SSR markers reveal diversity in Guinea yam (Dioscorea cayenensis/D. rotundata) core set

The genetic diversity of 219 accessions of Guinea yam germplasm from Benin, Congo, Côte d’ Ivoire, Equatorial Guinea, Gabon, Ghana, Nigeria, Sierra Leone and Togo was accessed using 15 microsatelliteloci. High diversity of 0.677 was found among the accessions. An allelic average of 8.06 and polymorphic information content (PIC) value of 0.65 was observed for the markers. The observed heterozygosity value of 0.563 suggests that spontaneous hybridization must have contributed to the ancestry of some of the accessions and improvement by farmers must have been far more often by selection of somatic mutants. The twenty distinct cluster groups generated by the radial phylogram shows that Dioscorea cayenensis and D. rotundata are distinct species with intermediate hybrid forms. There was no relationship between relatedness of the accessions and their geographical area of origin. This study contributes to an increased understanding of the genetic organisation of the coregermplasm

Assessment of genetic diversity within and between pearl millet landraces

A minimum core subset of pearl millet (Pennisetum glaucum), which comprised 504 landrace accessions, was recently established from the global pearl millet germplasm collection of ICRISAT. The accessions for this core were selected by a random proportional sampling strategy following stratification of the entire landrace collection (~16?000 accessions) according to their geographic origin and morpho-agronomic traits. In this study, RFLP probes were used to quantify the genetic diversity within and between landrace accessions of this minimum core using a subset comprising ten accessions of Indian origin. Twenty-five plants per accession were assayed with EcoRI, EcoRV, HindIII and DraI restriction enzymes, and 16 highly polymorphic RFLP probes, nine associated with a quantitative trait loci (QTLs) for downy mildew resistance, and five associated with a QTL for drought tolerance. A total of 51 alleles were detected using 16 different probe-enzyme combinations. The partitioning of variance components based on the analysis of molecular variance (AMOVA) for diversity analysis revealed high within-accession variability (30.9%), but the variability between accessions was significantly higher (69.1%) than that within the accessions. A dendrogram based on the dissimilarity matrix obtained using Ward's algorithm further delineated the 250 plants into ten major clusters, each comprised of plants from a single accession (with the exception of two single plants). A similar result was found in an earlier study using morpho-agronomic traits and geographic origin. This study demonstrated the utility of RFLP markers in detecting polymorphism and estimating genetic diversity in a highly cross-pollinated species such as pearl millet. When less-tedious marker systems are available, this method could be further extended to assess the genetic diversity between and within the remaining accessions in the pearl millet core subset

New molecular marker technologies for pearl millet improvement

At a time when most of the world still viewed molecular technology as a luxury, for use only with major staple crops, a DFID-JIC-ICRISAT project anticipated as early as 1991 the application of molecular diagnostics in the breeding of orphan crops for developing countries

Development of a Set of Chromosome Segment Substitution Lines in Pearl Millet [Pennisetum glaucum (L.) R. Br.]

The detection of minor quantitative trait loci (QTL) with conventional mapping populations can be complicated by the overshadowing effect of major QTL as well as by interactions between QTL. To overcome these constraints, we developed a set of chromosome segment substitution lines (CSSLs) by introgression of overlapping chromosome segments from 863B into ICMB 841 background for use in QTL detection, fine mapping, and trait mechanism studies, especially for complex traits. Since each CSSL carries one or a few donor segments in the genetic background of the recurrent genotype, the QTL interaction is confined to genes present on small homozygous substituted segments. Advanced generation backcross progenies (1492), expected to provide coverage across the mapped length of each of the seven pearl millet linkage groups (LGs), were genotyped at 74 marker loci [(48 simple sequence repeats (SSRs), 21 single strand conformation polymorphism-single nucleotide polymorphism (SSCP-SNP), and 5 sequence tagged sites (STSs)] identifying 124 segment introgression homozygotes (13 for LG1, 9 for LG2, 10 for LG3, 41 for LG4, 23 for LG5, 11 for LG6, and 17 for LG7). These CSSLs consisted of 1–3 homozygous introgression segments substituted from 863B in the genetic background of the recurrent parent ICMB 841 and among them, 54 represent unique lines with the donor chromosome segment averaging 100.69 cM. These CSSLs developed here provide a nearly ideal set of genetic stocks for mapping and fine mapping the multitude of traits for which their parents differ

Marker-assisted backcrossing to improve terminal drought tolerance in pearl millet

Several alternative marker-assisted backcrossing (MABC) procedures are described that can be used for transferring quantitative trait loci (QTLs) from a donor to an elite recurrent parent when these two lines have been used in forming the base mapping population. We describe ICRISAT’s experience to date in using these methods in pearl millet (Pennisetum glaucum (L.) R. Br.). We are attempting to improve terminal drought tolerance of elite inbred pollinator H 77/833-2 using donor PRLT 2/89-33, and elite inbred seed parent maintainer line ICMB 841 using donor 863B. The advantages and disadvantages of the alternatives are discusse

Teamwork delivers biotechnology products to Indian small-holder crop-livestock producers: Pearl millet hybrid “HHB 67 Improved” enters seed delivery pipeline

HHB 67, released in 1990 by CCS Haryana Agricultural University, is one such single-cross pearl millet hybrid. HHB 67 is highly popular because of its extra-early maturity (it needs less than 65 days from sowing to grain maturity) and is now grown on over 500 000 ha in Haryana and Rajasthan, India. Recent surveys have indicated that this hybrid is starting to succumb to downy mildew (DM; caused by the pseudo-fungus Sclerospora graminicola), showing up to 30% incidence in farmers' fields. By rapidly adopting hybrid "HHB 67 Improved", farmers in Haryana and Rajasthan can avoid grain production losses of Rs36 crores (US$8 million) which would be expected in the first year of a major DM outbreak on the original HHB 67

Foundation characteristics of edible Musa triploids revealed from allelic distribution of SSR markers

Background and Aims The production of triploid banana and plantain (Musa spp.) cultivars with improved characteristics (e.g. greater disease resistance or higher yield), while still preserving the main features of current popular cultivars (e.g. taste and cooking quality), remains a major challenge for Musa breeders. In this regard, breeders require a sound knowledge of the lineage of the current sterile triploid cultivars, to select diploid parents that are able to transmit desirable traits, together with a breeding strategy ensuring final triploidization and sterility. Highly polymorphic single sequence repeats (SSRs) are valuable markers for investigating phylogenetic relationships. Methods Here, the allelic distribution of each of 22 SSR loci across 561 Musa accessions is analysed. Key Results and ConclusionsWe determine the closest diploid progenitors of the triploid 'Cavendish' and 'Gros Michel' subgroups, valuable information for breeding programmes. Nevertheless, in establishing the likely monoclonal origin of the main edible triploid banana subgroups (i.e. 'Cavendish', 'Plantain' and 'Mutika- Lujugira'), we postulated that the huge phenotypic diversity observed within these subgroups did not result from gamete recombination, but rather from epigenetic regulations. This emphasizes the need to investigate the regulatory mechanisms of genome expression on a unique model in the plant kingdom. We also propose experimental standards to compare additional and independent genotyping data for reference. (Résumé d'auteur