Morphological Diversity and Cytological Studies in Some Accessions of Vigna vexillata (L.) A. Richard

Aim: The objectives of this study were to characterize and evaluate intraspecific relationship among twenty-six accessions of Vigna vexillata (L.) and work out interrelationship among the morphological traits which could be used for genetic improvement of cowpea, V. unguiculata (L.) Walp. Study Design: Field experiment was laid out in blocks of five buckets per accession in a row giving a total of 260 plants. Place and Duration of Study: At the experimental field of the Department of Biological Sciences, Covenant University, Ota, Ogun state, Nigeria, during the dry planting season (September – December, 2012). Methodology: A total of 26 traits comprising 18 quantitative and 8 qualitative traits of the vegetative, floral, pod and seed were evaluated using descriptive statistics, Pearson Correlation Coefficient (PCC), Principal Component Analysis (PCA) and Cluster Analysis (CA). Mitotic chromosome counts and meiotic behaviour were studied using root tip cells and pollen mother cells from young flower buds. Results: The analysis of variance showed that all quantitative morphological characters were significantly different among the accessions (P = 0.01) except stipule length and width. There were significant correlations among characters such as calyx lobe length, standard petal length and width, peduncle length, days to 50% flowering, days to 50% pod maturity, pod length and width, number of locules per pod, number of seeds per pod, and 100-seed weight which could be used for breeding and conservation purposes. The first six principal components accounted for 89.84% of the total variance. The cluster analysis segregated the 26 accessions into three main clusters; cluster I (15 accessions), cluster II (10 accessions) and cluster III (1 accession). Mitotic chromosome counts of 2n = 22 were recorded for all the accessions and meiosis was observed to be normal with the formation of eleven bivalents (n = 11). Conclusion: The intraspecific variabilities indicates plasticity in the genomes of the studied accessions, with high correlations among the morphological characters which are common to all accessions, thus justifying their grouping as a species. The morphological and reproductive attributes displayed by accessions TVnu93 and TVnu97 in terms of plant vigour, early flowering and pod maturity, longer pods and relatively high 100-seed weight made them good potential candidates in breeding for host plant resistance in cowpea

Selection for resistance to cassava mosaic disease in African cassava germplasm using single nucleotide polymorphism markers

Cassava mosaic disease (CMD) is one of the main constraints that hamper cassava production. Breeding for varieties that are CMD resistant is a major aim in cassava breeding programmes. However, the use of the conventional approach has its limitations, including a lengthy growth cycle and a low multiplication rate of planting materials. To increase breeding efficiency as well as genetic gain of traits, SNP markers can be used to screen and identify resistant genotypes. The objective of this study was to predict the performance of 145 cassava genotypes from open-pollinated crosses for CMD resistance using molecular markers. Two SNP markers (S12_7926132 and S14_4626854), previously converted into Kompetitive allele-specific PCR (KASP) assays, as well as CMD incidence and severity scores, were used for selection. About 76% of the genotypes were revealed to be resistant to CMD based on phenotypic scores, while over 24% of the total population were found to be susceptible. Significant effects were observed for alleles associated with marker S12_7926132 while the other marker had nonsignificant effects. The predictive accuracy (true positives and true negatives) of the major CMD2 locus on chromosome 12 was 77% in the population used in this study. Our study provides insight into the potential use of marker-assisted selection for CMD resistance in cassava breeding programmes. Significance:• With an aim towards reducing the food insecurity rate in Africa, we report on the use of genetic tools for a fast and efficient release of new cassava varieties to benefit breeders, farmers and consumers, given the food and industrial importance of this staple crop.• This study adds tremendous knowledge to phenotypic and molecular screening for CMD resistance. The outcome will encourage breeders in various cassava breeding programmes to accelerate genetic gains as well as increase breeding accuracy and efficiency for CMD resistance

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

Genome analyses reveal the hybrid origin of the staple crop white Guinea yam (Dioscorea rotundata)

西アフリカの主食作物ギニアヤムの起源を解明 --ギニアヤムはサバンナと熱帯雨林に生育する野生種の雑種起源--. 京都大学プレスリリース. 2020-12-11.White Guinea yam (Dioscorea rotundata) is an important staple tuber crop in West Africa. However, its origin remains unclear. In this study, we resequenced 336 accessions of white Guinea yam and compared them with the sequences of wild Dioscorea species using an improved reference genome sequence of D. rotundata. In contrast to a previous study suggesting that D. rotundata originated from a subgroup of Dioscorea praehensilis, our results suggest a hybrid origin of white Guinea yam from crosses between the wild rainforest species D. praehensilis and the savannah-adapted species Dioscorea abyssinica. We identified a greater genomic contribution from D. abyssinica in the sex chromosome of Guinea yam and extensive introgression around the SWEETIE gene. Our findings point to a complex domestication scenario for Guinea yam and highlight the importance of wild species as gene donors for improving this crop through molecular breeding

List of SNP markers for Genomic prediction

We described the methodology used to select highly informative SNP markers to be used for genomic selection and prediction for yam </p

Hapmap genotypic data

THIS IS HAPMAP FILE </p

Phenotypic and genotypic data data

Phenotypic and genotypic data</p

Identification of QTLs Controlling Resistance to Anthracnose Disease in Water Yam (Dioscorea alata)

Anthracnose disease caused by a fungus Colletotrichum gloeosporioides is the primary cause of yield loss in water yam (Dioscorea alata), the widely cultivated species of yam. Resistance to yam anthracnose disease (YAD) is a prime target in breeding initiatives to develop durable-resistant cultivars for sustainable management of the disease in water yam cultivation. This study aimed at tagging quantitative trait loci (QTL) for anthracnose disease resistance in a bi-parental mapping population of D. alata. Parent genotypes and their recombinant progenies were genotyped using the Genotyping by Sequencing (GBS) platform and phenotyped in two crop cycles for two years. A high-density genetic linkage map was built with 3184 polymorphic Single Nucleotide Polymorphism (NSP) markers well distributed across the genome, covering 1460.94 cM total length. On average, 163 SNP markers were mapped per chromosome with 0.58 genetic distances between SNPs. Four QTL regions related to yam anthracnose disease resistance were identified on three chromosomes. The proportion of phenotypic variance explained by these QTLs ranged from 29.54 to 39.40%. The QTL regions identified showed genes that code for known plant defense responses such as GDSL-like Lipase/Acylhydrolase, Protein kinase domain, and F-box protein. The results from the present study provide valuable insight into the genetic architecture of anthracnose resistance in water yam. The candidate markers identified herewith form a relevant resource to apply marker-assisted selection as an alternative to a conventional labor-intensive screening for anthracnose resistance in water yam