Impact of natural and human selection on the frequency of the F1 hybrid between cultivated and wild pearl millet (Pennisetum glaucum (L.) R. Br.)

In the Sahel, pearl millet yields are affected by the proportion of hybrid phenotype plants resulting from genetic mixing between domesticated and wild forms. Man counteracts this mixing by applying a production method, the efficiency of which is quantified in this study. Under experimental conditions, cultivated and wild pearl millet were hybridised in order to obtain cultivated pearl millet seeds including a known proportion of F1 hybrids tagged by two different allozymes. These seeds were sown in the field and the cultivation was conducted following practices common in the Sahel. The evolution of the survival rate of plants and the frequency of hybrids were followed over several stages during the season: sowing, germinating, emergence, thinning, flowering and maturing of the seeds. Owing to plant mortality in the experiment, the average tendency was a hybrid frequency that decreased steadily in the first part of the growing season from 42% during germination, to 37% at emergence. It then fell to 17% after the thinning of the plantlets by the farmer. At the end of the cycle, after thinning, only 11% of mature plants were hybrids. Thus, under the combined pressures of natural and human selection, the frequency of hybrids in the field declined drastically. In interaction with natural pressure, the farmer's practices of selection of seeds, sowing in pockets and thinning have the combined effect of heavily selecting the cultivated genotype and limiting without completely preventing the introgression of wild pearl millet genes into the cultivated genome. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of cytoplasmic-nuclear male sterility systems on microsporogenesis in pearl millet (Pennisetum glaucum (L.) R. Br.)

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 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 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. This revised version was published online in July 2006 with corrections to the Cover Date.     

Culturing shoot-tip clumps of pearl millet [Pennisetum glaucum (L.) R. Br.] and optimal microprojectile bombardment parameters for transient expression

Microprojectile bombardment and transient expression of the reporter gene, β-glucuronidase (GUS) in a novel target tissue, multiple-shoot-tip clumps of pearl millet [Pennisetum glaucum (L.) R. Br.] is reported here. The multiple-shoot-tip clumps were developed in vitro from shoot-apices of seedlings. Using this method, the apical meristems along with the germline cells were easily exposed for bombardment without loss of viability. Further growth of the multiple-shoot-tip clumps was not substantially affected by microprojectile bombardment. Transient expression of β-glucuronidase gene was detected in the form of blue transformed cell sectors in the bombarded tissue by an in situ enzyme assay. The blue sectors were used as convenient criteria to study several factors affecting gene transfer efficiency. Optimal conditions for efficient transient expression of the GUS gene have been defined to aid future strategies of genetic engineering in pearl millet with agronomically important genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of induced dwarf mutants in pearl millet,Pennisetum americanum (L.)Leeke

Summary Inheritance pattern of seven dwarf mutants revealed each of them to be controlled by a single recessive gene. Tests for allelism indicated existence of two groups of dwarfs, group 1 comprising six mutants and group 2 a single dwarf. The dwarfs of group 1 were found to be allelic to D₂ of the dwarf types already known in this crop and the dwarf of group 2 was allelic to D₁ of these types.Botany Department, R.V.V.N. College, Dharanikota, India.     

Screening sorghum genotypes for salinity tolerant biomass production

Genetic improvement of salt tolerance is of high importance due to the extent and the constant increase in salt affected areas. Sorghum [Sorghum bicolor (L.) Moench] has been considered relatively more salt tolerant than maize and has the potential as a grain and fodder crop for salt affected areas. One hundred sorghum genotypes were screened for salinity tolerance in pots containing Alfisol and initially irrigated with a 250-mM NaCl solution in a randomized block design with three replications. Subsequently 46 selected genotypes were assessed in a second trial to confirm their responses to salinity. Substantial variation in shoot biomass ratio was identified among the genotypes. The performance of genotypes was consistent across experiments. Seven salinity tolerant and ten salinity sensitive genotypes are reported. Relative shoot lengths of seedlings were genetically correlated to the shoot biomass ratios at all stages of sampling though the relationships were not close enough to use the trait as a selection criterion. In general, the whole-plant tolerance to salinity resulted in reduced shoot Na⁺ concentration. The K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were also positively related to tolerance but with a lesser r ². Therefore, it is concluded that genotypic diversity exists for salt tolerance biomass production and that Na⁺ exclusion from the shoot may be a major mechanism involved in that tolerance.     

Evidence of a partial reproductive barrier between wild and cultivated pearl millets (Pennisetum glaucum)

Summary The occurrence of seed malformation in association with reduced thousand grain weight and germination ability has been observed in crosses between cultivated female plants and wild male plants. A survey of 16 cultivated accessions (P. glaucum subsp. glaucum) and 11 wild accessions (P. glaucum subsp. monodii) ranging over the whole species diversity showed this postzygotic incompatibility was general, but its intensity varied greatly with the cultivated female accession used and very little with the wild male parent origin. About 15% of the 123 cultivated x wild crosses observed gave normal seeds. Seed malformation has never been observed in crosses between cultivated accessions and appeared independent of genetic distances between the parents. The reciprocal crosses between wild female plants and cultivated male plants gave normal-looking seeds with good germination but consistently reduced thousand grain weight. Both seed malformation and seed small size are an expression of a genetic imbalance. These slight reproductive barriers seem to have been built during the domestication process.Abbreviation ICRISAT International Crop Research Institute for the Semi-Arid Tropics     

Involvement of higher order interactions addressing complex polygenetically controlled inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot] resistance in pearl millet [Pennisetum glaucum (L.) R.Br.]

Inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot]resistance was studied using generation mean analysis in pearl millet [Pennisetum glaucum (L.) R.Br.]. Eleven basic generations, namely, P₁, P₂, F₁, F₂, B₁, B₂, B₁F₂, B₂F₂, L₁, L₂ and L₃ of three crosses involving six diverse lines for downy mildew incidence were evaluated under artificial epiphytotic conditions over two environments. The downy mildew incidence was best fitting for digenic, trigenic and tetragenic ratios when fitted into classical Mendelian ratios demonstrating involvement of two or more genes. Digenic and trigenic interaction models were adequate in the case of crosses I and III respectively, to account for the total variability in generation means. Unlike severity, comparative estimates of gene effects over two environments were mostly consistent in all crosses for prevalence. Most of the epistatic and major gene effects were found significant in all crosses for both the disease traits. Non-allelic interactions particularly at three-gene loci viz., w (additive × additive × additive) and y (additive × dominance × dominance) in cross II and all trigenic interactions in cross III were predominant. Duplicate dominance (cross I) and complementary epistasis (crosses II and III) were observed for both the traits revealing inconsistency of gene effects over crosses. The gd₁ (interaction of additive gene effect with e₁) and gh₁(interaction of dominant gene effect with e₁) were significant in crosses I and II, indicating interaction of additive and dominance gene effects with environments. Thus a breeding method that can mop up the resistant genes to form superior gene constellations interacting in a favorable manner against pathotype I would be more suitable to accelerate the pace of resistance improvement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Smut reaction of pearl millet hybrids affected by fertility restoration and genetic resistance of parental lines

Summary Pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids based on the A₁ cytoplasmic-nuclear male-sterile (CMS) lines are more susceptible to smut (Tolyposporium penicillariae Bref.) than open-pollinated varieties. Seventy eight pairs of hybrids, made onto male-sterile (A) lines and their counterpart maintainer (B) lines, were evaluated to examine the effects of male sterility and genetic resistance of parental lines on the smut severity of hybrids. The A-line hybrids had higher smut severity and lower selfed seedset than the counterpart B-line hybrids, indicating that it is the CMS-mediated male sterility rather than the A₁ cytoplasm per se that caused greater smut severity of A-line hybrids. However, with the use of resistant parental lines even male-sterile hybrids of A-lines, in several cases, were as resistant as some of the highly resistant male-fertile hybrids of B-lines. It would be possible to produce smut resistant hybrids (< 10% severity) on A-lines, albeit in low frequency, even if only one parent of a hybrid were resistant. However, the probability of producing such hybrids would be higher when both parents were resistant to smut. Thus, improvement in smut resistance of parental lines and fertility restoration ability of pollinators would provide the most effective genetic approach to smut disease management in hybrids.Submitted as JA No 1737 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).     

Ergot reaction of pearl millet hybrids affected by fertility restoration and genetic resistance of parental lines

Summary High ergot (Claviceps fusiformis Loveless) susceptibility of pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids has often been associated with the A₁ cytoplasm of male-sterile lines (A-lines). To understand the underlying basis of this association and to examine the prospects of breeding ergot-resistant hybrids, we evaluated 56 hybrids and their 15 parental lines for ergot reaction and selfed seedset for 2 years in disease nurseries at ICRISAT Asia Center. Hybrids were made by crossing seven pollen parents (2 susceptible and 5 resistant) onto two resistant and two susceptible A-lines, and their four corresponding maintainer lines (B-lines). A-lines had no selfed seedset while B-lines had 32–75% selfed seedset. Hybrids of A-lines had significantly less selfed seedset than the hybrids of the corresponding B-lines. The reduced seedset of A-lines and their hybrids, however, was not always accompanied by significantly higher ergot susceptibility. Highly resistant hybrids were obtained where both A-lines and pollen parents were highly resistant, regardless of male fertility levels of the hybrids. Thus, although the A₁ cytoplasm, by its reduction of male fertility, had a large and significant effect in increasing ergot severity of hybrids, the contribution of nuclear genetic factors of female parents was about 1.8 times larger than that of the cytoplasm.Submitted as JA No. 1776 by the International Crops Research Institute for the Semi Arid Tropies.     

Confirmation of a new source of cytoplasmic-genic male-sterility in bulrush millet (Pennisetum americanum (L.) Leeke)

Summary Results of a previous study indicated that the male-sterility discovered in a population of ex-Bornu bulrush millet, an improved selection from northern Nigeria, may represent a new source of male-sterility in the species. The present experiment was conducted to test this hypothesis.Tifton 23B₁, Tifton 239B₂ and L67B₃ which are male-sterility maintainers for the three known sources of cytoplasmic-genic male-sterility in bulrush millet viz. A₁, A₂ and A₃, respectively, were crossed with male-sterile ex-Bornu. All three maintained male-sterility in ex-Bornu but not as well as gero-B, which is the selfed progeny of an ex-Bornu plant was an excellent maintainer for ex-Bornu. Gero-B maintained male-sterility in Tifton 23A₁ and L67A₃ sources but was a partial fertility restorer for Tifton 239A₂. Tifton 186 which was reported to be a maintainer for A₁, A₂ and A₃ sources restored male-fertility in ex-Bornu. These results confirmed the view that male-sterile ex-Bornu is a new source of cytoplasmic-genic male-sterility in bulrush millet.     

Effect of d2 dwarfing gene on grain yield and yield components in pearl millet near-isogenic lines

Summary A d₂ dwarfing gene in pearl millet [Pennisetum glaucum (L.) R. Br.] is currently being extensively used for the development of hybrid parents. Its effect on grain yield and yield components is poorly understood. Twelve pairs of tall and dwarf near-isogenic lines developed in the diverse genetic background of three composites were evaluated for grain yield and yield components for 2 years at two locations in southern India. The d₂ gene or the genes linked to it, on an average, reduced plant height by 42%, grain yield by 14%, and head girth by 8% but increased head length and number of tillers per plant by about 5–6%. Large variations were observed among pairs (genetic background) for the difference between tall and dwarf near-isogenic lines for all of the above yield components resulting in no significant difference in five pairs and 17–35% less yield in dwarfs as compared to their tall counterparts in six pairs. Days to 50% flowering and seed weight were least affected by the d₂ gene with the average difference between tall and dwarf groups of near-isogenic lines being of the order of 1–2%. These results indicate that the advantageous effects of d₂ dwarfing gene can be effectively exploited by manipulating the genetic background. The difference between the average grain yields of tall and dwarf groups of near-isogenic lines showed considerable variation across environments with the dwarfs yielding as much as tall group in one environment and up to 30% less than the tall group in the other, thus, indicating that the d₂ gene effect may be substantially modified by the environments.Submitted as JA No. 979 by the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT).     

Diversity of penicillarian millets (Pennisetum glaucum and P. purpureum) as for the compatibility between their gynoecia and pollens from some other Poaceae

Summary The compatibility between gynoecia of different penicillarian millets (Pennisetum glaucum and P. purpureum) and pollens from some other Poaceae was evaluated in order to determine whether different penicillarian pistils showed the same pistil-pollen interactions with a same non-penicillarian pollen and to determine whether compatibility was dependent on the genetic divergence or the degree of sympatric evolution of the mating partners. Ten pearl millet lines (P. glaucum subsp. glaucum), six wild pearl millet accessions (P. glaucum subsp. monodii) and one P. purpureum accession were pollinated with five other Pennisetum species: P. pedicellatum, P. polystachyon, P. schweinfurthii, P. squamulatum, P. ramosum, and with three species from other genera: Cenchrus ciliaris, Panicum maximum and Zea mays. Each male species was represented by a unique accession. Pollen grain germination on the stigmata and pollen tube growth in the gynoecia were monitored by means of fluorescence microscopy after aniline blue staining. Significant compatibility differences were observed between a given pollen and gynoecia from different P. glaucum accessions. But there was no evidence of compatibility differences between the three female taxonomic groups. The eight pollen parents can be classified into three groups according to their mean degree of compatibility with the different penicillarian gynoecia. P. ramosum, P. schweinfurthii and P. squamulatum showed a high compatibility: more than 50% of penicillarian gynoecia had pollen tubes at the micropyle, six hours after pollination. Zea mays, Cenchrus ciliaris and Panicum maximum showed a low compatibility: pollen tubes were arrested in the style. P. pedicellatum and P. polystachyon showed nil compatibility: few pollen grains germinated on the stigmata and very rare tubes reached the entry of the style, where they stopped. It must be noted that such a strong gametic barrier has been observed only with pollinator species sympatric to pearl millet.     

Identification,characterization and geographic distribution of male-sterility restorer and maintainer lines from diverse pearl millet germplasm

Summary To determine the distribution and geographic specificity of sterility maintainers in pearl millet, Pennisetum americanum (L.) Leeke, 428 diverse pearl millet germplasm accessions representing variation from 12 countries were crossed with a male-sterile line 5141A. The F₁ hybrids were classified as male-fertile or male-sterile based on the seed set on bagged ear heads and an other morphology. Among these, 87 (20.3%) were classified as male-fertile, 32 (7.5%) as male-sterile, 282 (65.9%) as segregating for male-fertile/male-sterile and 27 (6.3%) behaved as male-fertile in the rainy and male-sterile in the postrainy season. Restorer lines were distributed in all the countries studied except Cameroon and USSR. Maintainer lines were observed from six countries but were concentrated in India. These maintainer lines differ from one another in several morphological and agronomic characters such as flowering, plant height, spike length and grain size. They may prove to be useful sources of material for generating new male-sterile lines. The restorers can be used to produce commercial hybrids.Submitted as J.A. No. 719 by the International Crops Research Institute for the Semi-Arid Topics (ICRISAT).     

Inheritance of genetic malesterility in Pennisetum americanum (L.) Leeke

Summary A spontaneously occurring male sterile condition was located in an inbred line Vg 272 of Pennisetum americanum. Male sterility was inherited as a monogenic recessive condition and showed independent assortment with hairy leaf surface phenotype. Transfer of male sterile allele to inbreds Vg 212 and IP 482 revealed no cytoplasmic effects on the expression of male sterility. Stigmas of the male sterile plants were found to possess the same amount of receptivity upto three days with normal seed set, upto six days with reduced seed set and almost with nil receptivity on the seventh day.     

Production of 27-, 28-, and 56-chromosome apomictic hybrid derivatives between pearl millet (2n=14) and Pennisetum squamulatum (2n=54)

Summary An interspecific hybridization program designed to transfer gene(s) controlling apomixis from Pennisetum squamulatum Fresen. (2n=6x=54) to induced tetraploid (2n=4x=28) cultivated pearl millet, Pennisetum americanum (L.) Leeke resulted in four offtype plants, two with 27 chromosomes and two with 28 chromosomes. These plants were found among 217 spaced plants established from open-pollinated seed of an apomictic 21-chromosome polyhaploid (2n=21) plant derived from an apomictic interspecific hybrid (2n=41) between tetraploid pearl millet and Pennisetum squamulatum. It appeared that a 21- (or 20-) chromosome unreduced egg from the apomictic polyhaploid united with a 7-chromosome pearl millet (2n=2x=14) gamete to produce a 28- (or 27-) chromosome offspring. Meiotic chromosome behavior was irregular averaging from 3.60 to 4.05 bivalents per microsporocyte in the 27- and 28-chromosome hybrids. The 27- or 28-chromosome hybrids, like the 21-chromosome female parent, shed no pollen, but set from 1.8 to 28 seed per panicle when allowed to outcross with pearl millet. Progeny of the 28-chromosome hybrids were uniform and identical to their respective female parents, indicating that apomixis had been effectively transferred through the egg. In addition, a 56-chromosome plant resulting from chromosome doubling of a 28-chromosome hybrid was identified. Pollen was 68 per cent stainable and the plant averaged 2.3 selfed seeds per panicle. Chromosomes of the 56-chromosome plant paired as bivalents (x=10.67) or associated in multivalents. Three to nine chromosomes remained unpaired at metaphase I. Multiple four-nucleate embryo sacs indicated the 56-chromosome hybrid was an obligate apomict. The production of 27-, 28-, and 56-chromosome hybrid derivatives were the results of interspecific hybridization, haploidization, fertilization of unreduced apomictic eggs, and spontaneous chromosome doubling. These mechanisms resulted in new unique genome combinations between x=7 and x=9 Pennisetum species.     

Genetics of tolerance to high concentrations of soil boron in peas (Pisum sativum L.)

Summary The inheritance of tolerance to high concentrations of soil boron in pea (Pisum sativum L.) was studied in five cross combinations and their reciprocals. Segregation patterns for boron response in F₂ populations and F₃ derived families were established by visual assessment of leaf damage. The segregation ratios were explained in terms of two major gene loci interacting in an additive manner with incomplete dominance at each locus. Evaluation of selected tolerant and susceptible families indicated that tolerant families contained a significantly lower concentration of boron in shoots than susceptible families.     

Male-sterility in nigerian bulrush millets (Pennisetum americanum (L.) K. Schum)

Summary The occurrence of three male-sterile plants is reported. One in a population of ex-Bormu, an improved recommended variety of day-length neutral gero bulrush millet and the two others in the selfed progeny of a population of maiwa bulrush millet, a short-day photoperiod-sensitive type. Tests confirmed the cytoplasmic-genic nature of the male-sterility in the gero population. No tests could be conducted for maiwa.The transfer of male-sterility from the male-sterile Tift 23A bulrush millet, obtained from the United States, into a maiwa population is also reported. After six backcrosses the maiwa genotype appeared to have been reconstituted against the background of a male-sterility inducing cytoplasm. Maiwa male-sterility maintainer plants have also been identified.     

SSR marker tightly linked to the Ti locus in Soybean [Glycine max (L.) Merr.]

Soybean is a major source of protein meal in the world. Soybean kunitz trypsin inhibitor (SKTI) protein is a responsible for the inferior nutritional quality of unheated or incompletely heated soybean meal. The primary objective of this research was to identify DNA markers linked to the Ti locus controlling presence and absence of kunitz trypsin inhibitor protein. Two mapping populations were developed. Population 1 was derived from a cross between cultivar Jinpumkong2 (TiTi) and C242 (titi). Population 2 was made from a mating between cultivar Clark (TiTi) and C242. The F₁ plants were grown in the greenhouse to produce F₂ seeds. Each F₂ seed from F₁ plants was analyzed electrophoretically to determine the presence of the SKTI protein band. One-thousand RAPD primers, 342 AFLP primer sets, and 35 SSR primers were used to map Ti locus in population 1 and 2. The presence of SKTI protein was dominant to the lack of a SKTI protein and kunitz trypsin inhibit protein band was controlled by a single locus. Twelve DNA markers (4 RAPD, 4 AFLP, and 3 SSR) and Ti locus were found to be genetically linked in population 1 consisted with 94 F₂ individual plants. Three SSR markers (Satt409, Satt228, and Satt429) were linked with Ti locus within 10 cM. Satt228 marker was tightly linked with Ti locus. Satt228 marker was tightly linked within 0–3.7 cM of the Ti locus and may be useful in a marker assisted selection program.     

Morphology,cytology and forage potential of Pennisetum americanum (L.) K. Schum. x P. Purpureum Schum. amphidiploids

Summary F₁ hybrids between short-day photoperiod- sensitive maiwa bulrush millet, Pennisetum americanum (2n=14), and elephant grass, P. purpureum (2n=28), are triploid (2n=21), sterile, and can only be propagated vegetatively. Fertile amphidiploids, (2n=42, with 21 bivalents) were produced by colchicine treatment. Good seed set was obtained upon selfing the amphidiploids and the progeny exhibited variable pollen fertility and bivalent univalent and multivalent formation.Reciprocal crosses between elephant grass and the colchicine-induced amphidiploid failed to produce seeds. The maiwa millet x amphidiploid cross resulted in poor seed set and the reciprocal failed. Maiwa x amphidiploid hybrids were pollen sterile with 2n=21, rather than the expected 2n=28, indicating chromosome elimination.Morphologically, the amphidiploids and maiwa x amphidiploid hybrids closely resembled elephant grass and the F₁ hybrid. The amphidiploids showed no superiority over the F₁ hybrid and elephant grass in either forage yield or quality but one maiwa x amphidiploid genotype surpassed a promising local elephant grass selection in forage dry matter yield and flowered for a relatively short period.     

Major gene control of tolerance of bread wheat (Triticum aestivum L.) to high concentrations of soil boron

Summary The genetic control of tolerance of wheat to high concentrations of soil boron was studied for five genotypes. Each genotype represented one of five categories of response to high levels of boron, ranging from very sensitive to tolerant. Tolerance to boron was expressed as a partially dominant character, although the response of an F₁ hybrid, relative to the parents, varied with the level of boron applied. The F₁ hybrids responded similarly to the more tolerant parent at low B treatments and intermediate to the parents at higher treatments. Ratios consistent with monogenic segregation were observed for the F₂ and F₃ generations for the combinations (WI^*MMC) × Kenya Farmer, Warigal × (WI^*MMC) and Halberd × Warigal. The three genes, Bo1, Bo2 and Bo3, while transgressive segregation between two tolerant genotypes, G61450 and Halberd, suggested a fourth locus controlling tolerance to boron.