ICRISAT conserves a large collection of pearl millet [Pennisetum glaucum L. R. (Br.)] comprising of 21,392 accessions. This includes landraces, cultivars, genetic stocks, breeding lines, and wild relatives from 50 countries. However, only a small fraction of this huge collection has been exhaustively used in the pearl millet improvement program. The objective of our research was to develop a core collection of pearl millet to enhance utilization of genetic resources in improvement programs and simplify their management. For this purpose, accessions were initially stratified according to geographical distribution followed by hierarchical clustering on 11 quantitative traits using Ward's method. This resulted in 25 distinct groups. Approximately 10% accessions were then randomly selected from each of these 25 distinct groups to form a core collection of 1,600 accessions. Different statistical methods like comparison of mean using Newman-Keuls test, variance using Levene's test, frequency distributions using Chi-square test, and Wilcoxon's rank-sum non-parametric test for the traits validated that the variation present in entire collection had been preserved in the core collection. The important phenotypic correlations among different traits that may be under the control of co-adapted gene complexes were also preserved in the core collection. The diversity represented in the core collection will therefore, be a guideline to breeders for a wider use of the pearl millet genetic resources available in the genebank.
A minimum core subset of pearl millet [ Pennisetum glaucum (L.) R. Br.], 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 (about 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.
Pearl millet [Pennisetum glaucum (L.) R. Br.] is grown under a wide range of environmental conditions in India. The All India Coordinated Pearl Millet Improvement Project (AICPMIP) has the responsibility of testing and releasing pearl millet cultivars adapted to such conditions. As a part of this process, AICPMIP has divided the entire pearl millet growing regions into three different zones (A1, A, and B) based on the rainfall pattern and local adaptation of the crop. This study was conducted to define the presently used test locations into possible mega‐environments and to identify essential test locations for cost‐effective evaluation of pearl millet cultivars. Grain yield data of different sets of 34 to 45 medium‐maturity pearl millet hybrids tested at 29 to 34 locations during 2006 to 2008 were analyzed using genotype main effects and genotype × environment interaction biplot method. Two distinct pearl millet mega‐environments with consistent grouping of locations across the years and corresponding to AICPMIP's designated A and B zones were identified. No such consistent grouping of locations corresponding to AICPMIP's designated A1 zone was, however, observed. Based on the discriminating ability, uniqueness, and research resources, 13 locations were identified as essential test locations for evaluation across the two mega‐environments. Testing at these locations appeared to provide good coverage of the whole pearl millet growing areas of India. Based on these findings, it is suggested to conduct initial yield trials at identified 13 locations across all the pearl millet growing zones represented by two mega‐environments followed by testing of selected hybrids with specific adaptation in their respective adaptation zones.
Pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids, grown widely in India and to some extent in the US, are all based on an A 1 CMS source, leaving the pearl millet hybrids vulnerable to potential disease or insect pest epidemics. A comparison of this CMS system with two additional CMS systems (A 4 and A 5 ) in the present study based on isonuclear A-lines (seed parents) and their isonuclear hybrids showed that A-lines with the A 4 cytoplasm had much fewer pollen shedders and much reduced selfed seed set in visually assessed non-shedding plants as compared to those with the A 1 cytoplasm. A-lines with the A 5 cytoplasm had neither any pollen shedders nor did they set any seed when selfed. This showed that the A 5 CMS system imparts complete and most stable male sterility, followed by the A 4 and A 1 CMS systems. The frequency of maintainers, averaged across a diverse range of 26 populations, was highest for the A 5 CMS system (98%), followed by the A 4 (59%) and the A 1 (34%) system indicating the greatest prospects for genetic diversiWcation of A-lines lies with the A 5 cytoplasm, and the least with the A 1 cytoplasm. Mean grain yield of hybrids with the A 1 cytoplasm was 5% more than the A 4 -system hybrids, while there was no diVerence between the mean grain yield of hybrids based on A 1 and A 5 CMS systems. Based on these results, it is suggested that seed parents breeding eYciency will be the greatest with the A 5 CMS system, followed by the A 4 CMS system, and least with the currently commercial A 1 CMS system.
Influence of a range of cytoplasms on microsporogenesis and anther development in pearl millet was studied using six isonuclear A-lines having five cytoplasms (A 1 , A 2 , A 3 , A 4 and A v) and the nuclear genome of 81B. 81B was used as a male-fertile control. Microsporogenesis and anther development were normal in 81B. However, pollen mother cell (PMC)/microspore/pollen degeneration in the six A-lines occurred at different stages of anther development. Each cytoplasm had its unique influence on microsporogenesis and anther development as evidenced by different developmental paths followed by them leading to pollen abortion. The cause of pollen abortion differed from line to line, from floret to floret within a spikelet, from anther to anther within a floret, and in some cases even from locule to locule within an anther. Events that led to male sterility included anomalies in tapetum and callose behaviour, persistence of tapetum, endothecium thickness, and other unknown causes. The present study also indicated that anther/pollen development was more irregular in Pb 406A 3. In 81A 4 and 81A 1 > 95% of anther locules followed a definite developmental path to pollen abortion. In the other A-lines many developmental paths were observed within the line and pollen degeneration occurred at various stages. This could be one of the reasons for greater instability of male sterility in the A 2 and A 3 systems and greater stability of male sterility in the A 1 and A 4 systems.
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