Genetic analysis of the anther-culture response of three spring wheat crosses

Summary Anther-culture response was examined among three spring wheat (Triticum aestivum L.) cultivars to evaluate the genetic component of response and to determine whether androgenetic performance could be improved by selection. The three lines, the three possible F₁'s among the three lines, their F₂'s, and the backcrosses to the parents were evaluated for callus production and regeneration capacity. Significant variation was observed among the generations of the three crosses for callus formation. Genetic variation for regenerability was nonsignificant. Callus production was negatively correlated (-0.24) with regeneration capacity. The random variation in the study was too great to determine whether major-gene differences for antherculture response exist among the three lines by examining population distributions. When the material was evaluated for quantitative gene effects, the estimates for the additive gene effects were generally greater than the estimates for the dominance gene effects for callus formation. Only the Pavon x Chris cross, however, exhibited a significant narrow sense heritability estimate for callusing response (0.94). Due to the large component of random variation and the varying selection potential among crosses for androgenetic performance, improving anther-culture response in wheat by selection could prove difficult unless the anther-culture process itself selects for response traits at the gametic level.     

Variation in nitrogen use efficiency among soft red winter wheat genotypes

Summary Nitrogen use efficiency (NUE), defined as grain dry weight or grain nitrogen as a function of N supply, was evaluated in 25 soft red winter wheat genotypes for two years at one location. Significant genotypic variation was observed for NUE, nitrogen harvest index, and grain yield. Genotype x environment interaction for these traits was not significant. Several variables including N uptake efficiency (total plant N as a function of N supply), grain harvest index, and N concentration at maturity were evaluated for their role in determining differences in NUE. Nitrogen uptake efficiency accounted for 54% of the genotypic variation in NUE for yield and 72% of the genotypic variation in NUE for protein. A path coefficient analysis revealed that the direct effect of uptake efficiency on NUE was high relative to indirect effects.The investigation reported in this paper (No. 85-3-122) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director     

Combining ability analysis over F1-F5 generations in diallel crosses of bread wheat

Summary Combining ability studies for grain yield and its primary component traits in diallel crosses involving seven diverse wheat cultivars of bread wheat (Triticum aestivum L.) over generations F₁-F₅ are reported. The general and specific combining ability variances were significant in all generations for all the traits except specific combining ability variance for number of spikes per plant in the F₅. The ratio of general to specific combining ability variances was significant for all the traits except grain yield in all the generations. This indicated an equal role of additive and non-additive gene effects in the inheritance of grain yield, and the predominance of the former for its component traits. The presence of significant specific combining ability variances in even the advanced generations may be the result of an additive x additive type of epistasis or evolutionary divergence among progenies in the same parental array. The relative breeding values of the parental varieties, as indicated by their general combining ability effects, did not vary much over the generations. The cheap and reliable procedure observed for making the choice of parents, selecting hybrids and predicting advanced generation (F₅) bulk hybrid performance was the determination of breeding values of the parents on the relative performance of their F₂ progeny bulks.     

Origin and diversity of North American hard spring wheats

Genetic diversity is an important safeguard against crop vulnerability to biotic and abiotic stresses. Coefficient-of-parentage (COP) values of 248 North American hard spring wheat (Triticum aestivum L. em. Thell) cultivars released from 1901 to 1991 were used to estimate the genetic similarity of cultivars. COP values were used: to (1) quantify germ plasm sources and their contributions to the North American hard spring wheat gene pool; (2) measure changes in genetic diversity through time; and (3) identify major groupings of related cultivars. Landraces and local cultivars that contributed to the formation of the gene pool were: spring wheat (64%), winter wheat (16%), T. turgidum var. durum L. (10%), and T. turgidum var. emmer L. (8%). Fife, Hard Red Calcutta, and Turkey Red accounted for 18%, 13%, and 8%, respectively, of the hard spring wheat origins. Era and Butte in the US, and Neepawa and HY 320 in Canada, were the most commonly used named parents of cultivars released from 1981 to 1991. Both Canada and US had the greatest level of similarity among new cultivar releases in the 1930s (Canada: r=0.39, US: r=0.34). Genetic similarity in the US declined to r=0.14 in the 1940s and remained relatively constant thereafter. Similarity among released Canadian cultivars remained relatively high until the 1970s when the introduction of new market classes resulted in a 50% reduction in genetic similarity to approximately the same level of similarity found in the US. Cluster analysis was used to group cultivars released after 1941 into 13 clusters of similar genotypes. The cultivar clusters may have value for the stratified sampling of spring wheat germ plasm or in identifying diverse germ plasm for intermating.Contribution of the Idaho Agric. Exp. Stn. publication no. 95731. Missouri Pub. No. 12338     

Prediction of heterosis in crosses between inbred lines of Drosophila melanogaster

Summary The aim of the experiment was to determine if the estimated genetic distance between two populations could be used to predict the amount of heterosis that would occur when they were crossed. Eight lines of known relatedness to each other were produced by eight generations of sib mating and sub-lining. This produced lines that varied in coefficient of coancestry from zero to 0.78. Fourteen reciprocal crosses of these lines were used to measure heterosis for larval viability and adult fecundity. Gene frequencies at six polymorphic enzyme loci were used to estimate the genetic distances between lines, which were then compared with the known degrees of coancestry. The estimated genetic differences were poorly correlated with the known coancestry coefficients (r=0.4), possibly due to the small number of loci typed. Also genetic distances were only about 1/3 of what was expected. Selection acting on blocks of genes linked to the enzyme loci probably prevented the expected increase in homozygosity. Coancestry coefficient was correlated with heterosis (r=0.44–0.71). This level of correlation implied differences in heterosis among parent lines with the same level of coancestry. This variability is expected if a small number of loci explain most of the heterosis. The average level of heterosis was less than expected after eight generations of sib mating. This is most likely due to selection opposing the increase in homozygosity caused by inbreeding. The combination of these two imperfect correlations resulted in no significant correlation between genetic distance estimated from markers and heterosis.     

The effect of take-all disease on gas-exchange rates and biomass in two winter wheat lines with different drought response

There have been no studies of the effect of take-all on leaf gas-exchange rates, despite the fact that take-all severely restricts plant water and nutrient uptake, which results in significant biomass and grain yield reduction. Here we describe the effect of inoculation with Gaeumannomyces graminis (Sacc.) var. tritici (Ggt) on carbon assimilation rate (A) and biomass production of wheat plants grown under two water regimes. We show that the impact of Ggt inoculation on plant growth and leaf A may be through reduced photosynthetic capacity of the leaves and not water stress per se. The nature of this reduced photosynthetic capacity remains uncertain but may involve nutrient deficiency and different enzymes produced by the fungus. In each of the 3 years the experiment was conducted, Ggt significantly reduced A, i.e. at anthesis by 18% in 2000, 15% in 2001, and 12% in 2002. In agreement with other field studies, Ggt reduced tiller number and production of all plant components, mostly root dry mass and grain mass per plant. Highly significant negative correlations were found between disease rating and A in all years, showing that at disease ratings equal or higher than 3 (on a scale from 1 to 4) A could practically be zero. While A decreased, intercellular CO₂ concentration increased or did not change, and stomatal conductance was relatively high. In addition, A was more reduced under high than under low soil moisture content. These results support the idea that water stress per se did not contribute to the observed reduction of A. The mechanism of photosynthetic capacity reduction due to the Ggt root-rotting fungus is of interest as it may lead to the molecular mechanisms of plant resistance and ultimately to the development of take-all resistant plants.     

Blocks of gliadin components in winter wheat detected by one-dimensional polyacrylamide gel electrophoresis

Summary Inheritance of gliadin components in winter wheat has been studied by one-dimensional polyacrylamide gel electrophoresis. Single F₂ grains from 36 intervarietal hybrid combinations have been analysed. The genetic analysis has revealed blocks, including 1–6 gliadin components, which are inherited as individual mendelian traits. About 80 variants of blocks have been detected. On the basis of the allelism test they are grouped into 6 series in accordance with the number of known gliadin-coding loci located on chromosomes of the homoeologous groups 1 and 6. Each series includes 8–18 blocks controlled by different alleles of one gliadin-coding locus. Blocks of components have been confirmed to be inherited codominantly in accordance to the gene dose in the triploid endosperm. The highest similarity between members of one series is observed in groups of blocks controlled by chromosomes ID and 6D. On the contrary, many blocks controlled by chromosomes 1A and 1B have no bands in common. The presented catalogue of blocks of components may be used to make up gliadin genetic formulae and to compare electrophoregrams obtained by different authors. Blocks of gliadin components are suitable genetic markers for use in revealing and studying heterogeneity of wheat varieties, in tracing their origin, in identifying recombinations, translocations and substitutions of the genetic material and in solving many other problems of the origin, evolution and selection of hexaploid wheat.     

Root growth and water uptake in winter wheat under deficit irrigation

Root growth is critical for crops to use soil water under water-limited conditions. A field study was conducted to investigate the effect of available soil water on root and shoot growth, and root water uptake in winter wheat (Triticum aestivum L.) under deficit irrigation in a semi-arid environment. Treatments consisted of rainfed, deficit irrigation at different developmental stages, and adequate irrigation. The rainfed plots had the lowest shoot dry weight because available soil water decreased rapidly from booting to late grain filling. For the deficit-irrigation treatments, crops that received irrigation at jointing and booting had higher shoot dry weight than those that received irrigation at anthesis and middle grain filling. Rapid root growth occurred in both rainfed and irrigated crops from floral initiation to anthesis, and maximum rooting depth occurred by booting. Root length density and dry weight decreased after anthesis. From floral initiation to booting, root length density and growth rate were higher in rainfed than in irrigated crops. However, root length density and growth rate were lower in rainfed than in irrigated crops from booting to anthesis. As a result, the difference in root length density between rainfed and irrigated treatments was small during grain filling. The root growth and water use below 1.4 m were limited by a caliche (45% CaCO₃) layer at about 1.4 m profile. The mean water uptake rate decreased as available soil water decreased. During grain filling, root water uptake was higher from the irrigated crops than from the rainfed. Irrigation from jointing to anthesis increased seasonal evapotranspiration, grain yield, harvest index and water-use efficiency based on yield (WUE), but did not affect water-use efficiency based on aboveground biomass. There was no significant difference in WUE among irrigation treatments except one-irrigation at middle grain filling. Due to a relatively deep root system in rainfed crops, the higher grain yield and WUE in irrigated crops compared to rainfed crops was not a result of rooting depth or root length density, but increased harvest index, and higher water uptake rate during grain filling.     

Effects on winter wheat seedling growth by toxin-producing rhizobacteria

Summary Root-colonizing pseudomonads capable of inhibiting seedling winter wheat (Triticum aestivum L.) root growth in an agar seedling bioassay also significantly inhibited wheat root growth in vermiculite; however, the inhibitory trait is quite labile in laboratory culturing. The extent of inhibition in both the agar and vermiculite medium depended on inoculum level. These pseudomonads were found to produce a toxin capable of inhibiting growth ofEscherichia coli C-la andBacillus subtilis. Field isolates that strongly inhibit growth of indicator bacteria also inhibited root growth. Toxin production by the bacteria appeared necessary for inhibition of root growth and indicator bacteria as toxin-negative (TOX^–) mutants no longer inhibited either. Antibiosis towardsE. coli as well as wheat seedling root inhibition in agar was reversed by L-methionine, providing further evidence that a toxin, produced by these organisms, is involved in growth retardation.Contribution in cooperation with the College of Agric. Res. Center, Washington State Univ., Pullman, WA 99164. Scientific Paper No. 6837.     

The effect of inoculation with Azospirillum brasilense on growth and nitrogen utilization by wheat plants

Azospirillium brasilense is a rhizosphere bacteria that has been reported to improve yield when inoculated on wheat plants. However, the mechanisms through which this effect is induced is still unclear. In the present work, we have studied the effects of inoculating a highly efficient A. brasilense strain on wheat plant grown in 5 kg pots with soil in a greenhouse, under three N regimes (0, 3 or 16 mM NO₃ ^–, 50 ml/pot once or twice-a -week), and in disinfected or non-disinfected soil. At the booting stage, the inoculated roots in both soils showed a similar colonization by Azospirillum sp. that was not affected by N addition. The plants grown in the disinfected soil showed a higher biomass, N content and N concentration than those in the non-disinfected soil, and in both soils the inoculation stimulated plant growth, N accumulation, and N and NO₃ ^– concentration in the tissues.At maturity, the inoculated plants showed a higher biomass, grain yield and N content than the uninoculated ones in both soils, and a higher grain protein concentration than the uninoculated. It is concluded that in the present experiments, A. brasilenseincreased plant growth by stimulating nitrogen uptake by the roots.     

Accelerated production of transgenic wheat (Triticum aestivum L.) plants

We have developed a method for the accelerated production of fertile transgenic wheat (Triticum aestivum L.) that yields rooted plants ready for transfer to soil in 8–9 weeks (56–66 days) after the initiation of cultures. This was made possible by improvements in the procedures used for culture, bombardment, and selection. Cultured immature embryos were given a 4–6 h pre-and 16 h post-bombardment osmotic treatment. The most consistent and satisfactory results were obtained with 30 g of gold particles/bombardment. No clear correlation was found between the frequencies of transient expression and stable transformation. The highest rates of regeneration and transformation were obtained when callus formation after bombardment was limited to two weeks in the dark, with or without selection, followed by selection during regeneration under light. Selection with bialaphos, and not phosphinothricin, yielded more vigorously growing transformed plantlets. The elongation of dark green plantlets in the presence of 4–5 mg/l bialaphos was found to be reliable for identifying transformed plants. Eighty independent transgenic wheat lines were produced in this study. Under optimum conditions, 32 transformed wheat plants were obtained from 2100 immature embryos in 56–66 days, making it possible to obtain R3 homozygous plants in less than a year.     

Retention of D genome chromosomes in pentaploid wheat crosses

The transfer of genes between Triticum aestivum (hexaploid bread wheat) and T. turgidum (tetraploid durum wheat) holds considerable potential for genetic improvement of both these closely related species. Five different T. aestivum/T. turgidum ssp. durum crosses were investigated using Diversity Arrays Technology (DArT) markers to determine the inheritance of parental A, B and D genome material in subsequent generations derived from these crosses. The proportions of A, B and D chromosomal segments inherited from the hexaploid parent were found to vary significantly among individual crosses. F(2) populations retained widely varying quantities of D genome material, ranging from 99% to none. The relative inheritance of bread wheat and durum alleles in the A and B genomes of derived lines also varied among the crosses. Within any one cross, progeny without D chromosomes in general had significantly more A and B genome durum alleles than lines retaining D chromosomes. The ability to select for and manipulate this non-random segregation in bread wheat/durum crosses will assist in efficient backcrossing of selected characters into the recurrent durum or hexaploid genotype of choice. This study illustrates the utility of DArT markers in the study of inter-specific crosses to commercial crop species.     

Cultivar and cultivar x environment effects on the development of callus and polyhaploid plants from anther cultures of wheat

Summary Plants of three common wheat (Triticum aestivum L. em. Thell) cultivars and one randomly selected doubled-haploid line derived by anther culture from each of the three cultivars were each grown in three environments, a field environment, a greenhouse environment, and a growth chamber environment. Anthers containing largely miduninucleate to late uninucleate microspores were cultured and calli were induced to regenerate plants in order to assess the effects of cultivar, cultivar family (cultivar and corresponding doubled-haploid derivative), anther-donor plant environment, and cultivar X environment interaction on androgenic responses. Large differences in response were observed among cultivars as well as between cultivars and doubled-haploids. Differences between cultivar and doubled-haploid within cultivar family usually resulted from higher frequency of response in the cultivar, contrary to the hypothesis that anther culture per se constitutes a general selective device for superior androgenic responses. Also, in a second experiment, anther callusing frequency was greater in the cultivar Kitt than in any of five unique doubled-haploid lines derived from Kitt. Significant effects were also observed in the first experiment for the interactions of cultivar family X environment as well as doubled-haploid vs. cultivar X environment, although the effect of environment itself was less significant than these interactions.Contribution from the USDA, SEA, AR, Beltsville, Md, and the Department of Agronomy, University of Maryland, College Park, Md, as scientific article No. A-3413, contribution No. 6486     

O3浓度升高和太阳辐射减弱对小麦根际土壤微生物功能多样性的影响

采用开顶箱(OTC)法和遮光网技术,设置100 n L/L臭氧熏气与3个辐射减弱梯度结合,模拟臭氧浓度升高和太阳辐射减弱的复合大气背景。用BIOLOG生态测试板,采用孔平均颜色变化率法(AWCD)测定冬小麦根际土壤微生物利用不同碳源的能力,计算微生物群落多样性指数,对不同碳源的利用率进行了主成分分析。两年试验结果显示,臭氧熏气与太阳辐射减弱复合作用,降低了土壤微生物对碳源的利用速度和利用总量;除了聚合物以外其它碳源利用率显著降低;对土壤微生物多样性没有直接的影响;对碳源降解的抑制效应大于增强的O3与减弱的太阳辐射两因素各自的单独作用。太阳辐射减弱20%,一定程度上增加了对聚合物类的分解。O3熏气条件下太阳辐射减弱,糖类、胺类代谢变异度较高,受环境影响较大。     

Molecular characterization of the fate of transgenes in transformed wheat (Triticum aestivum L.)

Molecular analysis of the transgenes bar and gus was carried out over successive generations in six independent transgenic lines of wheat, until the plants attained homozygosity. Data on expression and integration of the transgenes is presented. Five of the lines were found to be stably transformed, duly transferring the transgenes to the next generation. The copy number of the transgenes varied from one to five in the different lines. One line was unstable, first losing expression of and then eliminating both the transgenes in R3 plants. Although the gus gene was detected in all the lines, GUS expression had been lost in R2 plants of all but one line. Rearrangement of transgene sequences was observed, but it had no effect on gene expression. All the stable lines were found to segregate for transgene activity in a Mendelian fashion.     

Heat stress effects on ribulose-1,5-bisphosphate carboxylase/oxygenase,Rubisco binding protein and Rubisco activase in wheat leaves

Changes in chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) binding protein (RBP), Rubisco activase (RA), Rubisco large (LS) and small (SS) subunits, and electrolyte leakage were investigated in wheat leaf segments during heat stress (HS) for 1 h and for 24 h at 40 °C in darkness or in light, as well as after recovery from heat stress (HSR) for 24 h at 25 °C in light. The 24-h HS treatment in darkness decreased irreversibly photosynthetic pigments, soluble proteins, RBP, RA, Rubisco LS and SS. An increase in RA and RBP protein contents was observed under 24-h HS and HSR in light. This increase was in accordance with their role as chaperones and the function of RBP as a heat shock protein.This work was partially supported by Swiss National Science Foundation (Project 31-55289.98).     

Identification,characterization, and comparison of RNA-degrading enzymes of wheat and barley

RNA-degrading enzymes play an important role in regulating gene expression, and sequence analyses have revealed significant homology among several plant RNA-degrading enzymes. In this study we surveyed crude extracts of the above-ground part of the common wheat (Triticum aestivum L.) and the cultivated barley (Hordeum vulgare L.) for major RNA-degrading enzymes using a substrate-based SDS-PAGE assay. Fifteen wheat and fourteen barley RNA-degrading enzymes, with apparent molecular masses ranging from 16.3 to 40.1 kD, were identified. These RNA-degrading enzymes were characterized by their response to pH changes and addition of EDTA and ZnCl₂ to the preincubation or incubation buffers. The 33.2- to 40.1-kD wheat and barley, 31.7-kD wheat, and 32.0-kD barley enzyme activities were inhibited by both zinc and EDTA and were relatively tolerant to alkaline environment. The 22.7- to 28.2-kD enzymes were inhibited by zinc but stimulated by EDTA. The 18.8-kD enzyme exists in both wheat and barley. It was active in an acid environment, was inhibited by zinc, but was not affected by EDTA. Two enzyme activities (31.0 and 32.0 kD) are unique to the common wheat. Contribution from Agriculture Research Division, University of Nebraska, Journal Series No. 9895.     

Fertilizer nitrogen budgets of 15N-labelled sugarbeet (Beta vulgaris) tops and Na 15NO3 dressings split-applied to winter wheat (Triticum aestivum) in microplots on a loam soil

The fate of N from sugarbeet (Beta vulgaris L.) tops returned to the soil (50 T ha^-1) in autumn 1986 before sowing winter wheat (Triticum aestivum L.), and from NaNO₃ split-applied in 3 equal dressings (at tillering, stem elongation and flag leaf stages) was studied using isotopically labelled ¹⁵N in open stainless-steel cylinders pressed into the soil.At harvest, the percentage utilization (PU) of N from sugarbeet was very low (6.66%) and negatively influenced by fertilizer N (5.59%), while that of fertilizer N was rather high (69.64%) and unchanged by addition of tops. Residual N in soil represented 25.9% of the amount applied in tops and ranged from 33% for the tillering application to 21% for the flag leaf application. N losses (mainly denitrification) from sugar beet tops amounted to 67% and were very low for mineral fertilizer (less than 5%).     

The effect of polyamines on protein kinase activities of wheat (Triticum aestivum) L. anthers

Protein kinase activities were extracted from anther tissue of wheat (Triticum aestivum L. cv. Zaragoza) and characterized with regard to the effects of polyamines, second messengers and plant growth hormones. The protein kinases were inhibited by polyamines and cyclic nucleotides, but were stimulated by the addition of auxins, gibberellic acid and kinetin. The dominant polyamine-sensitive kinase activity was partially purified and characterized. The optimal pH of the reaction was 7.5 to 8.0 and casein was the preferred exogenous substrate. Polyamines were inhibiting in the decreasing order of putrecine > spermidine > spermine. The results are discussed against the context of the anther culture technique.