Chlorophyll inheritance patterns and extent of natural self-pollination in timothy

Three hundred sixty-five S₁ and 234 S₂ seedling populations of timothy (Phleum pratense L.) were examined for their segregations for chlorophyll deficiencies. Arrays of both self-and open-pollination families indicated a lack of concentration at definite levels, with ratios expressed forming a continuous series from 4.6:1 to 572:1 for green: chlorophyll-deficient types in the S₁ generation. The S₂ populations examined ranged from 1.8:1 to 244:1. Arrays were very similar in their distributions.Sixty-three plants yielded chlorophyll-deficient types in both S₁ and S₀ populations. From these, it was calculated that 7 to 8 percent of natural self-pollination may occur in timothy.Except at two levels (28:1 and 143:1 tetradisomic) assumption of tetradisomic or simpler inheritance patterns resulted in lower calculated percentages of natural self-pollination than resulted from assumed hexasomic inheritance. No apparent explanation is available to account for these divergences from the regular pattern encountered.Results of cooperative work of the Crops Research Division, Agriculture Research Service, U.S. Department of Agriculture and the Wisconsin Agricultural Experiment Station, Madison.Research Agronomist, Crops Research Division, Agriculture Research Service, U.S. Department of Agriculture and Associate Professor, and Professor of Agronomy, Wisconsin Agricultural Experiment Station, respectively.     

Cytogenetics of a tetraploid form of Phleum pratense L.

A tetraploid form of Phleum pratense from southwestern Europe was found to behave cytogenetically as an autotetraploid. Inheritance patterns in inbred seedlings artificially inoculated with stem rust agreed with this interpretation if chromosome and chromatid assortment are assumed.Results of cooperative investigations of the Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, and the Wisconsin Agricultural Experiment Station.Geneticist, Crops Research Division, A.R.S., U.S. Department of Agriculture, and former Graduate Assistant, Agronomy Department, Wisconsin Agricultural Experiment Station, Madison, Wisconsin.     

Intraplant instability in smooth bromegrass (Bromus inermis leyss)

Intraplant variation in smooth bromegrass was examined by determining pollen stainability and size in 6 moderately self-compatible S-2, and 12 self-incompatible OP-3 plants. Statistically significant differences in pollen stainability occurred between panicles within plants, between plants, and between plants x within plant interactions. Pollen diameter distributions for OP-3 plants tended to be trimodal, and bimodal distributions occurred in S-2 plants. In trimodal distributions, peaks occurred at known diploid and tetraploid chromosome levels, and it is presumed that the peak between these represented the triploid gametic number.Results of cooperative investigations of the Crops Research Division, ARS, USDA, and the Wisconsin Agricultural Experiment Station, Madison. The statistical analyses were made by the Numerical Analysis Laboratory, University of Wisconsin.     

Cytology of Phleum sp. affin. P. montanum C. Koch

Diploid, tetraploid, and hexaploid plants occurred in foreign plant introductions of P. sp. affin. P. montanum from Turkey and Iran. Within-progeny variations in polyploid levels indicate that divergent races occurred as interspersed but natural populations. One to six B-chromosomes of varying sizes in addition to the normal chromosome complement were present in some plants. Their behaviours appeared essentially similar to those recorded for other species. Certain of the plants examined exhibited cytological features similar to those observed in known hybrids. These included prophase pycnosis, stickiness, split metaphase I plates, unoriented chromosomes at M-1, and low levels of pollen stainability. These features were absent in microsporocytes of other plants. Low open-pollination seed set characterized all plants examined. This may be due to hybridity or possibly to response to ecological conditions of the new environment.Results of co-operative work of the Crops Research Division, A.R.S., U.S. Department of Agriculture, and the Wisconsin Agricultural Experiment Station, Madison, Wisconsin.Former Graduate Student, Department of Agronomy, Wisconsin Agricultural Experiment Station, and Geneticist, Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture.     

Cytology of tetraploid x hexaploid timothy (Phleum pratense L.)

Ten pentaploids were isolated from seedling populations developed from seed of tetraploid plants grown in association with hexaploid timothy. About 80% of the prophase sporocytes exhibited severe or moderate pycnosis. These pycnotic accumulations appear to arrest the meiotic processes and apparently result in sporocyte lethality. Surviving sporocytes at diakinesis possessed nuclei with configurations that varied from 1 VI+14 II+1 I to 9 II+17 I. It is suggested that the conventional sorts of irregularities (univalents, inversions and translocations) cannot account for the low percentages of stainable pollen. Pairing relations indicated that considerable duplication and/or autosyndesis occurred in the genomes combined, and suggest that even though the tetraploid (2n=28) and hexaploid (2n=42) forms of Phleum pratense are closely related they are not identical. A portion of the sterility observed may be due to nuclear-cytoplasmic interaction.Results of co-operative work of the Crops Research Division, A.R.S., U.S. Department of Agriculture, and the Wisconsin Agricultural Experiment Station, Madison, Wis.Geneticist, Crops Research Division, A.R.S., U.S. Department of Agriculture, and Graduate Assistant, Department of Agronomy, Wisconsin Agricultural Experiment Station.     

Inbreeding depression in diploid and autotetraploid sugarbeet,Beta vulgaris L.

Summary The effect of inbreeding on vegetative vigor, as measured by root yield, was evaluated in two diploid (2x) and equivalent autotetraploid (4x) sugarbeet strains, and one additional 2x and one 4x strain. Root yields of the 2x and 4x S₁ progenies each averaged 86.7% of their comparable open-pollinated progeny. Inbreeding depression of root yield was variable from strain to strain. The selfed 4x populations, when compared with their 2x equivalents, suffered more yield depression than was expected on the basis of the theoretic approach to homozygosity associated with selfing in autotetraploids. The inbreeding depression was partly attributed to (a) the approach to homozygosity, and (b) the fact that partially homozygous 4x S₁ individuals were probably unable to make compensating growth when located adjacent to a low vigor aneuploid plant. A major part of root yield depression remained unexplained. Sucrose content within strains and within ploidy levels was not significantly affected by one generation of selfing.Joint contribution of the Crops Research Division, Agricultural Research Service, US Department of Agriculture, the Colorado Agricultural Experiment Station, and the Beet Sugar Development Foundation. Published with the approval of the Director of the Colorado Agricultural Experiment Station as Scientific Series No. 1582.     

Haploid induction in potato: Cytological basis for the pollinator effect

Summary A hexaploid endosperm is regularly associated with a haploid embryo following 4x–2x crosses in potato. One explanation for this is that a single 24-chromosome restitution sperm nucleus fuses with the central cell of the megagametophyte. This suggests that a superior pollinator may be one that produces a high frequency of restitution sperm nuclei. To test this, a technique was developed for observing pollen tube mitosis in vitro following germination of potato pollen in a 20% lactose-50 ppm boric acid solution. A single 24-chromosome restitution sperm nucleus was found in up to 38% of the pollen tubes from a superior pollinator. Moreover, pollen from an inferior pollinator soaked in a sucrose-boric acid-colchicine solution produced 100% restitution sperm nuclei in vitro and a haploid frequency from a tetraploid cultivar comparable to that normally induced by an untreated superior pollinator. The data indicate that the effectiveness of a pollinator in inducing haploids in potato is determined by the frequency of restitution sperm nuclei it produces.Cooperative investigations of the Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, and the Wisconsin Agricultural Experiment Station. Part of a thesis submitted by the senior author in partial fulfilment of the requirements for the Ph. D. degree. Published with the approval of the Director of the Wisconsin Agricultural Experiment Station.Research Assistant, Department of Horticulture, University of Wisconsin, and Research Geneticist, Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, Madison, Wisconsin 53706.     

Characteristics of inbred progenies from morphologically unstable Sorghum plants

Progenies from 68 self-pollinated panicles of 10 somatically unstable sorghum-sudangrass hybrid sectors were grown. Data are presented for 25 progenies from three representative unstable plants. Highly uniform progenies were obtained from most panicles. Results indicate chromosome assortment was not always at random. Major distinctions between panicle progenies suggested that: (a) sorghum-like and sudangrass-like genomes functioned as units; (b) gene transfer and association were non-random further indicating that somatic chromosome substitution or somatic translocations, or other gross changes, may have occurred; and (c) other deviating behaviors implied genetic segregation.Results of cooperative work of the Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, and the Wisconsin Agricultural Experiment Station, Madison, Wisconsin 53706 U.S.A.     

Estimating the genetic relationship of hybrid bromegrass to smooth bromegrass and meadow bromegrass using RAPD markers

The two most widely grown bromegrass species in North America are smooth bromegrass, a hay type grass, and meadow bromegrass, a pasture type grass. Hybrid populations between these two species have been developed through hybridization and recurrent selection. The objective of this study was to determine the genetic relatedness of the hybrid bromegrass population S‐9073M to its parental populations using random amplified polymorphic DNA (RAPD) markers and to determine genetic variation within and between populations. Individuals from each of the three populations were genotyped at 43 polymorphic RAPD loci. One of the RAPD fragments was meadow bromegrass‐specific. Cluster analysis showed three groups representing the two parental populations and the hybrid population. An analysis of molecular variance (AMOVA), showed that the hybrid population had the highest within‐population variation, followed by meadow bromegrass and smooth bromegrass. The interpopulation genetic distance (phi‐statistic =Φ_st) was highest between meadow and smooth bromegrass and lowest between smooth and hybrid bromegrass. The hybrid population was genetically intermediate to smooth bromegrass and meadow bromegrass, but closer to smooth bromegrass, possibly reflecting the selection criteria used in the development of this hybrid.     

Genetic dissection of a chromosomal region conferring hybrid sterility using multi-donors from Oryza glaberrima

A chromosomal region containing a hybrid sterility locus, S ₁, from Oryza glaberrima, located on the short arm of chromosome 6, was investigated in 15 BC₇F₁ and one BC₃F₂ populations. As a gamete eliminator, S ₁ induced both male and female gamete abortion and responded to typical, spherical, or empty pollen abortion when it was heterozygous. The gametes carrying S ₁ ^a (Oryza sativa allele in S ₁) in the heterozygous S ₁ locus had been eliminated in previous studies. We found here that both male and female gametes carrying the S ₁ ^a allele were killed incompletely in heterozygous (S ₁ ^g S ₁ ^a ) plants, with 26.22% female and 9.06% male gametes with the S ₁ ^a genotype remaining when the BC₃F₁ sterile plant produced male and female gametes, which fits with the hypothesis that the ratio of S ₁ ^a gametes of the female that were killed is higher than that of the male gametes. In addition, in sterile BC₆F₁ plants with the heterozygous S ₁ locus, not only a majority of the female gametes carrying the S ₁ ^a allele, but also a quite number of those carrying the S ₁ ^g allele (O. glaberrima allele in S ₁) could not be transmitted to their offspring. This abnormal transmission of female gametes illustrates the complexity of the reproductive isolation mechanism caused by S ₁ and can not be explained by the ‘one locus, sporo-gametal interaction’ model alone. Interaction for female sterility between S ₁ and two other loci on chromosomes 1 and 4 that suppress the expression of S ₁ was identified. S ₁ is the main reproductive isolation locus when mining favorable traits/genes from O. glaberrima due to its ubiquity between these two species, and the development of bridge parents carrying S ₁ should be a useful method for overcoming or abating this obstacle between these two species. The chromosomal region of S ₁ may be the hot region of genetic diversity for speciation because several hybrid sterility loci between species, subspecies, and even intra-subspecies have been identified in the same region.     

Evaluating genetic variation and relationships among two bromegrass species and their hybrid using RAPD and AFLP markers

The two most widely grown bromegrass species in North America are smooth bromegrass (Bromus inermis Leyss.), a hay type grass, and meadow bromegrass (Bromus riparius Rehmann), a pasture type grass. Recently a hybrid bromegrass population between the two species has been produced as a dual-purpose hay-pasture grass. Molecular markers have the potential to improve selection procedures to enhance bromegrass breeding. The objective of this study was to use RAPD and AFLP markers to determine genetic relationships and variations among bromegrass populations. Forty-three RAPD markers from 21 primers and 83 AFLP markers from seven primer combinations were used. Both marker types were able to group the individuals into their respective populations. The relationships among the individuals within each of the populations were not similar between the two marker types. Analysis of molecular variance (AMOVA) detected greater within-population variation than among-population variation for both marker types. The highest variation was observed in the hybrid population followed by meadow and then smooth bromegrass. The inter-population distance from both markers indicated that the highest genetic distance was between meadow and smooth bromegrass and lowest between smooth and hybrid bromegrass, which reflect the breeding history of the hybrid population. This study showed that both markers are capable of differentiating bromegrass genotypes into their respective populations, detecting genetic variation and relationships of the populations. Results of this study suggest that these two markers can be used in the future to enhance the current breeding practices in bromegrass, however, AFLP markers would be the marker of choice due to the high number of polymorphic markers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reaction to the cotton root-knot nematodes and the pollen and seed fertility of kenaf-roselle (Hibiscus cannabinus × H. sabdariffa) allohexaploids

Summary Allohexaploid (2n = 108) F₂ and F₃ interspecific hybrids ofHibiscus cannabinus × H. sabdariffa were intermediate in their resistance to the cotton root-knot nematode (Meloidogyne incognita acrita Chitwood 1949) between their moderately resistant, tetraploid parent, roselle (Hibiscus sabdariffa L.) and their susceptible, diploid parent, kenaf (H. cannabinus L.). Whether or not this resistance, as measured by the amount of root galling, is sufficient to be of practical importance is not known at present. However, results were encouraging enough to suggest further testing of the hybrids for agronomic potential, stability, fertility, and response to root-knot, and other parasitic nematodes that attack this potentially important paper-pulp crop.Cooperative investigations of the Crops Research Division, Agricultural Research Service, US Department of Agriculture, and the Texas Agricultural Experiment Station.     

Quantity production of anther-derived haploids from a multiple disease resistant tobacco hybrid. I. Frequency of plants with resistance or susceptibility to tobacco mosaic virus (TMV), potato virus Y (PVY), and root knot (RK)

Summary Methods are described for producing large numbers of haploid plantlets from anthers of a flue-cured tobacco hybrid with monogenic resistance to tobacco mosaic virus, (TMV), potato virus Y (PVY) and root knot (RK), respectively. Additional details are given on colchicine treatment for converting haploids to doubled haploids (DH's) and on the frequency of spontaneous DH's among untreated plantlets. Disparate genetic ratios of TMV-resistant to TMV-susceptible plants were obtained among colchicine-treated haploid plantlets, induced DH's and untreated haploids when compared with F₂ and BC₁ progenies. Haploids (gametes) with the gene for TMV resistance occurred more frequently than expected and plantlets with the gene for RK resistance occurred less frequenctly than expected. Transmission of the gene for PVY resistance differed only slightly from Mendelian expectations. These unexpected ratios, in addition to the frequent occurrence of plastid chimeras among anther-derived plantlets, strengthened our conviction that haploidy is somehow associated with mutation.Joint contribution from the Departments of Genetics, Crop Science and Plant Pathology, North Carolina State University, and the Tobacco Research Laboratory, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Oxford, North Carolina. Paper No. 5576 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina.     

Gynoecious sex expression and stability in cucumber (Cucumis sativus L.)

Summary Results indicated that gynoecious stability in the F₁ is governed by partial dominance. The degree of gynoecious stability is dependent upon genotypes, stages of plant for AgNO₃ application and number of sprays. Depending upon the genotypes, the one-true-leaf stage and one spray of 250 ppm AgNO₃ showed more gynoecious stability in the F₁. Twice application of AgNO₃ at the two-true-leaf stage produced the maximum number of male flowers. Plants exposed to light for longer time (10.00 h) after AgNO₃ application produced less flowers than when exposed for shorter time (15.00 and 20.00 h).Present address: Division of Vegetable Crops, Indian Agricultural Research Institute, New Delhi-110012, India.     

Inheritance of incompatibility in hybrids between Solanum tuberosum haploids and diploid species

The inheritance of self-incompatibility in two South American cultivated diploid species, Solanum phureja and S. stenotomum subsp. stenotomum, conforms with the Nicotiana scheme of oppositional S alleles. Similar studies in hybrids between S. phureja and a haploid (US-W 253) derived from S. tuberosum subsp. andigena were explained on the assumption of S alleles at homologous loci. The cut-stem technique employed in haploid extraction was used to facilitate the analyses. Maintenance of a series of heterozygous S allele testers is accomplished via matings with a clone homozygous for the S allele common to the series. True seed obtained from such crosses consists of only the desired S genotype.Departments of Horticulture and Genetics, University of WisconsinPaper No. 951 from the Department of Genetics, College of Agriculture, University of Wisconsin. Supported in part by the National Science Foundation and the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation.     

Random amplified polymorphic DNA variation within and among meadow bromegrass progeny types

Ten meadow bromegrass genotypes tested as half‐sib (polycross, PX; open‐pollinated, OP) and selfed (S₁) progenies were surveyed using random amplified polymorphic DNA. Fourteen primers, which produced 32 markers, were selected to determine the genotypes of 360 individuals from the three progeny tests. Analysis of molecular variance was performed in each progeny test, and genetic distances between genotypes and progeny types were determined. Among genotype genetic variation in half‐sib (PX and OP) progenies was similar. Genetic variation among genotypes for S₁ progenies (30.5%) was about twice that found in the half‐sib progenies. Variation between individual S₁ progenies ranged from 15.7% to 50.1%, while in the half‐sib progenies, the range was 6.9‐24.1%. Based on average distances between progeny types for a given genotype, OP and PX were closer to each other than to the S₁. An analysis of variance of the molecular marker frequency occurrence was performed for 12 plants within each progeny type of each genotype. Marker frequencies, expressed in percentages, ranged from 10.7% to 84.3%. No significant differences were found for genotype and progeny type‐genotype interaction suggesting that all genotypes behave in a similar manner across the different progeny types.     

Self-incompatibility genotype identification and stability as influenced by inbreeding in red clover (Trifolium pratense L.)

Summary S allele genotypes of I₁ progenies from eight I₀ red clover (Trifolium pratense L.) clones were determined under isolated field conditions. Each I₁ progeny was vegetatively increased and isolated under a cage for pollination by honey bees. Clones within each I₁ progeny producing relatively large and small amounts of seed were classified homozygous and heterozygous, respectively, for S allele genotype. S allele genotypes were verified by extensive sib crosses in the greenhouse, and almost complete agreement was found with the field classification. I₂ progenies were reciprocally test-crossed with their parental I₀ clones to detect any changes in S specificity and also to confirm the previous S genotype classifications in the I₁ generation. It was concluded that the reliability of field and greenhouse sib classification of S genotypes is based on the strength of the incompatibility reaction in each particular clone. Most I₁'s showed a strong incompatibility reaction as evidenced by low seed set for heterozygous S genotypes, but one progeny showed a weak incompatibility reaction which resulted in S genotype misclassifications. An S specificity was changed in one I₂ progeny.Contribution from the Kentucky Agricultural Experiment Station. This paper (72-3-151) is published with the approval of the Director, Kentucky Agricultural Experiment Station, Lexington, Kentucky 40506, USA.     

Compatibility of evolutionary and mutation breeding methods

X-ray induced barley mutants and their prototype Hannchen were tested for their behaviour in evolutionary breeding (the term is used to indicate the application of population genetics to plant breeding). It was shown that only the better mutants survive. Eventually only the fittest mutants and recombinants will comprise the population.Contribution from the Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, and the Agronomy Departments of the University of California and of Arizona, co-operating. The mutants were selected from a culture grown for R. S. Caldecott at Brawley California in 1955.Research Agronomist and Geneticist, Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, and Field Station, Supt., University of California, respectively at Davis, California, Tucson, Arizona, and Tulelake, California.     

Developing tomatoes resistant to curly top virus

Summary Developing high levels of resistance to curly top virus (CTV) and combining it with good horticultural type in tomato lines has been difficult. However genes for resistance from severalLycopersicon species have been obtained and combined by intercrossing and selection in extensive greenhouse and field tests. Several tomato breeding lines have been developed which contain these genes in combination with those giving good horticultural characteristics. The effective utilization of these resistant breeding lines in crosses with commercial types to develop finished varieties will necessitate severe exposure to CTV in several successive tests. Large F₂ populations and large numbers of selections in the following filial generations must be screened. Horticultural selection should be done only in those tests in which disease exposure has been sufficient to eliminate the susceptible parent.Co-operative investigation of the Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, and the Agricultural Experiment Stations of Utah and Washington, Logan, Utah, and Pullman, Washington, respectively.     

Reed Canarygrass Forage Yield and Nutrient Uptake on a Year-round Wastewater Application Site

Reed canarygrass (Phalaris arundinacea L.) is often planted at wastewater treatment sites to provide ground cover and remove nutrients. Our overall objective was to determine the forage yield and nutrient uptake under year-round potato wastewater application in northern latitudes. Specifically, we determined the effect of N fertilization rate on forage dry matter yield and N and P uptake by reed canarygrass, and compared the forage yield, persistence and nutrient uptake of reed canarygrass relative to those of orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromis inermis Leyss), timothy (Phleum pratense L.) and quackgrass [Elytrigia repens (L.) Nevski]. With only wastewater application, reed canarygrass had a forage yield of 5.8 Mg ha⁻¹, with N and P uptake of 113 and 30 kg ha⁻¹, respectively. Forage dry matter yield, N uptake and P uptake increased to 14.5 Mg ha⁻¹, 383 kg ha⁻¹ and 64 kg ha⁻¹, respectively, with an N fertilization rate of 224 kg ha⁻¹. Forage yield and N uptake of reed canarygrass, orchardgrass, timothy and smooth bromegrass were similar and exceeded those of quackgrass. Reed canarygrass P uptake exceeded that of the other grasses. Reed canarygrass was less persistent than quackgrass or smooth bromegrass.