Population improvement in lucerne (Medicago sativa L.): genetic analyses in original and improved populations

1999 ◽  
Vol 39 (5) ◽  
pp. 549 ◽  
Author(s):  
C. A. Kimbeng ◽  
E. T. Bingham
Keyword(s):  
Quantitative Genetics ◽  
Genetic Load ◽  
Gene Interaction ◽  
Forage Yield ◽  
Fourth Degree ◽  
Repulsion Phase ◽  
Deleterious Alleles ◽  
Medicago Sativa L ◽  
Population Improvement ◽  
Population Interaction

Most quantitative genetics analyses are limited to the first (mean) and second (variance) degree statistics and their derivatives. Analyses based on third (skewness) and fourth (kurtosis) degree statistics can be useful especially for detecting and characterising the nature of gene interactions. Third and fourth degree statistics were analysed and used to interpret differences in forage yield among S1 families of lucerne derived from double-cross populations that were synthesised before (OGDC) and after (AGDC) improvement via inbreeding and selection. Higher levels of genetic load (deleterious alleles) were revealed in the OGDC population compared with the improved population. The analyses also revealed the importance of gene interaction for forage yield in lucerne. In the unselected OGDC population, interaction between alleles in repulsion phase linkages was more important, whereas, in the selected AGDC population, interaction between alleles linked in coupling phase assumed greater importance. The above results suggest that inbreeding and selection in lucerne can accumulate favourable alleles over generations of selection and result in population improvement. Skewness and kurtosis are relatively easy to compute and interpret and should serve as valuable tools in tetraploid quantitative genetics analyses.

Population improvement in lucerne (Medicago sativa L.): components of inbreeding depression are different in original and improved populations

1998 ◽  
Vol 38 (8) ◽  
pp. 831 ◽  
Author(s):  
C. A. Kimbeng ◽  
E. T. Bingham
Keyword(s):  
Inbreeding Depression ◽  
Chromosome Doubling ◽  
Genetic Load ◽  
Field Trials ◽  
Improvement Strategy ◽  
Improvement Program ◽  
Original Population ◽  
Deleterious Alleles ◽  
Herbage Yield ◽  
Population Improvement

Summary. Inbreeding depression, the lowered fitness of inbred individuals compared with their non-inbred counterparts, is an important concept in lucerne improvement; but is poorly understood. Two-allele autotetraploid populations are suitable for studying inbreeding depression, especially when the population improvement strategy involves inbreeding, because they are derived from chromosome-doubling of hybrid diploid plants. They have a maximum of 2 alleles and a single allelic interaction per locus. Inbreeding depression was compared in original 2-allele autotetraploid populations and populations that had undergone inbreeding and selection. The original and improved (selected) populations were produced by intercrossing 2 single-cross lines from the original and improved 2-allele autotetraploid populations respectively. Herbage yield of the S1 and intercrossed generations derived from these populations was evaluated in field trials at Arlington, Wisconsin, USA, and used to estimate inbreeding depression. Herbage yield of the S1 and intercrossed generations derived from the improved population were significantly (P<0.01) higher, by 13.3 and 24%, respectively, than those derived from the original population. Selection during inbreeding probably decreased the frequency of deleterious alleles and accumulated favourable alleles. Inbreeding depression values were higher in the improved compared with the original population. Genetic load of deleterious alleles may account for much of the inbreeding depression observed in the original population, whereas, in the improved population, loss of heterozygosity or non-additive gene interactions between favourable alleles on linked chromosome segments may account for the substantial inbreeding depression. Therefore, in a population improvement program, the causes of inbreeding depression seem to be more important than their estimated value.

scholarly journals Irrigation Timing as a Practice of Effective Weed Management in Established Alfalfa (Medicago sativa L.) Crop

Agronomy ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 550
Author(s):  
Panagiotis Kanatas ◽  
Ioannis Gazoulis ◽  
Ilias Travlos
Keyword(s):  
Medicago Sativa ◽  
Weed Management ◽  
Cultural Practices ◽  
Block Design ◽  
Chenopodium Album ◽  
Stand Density ◽  
Climatic Conditions ◽  
Amaranthus Retroflexus ◽  
Forage Yield ◽  
Medicago Sativa L

Irrigation is an agronomic practice of major importance in alfalfa (Medicago sativa L), especially in the semiarid environments of Southern Europe. Field experimentation was conducted in Western Greece (2016–2018) to evaluate the effects of irrigation timing on weed presence, alfalfa yield performance, and forage quality. In a randomized complete block design (four replications), two cultivars (“Ypati 84” and “Hyliki”) were the main plots, while three irrigation timings were the subplots (split-plot). The irrigation timings were IT-1, IT-2, and IT-3, denoting irrigation 1 week before harvest, 1 week after harvest, and 2 weeks after harvest, respectively. IT-1 reduced Solanum nigrum L. density by 54% and 79% as compared to IT-3 and IT-2, respectively. Chenopodium album L. density was the highest under IT-2. IT-3 resulted in 41% lower Amaranthus retroflexus L. density in comparison to IT-2, while the lowest values were observed under IT-1. Stand density and stems·plant−1 varied between years (p ≤ 0.05). Mass·stem−1 and alfalfa forage yield were affected by the irrigation timings (p ≤ 0.001). Total weed density and forage yield were negatively correlated in both the second (R2 = 87.013%) and the fourth (R2 = 82.691%) harvests. IT-1 and IT-3 increased forage yield, leaf per stem ratio, and crude protein as compared to IT-2. Further research is required to utilize the use of cultural practices for weed management in perennial forages under different soil and climatic conditions.

Establishment and productivity of cicer milkvetch (Astragalus cicer L.) in alfalfa (Medicago sativa L.) or alfalfa- hybrid bromegrass mixtures

2021 ◽  
Author(s):  
Allan Foster ◽  
Bill Biligetu
Keyword(s):  
Medicago Sativa ◽  
Aqueous Extract ◽  
Nutritive Value ◽  
Forage Yield ◽  
Allelopathic Effect ◽  
Limited Information ◽  
Seeding Rate ◽  
Bromus Riparius ◽  
Medicago Sativa L ◽  
Astragalus Cicer

Cicer milkvetch (Astragalus cicer L.) (CMV) is a non-bloating, perennial legume that has shown persistence under grazing. Limited information is available on its seedling establishment and subsequent forage yield and nutritive value in alfalfa (Medicago sativa L.) mixtures. Field plots were seeded in May 2013 at Melfort, SK, Canada to evaluate ‘Oxley II’ cicer milkvetch performance in ‘AC Grazeland’ alfalfa or alfalfa and ‘AC Success’ hybrid bromegrass (Bromus riparius × B. inermis) mixtures from 2014 to 2017. Two controlled environment tests were also conducted by treating seeds of CMV using alfalfa root aqueous extract. Seed germination and seedling height of CMV were significantly reduced in aqueous extract. In field, establishment of CMV in a mixture containing alfalfa was reduced, and CMV dry matter proportion in the mixture increased only 3.5% over three years. Increasing CMV seeding rate did not increase its DM percent in the mixtures, indicating a high allelopathic effect of alfalfa. Forage DM yield of all mixtures was linearly correlated to the proportion of alfalfa, and adding hybrid brome did not increase the DM yield. Forage DM yield was higher for the three-cut than the two-cut treatments for CMV-alfalfa mixtures, but there was no difference between the cutting frequency for CMV-alfalfa- hybrid brome mixtures. Fiber concentrations decreased linearly with increased CMV seeding rate in the mixtures. This study showed CMV establishment in alfalfa mixtures was reduced in a same row seeding, and the allelopathic effect was not reduced by lower alfalfa seeding rates or adding a grass.

Genetic load and biological changes to extant humans

2020 ◽  
pp. 1-4
Author(s):  
Arthur Saniotis ◽  
Maciej Henneberg ◽  
Kazhaleh Mohammadi
Keyword(s):  
Natural Selection ◽  
Current Knowledge ◽  
Genetic Load ◽  
Differential Fertility ◽  
Medical Interventions ◽  
Deleterious Alleles ◽  
Gradual Process ◽  
Genetic Complexity ◽  
Sexual Recombination ◽  
Improved Sanitation

Abstract Extant humans are currently increasing their genetic load, which is informing present and future human microevolution. This has been a gradual process that has been rising over the last centuries as a consequence of improved sanitation, nutritional improvements, advancements in microbiology and medical interventions, which have relaxed natural selection. Moreover, a reduction in infant and child mortality and changing societal attitudes towards fertility have led to a decrease in total fertility rates (TFRs) since the 19th century. Generally speaking, decreases in differential fertility and mortality have meant that there is less opportunity for natural selection to eliminate deleterious mutations from the human gene pool. It has been argued that the average human may carry ~250–300 mutations that are mostly deleterious, as well as several hundred less-deleterious variants. These deleterious alleles in extant humans mean that our fitness is being constrained. While such alleles are viewed as reducing human fitness, they may also have had an adaptive function in the past, such as assisting in genetic complexity, sexual recombination and diploidy. Saying this, our current knowledge on these fitness compromising alleles is still lacking.

Evaluation of Alfalfa Weevil (Coleoptera: Curculionidae) Densities and Regrowth Characteristics of Alfalfa Grazed by Sheep in Winter and Spring

2004 ◽  
Vol 39 (4) ◽  
pp. 598-610 ◽  
Author(s):  
Hayes B. Goosey ◽  
Patrick G. Hatfield ◽  
Sue L. Blodgett ◽  
S. Dennis Cash
Keyword(s):  
Crude Protein ◽  
Forage Yield ◽  
Sheep Grazing ◽  
Alfalfa Weevil ◽  
Nutrient Quality ◽  
Hypera Postica ◽  
Medicago Sativa L ◽  
The Impact ◽  
Neutral Detergent Fibers ◽  
Crop Health

Fall regrowth of alfalfa, Medicago sativa (L.), serves as a major source of winter pasture for Montana sheep producers. In years of drought, alfalfa fields are extensively winter/spring grazed; however, the impact on crop health is unknown. Alfalfa paddocks were continuously grazed for 95 d in 2002 and 98 d in 2003 during winter and spring to determine the impact on spring and summer alfalfa regrowth, nutrient quality characteristics, and alfalfa weevil, Hypera postica Gyllenhal, densities. Grazed and non-grazed forage yield, crude protein (%), and acid and neutral detergent fibers (%) did not differ at harvest (P&gt; 0.17) during either study year. Acid and neutral detergent fibers (kg/ha) were greater (P &lt; 0.05) in non-grazed compared to grazed plots during 2002–2003. Alfalfa weevil densities were lower in grazed than non-grazed plots (P&lt; 0.03) over four sampling dates during both study years. Winter/spring sheep grazing appears to offer potential for alfalfa weevil management without compromising yield or nutritive factors of subsequent alfalfa production.

Productivity and sustainability of four grazed grass – alfalfa mixtures

1999 ◽  
Vol 79 (1) ◽  
pp. 83-89 ◽  
Author(s):  
N. W. Holt ◽  
P. G. Jefferson
Keyword(s):  
Medicago Sativa ◽  
Great Plains ◽  
Ground Cover ◽  
Forage Yield ◽  
Intermediate Wheatgrass ◽  
Bromus Riparius ◽  
Russian Wildrye ◽  
Medicago Sativa L ◽  
Meadow Bromegrass ◽  
Forage Yields

Forage grasses need to be evaluated in pasture trials in the Great Plains region of North America. The objective of this study was to compare four grass–alfalfa (Medicago sativa L.) mixtures for productivity and persistence when grazed during spring and summer. The grasses were Altai wildrye (Leymus angustus [Trin.] Pilger), intermediate wheatgrass (Elytrigia intermedia [Host] Nevski), meadow bromegrass (Bromus riparius Rehm. syn. B. biebersteinii Roem. & Schult.) and Russian wildrye (Psathyrostachys junceus [Fisch.] Nevski), with grass rows seeded perpendicular to the alfalfa rows. Two sites, 4 km apart, were grazed with yearling beef cattle from 1987 to 1993. Forage yield differed among grass treatments in 4 of 5 years, but differences were inconsistent over time. Five-year mean forage yields and total livestock production were not significantly different among the four grasses. Mean annual forage yields ranged from 800 to 8170 kg ha−1 and were related to the amount of growing season (April–August) precipitation. Carrying capacity ranged from 35 steer grazing days per hectare in 1992 to 176 in 1991. Grasses in the mixtures did have a significant effect on the grass–alfalfa ratio and on ground cover. Alfalfa content was highest when grown with Altai wildrye and lowest when grown with Russian wildrye. Percentage of ground cover by the grass plus alfalfa increased from an average of 3.8% in 1987 to 16.1% at one site and 31.9% at the second site by 1993. Russian wildrye contained the least alfalfa and weeds after 7 yr. Intermediate wheatgrass and Altai wildrye did not compete with invading weeds at one site, or with alfalfa at the other, and should not be recommended for spring–summer pastures in semiarid regions. Meadow bromegrass maintained a balance of grass and alfalfa and further research should confirm its persistence in semiarid climates. Key words: Leymus angustus, Elytrigia intermedia, Bromus riparius, Psathyrostachys junceus, Medicago sativa, grazing with cattle

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