Effect of combined inoculation ofAzospirillum brasilense and vesicular-arbuscular mycorrhiza on pearl millet (Pennisetum americanum)

Summary Growth and phosphorus uptake of pearl millet (Pennisetum americanum) on an unsterile, phosphorus-deficient soil was improved by the seed inoculation withAzospirillum brasilense or soil inoculation with the vesicular-arbuscular mycorrhizal fungi (Acaulospora,Gigaspora margarita, Glomus fasciculatum). These microorganisms acted synergistically when added simultaneously and the response was significant withAzospirillum brasilense + Gigaspora margarita andAzospirillum brasilense + Glomus fasciculatum combinations over uninoculated control as far as the dry matter content of shoots, root biomass and phosphorus uptake of the millet was concerned.     

Effect of mycorrhizal inoculation and soluble phosphorus fertilizer on growth and phosphorus uptake of pearl millet

Summary Six mycorrhizal fungi were tested as inoculants for pearl millet (Pennisetum americanum Leeke) grown in pots maintained in a greenhouse. VAM fungi varied in their ability to stimulate plant growth and phosphorus uptake. Inoculation withGigaspora margarita, G. calospora andGlomus fasciculatum increased shoot drymatter 1.3 fold over uninoculated control. In another pot trial, inoculation withGigaspora calospora andGlomus fasciculatum resulted in dry matter and phosphorus uptake equivalent to that produced by adding phosphorus at 8 kg/ha.The influence of inoculatingGigaspora calospora on pearl millet at different levels of phosphorus fertilizer (0 to 60 kg P/ha) as triple superphosphate in sterile and unsterile alfisol soil was also studied. In sterile soil, mycorrhizal inoculation increased dry matter and phosphorus uptake at levels less than 20 kg/ha. At higher P levels the mycorrhizal effect was decreased. These studies performed in sterilized soil suggest that inoculation of pearl millet with efficient VAM fungi could be extremely useful in P deficient soils. However, its practical utility depends on screening and isolation of fungal strains which perform efficiently in natural (unsterilized) field conditions.     

An RFLP-based genetic map of pearl millet (Pennisetum glaucum)

Analysis of a sample of diverse pearl millet genotypes with 200 genomic DNA probes revealed this crop species to be extremely polymorphic. Among these genotypes, 85% of probes detected polymorphism using only two restriction enzymes, with an average pair-wise polymorphism between all of the probe-enzyme combinations of 56%. Two crosses were employed to construct an RFLP-based genetic map. In an intervarietal F₂ population, derived from a single F₁ plant, 181 loci were placed on a linkage map. The total length of this map, which comprised seven linkage groups, was 303 cM and the average map distance between loci was about 2 cM, although a few intervals in excess of 10 cM were present at the ends of a few linkage groups. Very few clones, including those which hybridized to more than one copy, detected more than one locus in the pearl millet genome. The analysis was complicated initially because 83 of the 181 loci mapped to a single linkage group. Analysis of a second cross identified a probable translocation breakpoint in the middle of this large linkage group.     

Effects of the d 2 dwarfing gene in pearl millet

Summary Dwarf varieties have had virtually no impact on the production of pearl millet, in contrast to the case of wheat, rice, and sorghum. This research compared tall and dwarf near-isogenic F₁ hybrids to attempt to determine if there were deleterious effects of the d ₂ dwarfing gene that might account for the lack of release/cultivation of dwarf pearl millet cultivars. Dwarf isohybrids on average yielded less than the tails, because of a smaller average seed size combined with a similar grain number per unit area. There was, however, a larger contribution of background genetic variation (pollinator, male-sterile, and interaction effects) to hybrid variation for nearly all characters measured, including seed size, than there was of the dwarfing gene. Selection of dwarf parents capable of producing hybrids with equal seed size and yield to that of tall parents should not be difficult.Journal article no. 1469 of the International Crops Research Institute for the Semi-Arid Tropics, Patancheru, A.P. 502 324, India     

Genetics of desynaptic mutants in pearl millet

Summary Two desynaptic mutants, one of spontaneous origin and the other induced through colchicine treatment, were obtained in pearl millet. The desynpatic character was a monogenically controlled recessive one. Tests for allelism have indicated that the desynaptic genes of the two sources were allelic. Both complete and medium-strong desynaptic plants followed a monogenic pattern of inheritance and were found to be allelic. Medium-strong desynpatic plants on selfing produced both complete and medium-strong desynaptics in approximately equal numbers. It is suggested that the differential expression of the desynaptic character might be due to the presence of modifying genes.     

Fertility and meiotic chromosome behaviour in autotetraploid pearl millet

Summary Tetraploidy was induced in outbred pearl millet and selection for high and low seed set was started in the C₁ generation. Segregation in the C₃ generation was observed for fertility and also for meiotic features: per cent seed set in selfed earhead, chiasma frequency, chromosome association and chromosome distribution in pollen mother cells were all affected. However, variation in seed set was observed even between samples not differing in meiotic features. It is apparent that factors regulating seed set in autotetraploid pearl millet were genic as well as chromosomal.A high frequency of univalents and trivalents was the main cause of sterility; quadrivalent misdisjunction was not a significant factor. As univalency decreased with increased chiasma formation, the gain was in the form of quadrivalents. However, individuals not differing in chiasma frequency did differ in chromosome association frequencies, indicating that the dependence of chromosome pairing behaviour on chiasmata was subject to genotypic influence.     

Transmission of primary trisomics in pearl millet

Summary Transmission rates of extra chromosomes found in the full set of trisomics of pearl millet (Pennisetum americanum) (2n = 14) were estimated by examining the progeny of selfed trisomics and the progeny of trisomics crossed to disomics. When the trisomics were selfed, dark green and tiny had the highest transmission rate (23.8% and 23.3%, respectively) and pseudonormal the lowest (13.8%). Other trisomics had an intermediate rate of transmission. When the trisomics were used as females in crosses with disomics, both dark green and tiny again had the highest transmission rate and pseudonormal the lowest. When the trisomics were used as males in crosses to disomics, no trisomic was transmitted to the progeny except for spindle, and this occurred with a very low frequency (2.0%). A variation in transmission rate was observed from plant to plant and season to season for the same trisomic type. A study of the transmission rate of the extra chromosomes indicated that the following factors were probably contributing to the lower rate of transmission: small- or light-weight seeds tended to have a higher proportion of trisomics than heavier seeds; lighter seeds had a lower percentage germination; a positive and significant correlation was noticed between trivalent frequency and transmission rate. Plants with reduced vigour produced a higher frequency of trisomics. Though trisomics involving longer extra chromosomes showed a high degree of pollen and ovule sterility, they were highly transmissible. This has resulted in a close relationship between gametic sterility and transmission rate of extra chromosome.     

Molecular markers for rust and pyricularia leaf spot disease resistance in pearl millet

 Pearl millet [Pennisetum glaucum (L.) R.Br.] is a warm-season grass used for food, feed, fodder and forage, primarily in countries of Africa and India but grown around the world. The two most-destructive diseases to pearl millet in the United States are rust (caused by Puccinia substriata var. indica) and pyricularia leaf spot (caused by Pyricularia grisea). Genes for disease resistance to both pathogens have been transferred into agronomically acceptable forage and grain cultivars. A study was undertaken to identify molecular markers for three rust loci and one pyricularia resistance locus. Three segregating populations were screened for RAPDs using random decamer primers and for RFLPs using a core set of probes detecting single-copy markers on the pearl millet map. The rust resistance gene Rr ₁ from the pearl millet subspecies P. glaucum ssp. monodii was linked 8.5 cM from the RAPD OP-G8₃₅₀. The linkage of two RFLP markers, Xpsm108 (15.5 cM) and Xpsm174 (17.7 cM), placed the Rr ₁ gene on linkage-group 3 of the pearl millet map. Rust resistance genes from both Tift 89D₂ and ICMP 83506 were placed on linkage-group 4 by determining genetic linkage to the RFLP marker Xpsm716 (4.9 and 0.0 cM, respectively). Resistance in ICMP 83506 was also linked to the RFLP marker Xpsm306 (10.0 cM), while resistance in Tift 89D₂ was linked to RAPD markers OP-K19₃₅₀ (8.8 cM) and OP-O8₃₅₀ (19.6 cM). Fragments from OP-K19 and OP-O8 in the ICMP 83506 population, and Xpsm306 in the Tift 89D₂ population, were monomorphic. Only one RAPD marker (OP-D11₇₀₀, 5.6 cM) was linked to pyricularia leaf spot resistance. Attempts to detect polymorphisms with rice RFLP probes linked to rice blast resistance (Pyricularia oryzae; syn=P. grisea) were unsuccessful. Received: 19 May 1997 / Accepted: 21 October 1997     

Full-sib and reciprocal recurrent selection in relation to pearl millet improvement

Summary During the years 1973 to 1976 two populations of Pearl millet with wide genetic base, namely, Delhi composite (DC) and Vijay composite (VC) were used to compare the response to selection by the full-sib family method from biparental material and reciprocal recurrent selection (RRS). The results indicated that it was possible to advance grain yield with one cycle of RRS by about 23 percent in the case of population DC and 21 percent in population VC, while for the full-sib selection method, the improvement in grain yield was not so rapid. The studies on the nature of gene action indicated that both additive and dominance gene actions were important for grain yield, ear length and ear girth. The coefficient of variation as a result of RRS was reduced in population DC, while it was comparable to base population in the other population. The correlation studies indicated that the magnitude of favourable correlation of different characters with grain yield were higher in case of RRS compared to the full-sib system. The presence of negative correlation of plant height with grain yield in both the improved populations indicated the possibility of breakage of unfavourable gene combinations through RRS and full-sibs developed from biparental mating.     

Repeatability of stability estimators for downy mildew incidence in pearl millet

Summary Repeatability of mean downy mildew (Sclerospora graminicola (Sacc.) Schroet.) incidence, regression coefficients and deviation mean squares were investigated for 25 pearl millet (Pennisetum typhoides (Burm.) Stapf. & Hubb.) genotypes in 20 environments by correlating arrays of these stability parameters over subsets of the 20 environments arranged according to the year-wise, random, stratified and extreme methods of environmental division. Correlation coefficients between arrays of mean downy mildew incidence from different pairs of subsets ranged from 0.57 to 0.98 and those of deviation mean squares from 0.58 to 0.96 indicating good repeatability of these parameters. Arrays of regression coefficients from different subsets, on the other hand, showed correlation coefficients that ranged from –0.58 to 0.96. Apparently, the regression index of stability was not repeatable for the genotypes and environments studied. Therefore, in order to identify a widely adapted genotype, testing is required to be carried out over a wider range of environments.     

New sources of dwarfing genes in pearl millet (Pennisetum americanum)

Summary Thirteen naturally occurring dwarf lines of pearl millet [Pennisetum americanum (L.) Leeke], identified from the world collection, varied for several morphological and agronomic characters. Extreme dwarfs were characterized by a tufted growth habit which could be distinguished from the time of germination, while the other dwarf lines could be distinguished only after anthesis. The F₁ hybrids between the tall and dwarf genotypes were tall, indicating that dwarfness is a recessive trait. In 10 out of the 13 crosses, the F₂ segregation ratio was three tall to one dwarf (31) suggesting that the dwarfness is controlled by a single recessive gene, while the height differences in 3 of the dwarfs (IP 8056, IP 8210 and IP 8214) were controlled by more than one gene as they showed continuous variation for plant height in F₂. When the remaining 10 single gene dwarfs were crossed to either d ₁ (Tift 238) or d ₂ (Tift 23 DB) dwarfs, only 2 crosses produced tall F₂ hybrids and they segregated for height in F₂ indicating that these 2 dwarfs are non-allelic to d ₁ and d ₂. Reciprocal crosses of these 2 dwarfs produced tall F₁ hybrids and showed a dihybrid segregation of 934 in F₂ indicating that the dwarfing genes of these 2 parents are non-allelic to each other. These non-allelic dwarfs were assigned the gene symbols d ₃ (IP 10401), and d ₄ (IP 10402).Submitted as J.A. No. 429 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Selfing rates of pearl millet (Pennisetum typhoides Stapf and Hubb.) under natural conditions

The selfing rate of pearl millet (Pennisetum typhoides Stapf and Hubb.) has been determined under natural conditions. This species is said to be allogamous. Nine test plants homozygous for a particular allele on the alcohol dehydrogenase: ADH A locus (A₁A₁) were sown 2.5 m one from each other interspersed among 300 plants homozygous for the same locus (A₂A₂); these nine plants served as indicators of selfing. In the 20 spikes produced by these a test plants, the selfing rates varied between 2.2% and 21.7%. Selfmg rates were not significantly different within spikes of the same plant, except for one individual. There was no significant correlation between the rate of selfing and the density of the pollen shadow (estimated from the number of spikes producing pollen during the female phase of test plants) or variation in protogyny.     

Genetic variation in grain-filling ability in dwarf pearl millet [Pennisetum glaucum (L.) R. Br.] restorer lines

The d2 dwarfing gene in pearl millet [Pennisetum glaucum (L.) R. Br.] carries a yield penalty due to an associated reduction in individual grain mass. This reduction, however, varies with genetic background, indicating that it may be possible to select against poor grain filling in d2 dwarfbackgrounds, given an effective measure of grain filling. This study was conducted to assess genetic variability forgrain-filling ability (in contrast to simply grain size),and its relationship to grain yield,indwarf pearl milletrestorer (R) lines. The grain-filling ability (GFA) of an individual R line was defined as the least squares estimate of its effect on individual grain mass in the analysis of variance, following a linear covariance adjustment for grain number. The study was based on 93dwarf hybrids involving31 d2 dwarfR-lines, evaluated over 3 years. Half of the variation in individual grain mass in the 93 hybrids was related to variation in grain number. Covariance adjustment in individual grain mass for grain number resulted in highly significant differences among hybrids and R lines in GFA. The R-line combining ability for GFA accounted for 26% of the variation in the R-line combining ability for yield, compared to 46% for the combining ability for grain number, and just 8% for the combining ability of individual grain mass. The combining ability for GFA was independent of the combining ability for various pre-flowering effects, including grain number, but was related to the combining ability for individual grain mass and harvest index. Improvement in individual grain mass achieved through selection for GFA should translate directly into yield improvement, whereasimprovement by direct selectionfor individual grain mass is less-likely to do so. Received: 9 April 2000 / Accepted: 16 May 2000     

Comparative mapping reveals a complex relationship between the pearl millet genome and those of foxtail millet and rice

Comparative genetic maps were constructed of the pearl millet genome with foxtail millet and used to describe the homoeology between the genomes of pearl millet, foxtail millet and rice. Despite the close taxonomic relationship of pearl and foxtail millet, their genomes were highly, rearranged. A comparison of the millet and rice genomes indicated that most of these rearrangements were likely to have taken place in pearl millet. Two duplications were identified in pearl millet. A duplication between the distal segments of linkage groups 1 and 4 corresponds to the ancient duplication previously identified between rice chromosome arms 11S and 12S and foxtail millet chromosomes VII and VIII. The other putative duplication, also between regions of linkage groups 1 and 4, is likely to be species-specific. The exploitation of the comparative maps in pearl millet research is discussed. Received: 10 February 1999 / Accepted: 6 July 1999     

Sclerospora graminicola- and arachidonic acid-induced autofluorescence in downy mildew resistant and susceptible genotypes of pearl millet

Autofluorescence of downy mildew resistant and susceptible cells of pearl millet seedlings undergoing hypersensitive reaction (HR) upon Sclerospora graminicola-inoculation and arachidonic acid (AA)-treatment was studied. Two-day-old seedlings of a highly resistant (IP 18296) and a highly susceptible (23D₂B) genotype of pearl millet were either inoculated with zoospore suspension of S. graminicola or treated with AA for 24 h. The coleoptiles with hypersensitive necrotic spots were processed by the standard procedure, and the tissues were subjected to fluorescence microscopy. A differential accumulation of autofluor-escent compounds in resistant and susceptible pearl millet genotypes was observed with most accumulation occurring in resistant cells treated with AA. The variation in the degree of fluorescence and the spatial accumulation of autofluorescent compounds among the two inoculated/treated genotypes is discussed.     

Combining ability analysis of beta-Carotene,total carotenoids and other grain characteristics in pearl millet

Summary Combining ability studies with respect to grain quality characteristics viz., beta-Carotene, total carotenoids, protein content, 250-grain weight, grain hardness and grain yield were carried out from a 13x13 diallel cross set in pearl millet [Pennisetum typhoides (Burm S&H)].The parents versus hybrids comparison indicated significant heterosis for all the traits under study. In general the hybrids having higher grain yield had bold hard grains with more carotene but low protein content, although a few hybrids combined high yield with an average protein percentage. The relative proportions of the general and specific combining ability variances indicated predominance of non-additive genetic variance with respect to all the traits. The per se performance of parents provided a fairly good indication of their combining ability in most cases. Parents possessing desirable grain quality characteristics were identified. Breeding implications are discussed.Part of the Ph.D. dissertation submitted to the Punjab Agricultural University by the senior author in partial fulfilment of the requirements for the degree     

Quantitative trait loci associated with traits determining grain and stover yield in pearl millet under terminal drought-stress conditions

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. Received: 15 November 2000 / Accepted: 12 April 2001     

Influence of genes determining supernodulation on root colonization by the mycorrhizal fungus Glomus mosseae in Pisum sativum and Medicago truncatula mutants

Pisum sativum (pea) mutants of the wild type cv. Frisson and six supernodulating Medicago truncatula mutants of the wild-type cv. Jemalong line J5 for their ability to form endomycorrhizas. The six mutants of M. truncatula were shown to be allelic mutants of the same gene Mtsym12, whereas distinct genes (sym28 and sym29) are known to determine the supernodulation character of the P64 and P88 pea mutants, respectively. Mutant P88 of pea and the majority of the M. truncatula mutants were significantly more colonized by the mycorrhizal fungus Glomus mosseae than their corresponding wild types, 4 weeks and 30 days after inoculation, respectively. These differences were expressed essentially in transversal intensity rather than in length intensity of root colonization and appeared to correspond to an increase in arbuscule formation. Results are discussed in relation to the mutated genes and, in particular, whether the observed effects are due indirectly to plant physiological modifications or are a direct result of possible common factors of regulation of nodulation and mycorrhizal development. Accepted: 9 February 2000