Effect of crop residues on root growth and phosphorus acquisition of pearl millet in an acid sandy soil in Niger

The effect of long-term (1983–1988) applications of crop residues (millet straw, 2–4 t ha^-1 yr^–1) and/or mineral fertilizer (30 kg N, 13 kg P and 25 kg K ha^-1 yr^-1) on uptake of phosphorus (P) and other nutrients, root growth and mycorrhizal colonization of pearl millet (Pennisetum glaucum L.) was examined for two seasons (1987 and 1988) on an acid sandy soil in Niger. Treatments of the long-term field experiment were: control (–CR–F), mineral fertilizer only (–CR+F), crop residues only (+CR–F), and crop residues plus mineral fertilizer (+CR+F).In both years, total P uptake was similar for +CR–F and –CR+F treatments (1.6–3.5 kg P ha^-1), although available soil P concentration (Bray I P) was considerably lower in +CR–F (3.2 mg P kg^-1 soil) than in –CR+F (7.4) soil. In the treatments with mineral fertilizers (–CR+F; +CR+F), crop residues increased available soil P concentrations (Bray I P) from 7.4 to 8.9 mg kg^-1 soil, while total P uptake increased from 3.6 to 10.6 kg P ha^-1. In 1987 (with 450 mm of rainfall), leaf P concentrations of 30-day-old millet plants were in the deficiency range, but highest in the +CR+F treatment. In 1988 (699 mm), leaf P concentrations were distinctly higher, and again highest in the +CR+F treatment. In the treatments without crop residues (–CR–F; –CR+F), potassium (K) concentrations in the leaves indicated K deficiency, while application of crop residues (+CR–F; +CR+F) substantially raised leaf K concentrations and total K uptake. Leaf concentrations of calcium (Ca) and magnesium (Mg) were hardly affected by the different treatments.In the topsoil (0–30 cm), root length density of millet plants was greater for +CR+F (6.5 cm cm^-3) than for +CR–F (4.5 cm cm^-3) and –CR+F (4.2 cm cm^-3) treatments. Below 30 cm soil depth, root length density of all treatments declined rapidly from about 0.6 cm cm^-3 (30–60 cm soil depth) to 0.2 cm cm^-3 (120–180 cm soil depth). During the period of high uptake rates of P (42–80 DAP), root colonization with vesicular-arbuscular mycorrhizal (VAM) fungi was low in 1987 (15–20%), but distinctly higher in 1988 (55–60%). Higher P uptake of +CR+F plants was related to a greater total root length in 0–30 cm and also to a higher P uptake rate per unit root length (P influx). Beneficial effects of crop residues on P uptake were primarily attributed to higher P mobility in the soil due to decreased concentrations of exchangeable Al, and enhancement of root growth. In contrast, the beneficial effect of crop residues on K uptake was caused by direct K supply with the millet straw.     

Pearl millet transformation system using the positive selectable marker gene phosphomannose isomerase

Fertile transgenic pearl millet plants expressing a phosphomannose isomerase (PMI) transgene under control of the maize ubiquitin constitutive promoter were obtained using the transformation system described here. Proliferating immature zygotic embryos were used as target tissue for bombardment using a particle inflow gun. Different culture and selection strategies were assessed in order to obtain an optimised mannose selection protocol. Stable integration of the manA gene into the genome of pearl millet was confirmed by PCR and Southern blot analysis. Stable integration of the manA transgene into the genome of pearl millet was demonstrated in T₁ and T₂ progeny of two independent transformation events with no more than four to ten copies of the transgene. Similar to results obtained from previous studies with maize and wheat, the manA gene was shown to be a superior selectable marker gene for improving transformation efficiencies when compared to antibiotic or herbicide selectable marker genes.Abbreviations 2,4-D: 2,4-Diclorophenoxyacetic acid - IAA: Indole acetic acid - ICRISAT: International Crops Research Institute for the Semi-Arid Tropics - IZEs Immature zygotic embryos Communicated by H. Lörz     

Effect of fertilizer levels on grain yield,incidence and severity of downy mildew in pearl millet

The effect of various levels of nitrogen (0.0, 30.0, 60.0, 120.0) and phosphorus (0.0, 6.5, 13.0, 36.0) on the incidence and severity of downy mildew of pearl millet and yield of two pearl millet varieties (Zango and GB8375) were studied under field conditions in 2000 and 2001 respectively. Both nitrogen and phosphorus significantly increased incidence and severity of the disease in the two varieties. Grain yield and 1000 grain weight of the varieties also increased with nitrogen and phosphorus levels.     

In vitro morphogenesis of pearl millet [Pennisetum glaucum (L.) R.Br.]: efficient production of multiple shoots and inflorescences from shoot apices

 This report presents a procedure for high-frequency multiple shoot production from cultured shoot apical meristems of pearl millet [Pennisetum glaucum (L.) R. Br.]. Shoot apices from 1-week-old aseptically germinated seedlings were cultured in vitro on MS medium containing various concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and benzyladenine (BA) with biweekly subculture. A low concentration of 2,4-D coupled with four different concentrations of BA induced the production of adventitious shoots from the enlarged shoot apical meristems. Somatic embryogenesis was also observed at higher concentrations of BA. The use of higher levels of 2,4-D resulted in callusing of shoot apical meristems, while the shoot tips produced many leaves and in vitro flowering in 2,4-D-free media containing BA. All four pearl millet genotypes produced similar results. Fertile pearl millet plants were produced from in vitro-produced multiple shoots. Received: 1 April 1999 / Revision received: 8 July 1999 / Accepted: 17 August 1999     

Effect of delayed harvest on contamination of pearl millet grain with mycotoxin-producing fungi and mycotoxins

The response to delayed harvest of fungal and mycotoxin contamination of grain of the pearl millet hybrid HGM 100 was examined in 1992 and 1993. Samples of grain were assayed from seven plantings at locations near Tifton, Georgia, USA. Grain was harvested at 30, 40, and 50 days after anthesis and evaluated for infection byFusarium species andAspergillus flavus, and mycotoxin contamination. Mean isolation frequencies ofF. semitectum (35.6%) andF. chlamydosporum (17.2%) increased linearly with delayed harvest.Fusarium moniliforme andF. equisiti were infrequently isolated (<0.5%) and did not increase in the grain when harvest was delayed. Low mean concentrations of zearalenone (0.17 ppm), nivalenol (0.42 ppm), and deoxynivalenol (0.01 ppm) were detected but were not affected by delayed harvest. Isolation frequencies ofF. chlamydosporum andF. equiseti were correlated (P=0.07) with levels of nivalenol.Aspergillus flavus was not isolated from the grain, and aflatoxin concentrations averaged 1.9 ppb.     

Cytogenetics of pearl millet

Summary The somatic karyotype of pearl millet Pennisetum americanum (L.) Leeke. (2n = 14) has been studied in several cultivars, but few cytological markers have been discovered which could help in the easy identification of the chromosomes. Analysis of pachytene bivalents permits such identification but is feasible only in a few cultivars. Recently, several lines having telocentric chromosomes have been produced and classified but their potentialities as cytogenetic tools have yet to be explored. Some African populations of pearl millet carry B-chromosomes in their karyotype. Cytogenetics of B-chromosomes has been reported in great detail. Bs undergo spontaneous changes to produce deficient- and iso-chromosomes. The main effect of B-chromosomes is on chiasma frequency which is exerted by the relative amounts of chiasma promoting euchromatin and the chiasma depressing heterochromatin in the Bs. Haploid plants occur occasionally and sometimes show a low degree of seed set, offering a possibility of establishing homozygous inbred lines. Cytogenetics of several spontaneous and induced autotetraploids have been reported. In general quadrivalent formation between the seven sets of four homologues was random. Seed set of the autotetraploids could be improved by selection; improved seed fertility was found to be associated with increased chiasma frequency, increased quadrivalent frequency and regular distribution of chromosomes at anaphase I. Genes controlling morphological characters of plant phenotype segregate independent of those controlling fertility and in pearl millet polyploidy per se is not limiting to plant vigour. Primary trisomics represent the best studied among the aneuploids of pearl millet. All the seven primary trisomics have been identified and described. Some were used in assigning genes to specific chromosomes but in general trisomies have poor vigour and fertility, and show low frequency of transmission. Apart from B-chromosomes, cytogenetics of interchanges has been the best studied aspect of pearl millet. The frequency of co-orientation of an interchange complex at metaphase I, which determines the fertility or sterility of the interchange heterozygote, is influenced by the genetic background and thus is theoretically amenable for selection leading to improved fertility of the heterozygote. Interchange tester-stocks have been assembled which can be used to identify the chromosomes involved in any newly obtained interchange. A complex interchange line involving all the chromosomes of the complement has also been produced, but the ring-of-fourteen produces total male and female sterility.Genotypic control of mitosis and meiosis has been reported, with reference to chromosome numerical mosaicism, multiploid sporocytes, desynapsis and chromosome fragmentation, and male sterility. Pearl millet being a largely outbreeding species, forced inbreeding was mainly found to result in loss of morphological vigour and reduction in mean chiasma frequency per PMC. Interspecific hybrids between pearl millet and several related species have been cytologically investigated and homology of the seven chromosomes of pearl millet with seven of the fourteen chromosomes of P. purpureum has been demonstrated. Cytogenetic evidence from haploids, autopolyploids and interspecific hybrids has indications to suggest that the haploid number of x = 7 is derived from x = 5, but the evidence is inconclusive and needs critical evaluation.     

Telo aneuploids in pearl millet

Summary Nomenclature and chromosome constitution for twenty different aneuploids with telocentrics in Pennisetum typhoides are presented.     

Osmotic adjustment to water stress in pearl millet (Pennisetum americanum [L.] Leeke) under field conditions

Abstract. Osmotic adjustment, a mechanism whereby plants maintain positive turgor despite low water potential (ψ), was investigated in pearl millet ( Pennisetum americanum [L.] Leeke) in three types of field experiment at Hyderabad, India:

• (1)

  Osmotic adjustment during the growing season was evaluated by comparing solute potential (ψ_s) of leaves taken at midday from irrigated and droughted plots and allowed to rehydrate in the laboratory. The degree of seasonal adjustment was also estimated by comparing observed values of ψ_s in the field with those expected if ψ_s decreased solely in proportion to water loss. Both types of assessment indicated the maximum seasonal adjustment to be about 0.2 MPa. The cultivars BJ 104 and Serere 39 differed in their capacity to adjust osmotically over the season; Serere 39 was least able to osmoregulate.
• (2)

  Measurements of diurnal variations in ψ and ψ_s in BJ 104 revealed osmotic adjustment during the afternoon hours. At a given value of ψ, turgor (ψ_p) was about 0.1 MPa higher in irrigated, and over 0.2 MPa higher in droughted plants, in the afternoon, than in the morning.
• (3)

  Osmotic adjustment of different leaves within the canopy was investigated. Upper leaves had lower ψ than basal leaves. Differences in ψ were matched by gradients in ψ_s, so that turgor was similar for all leaf layers.

     

Acetylene reduction activity of pearl millet inbred lines grown in soil

Pearl millet inbred lines previously selected for differences in acetylene reduction activity (ARA) in seedling agar tubes were found to support low soil ARA. Lines selected for high ARA gave better performance than lines selected for low ARA. None of the high ARA lines was found to approach the ARA of alfalfa with their average rates over 40 fold lower.     

Correlation and path-coefficient analyses of seed-yield components in pearl millet x elephantgrass hybrids

Correlation and path-coefficient analyses have been successful tools in developing selection criteria. Since increased seed yield is an important goal in our pearl millet x elephantgrass [Pennisetum glaucum (L.) R.Br. x P. purpureum Schum.] hexaploid breeding program, we used correlation and path-coefficient analyses on seed data. This study was conducted to develop appropriate selection criteria by determining the direct and indirect effects of seed-yield components on seed yield plant^-1. Number of tillers plant^-1, panicles tiller^-1, seeds panicle^-1, 100-seed weight, and seed yield plant^-1, were estimated for individual plants in seven families. Phenotypic (r_p) and genetic correlations (r_g) were calculated, and path analyses (phenotypic and genetic) were carried out according to predetermined causal relationships. Phenotypic and genetic correlations differed in several cases due to large environmental variance and covariance. Phenotypically, all components were positively and significantly associated with seed yield plant^-1. Genotypically, only seeds panicle^-1 and 100-seed weight were significantly correlated. These two components were also positively correlated (r _p=0.55, r _g=0.63), so simultaneous improvement for both components would be feasible. Panicles tiller^-1 and seeds panicle^-1 were negatively correlated (r _g=-0.97). In the path analyses, all direct effects of the components on seed yield plant^-1 were positive. Phenotypic indirect effects were not as important as genetic indirect effects. The components seeds panicle^-1 and 100-seed weight influenced seed yield plant^-1 the greatest, both directly and indirectly.Florida Agricultural Experimental Station Journal Series No. R-03339     

Stomatal responses of pearl millet (Pennisetum americanum [L.] Leeke) to leaf water status and environmental factors in the field

Abstract. Factors affecting stomatal conductance (g₁) of pearl millet ( Pennisetum americanum [L.] Leeke), cultivar BJ 104, were examined in the field in India during the dry season.
Diurnal changes in g₁ were evaluated for upper expanded leaves at flowering on two occasions using plants subjected to varying degrees of water stress. Except for the most severely stressed treatment, diurnal changes in g₁ closely matched changes in irradiance ( I ), the promotive effect of which largely overcame opposing influences on g₁ of increasing atmospheric vapour pressure deficit, and decreasing leaf water and turgor potentials (Ψ, Ψ_p).
Two main effects of water stress on g₁ were evident: (i) a decrease in the amplitude of the mid-day peak in g₁, and (ii) a decrease in the time over which high g₁ was maintained, resulting in early (mid-day) closure and hysteresis in the relationship between g₁ and I .
Leaf conductance was greatest for upper leaves and decreased down the canopy. At equivalent depths in the canopy g₁ was higher in flowering than in photoperiodically-retarded plants of the same age. The magnitude of water stress-induced stomatal closure increased down the plant, and was more marked in retarded than in flowering plants.
Within individual stress treatments Ψ of upper leaves decreased linearly as transpiration flux increased. It is concluded that stomatal behaviour of upper leaves of pearl millet at flowering largely operates to maximize assimilation rather than to minimize water loss.     

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.     

Development of transgenic pearl millet (Pennisetum glaucum (L.) R. Br.) plants resistant to downy mildew

Transgenic pearl millet lines expressing pin gene—exhibiting high resistance to downy mildew pathogen, Sclerospora graminicola—were produced using particle-inflow-gun (PIG) method. Shoot-tip-derived embryogenic calli were co-bombarded with plasmids containing pin and bar genes driven by CaMV 35S promoter. Bombarded calli were cultured on MS medium with phosphinothricin as a selection agent. Primary transformants 1T₀, 2T₀, and 3T₀ showed the presence of both bar and pin coding sequences as evidenced by PCR and Southern blot analysis, respectively. T₁ progenies of three primary transformants, when evaluated for downy mildew resistance, segregated into resistant and susceptible phenotypes. T₁ plants resistant to downy mildew invariably exhibited tolerance to Basta suggesting co-segregation of pin and bar genes. Further, the downy mildew resistant 1T₁ plants were found positive for pin gene in Southern and Northern analyses thereby confirming stable integration, expression, and transmission of pin gene. 1T₂ progenies of 1T₀ conformed to dihybrid segregation of 15 resistant:1 susceptible plants.     

Longevity of pearl millet (Pennisetum glaucum) seeds harvested at different stages of maturity

The storage potential of seeds harvested at weekly intervals after controlled pollination was studied in three diverse cytoplasmic male sterile pearl millet (Pennisetum glaucum) lines. In the first experiment in 1989, a comparison of p₅₀ (time for viability to decline to 50% during storage) among seeds of the line DSA 105A harvested 14, 21, 28, 35 and 42 days after pollination (DAP), and then stored at 35°C with 15% moisture content or 40°C with 13% moisture content, showed that those harvested 35 DAP had the greatest longevity. In the second experiment in 1990, a comparison of p₅₀ within the lines 5141A and L 67A harvested 28, 35 and 42 DAP, and then stored at 40°C with 13% moisture content, showed that seeds of both lines harvested 42 DAP had the greatest longevity. In both the seasons, and in all three lines, maximum seed longevity (p₅₀) was attained one week after physiological maturity (defined as the end of the grain filling period), which is therefore the optimum time of harvest to obtain good quality seeds for conservation.     

Effect of A1 cytoplasm on the combining ability for smut severity in pearl millet

Among the various available sources of male-sterile cytoplasm in pearl millet [Pennisetum glaucum (L.) R.Br.], the A₁ source has been exploited the most for the breeding of commercial F₁ hybrids. The effect of this source on the combining ability (CA) for smut severity was studied since it is the CA that determines the performance of hybrids. The effect was estimated by comparing the CA estimates of 5 pairs of lines and 35 pairs of crosses with and without A₁ cytoplasm. The cytoplasm showed either a significantly desirable or at least no adverse effect on the CA of 4 out of the 5 line pairs and 56 out of 70 pairs of comparison of crosses in two environments. The differential effect of cytoplasm in some pairs might be due to its interaction with nuclear genes. These results further substantiated that the A₁ cytoplasm is not linked with increased smut severity in pearl millet hybrids.     

Dynamics of antimonate-precipitated calcium and degeneration in unpollinated pearl millet synergids after maturity

Pearl millet synergids from unpollinated pistils at 1.5–2 and 2.5–3 days postmaturity (dpm) were examined using transmission electron microscopy following antimonate fixation to precipitate loosely-bound calcium (Ca). With increasing age of synergids, the gap above filiform apparatus (FA) and the coalesced vacuoles in midchalazal core extended and merged. The FAs became compressed and precipitates along their common wall were dispersed. The matrix material in numerous small chalazal vacuoles changed from dense to flocculent. Precipitates in vacuoles appeared mainly as clumps without or with a halo in the dense matrix and mostly finely distributed in the flocculent matrix. Eventually, vacuoles became free of both matrix and precipitates. Precipitates bound to nucleus, nucleolus, and micropylar cytoplasm increased initially, but then seemed to decrease, while the nucleus became disorganized and the nucleolus disappeared. Precipitates in the embryo sac wall and nucellar cells also increased initially, but then decreased. At very late stages, egg apparatus and ES lost structural integrity and lacked precipitates. Differences in degeneration and Ca levels of sister synergids were smaller at 1.5–2 dpm than at 2.5–3 dpm. A logical and correlative scheme of degenerative events and Ca distributional changes occurring in pearl millet synergids from maturity to 2.5–3 dpm is presented. The significance of results in pollen tube/sperm cell interactions with synergids and Ca is addressed.On Specific Cooperative Agreement 58-6612-8-002 with the Department of Biochemistry, University of Georgia, Athens, GA 30602, USA     

Influence of weeding regimes and pearl millet genotypes on parasitism of the Oriental armyworm, <Emphasis Type="Italic">Mythimna separata</Emphasis>

We studied the effect of four weeding regimes (weed free, one manual weeding, one manual weeding+atrazine, and a weedy check) on larval density and leaf defoliation in four pear millet genotypes by the larvae of Oriental armyworm, Mythimna separata. Data were also recorded on the extent of larval parasitism under different weeding regimes, and the parasitoids involved. The leaf damage and larval densities were lower in weed free plots as compared to the weedy plots. This was also reflected in grain yield, as maximum grain yield was recorded in weed-free plots as compared to the weedy plots. Seven parasitoids (Cotesia ruficrus, Metopius rufus, Sturmiopsis inferens, Palexorista solemnis, P. laxa, Carcelia sp., and the entomopathogenic nematode Neoplectana sp. were recorded from M. separata larvae, of which M. rufus, Carceliasp., and Neoplectanasp. were the most abundant. Parasitism by M. rufus was greater in plots with a weed cover and least in weed-free plots, while parasitsm by Carcelia sp. was lower in plots with one hand weeding than in weedy plots. Numerically, parasitism by Neopletana sp. was low in plots treated with atrazine, and maximum in plots weeded manually. Therefore, the minimum level of weeding, which does not affect the crop adversely should be undertaken to promote the biological control of M. separata in pearl millet.     

Changes in fungi and mycotoxins in pearl millet under controlled storage conditions

Pearl millet is increasingly being grown as a premium-value grain for the recreational wildlife and poultry industries in the southern US. We conducted three experiments to assess grain mold development in storage conditions typically encountered in the region of production. Variables included production year, temperature, relative humidity, atmosphere, and grain moisture content. In the first experiment, grain was stored for 9 weeks at 20 or 25°C and maintained at 86% or 91% relative humidity (r.h.). In the second experiment, grain was stored for 9 weeks at 20 or 25°C in either air (aerobic) or N₂ (anaerobic), and maintained at 100% r.h. In the third experiment, high-moisture grain was stored for 3 weeks at 20 or 25°C and maintained at 100% r.h. Grain was sampled at weekly intervals and plated to determine changes in fungal frequency. Fungi isolated included Fusarium chlamydosporum (19% of grain), Curvularia spp. (14%), F. semitectum (16%), Alternaria spp. (9%), Aspergillus flavus (8%), “Helminthosporium”-type spp. (6%), and F. moniliforme sensu lato (3%). Year of grain production significantly affected isolation frequency of fungi. Isolation frequencies from low-moisture grain were rarely affected by temperature, relative humidity, or atmosphere treatments, but was affected by storage duration for some fungi. Changes in isolation of toxigenic fungi occurred in high-moisture grain. Isolation frequency of F. chlamydosporum increased in grain stored at 86% and 91% r.h. Incidence of A. flavus increased in high-moisture grain treatments, particularly at 25°C. Incidence of deoxynivalenol was not affected by storage treatment. Low concentrations of nivalenol were detected in most grain incubated at 100% r.h. Zearalenone was detected only when grain moisture content was 20–22%. Aflatoxin contamination averaged 174 ng g⁻¹ over all treatments, and increased up to 798 ng g⁻¹ in high-moisture grain at stored at 25°C.     

Downy mildew incidence of pearl millet hybrids with different male-sterility inducing cytoplasms

The use of different sources of cytoplasmic male sterility (CMS) in hybrid seed production of pearl millet [Pennisetum glaucum (L.) R. Br.] is advocated to avoid possible disease epidemics occurring due to cytoplasmic uniformity. The effects of commercially unexploited, but potentially exploitable, sources of CMS, like A₂, A₃ and A₄, on downy mildew [Sclerospora graminicola (Sacc.) Schroet] incidence were studied by using the disease incidence of isonuclear hybrids with male-sterile and fertile cytoplasm. The mean downy mildew incidence of hybrids carrying different male-sterile cytoplasm was similar to that of hybrids retaining the fertile cytoplasm. The cytoplasm accounted for only 0.6% of the total variation and its effect was non-significant; pollinators could explain most of the variation in determining the disease incidence of hybrids. This suggested that these male-sterile cytoplasms are not linked to downy mildew susceptibility and thus can be exploited commercially to broaden the cytoplasmic base of the male-sterile lines and, ultimately, of hybrids.