.4) to medium (r=0.4-0.8). The genotype–trait (GT) biplot display revealed superior clones with desirable genetic values for the key traits. These results are relevant for parental selection aimed at improving key agronomic traits in white Guinea yam.

Optimization of treatments for the germination and establishment of botanical yam (Dioscorea rotundata) seeds

Botanical yam (Dioscorea rotundata) seeds are currently used by yam breeders to generate and conserve new varieties of yam instead of seed yams (vegetative propagule). Yam seed treatment through scarification is one of the most effective methods of improving seed germination and seedling establishment. This study was carried out under greenhouse condition to determine the best seed treatment for the germination and establishment of botanical yam seeds. The set up involved a soil mixed with carbonized rice husk using five different seed treatments; dry heating (DHS) at 60 0C, mechanical scarification + gibberellic acid (MSS + GA), mechanical scarification (MSS), acid scarification with sulphuric acid (ASS) and soaking in hot water at 80 0C (SOS). The findings showed that the treatment, MSS + GA and MSS only, had significant (P<0.05) positive effect on the seed emergence and seedling establishment compared to the untreated control (COS) and other treatments. ASS caused seed damage resulting to no emergence. The findings showed that carbonized grain waste (rice husk) enhanced soil fertility and seed treatment (MSS + GA) was the best to improve yam seed germination and seedling establishment. These treatments can be efficiently applied to reduce the long gestation periods and increase yield in yam breeding programmes.

Farmers’ perspective toward a demand led yam breeding in Nigeria

This study seeks to increase the efficiency of yam breeding practice using farmers’ insight at the trait and socioeconomic levels. A three-staged multisampling procedure was employed and 792 yam farmers from four geopolitical zones, comprising 10 states and the Federal Capital Territory, Abuja in Nigeria were randomly selected. Farmer’s preference criteria and factors pertinent to improving the efficiency of yam breeding in Nigeria were documented. The data obtained were analyzed using a 5-point Likert scale to identify major traits farmers consider in the yam cultivar selection decision. Kendall’s coefficient of concordance was used to measure the degree of agreement of ranking among the farmers. Factors influencing farmers’ trait preference for yam cultivars were evaluated using a multinomial-ordered logistic regression model. The result revealed that yam varieties with high germination rates, disease-free quality, big tuber sizes, early maturity, and good pounding attributes are held in high esteem. The most critical constraint limiting the production of yam in the study area includes pest and disease attack, climate change, high cost of seed yam, high cost of staking, and weed infestation. Sex, age, access to credit, membership to yam association, total land owned, and years of experience as a yam farmer significantly influence farmers’ ability to select yam cultivars with preferred attributes. A strategic effort needs to be given to these farmers’ desired yam attributes and factored into developing improved yam varieties for increased adoption and enhanced food security in Nigeria.

Food quality profile of pounded yam and implications for yam breeding.

Assessment of the key preferred quality traits in pounded yam, a popularly consumed yam food product in West Africa, is often done through sensory evaluation. Such assessment is time-consuming and results may be biased. Therefore, there is a need to develop objective, high-throughput methods to predict the quality of consumer-preferred traits in pounded yam. This study focused on how key quality traits in pounded yam proposed to yam breeders were determined, measured by biophysical and biochemical methods, in order to shorten the breeding selection cycle through adoption of these methods by breeders. Consumer tests and sensory quantitative descriptive analysis (QDA) validated that preferred priority quality traits in pounded yam were related to textural quality (smooth, stretchable, moldable, slightly sticky and moderately hard) and color (white, cream or light yellow). There were significant correlations between sensory textural quality attributes cohesiveness/moldability, hardness, and adhesiveness/stickiness, with textural quality measurements from instrumental texture profile analysis (TPA). Color measurement parameters (L*, a*, and b*) with chromameter agreed with that of sensory evaluation and can replace the sensory panel approach. The smoothness (R2 = 1.00), stickiness (R2 = 1.00), stretchability (R2 = 1.00), hardness (R2 = 0.99), and moldability (R2 = 0.53) of pounded yam samples can be predicted by the starch, amylose, and protein contents of yam tubers estimated by near-infrared spectroscopy. TPA and Hunter colorimeter can be used as medium-high throughput methods to evaluate the textural quality and color of pounded yam in place of the sensory panelists. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Yield and Post-Harvest Pest Status of Some White Yam (Dioscorea rotundata Poir.) Landraces in Uyo Southeastern Nigeria

Field experiment was conducted at National Cereals Research Institute (NCRI),Uyo out- Station in 2012 and 2013 to evaluated yield and post-harvest pest status of some yam landraces in Nigeria. The experiment was laid out in a randomized complete block design (RCBD), replicated thrice. Treatments were eight white yam landraces; Nwopoko, Obiotorugo, Offala, Hambakwashe, Aloshi, Udeanyi, Pepa and Eteme and one improved yam cultivar TDr 89/02665. Data obtained from yield and pest severity were subjected to analysis of variance. Result showed that Hambakwase produced significant tuber yield of 31.10 and 33.01 t/ha in 2012 and 2013, respectively. Obioturugo produced 28.18 and 28.02 t/ha, respectively. Eteme produced the least tuber yield of 16.23 and 15.33 t/ha. Udanyi had significant higher number of rotten tubers per plot at harvest; 2.41 and 2.08 in both years. At 3 months in storage, Offala had significant dry rot of 1.73 and 2.01, followed by 1.61 and 0.91 dry rot tubers per plot, recorded in Aloshi. Number of wet rot tubers per plot as influenced by white yam landraces at 3 months storage varied significantly different (p<0.05). Udanyi had significant higher number of wet tuber rot; 4.30 and 3.22 in 2012 and 2013. Presence of mealy bug infestation were seen Offala, Aloshi,Udanyi and Eteme in 2012. In 2013, Offala, Udanyi, Eteme and TDr 89/02665 had mealy bug infestation. .Among the yam landraces, scale insects were observed in the following; Obioturugo, Hambakwase and Udanyi in 2012 while in 2013, Obioturugo, Udanyi and Eteme had presence of scale insect in tubers at 3 months storage. This study therefore recommended Hambakwase and Nwopok for high tuber yield, less susceptible to rot, beetle and termite attack. Also, these promising yam landraces showed be incorporated into yam breeding programme in Nigeria.

Analysis of Genetic Diversity and Population Structure in Yam (Dioscorea Species) Germplasm Using Start Codon Targeted (SCoT) Molecular Markers

Yam (Dioscorea spp.) is an important food security crop with economic, nutritional, and medicinal value. It is a source of carbohydrates for millions of people in tropical and sub-tropical regions of Africa, Asia, South America, the Caribbean, and the South Pacific Islands. Determining the appropriate parents for breeding programs is the most important decision that plant breeders must make to maximize genetic variability and produce excellent recombinant varieties. However, adequate genetic diversity and the population structure of yam accessions in Kenya are not available to guide accurate selection of parents for breeding. In the present study, 25 start-codon-targeted (SCoT) molecular markers were used to determine the genetic diversity and population structure among 20 yam accessions grown in Kenya. A total of 294 fragments were amplified, of which 95% were polymorphic with an average of 11.16 polymorphic fragments per primer. The polymorphic information content (PIC) value and primer resolving power (Rp) of 0.58 and 5.91, respectively, revealed high genetic diversity among the accessions. A dendrogram based on the unweighted pair group method of arithmetic means (UPGMA) grouped the 20 yam accessions into two clusters at 0.61 genetic similarity coefficients. Bayesian structure analysis revealed the existence of three subpopulations and some admixed accessions. Analysis of molecular variance (AMOVA) revealed a variance of 60% within the subpopulations and 40% among the subpopulations. The high degree of genetic diversity in the yam accessions successfully exhibited by SCoT molecular markers may serve as a valuable aid to widen the genetic base in yam breeding programs. The selection and hybridization of parental lines from the different clusters and sub-clusters identified could provide a foundation and could be exploited for yam breeding and variety development.

Multi-Trait Selection Index for Superior Agronomic and Tuber Quality Traits in Bush Yam (Dioscorea praehensilis Benth.)

Dioscorea praehensilis Benth. is a semi-wild yam species and a valuable source of resistance trait genes. To access the agronomic and tuber quality performance, eleven quantitative phenotypic traits were used to discriminate and identify promising accessions among 162 accessions of D. praehensilis collected in Ghana. Significant and high genetic variability (p < 0.001) for all eleven quantitative traits was found among the evaluated accessions. Moderate broad-sense heritability (H2) (30–60%) was observed for all the evaluated quantitative traits except the response to YMV and tuber hardness. The accessions were clustered into three groups; each cluster displayed genotypes with good potentiality for the different traits evaluated. Path coefficient analysis revealed positive contributions (p < 0.01) of the number of tubers per plant, tuber length, tuber width, stem internode length, number of internodes, and tuber flesh hardness to the total tuber weight per plant. Through the multi-trait genotype–ideotype distance index (MGIDI), 24 accessions were identified from the 162 evaluated accessions as top-ranking and could be used as progenitors for trait introgression. The results of this study provide insight for future yam breeding and improvement programs in West Africa.

Variability and genetic merits of white Guinea yam landraces in Nigeria.

Landraces represent a significant gene pool of African cultivated white Guinea yam diversity. They could, therefore, serve as a potential donor of important traits such as resilience to stresses as well as food quality attributes that may be useful in modern yam breeding. This study assessed the pattern of genetic variability, quantitative trait loci (QTLs), alleles, and genetic merits of landraces, which could be exploited in breeding for more sustainable yam production in Africa. A total of 86 white Guinea yam landraces representing the popular landraces in Nigeria alongside 16 elite clones were used for this study. The yam landraces were genotyped using 4,819 DArTseq SNP markers and profiled using key productivity and food quality traits. Genetic population structure through admixture and hierarchical clustering methods revealed the presence of three major genetic groups. Genome-wide association scan identified thirteen SNP markers associated with five key traits, suggesting that landraces constitute a source of valuable genes for productivity and food quality traits. Further dissection of their genetic merits in yam breeding using the Genomic Prediction of Cross Performance (GPCP) allowed identifying several landraces with high crossing merit for multiple traits. Thirteen landraces were identified as potential genitors to develop segregating progenies to improve multiple traits simultaneously for desired gains in yam breeding. Results of this study provide valuable insights into the patterns and the merits of local genetic diversity which can be utilized for identifying desirable genes and alleles of interest in yam breeding for Africa.

Morphological Variabilities and Identification of Yam (Dioscorea spp.) Genotypes from Major Growing Regions in Tanzania

Yam (Dioscorea spp.) is a vegetatively propagated crop that belongs to the family Dioscoreaceae. In Tanzania, yam is mainly grown as a source of food and income generation, especially for smallholder farmers. In this study, an assessment of morphological variations among 74 genotypes of Dioscorea spp. collected from six major growing regions was conducted. Yam genotypes were maintained and planted at Tanzania Agricultural Research Institute-Kibaha for characterization. Data from fifty morphological variables were subjected to multivariate analysis using principal component analysis and cluster analysis. The first nine principal components with Eigenvalues > 1 accounted for 86.28% of the total variations. Some traits that contributed to the variabilities include stem length, leaf margin colour, vein colour, absence/presence of wings, wing colour, hairiness, spines on stem base, aerial tubers, and inner skin colour. The dendrogram separated the 74 yam genotypes into two major clusters with six sub-clusters. Based on the results, four yam species were identified from the collected genotypes, and these included D. alata, D. bulbifera, D. cayenensis, and D. dumetorum. The results revealed high morphological variabilities among the yam genotypes. Information obtained in this study is very useful in yam breeding programs in Tanzania.
 Keywords: Cluster analysis, multivariate analysis, phenotypic variabilities, yam in Tanzania

Multiple-Traits Selection in White Guinea Yam (Dioscorea rotundata) Genotypes.

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.

Optimum time for hand pollination in yam (Dioscorea spp.).

Hand pollination success rate is low in yam (Dioscorea spp.), due partly to suboptimal weather conditions. Thus, determining the most suitable time for pollination could improve the pollination success in yam breeding programs. We performed continuous hand pollination within flowering windows of D. rotundata and D. alata for two consecutive years to determine the most appropriate month, week, and hours of the day allowing maximum pollination success. In D. alata crossing block, we observed significant differences among crossing hours for pollination success (p = 0.003); morning hours (8–12 a.m.) being more conducive than afternoons (12–5 p.m.). No significant differences existed between crossing hours in D. rotundata, though the mid-day seemed optimal. For both species, the time interval 11–12 a.m. was more appropriate for crossing while 4–5 p.m. was the poorest. However, in vitro pollen germination tests showed that mid-day pollen collection (12 noon–2 p.m.) had better results than both extremes, though there were strong genotypic effects on outcomes. Pollination success rates differed significantly among months for D. alata (p < 0.001) but not for D. rotundata (p > 0.05). Differences in pollination success existed across weeks within flowering windows of both D. alata (p < 0.001) and D. rotundata (p = 0.004). The seed production efficiency (SPE) had a similar trend as the pollination success rate. No clear pattern existed between the pollination time and the seed setting rate (SSR) or seed viability (SV), though their dynamics varied with weeks and months. This study provided an insight on the dynamics of pollination outcomes under the influence of pollination times and allows detecting months, weeks, and hours of the day when hybridization activities should be focused for better results.

The effect of gender on end-user preferences for yam quality descriptors.

Improving the effectiveness of breeding programs could be achieved by breeding for consumers' preferences. The relationship between gender and consumer preferences for yam was studied using purposeful sampling for key informants, focus group discussions (FGDs), and individual interviews. Data from qualitative interviews were transcribed and quantitative data analyzed using SPSS (version 20). Cramer's V (Phi) and logistic regressions were used to explain the observations. Males prioritized income-generating varieties over females, while females ranked tuber morphological characteristics high. Sex-based preference for yams showed that moldability and sweet taste are preferred by both females and males. Moderately hard boiled yams and shelf stable food products are liked by males, whereas aroma is rated highly by females. Males described yams that have a longer digestion time as "heavy" and preferred such varieties. Watery tubers and tubers not turning brown are important characteristics during processing. The Phi of 0.157 and 0.163 for sex and ethnic groups show moderate to strong associations between choices for descriptors by females, males, and various ethnic groups. These findings imply that gender disaggregation of information on preference for yam quality descriptors should be considered in future yam breeding programs as it may improve adoption rate and enhance food security.

Genetic Analysis of Agronomic and Quality Traits from Multi-Location white Yam Trials using Mixed Model with Genomic Relationship Matrix

Traits that define the suitability of a crop for production and consumption are often assessed and predicted to identify superior genotypes for commercial deployment. This study assessed genetic parameter estimates and prediction for 25 agronomic and quality traits in 49 white yam clones. It employed best linear unbiased prediction (BLUP) in a mixed model analysis using genomic relationship matrix derived from 6337 Diversity Array Technology (DArT) molecular markers, multivariate technique of the principal component and canonical discriminant analysis with BLUP predicted values to select key traits for yam breeding. Findings revealed that additive genetic, non-additive genetic and non-genetic factors contributed substantially to phenotypic variation of the studied yam traits. The non-genetic effects accounted for higher variation than the total genetic effects for majority of the traits except yam mosaic virus (YMV), tuber number per plant, ash content, flour yield, peel loss, and protein content. The narrow sense heritability was generally low (&lt;0.30) for all traits except yam anthracnose (0.31), ash content (0.30) and peel loss (0.89). Trait selection with multivariate analysis identified 15 from the 25 traits with fresh tuber yield, tuber dry matter content (DMC), YMV, root-knot and Scutellonema bradys nematode susceptibility as the most important traits for white yam variety testing. This paper presents the importance of complementing BLUP prediction that accounts for the relationship among the genotypes with multivariate analysis for genetic parameter estimation, prediction and selection in yam breeding trials to accelerate the genetic gains.

English

The persistent low yield and farmers&rsquo; preference of their traditional yam varieties over the improved varieties necessitated this study to verify the adoption status of the released varieties in Nigeria. A total of 48 accessions of white yam (Dioscorea rotundata) were sampled from six states of Ebonyi, Enugu, Benue, Kogi, Nassarawa and Oyo within Nigeria yam-belt and were genotyped for relatedness to four released varieties from the National Root Crops Research Institute (NRCRI), Umudike yam breeding programme, while 14 accessions of water yam (D. alata) were sampled from four states of Benue, Kogi, Nassarawa and Oyo and were also genotyped for relatedness to three released varieties from International Institute for Tropical Agriculture (IITA), Ibadan. A total of 29 alleles were found in 5 sets of primers analyzed for 52 D. rotundata accessions and the number of alleles ranged from 5 (Dald08, SSR 51 and YM 34) to 8 (Dab2E07) with an average of 5.8 per locus. The observed heterozygosity ranged from 0.19 (YM34) to 0.77 (YM30). A total gene diversity of 0.63 according to Nei (1978) genetic distance coefficients was observed among the 52 D. rotundata accessions. Similarly, a total of 37 alleles were observed when 17 D. alata accessions were analysed with the 7 selected sets of primers. An average of 5.29 alleles was observed per locus. The observed heterozygosity varied from 0.47 (Dab2D06) to 0.82 (YM34). A total gene diversity of 0.58 was observed among 17 D. alata accessions according to Nei&rsquo; genetic distance coefficients. Cluster analysis showed that the D. rotundata accessions were classified into 8 clusters. While, 17 accessions of D. alata were classified into 4 clusters. There were relationships between some released varieties and farmers accessions and also among the farmers&rsquo; accessions from different locations, indicating that farmers might have given a preferred local name to the released varieties. &nbsp; Key words: Verification, adoption, status, yam, microsatellites-markers.

English

Yam anthracnose disease (YAD), caused by the fungus Colletotrichum gloeosporioides Penz, is the most damaging fungal disease of Dioscorea alata yam worldwide. Local yam varieties, which sustain C&ocirc;te d&#39;Ivoire&rsquo;s farmers and other end-users livelihoods, are highly susceptible to this pathogen. Thus, there is a need for developing new yam cultivars to sustain yam production in C&ocirc;te d&#39;Ivoire. To achieve such objective, identifying and selecting sources of resistance within the existing germplasm is crucial prior to the establishment of a breeding program. This study, therefore, aimed at determining the field resistance to C. gloeosporioides of 115 D. alata landrace varieties. Field experiments were conducted at the Research Station for Food Crops (SRCV) of the CNRA, Bouak&eacute; City, in Central C&ocirc;te d&#39;Ivoire, for three growing seasons. Results showed that symptoms of the anthracnose disease were more noticeable four months after planting (P3): high disease severity and incidence scores. At this period, &lsquo;Betebete&rsquo; group (DSS = 3.40 and DI = 99.81%) was the most sensitive to anthracnose disease across years. In contrast, &lsquo;Brazo&rsquo; (DSS = 2.24 and DI = 94.81%) and &lsquo;Florido&rsquo; (DSS = 2.59 and DI = 97.23%) groups were the least sensitive. This finding indicates that local yam accessions from C&ocirc;te d&rsquo;Ivoire have different sensitivity levels to anthracnose disease attacks. Therefore, the genetic diversity from this work should be further exploited by yam breeding and genetic improvement programs for developing cultivars, combining resistance to YAD, high yield potential, and superior tuber quality to meet producers and consumers&rsquo; needs. Key words: Anthracnose, C&ocirc;te d&#39;Ivoire, disease resistance, environment, Dioscorea alata, plant breeding.

Cross compatibility in intraspecific and interspecific hybridization in yam (Dioscorea spp.)

Yam (Dioscorea spp.) is a staple crop for millions of people in the tropics and subtropics. Its genetic improvement through breeding is being challenged by pre-zygotic and post-zygotic cross-compatibility barriers within and among species. Studies dissecting hybridization barriers on yam for improving the crossability rates are limited. This study aimed to assess the cross-compatibility, which yielded fruit set, viable seeds and progeny plants in an extensive intraspecific and interspecific crossing combinations in a yam genetic improvement effort to understand the internal and exogenous factors influencing pollination success. Cross-compatability was analyzed at the individual genotype or family level using historical data from crossing blocks and seedling nurseries from 2010 to 2020 at the International Institute of Tropical Agriculture (IITA). The average crossability rate (ACR) was lower in interspecific crossing combinations (6.1%) than intraspecific ones (27.6%). The seed production efficiency (SPE) values were 1.1 and 9.3% for interspecific and intraspecific crosses, respectively. Weather conditions and pollinator's skills are the main contributors to the low success rate in the intraspecific cross combinations in yam breeding. At the same time, genetic distance and heterozygosity played little role. Interspecific cross barriers were both pre-zygotic and post-zygotic, resulting from the evolutionary divergence among the yam species. Dioscorea rotundata had higher interspecific cross-compatibility indices than D. alata. Distant parents produced intraspecific crossbred seeds with higher germination rates compared to closest parents (r = 0.21, p = 0.033). This work provided important insights into interspecific and intraspecific cross-compatibility in yam and suggested actions for improving hybridization practices in yam breeding programs.

Effect of Pot Size and Transplanting Date on Tuber Production Using Micro-Tubers of White Yam

Low multiplication ratio, long growth and development duration contribute to the long conventional breeding cycle of yams. Moreover, little is known about the effect of pot size and transplanting date on the yield of introduced semi-autotrophic hydroponics (SAH) derived micro-tubers of white yam (Dioscrearotundata Poir). This study was carried out to evaluate the effect of pot size and transplanting date on tuber production of introduced SAH micro-tuber derived white yam var TDr9719177 in shed-house conditions. The SAH materials were introduced from the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. The trial involved two factors including two different pot sizes (38.5×28.5cm and 29.5×23.0cm) and two transplanting dates (September, 2020 and October, 2020). The results showed that micro-tubers grown in the big pot (38.5×28.5cm) significantly out yielded those established in the small pot (29.5×23.0cm). Transplanting in September produced heavier fresh tubers per plant (123.4g)and fresh tuber weight per tuber (88.8g) than transplanting in October, which had 17.4g and 14.1g, respectively. The mean difference of fresh tuber weight per plant between the transplanting pots was 68.4%, and between the transplanting dates was 85.9%. The mean difference of weight per tuber between the transplanting pots was 74.2%, and between the transplanting dates was 84.1%. The results suggested the relevance of early transplanting of healthy seedlings from SAH derived micro-tubers that could be exploited for deployment and promotion to seed yam producers for increased yam productivity. It also depicted the relevance of transplanting SAH micro-tubers in big container that promotes higher tuber production that could be exploited for the rapid multiplication of early generation seeds in yam breeding.