African yam bean (AYB, Sphenostylis stenocarpa Hochst. ex A. Rich.) Harms is a tuber and seed crop, rich in protein, with the potential to contribute to food security. To date, available information on the diversity of AYB is scarce. This study aims at understanding the genetic diversity of 79 AYB accessions of various origins. Twenty-four morphological and taxonomic features of high descriptive values were used and the diversity within the germplasm was assessed by clustering analysis. The 79 accessions differed significantly, with the similarity distances spanning from 0.0646 to 0.5720 and a mean distance of 0.2820. The accessions were grouped into five clusters of 10-26 members. Of the 24 phenotypic variables analyzed, variegation in testa color was the most discriminatory trait, classifying the accessions in the proportion of 25% with variegated to 75% with non-variegated seeds. The ranking by significance (P B 0.05) of the ordinal variables of discriminating importance were in the order of pattern of testa variegation, basal color of variegated seeds, and testa basal color. The stepwise discriminant and frequency procedures in SAS identified other phenotypic variables with significant discriminatory attributes, such as pigmentation of plant parts, seed cavity ridges, and pod dehiscence. Accessions with desirable agronomic traits, such as longer pod length, high number of seeds/pod, non-shattering characteristics of pods at maturity, lower number of days to flowering, and a higher seed set percentage, were also identified in this study. These discriminatory traits are discussed and proposed for germplasm conservation and use.
Grain legumes contribute significantly to total world food production. Legumes are the primary source of dietary proteins in many developing countries, where protein hunger and malnutrition are widespread. Grain legumes germplasm constitute ~15% of the 7.4 M accessions preserved globally. Nearly, 78% of the CGIAR?s, 0.217 M accessions, have been characterized, compared to 34% of national genebank collections. Interestingly, limited data on grain quality are available as the primary focus has been on morpho-agronomic traits. Clearly, more resources should be targeted on biochemical evaluation to identify nutritionally rich and genetically diverse germplasm. The formation of core and mini core collections has provided crop breeders with a systematic yet manageable entry point into global germplasm resources. These subsets have been reported for most legumes and have proved useful in identifying new sources of variation. They may however not eliminate the need to evaluate entire collections, particularly for very rare traits. Molecular characterization and association mapping will further aid to insights into the structure of legume diversity and facilitate greater use of collections. The use of high resolution elevational climate models has greatly improved our capacity to characterize plant habitats and species? adaptive responses to stresses. Evidence suggests that there has been increased use of wild relatives as well as new resources resulting from mutagenesis to enhance the genetic base of legume cultigens.Peer reviewe
SummaryA modified encapsulation -dehydration cryopreservation protocol based on the replacement of cold acclimation with high-sucrose pretreatment was assessed for the long-term storage of Ribes germplasm. Four steps in the procedure were examined for eight genotypes: (1) pregrowth of shoot tips in sucrose-supplemented solid growth medium for 1 wk; (2) pretreatment of alginate-encapsulated shoot tips in sucrose-supplemented liquid culture medium for 21 h; (3) evaporative desiccation of encapsulated -dehydrated shoot tips; and (4) exposure to liquid nitrogen (LN). Differential responses were observed for black currant and gooseberry genotypes. Recovery of growing shoots was high (72-100%) at all four steps for the five black currants tested. Evaporative desiccation slightly decreased viability for some black currants and in some cases LN exposure reduced regrowth. In contrast, three gooseberry species had poor recovery from the initial sucrose culture step (32 -67%), indicating sensitivity to osmotic stress, which predisposed these genotypes to poor survival after LN exposure (12-26%). The effectiveness of the modified protocol for conserving a wider range of Ribes genotypes was further ascertained by screening 22 genotypes derived from nine Ribes species. The procedure was successful for 18 of the 22 genotypes in the gene bank in Scotland. Screening genotype responses at the time of storage demonstrated regrowth $60% for 15 genotypes, and only four genotypes had regrowth of 0 -28%. Additional genotypes were also added to the USDA cryopreserved Ribes collection.
Accurate knowledge of intra-specific diversity of underutilized crop species is a prerequisite for their genetic improvement and utilization. The diversity of 77 accessions of African yam bean (AYB, Sphenostylis stenocarpa) was assessed by amplified fragment length polymorphism (AFLP) markers. A total of EcoRI/MseI primer pairs were selected and 227 AFLP bands were generated, of which 59(26%) were found to be polymorphic in the 77 accessions of AYB. The most efficient primer combination for polymorphic detection was E-ACT/M-CAG with a polymorphic efficiency of 85.5%, while the least efficient was E-AGC/M-CAG with a polymorphic efficiency of 80.6%. The Jaccard genetic distance among the accessions of AYB ranged between 0.048 and 0.842 with a mean of 0.444. TSs98 and TSs104B were found to be the most similar accessions with a genetic similarity of 0.952. The neighbour-joining dendrogram grouped the 77 accessions of AYB into four distinct clusters comprising 8, 20, 21 and 28 accessions. The major clustering of the accessions was not related to their geographical origin. Cluster I was found to be the most diverse. The mean fixation index (0.203) and the mean expected heterozygosity (0.284) revealed a broad genetic base of the AYB accessions. The same germplasm set was previously evaluated for several agro-morphological traits. As the collection of additional AYB germplasm continues, the phenotypic profile, the clustering of the accessions and the AFLP primer combinations from this study can be used to augment breeding programmes.
The standard cryopreservation process previously developed for oil palm clones using shiny white, finger-like somatic embryos could be applied in some cases to standard cultures. Its efficiency was markedly improved by completing the 7-day pregrowth period on 0.75 M sucrose by an additional dehydration period carried out either by placing the embryos in the air current of the laminar flow cabinet or in an air tight box containing silica gel. This improved process was successfully applied to 7 different clones. It will facilitate the routine uof cryopreservation for oil palm cultures.
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