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Over the past 10 years, resources have been established for the genetic analysis of pearl millet,Pennisetum glaucum(L.) R. Br., an important staple crop of the semi-arid regions of India and Africa. Among these resources are detailed genetic maps containing both homologous and heterologous restriction fragment length polymorphism (RFLP) markers, and simple sequence repeats (SSRs). Genetic maps produced in four different crosses have been integrated to develop a consensus map of 353 RFLP and 65 SSR markers. Some 85% of the markers are clustered and occupy less than a third of the total map length. This phenomenon is independent of the cross. Our data suggest that extreme localization of recombination toward the chromosome ends, resulting in gaps on the genetic map of 30 cM or more in the distal regions, is typical for pearl millet. The unequal distribution of recombination has consequences for the transfer of genes controlling important agronomic traits from donor to elite pearl millet germplasm. The paper also describes the generation of 44 SSR markers from a (CA)n-enriched small-insert genomic library. Previously, pearl millet SSRs had been generated from BAC clones, and the relative merits of both methodologies are discussed. [ABSTRACT FROM AUTHOR]

A mapping population of 104 F3 lines of pearl millet, derived from a cross between two inbred lines H 77/833-2 × PRLT 2/89-33, was evaluated, as testcrosses on a common tester, for traits determining grain and stover yield in seven different field trials, distributed over 3 years and two seasons. The total genetic variation was partitioned into effects due to season (S), genotype (G), genotype × season interaction (G × S), and genotype × environment-within-season interaction [G × E(S)]. QTLs were determined for traits for their G, G × S, and G × E(S) effects, to assess the magnitude and the nature (cross over/non-crossover) of environmental interaction effects on individual QTLs. QTLs for some traits were associated with G effects only, while others were associated with the effects of both G and G × S and/or G, G × S and G × E(S) effects. The major G × S QTLs detected were for flowering time (on LG 4 and LG 6), and mapped to the same intervals as G × S QTLs for several other traits (including stover yield, harvest index, biomass yield and panicle number m–2). All three QTLs detected for grain yield were unaffected by G × S interaction however. All three QTLs for stover yield (mapping on LG 2, LG 4 and LG 6) and one of the three QTLs for grain yield (mapping on LG 4) were also free of QTL × E(S) interactions. The grain yield QTLs that were affected by QTL × E(S) interactions (mapping on LG 2 and LG 6), appeared to be linked to parallel QTL × E(S) interactions of the QTLs for panicle number m–2 on (LG 2) and of QTLs for both panicle number m–2 and harvest index (LG 6). In general, QTL × E(S) interactions were more frequently observed for component traits of grain and stover yield, than for grain or stover yield per se. [ABSTRACT FROM AUTHOR]

Drought stress during the reproductive stage is one of the most important environmental factors reducing the grain yield and yield stability of pearl millet. A QTL mapping approach has been used in this study to understand the genetic and physiological basis of drought tolerance in pearl millet and to provide a more-targeted approach to improving the drought tolerance and yield of this crop in water-limited environments. The aim was to identify specific genomic regions associated with the enhanced tolerance of pearl millet to drought stress during the flowering and grain-filling stages. Testcrosses of a set of mapping-population progenies, derived from a cross of two inbred pollinators that differed in their response to drought, were evaluated in a range of managed terminal drought-stress environments. A number of genomic regions were associated with drought tolerance in terms of both grain yield and its components. For example, a QTL associated with grain yield per se and for the drought tolerance of grain yield mapped on linkage group 2 and explained up to 23% of the phenotypic variation. Some of these QTLs were common across stress environments whereas others were specific to only a particular stress environment. All the QTLs that contributed to increased drought tolerance did so either through better than average maintenance (compared to non-stress environments) of harvest index, or harvest index and biomass productivity. It is concluded that there is considerable potential for marker-assisted backcross transfer of selected QTLs to the elite parent of the mapping population and for their general use in the improvement of pearl millet productivity in water-limited environments. [ABSTRACT FROM AUTHOR]

Marker-assisted selection (MAS) for resistance genes (R-genes), identified using molecular markers and quantitative trait loci (QTL) analysis, is now possible in many crops. MAS can be used to pyramid several R-genes into a single host genotype. However, this may not provide durable genetic resistance because the pathogen is exposed to a full homozygous pyramid during hybrid seed production and to a full heterozygous pyramid in the resultant hybrid. Alternative gene deployment strategies that generate genetic variability were analysed, for hybrid cereal cultivars of pearl millet, maize, sorghum and rice, using maintainer lines (B-lines) with two smaller complementary pyramids. An F1 seed parent, produced on two such B-lines, can be used to produce a three-way hybrid. All target loci are heterozygous for resistance alleles in the F1 seed parent, and the pathogen is exposed in the hybrid to a host population that is heterogeneous and heterozygous for alleles at the resistance loci targeted by MAS. Alternatively, single-cross hybrids can be made on seed parents that are maintained by two B-lines that differ for the complementary resistance gene pyramids. In a cross-pollinated crop, the B-lines are allowed to intermate to produce a synthetic B-line. In an inbreeding crop, the B-lines are equivalent to a two-component multiline variety. In inbreeding crops, because there is no intermating between the B-line components, the resultant synthetic seed parents have a higher frequency of genotypes with resistance alleles (R-alleles) at several resistance loci. However, in both cross-pollinated and inbreeding crops the genotypic structure in the hybrids is almost the same. All alternatives to a single-cross hybrid having a full pyramid produce hybrid cultivars having lower frequencies of resistance alleles. The frequency of genotypes having R-alleles at several loci increases greatly in both seed parent and hybrid when the overall frequency of R-alleles in the maintainer lines increases. This is simply done by adding a maintainer line that has a full pyramid or by the component lines having overlapping pyramids. [ABSTRACT FROM AUTHOR]

Influence of a range of cytoplasms on microsporogenesis and anther development in pearl millet was studied using six isonuclear A-lines having five cytoplasms (A1, A2, A3, A4 and Av) 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 406A3. In 81A4 and 81A1 > 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 A2 and A3 systems and greater stability of male sterility in the A1 and A4 systems. [ABSTRACT FROM AUTHOR]