Reproductive Behavior of Hexaploid/Diploid Wheat Hybrids 1

The bottleneck restricting introgression of useful genes directly from diploid into hexaploid wheats is the low number of BC₁F₁ seeds obtained. In crosses between hexaploid wheat (Triticum aestivum L.; AABBDD) and Aegilops squarrosa L. (DD) or T. urartu Thum. (AA), this bottleneck may be overcome simply by pollinating a sufficient number of F₁ spikes. However, hybrids between hexaploid wheat cultivars (T. aestivum) and T. monococcum L. (AA) generally are highly female-sterile, often having no pistils. One T. monococcum accession, PI 355520, when crossed with T. aestivum, produced hybrids with female fertility in the same range as that of T. aestivum/A. squarrosa or T. aestivum/T. urartu hybrids, ca. 0.5 to 1.0 backcross seed per spike. We found that female fertility was controlled by two duplicate genes in PI 355520, and that this accession can be used as a bridging parent to introgress genes from other T. monococcum accessions into hexaploid wheat. Pairing of homologous chromosomes was less frequent and weaker in such crosses than in T. aestivum/A. squarrosa crosses, but homoeologous bivalents occurred at a rate of almost 0.5 II per cell. Restitution division was detected in crosses involving all three diploid species and was confirmed cytologically in crosses with PI 355520. Chromosome numbers of BC₁F₁ plants ranged from 35 to 67; plants with 49 or more chromosomes occurred at frequencies of 0.09 to 0.21 among progeny of A. squarrosa and T. urartu and 0.29 in progeny of T. aestivum/T. monococcum crosses involving PI 355520. These results are consistent with those of previous studies, demonstrating the potential of direct Hexaploid/diploid crosses for rapidly introgressing useful genes into Hexaploid wheat with minimum disturbance of the background genotype.     

Inheritance of Induced Morphological Mutants in Triticutn monococcum L.

The mode of inheritance of fifteen induced morphological mutants in diploid wheat Triticum monococcum L. was determined. The results showed that earliness, reduced height, uniculm, liguleless branched spike, compact ear, and free-threshing habit of each of these mutants is the result of a single recessive mutation. Red awns and xantha traits are controlled by two recessive genes with duplicate and inhibitory gene interactions, respectively. Some of the early and dwarf mutants were non-allelic. One dwarf GA₃-insensitive mutant with recessive gene action may be a new source. Mutants such as early maturing, dwarf and free threshing habit may be of significance in breeding diploid wheat.     

The implications of 2n egg gametes in nobilization and breeding of sugarcane

Summary Nobilization in sugarcane is viewed from a genetic angle considering the significance of 2n gametes. The inbreeding coefficients resulting from 2n gametes, for first and second nobilizations are worked out. The implication of 2n gametes to sugarcane breeding are discussed.     

Wheat embryogenesis and haploid production in wheat × maize hybrids

Summary Embryogenesis was analyzed in wheat × maize hybrids using paraffin sectioning. Embryogenesis in wheat × maize hybrids is different from that in self-pollinated wheat plants. Development of the embryo is not accompanied by the formation of an endosperm. The endosperm nuclei remain free in the cytoplasm, fail to advance into the cellular stage, and degenerate at a later time. The antipodal cells quickly degenerate in the fertilized ovaries of wheat × maize hybrids similar to self-pollinated ovaries. The antipodal cells remain normal in unpollinated ovaries. The pre-embryo will abort if it is allowed to develop on the plant, because of a nutritional shortage in the absence of an endosperm. Therefore, embryo rescue is necessary for haploid production from a wheat × maize hybrids. Haploid polyembryos were obtained from spikelet culture of wheat × maize hybrids. The formation of polyembryos is due to the cleavage of the pre-embryo and the effect of 2,4-D. The frequency of haploid embryo production and plant regeneration is affected significantly by maize genotypes, but not by wheat genotypes. The concentration of 2,4-D affects only the size of the embryo.     

Stability analysis over seasons and locations of multilines of wheat (Triticum aestivum L.)

Summary Three multilines each of Kalyansona and PV 18 varieties of wheat were compared for their stability of yield and agronomic characters and disease resistance against the respective recurrent parents. The experiments were conducted for four years at nine locations.The multilines had more tillers and bolder seeds than the recurrent parents. There were, however, no differences for plant height, ear length and number of spikelets per spike.The genotypes x years x locations interaction was much more important than genotypes x years or genotypes x locations interaction as well as the main effects for genotypes. It is suggested that the number of test locations should be increased while decreasing the number of years.The stability parameters indicated that the multilines had a higher mean yield in the case of Kalyansona multilines whereas the yield of multilines of PV 18 was not significantly inferior to that of the recurrent parent. The regression coefficients were very close to unity except for KSML 3 (b=1.132). The deviations from regression were much larger for the multilines than for the recurrent parents.For rust resistance the multilines were superior over the varieties Kalyansona and PV 18.This is publication No. 9 of the series Studies on multilines in wheat (Triticum aestivum L.)     

Bioavailable potassium in river-bed sediments and release of interlayer potassium in irrigated arid soils

Abstract. Crop responses to applied potassium fertilizers are erratic in many arid and semi-arid soils. The potassium supplying potential of river-bed sediments and release of interlayer potassium from eleven alkaline soils were measured in two separate experiments. Sediments from the Chenab and Ravi Rivers in Pakistan were exhausted of potassium by successively growing wheat, maize, mungbean, and wheat in them for a total of 200 days, using Hoagland solution to supply optimum amounts of other nutrients. Cumulative plant dry matter yield was significantly greater on the Chenab sediments. The quantities of potassium supplied to plants from the sediments of the two rivers were also significantly different. Interlayer potassium was extracted for 1230 minutes from a Udic Haplustalf (Pindorian series) by twelve different solutions each with the same electrolyte content (100 cmol). The sodium adsorption ratios (SAR) of the solutions were adjusted to 5, 10, 25, and 50, each with Ca: Mg ratios of 25:75, 50: 50 or 75:25, using solutions of sodium, calcium and magnesium chloride. The potassium released from the soil was inversely related to solution SAR. Increasing proportions of magnesium relative to calcium in solution favoured the release of potassium, except in the SAR 50 solution. Significantly different quantities of potassium were extracted by various solutions. Maximum potassium (442 mg/kg) was extracted by SAR 5 solution with a Ca: Mg ratio of 25:75. Interlayer potassium subsequently removed by this solution from 11 alkaline soils ranged from 407 to 499 mg/kg. The potassium released from all but three of the soils was related to their clay content (r= 0.72; n= 8). The release of potassium from the soils followed the Elovich function. The intercept (X₁) and slope (X₂) estimated for the function was related to potassium released (y) by the equation: y=?1.13 + 2.74X₁?0.014X₂ (r= 0.998; n= 8) The results imply that river sediments treated with irrigation water containing magnesium and sodium ions can contribute substantial amounts of available potassium for plant growth.     

Nitrogen fixation,biomass production,and nutrient uptake by annual Sesbania species in an alkaline soil

Summary In three field trials conducted during the summer season of 1986, 1987 and 1989 in an alkaline soil, 17 accessions of annual Sesbania spp. were evaluated for nodulation, N₂ fixation (acetylene reduction assay), dry weight of roots and shoots, woody biomass production, and nutrient uptake. At 50 days after sowing all the accessions were effectively nodulated (average 36.4 root nodules plant^-1) with a high nodule score (3.4). There was a lot of variation in nodule volume and mass and in acetylene reduction activity but not in N content (5.2%). N uptake in shoots, roots and nodules averaged 639, 31, and 13 mg plant^-1, respectively, and much of the fixed N remained in shoots. Accessions of S. cannabina complex performed better than others. S. rostrata had poor root nodulation but exhibited excellent stem nodulation (300 nodules plant^-1) even though not inoculated with Azorhizobium sp. Average concentrations of N, P, K, S, Ca, and Mg in the shoots were high, at 3.2, 0.28, 1.5, 0.28, 1.5, and 0.4% respectively, and Na was low (0.15%), reflecting the usefulness of Sesbania spp. as an integrated biofertilizer source. Green matter production was 26.0 Mg ha^-1 (5.9 Mg dry matter) and N uptake was 158 kg ha^-1, 54 days after sowing. Average woody biomass of six accessions at maturity, 200 days after sowing, was high (19.9 Mg ha^-1), showing its potential for shortterm firewood production. Total nutrient uptake for production of woody biomass (200 days of growth) was no more demanding than growing the plant to the green-manuring stage of 50–60 days' growth.     

Cassini measurements of cold plasma in the ionosphere of Titan

The Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP) sensor observed the cold plasma environment around Titan during the first two flybys. The data show that conditions in Saturn's magnetosphere affect the structure and dynamics deep in the ionosphere of Titan. The maximum measured ionospheric electron number density reached 3800 per cubic centimeter near closest approach, and a complex chemistry was indicated. The electron temperature profiles are consistent with electron heat conduction from the hotter Titan wake. The ionospheric escape flux was estimated to be 10(25) ions per second.     

Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides

The silica-supported transition metal hydrides (=Si-O-Si=)(=Si-O-)2Ta-H and (=Si-O-)xM-H (M, chromium or tungsten) catalyze the metathesis reaction of linear or branched alkanes into the next higher and lower alkanes at moderate temperature (25degrees to 200degreesC). With (=Si-O-Si=)(=Si-O-)2Ta-H, ethane was transformed at room temperature into an equimolar mixture of propane and methane. Higher and lower homologs were obtained from propane, butane, and pentane as well as from branched alkanes such as isobutane and isopentane. The mechanism of the step leading to carbon-carbon bond cleavage and formation likely involves a four-centered transition state between a tantalum-alkyl intermediate and a carbon-carbon final sigma-bond of a second molecule of alkane.