Selection for seed retention in Phalaris tuberosa L.

1963 ◽  
Vol 14 (6) ◽  
pp. 755 ◽  
Author(s):  
JR McWilliam
Keyword(s):  
Genetic Variation ◽  
Perennial Grass ◽  
Economic Problem ◽  
Base Population ◽  
Response To Selection ◽  
Seed Shattering ◽  
Commercial Strain ◽  
Seed Retention ◽  
Eastern Australia ◽  
Selection For

Loss of seed from the maturing inflorescence (seed shattering) is common in grasses and constitutes a serious economic problem in many species. This paper reports the results of artificial selection to improve seed retention in Phalaris tuberosa, an important perennial grass in south-eastern Australia. A study of the factors controlling the loss of seed in this species has revealed that the seed lies free within the inflorescence at maturity, and its loss is promoted by the opening of the glumes. This in turn is influenced by the structure of the inflorescence. The highest seed retention has been found in plants with a short rigid inflorescence containing a large number of densely packed spikelets. Wide variation for seed retention exists between strains of P. tuberosa. The lowest value (25%) was found for natural ecotypes from Algeria and Morocco, and the highest for a selection from a strain of the Australian commercial type obtained from Argentina (81%). An estimate of the heritability for seed retention was high (0.92 ± 0.11), and most of the genetic variation appeared to be additive. There was a marked response to selection for high seed retention. With the Argentine variety as the base population, an increase of 29% in the average level of seed retention was achieved from the first cycle of selection. This level represents an increase of 60% by comparison with the widely grown commercial strain. The importance of high seed retention in relation to the economics of Phalaris seed production is briefly discussed.

Recurrent selection for grazing tolerance in winter-active populations of the perennial grass, Phalaris aquatica L.

2006 ◽  
Vol 12 ◽  
pp. 89-92
Author(s):  
Richard Culvenor ◽  
Suzanne Boschma ◽  
Kevin Reed
Keyword(s):  
Recurrent Selection ◽  
Perennial Grass ◽  
Grazing Pressure ◽  
Soil Conditions ◽  
Environment Interaction ◽  
Response To Selection ◽  
North West ◽  
Phalaris Aquatica ◽  
Eastern Australia ◽  
Selection For

Phalaris (Phalaris aquatica L.) is a perennial grass of Mediterranean origin used widely by the sheep and cattle industries of south-eastern Australia. Winter-active cultivars released since the 1970's have the potential for higher herbage productivity than the earlier, semi-winter dormant cultivars but have been reported to be less persistent under sub-optimal grazing management and soil conditions. To improve genetic potential for persistence in winter-active phalaris, a program of recurrent selection was conducted by subjecting three populations of half-sib families to two cycles of selection for persistence under heavy, largely continuous grazing pressure. Cycle 2 progeny families and bulked seedlots of each generation were grown in separate grazed plot trials in Western Victoria and the Southern Tablelands and North-West Slopes of New South Wales from 1999-2003 to assess response to selection. Positive linear response to selection was observed in all populations at the Western Victorian and Southern Tablelands sites. Response to selection was absent and persistence was very low under higher temperature and drought stress on the North-West Slopes. This high level of genotype × environment interaction for persistence was also observed among final generation families. Families with better persistence than current winteractive cultivars at the two southern sites were identified in each population and a new cultivar is being formed from the parents.

scholarly journals The quantitative relations between variation in red eye pigment and related pteridine compounds inDrosophila melanogaster

1970 ◽  
Vol 15 (1) ◽  
pp. 65-86 ◽  
Author(s):  
Ilse B. Barthelmess ◽  
Forbes W. Robertson
Keyword(s):  
Genetic Variation ◽  
Biochemical Properties ◽  
Pigment Content ◽  
Red Pigment ◽  
Base Population ◽  
Stock Selection ◽  
Metabolic Pattern ◽  
Red Eye ◽  
Genetic Behaviour ◽  
Selection For

SUMMARYThe relations between the quantity of red eye pigment and related pteridine compounds ofDrosophila melanogasterhave been studied in a variety of genotypes, which include strains selected for high or low pigment content, various derivatives of these lines and also lines in which one or other of the major autosome pairs were represented by homozygous chromosome pairs, derived by random sampling from the base population and also inbred lines. The quantity of red pigment was defined by the optical density when whole heads were extracted in a suitable solvent, while the pteridines were separated by chromatography and their amounts estimated by means of their characteristic fluorescence.The evidence from selection, inbreeding and chromosome sampling from the base population demonstrated the presence of substantial genetic variation for pigment content and amounts of related pteridines.The genetic and biochemical properties of the selected lines differed according to the direction of selection. High lines remained heterozygous after many generations of selection and displayed dominance and epistasis in favour of higher pigment content in crosses to the unselected stock. Selection for low pigment content led to fixation of recessive effects, attributable to particular chromosomes. The dominance-recessive relationship in red pigment differences was also applicable to the associated pteridines.The metabolic pattern in all lines with reduced pigment content is compatible with the assumption of reduced enzyme activity at particular steps of the pathway leading to the drosopterins (red eye pigments). The two steps accessible to study are subject to genetic variation in the base population, while inbreeding or selection for low pigment content leads to genetically fixed alterations at one or other of these steps. The genetic analysis was consistent with the biochemical evidence.Increase in pigment content above the normal level, either by selection or chance fixation, is accompanied by correlated increase in all the precursors. Several alternatives are possible but it is suggested that this may be due to an increase in early precursors, before the stages which have been altered in the low pigment lines.Attention is drawn to the similarity in genetic behaviour between pigment content and body size. Particular emphasis is laid on the value of selection as a means of creating biochemical differences which offer a basis for relating biochemical function and genetic behaviour.

scholarly journals Artificial selection with differing population structures

1980 ◽  
Vol 36 (2) ◽  
pp. 117-131 ◽  
Author(s):  
K. A. Rathie ◽  
F. W. Nicholas
Keyword(s):  
Close Agreement ◽  
Large Population ◽  
Additive Model ◽  
Directional Selection ◽  
Base Population ◽  
Average Response ◽  
Response To Selection ◽  
Bristle Number ◽  
Population Structures ◽  
Selection For

SUMMARYThe effect of subdivision of a population on response to artificial directional selection for abdominal bristle number in Drosophila melanogaster was compared using large, replicated lines. Three different population structures were compared: (i) selection in an Undivided, large population with 50 pairs of parents (treatment U); (ii) selection in each of 10 sublines which were reconstituted every 6th generation by Crossing after Culling the 5 lowest sublines (treatment CC); and (iii) selection in each of 10 sublines which were reconstituted every 6th generation by Crossing after Retaining all 10 sublines (treatment CR). At the end of three cycles of selection and crossing, neither CR nor CC was superior to U; sublining did not increase response to selection. These results agree with the predictions arising from an entirely additive model and provide no evidence for the presence of epistasis.A comparison of 50-pair lines (U) with several 5-pair lines was made over 31 generations. For the 50-pair lines, there was close agreement between response predicted from the base population (using ih2σp) and observed response throughout all 31 generations of selection. Although the best of the 5-pair lines exceeded the 50-pair lines in the early generations, average response to directional selection in the 5-pair lines soon fell behind that predicted from ih2σp, and soon reached a plateau.

Mating frequency in male Japanese quail: crosses among selected and unselected lines

1983 ◽  
Vol 25 (5) ◽  
pp. 450-456 ◽  
Author(s):  
D. E. Bernon ◽  
P. B. Siegel
Keyword(s):  
Genetic Variation ◽  
Mating Behavior ◽  
Japanese Quail ◽  
Mating Frequency ◽  
Base Population ◽  
Selected Lines ◽  
Gland Size ◽  
Parental Lines ◽  
Selection For ◽  
Cloacal Gland

The genetics of mating behavior in Japanese quail was investigated in replicated lines selected for high or low number of completed matings and the random bred control which served as the base population for the selected lines. Comparisons involved the parental lines, F1, F2, and backcross generations. Results indicate that mating frequency is influenced by additive and nonadditive genetic variation with the former being the primary heritable influence. The relationships between mating behavior, cloacal gland size, and relative aggressiveness suggest that selection for mating frequency influences factors commonly affecting these traits.

Response to selection for grazing tolerance in winter-active populations of phalaris (Phalaris aquatica L.). 1. Persistence under grazing in three environments

2009 ◽  
Vol 60 (11) ◽  
pp. 1097 ◽  
Author(s):  
R. A. Culvenor ◽  
S. P. Boschma ◽  
K. F. M. Reed
Keyword(s):  
Linear Response ◽  
Perennial Grass ◽  
Grazing Pressure ◽  
Response To Selection ◽  
North West ◽  
Phalaris Aquatica ◽  
Grazing Tolerance ◽  
The North ◽  
Breeding Populations ◽  
Selection For

Forage grass cultivars must have adequate grazing tolerance for use in the grazing systems for which they are intended. Response to 2 cycles of selection for persistence under heavy grazing pressure was examined in 3 winter-active breeding populations of the productive perennial grass, phalaris (Phalaris aquatica L.), from 2000 to 2003, at Bulart in western Victoria and Rye Park on the Southern Tablelands and Tamworth on the North-West Slopes of New South Wales. There was one continuously grazed and one rotationally grazed set of plots at Bulart to examine the effect of grazing management. All sites were affected by drought in later years but drought stress was most severe at Tamworth. A strongly positive linear response to selection was observed in an analysis of persistence measured as frequency of phalaris plant base across the 3 sites (excluding the rotational treatment at Bulart), but response interacted with site. By 2003, linear response averaged 14% frequency units or 34–40% proportional response per cycle at Rye Park and the continuously grazed plots at Bulart, sites that were environmentally suited to survival of phalaris. In contrast, response to selection was absent or slightly negative at Tamworth where conditions were drier and hotter. Populations responded similarly in analyses across all 3 sites but 1 population was less responsive when analyses were restricted to Bulart and Rye Park. Herbage mass measurements in 2001 at Bulart and 2002 at Rye Park indicated positive responses to selection, which were increasingly linked to frequency over time. Rotationally grazed plots at Bulart displayed higher frequency than continuously grazed plots after 3 years of grazing. The experiment showed that grazing tolerance was a heritable trait in the populations tested when environmental constraints were not limiting and that useful improvements in persistence had been obtained compared with existing cultivars.

Breeding for improved nutritive value of Phalaris tuberosa herbage: an evaluation of alternative sources of genetic variation

1973 ◽  
Vol 24 (1) ◽  
pp. 21 ◽  
Author(s):  
RJ Clements
Keyword(s):  
Genetic Variation ◽  
Nitrogen Content ◽  
Nutritive Value ◽  
Negative Relationship ◽  
Heading Date ◽  
Breeding Program ◽  
Response To Selection ◽  
Annual Species ◽  
Selection For ◽  
Heading Stage

The variation in herbage nitrogen content and in vitro organic matter digestibility (IVDOM) among Phalaris species and hybrids, within an Algerian ecotype of P. tuherosa and among plants derived from a broadly based P. tuberosa breeding population, was examined. Variation was extensive in each of the three populations, and appears adequate for plant breeding purposes. In each population, IVDOM was negatively related to heading date. Another feature common to all populations at the heading stage was a negative relationship between WDOM and nitrogen content, demonstrable particularly when other factors having similar effects on both characters were held constant. In mature herbage of the P. tuberosa ecotype there was a positive genetic correlation between nitrogen content and IVDOM, but IVDOM at maturity was negatively related to nitrogen content at heading. Annual Phalaris species had higher average IVDOM values at heading (mean 70.5 %) than perennial species (mean 66.1 %) when data were adjusted to a common heading date. Although there was considerable intraspecific variation, only the annual species were sufficiently superior to the best P. tuberosa strains to warrant consideration for hybridizing with P. tuberosa. Since such hybrids have reduced perenniality, and are cytologically unstable, interspecific hybridization appears to have the least value as a source of herbage quality for a P. tuberosa breeding program. In addition, annual species were lower in nitrogen content (mean 1 .15 %) than perennials (mean 1.70 %) at a common heading date. Estimated heritabilities of IVDOM and nitrogen content of mature herbage of the P. tuberosa ecotype were 0.78 and 0.59 respectively, for a family mean based on replicated eight-plant rows. Genetic statistics indicated that a substantial response to selection for improved digestibility of mature herbage would be accompanied by a correlated increase in IVDOM at heading, a slight increase in nitrogen content at maturity, a decrease in nitrogen content at heading, little change in heading date, and perhaps some increase in the weight of individual tillers. Response to selection for increased nitrogen content would be small, and would be accompanied by a reduction in tiller weight. Individual plants derived from the broadly based population ranged from 56 to 76% IVDOM at the heading stage. This population, because of its agronomic superiority, is considered to be the most suitable source of genetic variation on which to base a breeding program.

scholarly journals Recurrent evolution of cross-resistance in response to selection for improved post-infection survival in Drosophila melanogaster

2021 ◽  
Author(s):  
Aparajita Singh ◽  
Aabeer Basu ◽  
Biswajit Shit ◽  
Tejashwini Hegde ◽  
Nitin Bansal ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Variation ◽  
Bacterial Pathogen ◽  
Host Population ◽  
Host Susceptibility ◽  
Cross Resistance ◽  
Response To Selection ◽  
Host Sex ◽  
Determining Factors ◽  
Selection For

The host susceptibility to one pathogen can decrease, increase, or remain unaffected by virtue of the host evolving resistance towards a second pathogen. Negative correlations between a host susceptibility to different pathogens is an often-cited explanation for maintenance of genetic variation in immune function determining traits in a host population. In this study, we investigated the change in susceptibility of Drosophila melanogaster flies to various novel bacterial pathogens after being experimentally selected for increased resistance to one particular bacterial pathogen. We independently selected flies to become more resistant towards Enterococcus faecalis and Pseudomonas entomophila, and baring a few exceptions the evolved populations exhibited cross-resistance against the range of pathogens tested in the study. Neither the identity of the native pathogen nor the host sex was major determining factors in predicting the pattern of cross-resistance exhibited by the selected populations. We therefore report that a generalized cross-resistance to novel pathogens can repeatedly evolve in response to selection for resistance against a single pathogen.

scholarly journals Genetic Variation and Selection for Carotene Content in Carrots

HortScience ◽  
1995 ◽  
Vol 30 (4) ◽  
pp. 821E-821
Author(s):  
Philipp Simon
Keyword(s):  
Genetic Variation ◽  
Combining Ability ◽  
General Combining Ability ◽  
Mass Selection ◽  
Realized Heritability ◽  
Response To Selection ◽  
Carotene Content ◽  
Selection For ◽  
Variation And Selection ◽  
Made In

A six-parent diallel which included carrot inbreds with a range of carotene content from 80 to 490 ppm was evaluated over 2 years. General combining ability accounted for most of the variation observed. Phenotypic mass selection was exercised for high carotene content in three carrot populations. Response to selection continued to be high in one population, HCM, after 11 cycles of selection. In contrast, after three generations of selection, little progress was able to be made in a population derived from primarily Nantes-type open-pollinated cultivars. Realized heritability estimates varied from 15% to 49%. Environment contributed significantly to variation in carotene content.

scholarly journals The number of loci affecting a quantitative trait in Drosophila melanogaster revealed by artificial selection

1983 ◽  
Vol 42 (2) ◽  
pp. 137-149 ◽  
Author(s):  
Araceli Gallego ◽  
Carlos López-Fanjul
Keyword(s):  
Initial Response ◽  
Selection Method ◽  
Base Population ◽  
Response To Selection ◽  
Family Selection ◽  
Selected Lines ◽  
Additive Variance ◽  
Bristle Number ◽  
Selection Limit ◽  
Selection For

SUMMARYIndividual and within-full-sib family selection for low sternopleural bristle number was carried out for 17 generations, with six replicate lines for each selection method. Our results can be summarized as follows: (1) the response to selection was exhausted very quickly, (2) the additive variance of the selected lines declined rapidly, (3) the variation in response to selection decreased as selection progressed, (4) genetic differences among replicates at the selection limit were small, (5) individual selection resulted in a higher initial response than within-family selection, but similar limits were achieved with both procedures. These observations are consistent with the hypothesis that the pattern of response to selection is due to the segregation in the base population of only a few loci with large effects, at intermediate frequencies.

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