Spatial distribution of roots of pearl millet on sandy soils of Niger

Root sampling in crop stands of low planting density requires reliable information on horizontal distribution of roots. This applies particularly to pearl millet in the Sahel, which is sown at a rate of less than two pockets of seed per m². The objective of this study was to investigate the spatial variability of root length density (RLD) among sampling positions in an improved management system with ridging and under traditional sowing. RLD between ridges (bR) was lower compared to sampling positions within ridges (wR) at soil depth layers from 0 to 80 cm soil depth. We found a highly significant, positive correlation between the sum of the root length (RL) of four sampling dates (tillering, booting, flowering, and maturity) with shoot dry mass (SDM) at maturity. The square of the correlation coefficient was highest when calculation of RL was based on RLD at all four sampling positions. While SDM exhibited significant differences among three pearl millet varieties, sole root sampling wR at a lateral distance of 60 cm relative to the pocket would not allow for the detection of varietal differences in RL, while all other sampling positions did. The correlation between RL and SDM was considerably improved if information of RLD bR was included. Under traditional sowing, RLD directly under the plant was lower compared to sampling positions at lateral distance 25 and 50 cm from the centre of the pocket, but this effect of sampling position was not significant. RLD estimates within deeper soil layers were not systematically affected by direction and lateral distance. To obtain accurate information about depth of rooting and RL under traditional sowing, samples should be taken from lateral distances between 20 and 40 cm from the pocket centre.     

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.     

Decomposition of cowpea and millet amendments to a sandy Alfisol in Niger

Current inputs of organic materials to cropped lands on sandy Alfisols and Entisols in Sahelian West Africa are insufficient to arrest soil organic matter (SOM) decline. Crop residues and green manures require proper management in order to maximize their contribution to nutrient supply and SOM maintenance. The objectives of this study were to quantify the rates of C and N mineralization from cowpea (Vigna unguiculata (L.) Walp.) green manure, cowpea residue, and millet (Pennisetum glaucum (L.) R.Br.) residue under field conditions in Niger and to determine the effect of these organic amendments on pearl millet yield. Millet was grown (1) as sole crop, (2) as intercrop with cowpea, (3) as intercrop with cowpea that was incorporated as green manure during the second half of the growing season, (4) with incorporated cowpea residue (2000 kg ha^–1), (5) with millet residue mulch (3000 kg ha^–1), and (6) with N fertilizer. Carbon loss as CO₂ from soil with and without organic amendment was measured three times per week during the growing season. Nitrogen fertilizer increased millet yield only in a year with a favorable rainfall distribution. Cowpea grown in intercrop with millet during the first part of the growing season and subsequently incorporated as green manure between millet rows increased millet grain yield in a year with sufficient early rainfall, which could be attributed to the rapid rate of decomposition and nutrient release during the first 3 weeks after incorporation. In a year with limited early rainfall, however, densely planted green manure cowpeas competed for water and nutrients with the growing millet crop. Incorporated cowpea residue and millet residue mulch increased millet yield. Surface applied millet residue had high rates of decomposition only during the first 3 days after a rainfall event, with 34% of the millet residue C lost as CO₂ in one rainy season. Recovery of undecomposed millet residue at the end of the rainy season was related to presence or absence of termites, but not to seasonal C loss. Millet residue mulch increased soil organic C content of this sandy Alfisol in Niger. Cowpea and millet residues had a greater effect on SOM and millet yield than cowpea green manure due to their greater rate of application and slower rate of decomposition.     

Genetic analysis of reciprocal differences in the inheritance of in vitro characters in pearl millet

Reciprocal differences persist in nature because of the unequal contribution of cytoplasmic determinants from male and female gametes to the zygote. The inheritance of genetic differences is an important factor that influences various traits, including somatic embryogenesis and regeneration in vitro. In this report, we estimate the cytoplasmic and maternal effects in pearl millet and their adequacy in describing the observed reciprocal differences based on an in depth study of the parents, F₂s and reciprocal backcross progenies needed for fitting genetical models. Our study revealed that of the two characters examined, embryogenic callus quantity and regeneration frequency, the former showed a greater proportion of cytoplasmic nuclear interaction whereas the latter showed a greater role of nuclear factors. Additive-maternal effects influenced total callus quantity and dominance-maternal effects influenced total callus quantity, embryogenic callus quantity and regeneration frequency. Dwarfing was associated with the production of large quantities of embryogenic callus that had visually recognizable characteristics. The phenotypic nature of dwarf parents (green dwarf with long narrow leaves) with a genetic basis for a given character controlled by nuclear and cytoplasmic determinants can be exploited for other breeding programs.     

Inference of domestication history and differentiation between early‐ and late‐flowering varieties in pearl millet

Pearl millet (Pennisetum glaucum) is a staple crop in Sahelian Africa. Farmers usually grow varieties with different cycle lengths and complementary functions in Sahelian agrosystems. Both the level of genetic differentiation of these varieties and the domestication history of pearl millet have been poorly studied. We investigated the neutral genetic diversity and population genetic structure of early‐ and late‐flowering domesticated and wild pearl millet populations using 18 microsatellite loci and 8 nucleotide sequences. Strikingly, early‐ and late‐flowering domesticated varieties were not differentiated over their whole distribution area, despite a clear difference in their isolation‐by‐distance pattern. Conversely, our data brought evidence for two well‐differentiated genetic pools in wild pearl millet, allowing us to test scenarios with different numbers and origins of domestication using approximate Bayesian computation (ABC). The ABC analysis showed the likely existence of asymmetric migration between wild and domesticated populations. The model choice procedure indicated that a single domestication from the eastern wild populations was the more likely scenario to explain the polymorphism patterns observed in cultivated pearl millet.     

Genetic analysis of alcohol dehydrogenase isozymes in pearl millet (Pennisetum typhoides)

Pearl millet (Pennisetum typhoides) produces three ADH isozymes, sets I, II, and III, with set III being expressed only in anaerobically treated seeds or seedlings. Variant strains have been identified which produce ADH isozymes with altered electrophoretic mobilities for sets I and II but not for set III activity. Based on genetic analysis of these variants and on dissociation-reassociation experiments, we propose that the three ADH isozymes are dimers of subunits coded by two structural genes, Adh1 and Adh2, with set I being a homodimer specified by Adh1, set III a homodimer specified by Adh2, and set II a heterodimer formed between the products of Adh1 and Adh2.This work was supported by BRSG Grant RR 07080 awarded by the Biomedical Research Grant Program, Division of Research Grants, National Institutes of Health, to D. R. H., and by funds from the Margenroth Endowment to F. B.-B., who is a PHS Research Service Award Trainee in Genetics.     

Linkage of the alcohol dehydrogenase structural genes in pearl millet (Pennisetum typhoides)

Pearl millet produces three ADH isozymes, Sets I, II, and III. Naturally occurring ADH electrophoretic variants affecting Sets I and II isozymes but not III have been previously described. Analysis of such variants led to the identification of the Adh1 structural gene. The existence of a second Adh structural gene was inferred from dissociation-reassociation studies of Set II. In the present report, a naturally occurring variant affecting the electrophoretic mobility of Sets III and II but not Set I is described. Analysis of this variant confirms the existence of a second structural gene, Adh2. Crosses utilizing this Adh2 marker reveal a dissimilarity with maize and other plants such as sunflower and narrow-leafed lupins. Adh1 and Adh2 of pearl millet do not segregate independently; indeed, no recombinants have been observed. This is the first major difference encountered in an otherwise remarkably similar genetic and environmental control of the ADH isozymes in maize and millet. The organization of the Adh genes of pearl millet may reflect a more primitive arrangement than that of maize.This work was supported by a PHS National Research Service Award Training Grant in Genetics to the Biology Department of the University of Oregon.     

The effect of soil tillage and fertilizer use on pearl millet yields in Niger

Farmers in Niger generally do not plow their fields and are therefore unable to incorporate phosphate. Experiments were conducted in Niger to assess the effect of soil tillage, P source, and fertilizer placement on yields of pearl millet (Pennisetum glaucum [L.] R. Br.). Treatments included single superphosphate (SSP) or ground Tahoua phosphate rock (PRT) incorporated into the soil during tillage or SSP surface applied after tillage. In plots which were not tilled, P sources (SSP, PRT, and PAPR-partially acidulated rock) were broadcast on the soil surface with no incorporation. In order to improve P efficiency under zero tillage, P was point placed in the soil near the plant with either broadcast or point-placed urea. Treatments in which tillage was used showed a slight though nonsignificant yield increase over untilled plots. The yield increase did not appear to be due to phosphate incorporation but rather to direct tillage effects on early plant growth. In a comparison of SSP with PRT or PAPR broadcast on soils not receiving tillage, PRT performed poorly relative to the other P sources. SSP outyielded PAPR and PRT in 1986, but in subsequent years, no significant difference was found between PAPR and SSP. Point placement of P or N near the plant did not significantly increase yields over broadcast treatments even though the millet was planted with wide 1×1 m spacing.     

Phenol metabolism in downy mildew resistant and susceptible genotypes of pearl millet

Biochemical characterisation of pearl millet genotypes was carried at pre- (45 DAS) and post-infection (57 DAS i.e. 7 days after infection) stages. Total phenol content at pre-infection stage did not show inherent resistance or susceptibility. While the total phenol content was found to be higher in susceptible genotypes at post-infection stage, qualitative analysis of phenol through high-performance thin layer chromatography showed absence of ferulic acid in resistant genotypes at pre-infection stage. Peroxidase (POX) activity was higher in susceptible genotypes at both the stages of analysis. Constitutive activity of phenylalanine ammonia lyase was higher in resistant genotype whereas induced activity was recorded higher in susceptible genotypes. Native poly-acrylamide gel electrophoresis isozyme banding pattern of POX showed some inducible band(s) due to disease infection in resistant and susceptible genotypes.     

Physiological and molecular responses of pearl millet seedling to atrazine stress

Pearl millet has been recommended beneficial for several therapeutic purposes. However, little is known of the physiological responses to abiotic stressors, especially of atrazine. In order to elucidate the physiological and molecular responses of pearl millet to atrazine stress, we studied the response of various biomarkers under increasing herbicide concentrations (0, 5, 10, and 50 mg/kg). We also quantified the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O₂?^?) produced in the leaves to evaluate the extent of oxidative damage. Increasing atrazine concentrations significantly increased ROS and MDA production in the plant leaves. Ascorbate peroxidase (APX) and peroxidase (POD) activities increased, while catalase (CAT) and superoxide dismutase activities reduced with increasing atrazine concentrations. Generally, atrazine applied at 50 mg/kg suppressed chlorophyll contents, whereas, chlorophyll (a/b) ratio was increased. Atrazine applied at 50 mg/kg significantly suppressed antioxidant gene expressions to the lowest. The APX gene showed overall low response to the atrazine treatments. The chloroplastic psbA gene showed highest expression with 10 mg/kg atrazine, whereas atrazine at 50 mg/kg significantly suppressed the gene expression to its lowest. Pearl millet was able to suppress oxidative stress under low atrazine levels, but high atrazine concentration could induce more oxidative damage.     

Salinity effects on five cultivars/lines of pearl millet (Pennisetum americanum [L] leeke)

The effects of increased salinity [NaCl + CaCl₂] on seedlings of five accessions of pearl millet grown for 2 and 7 weeks, respectively, in salinised solution cultures at EC 0.6, 4, 8, 12, 16, and 20 ds m⁻¹ and sand cultures at EC 0.6 and 20 were assessed. There were no consistent relationships between seedlings characters at two and seven weeks in response to increased salinity, and no single character provided an acceptable means of differentiating cultivar/line response. The line having lower shoot mortality had a high root weight, a shoot:root ratio approaching 1, the greatest shoot water content, and the greatest plant height. No relationship was found between these whole-plant characters which suggest greater salinity tolerance, and the pattern of ion distribution, particularly Na⁺ and Cl⁻. Sufficient inter-cultivar/line variation in response to salinity was found to suggest that selection of individuals with increased salinity tolerance is possible within pearl millet.     

Genetic architecture of purple pigmentation and tagging of some loci to SSR markers in pearl millet, Pennisetum glaucum (L.) R. Br

This report describes the construction of integrated genetic maps in pearl millet involving certain purple phenotype and simple sequence repeat (SSR) markers. These maps provide a direct means of implementing DNA marker-assisted selection and of facilitating "map-based cloning" for engineering novel traits. The purple pigmentation of leaf sheath, midrib and leaf margin was inherited together 'en bloc' under the control of a single dominant locus (the 'midrib complex') and was inseparably associated with the locus governing the purple coloration of the internode. The purple panicle was caused by a single dominant locus. Each of the three characters (purple lamina, purple stigma and purple seed) was governed by two complementary loci. One of the two loci governing purple seed was associated with the SSR locus Xpsmp2090 in linkage group 1, with a linkage value of 22 cM, while the other locus was associated with the SSR locus Xpsmp2270 in linkage group 6, with a linkage value of 23 cM. The locus for purple pigmentation of the midrib complex was either responsible for pigmentation of the panicle in a pleiotropic manner or was linked to it very closely and associated with the SSR locus Xpsmp2086 in linkage group 4, with a suggestive linkage value of 21 cM. A dominant allele at this locus seems to be a prerequisite for the development of purple pigmentation in the lamina, stigma and seed. These findings suggest that the locus for pigmentation of the midrib complex might regulate the basic steps in anthocyanin pigment development by acting as a structural gene while other loci regulate the formation of color in specific plant parts.     

Aflatoxin contamination of pearl millet during field and storage conditions with reference to stage of grain maturation and insect damage

Aflatoxin contamination in five varieties of pearl millet (ICMH-451, ICMP-50I, ICTP-8203, WCC-75 and ICMV-155) was studied from field and storage conditions in three districts of Andhra Pradesh State, India and the inter-relationships between various parameters such as stage of grain maturation in the field and insect pest infestation in storage in relation to aflatoxin production were evaluated. Aflatoxin contamination was more frequent in the seed samples collected from the fields during rainy season than winter season. All major aflatoxins were isolated from one or the other varieties of pearl millet, whereas aflatoxin G₂ was not commonly observed in the seed samples collected during winter. Among all the varieties tested, ICMH-451 was vulnerable to aflatoxin contamination whereas ICMV-155 was the least susceptible variety. The higher amount of aflatoxins was observed in the matured seed samples followed by pre-matured and milky stage. Among all the toxins reported in the field, aflatoxin B₁ was found in higher concentration (185 (μg/kg) followed by B₂ (105 μg/kg). The four major types of aflatoxins with higher levels (35, 40, 140, 190 μg/kg of G₁, G₂, B₂, B₁ were reported in the rainy season seed samples after six months of storage, whereas aflatoxin G₁ was not observed in any variety of stored seed sample from winter. Statistical analysis revealed that the aflatoxin incidence in relation to different parameters studied was significantly different for each factor. The relationship between aflatoxin contamination and insect damaged-grain clearly indicated that the seed samples with 16-40% of insect damage contained higher amounts of aflatoxins (758 μg/kg). Presented at the 29^th Mykotoxin-Workshop, Fellbach, Germany, May 14–16, 2007     

Comparative evaluation of Pseudomonas fluorescens and their lipopolysaccharides as implicated in induction of resistance against pearl millet downy mildew

Two plant growth promoting Pseudomonas fluorescens isolates namely UOM SAR 14 and UOM SAR 80 most effectively induced resistance against downy mildew disease of pearl millet both under greenhouse and field conditions. Relative assessment of live cultures of P. fluorescens UOM SAR 14 and UOM SAR 80 and their lipopolysaccharides (LPS) extracted from their cell walls were evaluated for their ability to induce resistance against pearl millet downy mildew. Treatment with P. fluorescens and their LPS enhanced the seed germination and seedling vigour considerably. Although both live cultures and their LPS treatment induced resistance in pearl millet against downy mildew disease both under greenhouse and field conditions as evidenced by the significant reduction of the disease, live cultures were more effective than the LPS in level of resistance induced. Live cultures of UOM SAR 14 and UOM SAR 80 induced 66% and 57% protection while their respective LPS extracts offered 59 and 53% protection against downy mildew disease under greenhouse conditions. Similarly, under field conditions with very heavy inoculum pressure live cultures offered 75% and 70%, and their LPS offered 71% and 67% protection, respectively. In either case, the time gap required for the building up of resistance was found to be 3 days and nature of the resistance induced was systemic and durable with both live cultures and their lipopolysaccharides. It was also noticed that the live bacteria significantly varied in the degree of protection offered and so also their respective LPS.     

Assessment of cytoplasmic differences of near-isonuclear male-sterile lines in pearl millet

Four near-isonuclear polycytoplasmic versions of 81A and two of Pb 402A male-sterile lines of pearl millet (Pennisetum typhoides) were used in factorial matings with five inbred male testers in different combinations in three sets. The cytoplasmic differences were studied for several agronomic traits using mean values and general combining effects (gca) of male-sterile lines, and specific combining ability effects of hybrids. The fertility/ sterility behaviour of different male-sterile lines in crosses with common male parents was also studied. Significant differences among near-isonuclear polycytoplasmic lines were observed in mean values for a few traits such as plant height, leaf length and peduncle length, but the differences for combining ability were more pronounced. The A₃ cytoplasm was a better general combiner than the A₂ cytoplasm for grain yield and both A₂ and A₃ cytoplasms were better general combiners for leaf length and peduncle length. In addition, superiority of A₃ cytoplasm for gca was observed for plant height and ear characters over the A₂ cytoplasm in set II. A differential behaviour of cytoplasms, both in combination with a common pollinator and across pollinators, was observed for several traits. The results provide evidence for the distinctiveness of different cytoplasmic sources in pearl millet and for the influence of cytoplasmic factors on the phenotypic expression of nuclear genes. A diversification of male sterility sources in the breeding of pearl millet hybrids is suggested.     

A novel approach to the establishment of dual cultures of pearl millet and Sclerospora graminicola

Dual cultures were successfully established using malformed florets of pearl millet infected with Sclerospora graminicola, the downy mildew pathogen. A higher proportion (86%) of calli from malformed florets formed dual cultures on Murashige and Skoog's (MS) medium with 2 mg 1^-1 of 2,4-dichlorophenoxy acetic acid (2,4-d), compared to shoot tips (25%). Fungal mycelium covered the entire surface of the callus within 30 days of placement of explants on the MS medium with 2 mg 1^-1 of 2,4-d. The infected calli also differentiated and produced plantlets when transferred to MS medium without 2,4-d.     

Comparative analysis of activities of vital defence enzymes during induction of resistance in pearl millet against downy mildew

Pearl millet [Pennisetum glaucum (L.) R. Br.] has the seventh largest annual production in the world giving it significant economic importance. Although generally well adapted to the growing conditions in arid and semi-arid regions, major constraints to yields are susceptibility to downy mildew disease caused by the oomycete Sclerospora graminicola (Sacc.) Schroet. Induction of resistance against downy mildew disease of pearl millet has been well established using various biotic and abiotic inducers. The present study demonstrated the comparative analysis of the involvement of the important defence enzymes like β-1,3-Glucanase, chitinase, phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO) and lipoxygenase (LOX) during induced systemic resistance (ISR) mediated by inducers like Benzo(1,2,3)-thiadiazole-7-carbothionic acid-S-methyl ester (BTH), Beta amino butyric acid (BABA), Chitosan and Cerebroside against pearl millet downy mildew disease. Native-PAGE showed six POX isozymes in all categories of uninoculated pearl millet seedlings and maximum intensity of bands was noticed in resistant seedlings. After inoculation in Cerebroside-treated seedlings, there were seven isoforms, POX-4 was not present in any other seedlings. Native-PAGE analysis showed the presence of five PPO isozymes in all categories of uninoculated pearl millet seedlings and after inoculation seven isoforms of PPO-7 were noticed, and the intensity of banding was more in resistant and Cerebroside-treated seedlings. The isoforms PPO-3 were present as an extra band after inoculation in all seedlings. Isoform PPO-7, though found in all seedlings, was very prominent in Chitosan- and Cerebroside-treated seedlings. β-1,3-Glucanase Native-PAGE analysis showed the presence of only one isozyme in all categories of uninoculated/inoculated pearl millet seedlings. Glu-1 isozyme was very prominent in all seedlings including resistant and susceptible seedlings. Among the induced resistant seedlings, highest intensity was observed in Cerebroside-treated seedlings. Native-PAGE analysis showed the presence of three LOX isozymes in all categories of uninoculated pearl millet seedlings, and the intensity of banding pattern was very low in BTH-treated seedlings. LOX-1 and LOX-2 were very prominent in resistant, Chitosan- and Cerebroside-treated seedlings. Upon inoculation, one extra band, LOX-3, was exclusively noticed in Cerebroside-treated seedlings. In inoculated seedlings, LOX-1, LOX-2 and LOX-4 were very prominent in Chitosan Cerebroside-treated seedlings compared to other seedlings.     

Varietal differences in root phosphatase activity as related to the utilization of organic phosphates

This paper presents results of a comparative study of phosphorus utilization from inositol hexaphosphate by various varieties of Phaseolus vulgaris in relation to the activity and characteristics of their root phosphatases. Bean varieties show significant differences in their uptake of phosphorus from inositol hexaphosphate with a clear dependency on the phosphatase activity of their roots at pH 5. The results which are discussed in connection with the phosphorus turnover in the rhizosphere suggest that root phosphatase activity is a significant factor of nutritional efficiency under limited mineral phosphorus supply.     

Variation in response of accessions of minor millets,Pennisetum americanum (L.) Leeke (pearl millet) and Eleusine coracana (L.) Gaertn (finger millet), and Eragrostis tef (Zucc.) Trotter (tef) to salinity in early seedling growth

The response to increasing NaCl concentration of seedlings of 25 accessions of Ethiopian land races of each of Pennisetum americanum (L.) Leeke (pearl millet) and Eleusine coracana (L.) Gaertn (finger millet), and 15 accessions of Eragrostis tef (Zucc.) Trotter (tef), was examined after two week's growth in NaCl solution culture. Although increasing NaCl concentration significantly reduced seedling root lengths, there was considerable variation within, and between accessions within each species.Analysis based upon a non-linear least square inversion method, using root length data, revealed significant differences in accessions of P. americanum and E. tef on the basis of the estimated salinity threshold, C _t , the NaCl concentrations at which root length begins to decrease. C _t did not differ significantly between E. coracana accessions. Estimates of C₅₀ and C₀, mininum concentrations causing a 50% decrease in root length, and zero root growth respectively, revealed differences between and within accessions for all three species. Overall, finger millet was more tolerant than tef, which was more tolerant than pearl millet. There is clear evidence that differences in tolerance are genetically based from broad sense heritability estimates.     

Genetic control of weediness traits and the maintenance of sympatric crop-weed polymorphism in pearl millet (Pennisetum glaucum)

Pearl millet (Pennisetum glaucum), a diploid outcrossing crop widely grown in semiarid tropics, provides a unique extant material for the study of crop-weed interactive evolution. Co-occurrence of a weedy, shattering type of pearl millet with the cultivated one is the rule in the traditional agro-ecosystem in the Sahel zone of Africa. Selfed progeny of weed-type plants invariably segregated into distinct weed and crop types in an approximately 3:1 ratio. Genetic analysis using a cleaved amplified polymorphic sequence (CAPS) marker strongly suggested that a series of differences between the crop and the weed types are determined by a single putative supergene that has two allelic types, C and W. The crop-type plants are CC homozygotes, and the weed-type plants are CW heterozygotes. WW homozygotes are sterile and rare in the field. Thus, the CW weed plants recurrently arise from crosses between the crop and the weed, as well as from crosses among the weed-type plants. The weed type appears to have a sufficiently high fitness to maintain the W allele in the pearl millet population, resulting in the perpetuation of this unique crop-weed polymorphism.