Evidence That 2n Eggs Explain Partial Hybrids between Medicago sativa and Medicago arborea

Bingham, E. T.; Irwin, J. A. G.

doi:10.3390/plants11101380

Cited by 3 publications

(8 citation statements)

References 10 publications

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“…They are near tetraploid, phenotypically more closely resemble the alfalfa egg parent, but demonstrate some M. arborea phenotypic traits and only contain around 5% of M. arborea-specific alleles [27]. Unreduced eggs and pollen have been reported in Alborea parents [23,34], which were also produced in Tripsacum [33].…”

Section: Similarities Between Alborea and Other Asymmetric Plant Hybridsmentioning

confidence: 98%

“…MB and its derivatives represented the first level of weakening the hybridisation barrier between M. sativa and M. arborea. The hybrids were described as a new cultigen, Alborea [22]. Another alfalfa genotype, M8, was discovered in Wisconsin, which was a more efficient hybridiser with M. arborea than MB and its derivatives [21].…”

Section: Generation Of Alborea and Its Characteristicsmentioning

confidence: 99%

“…M. arborea introgression into 7 hybrids generated in Wisconsin [28] was investigated using the marker profiles generated by 46 SSR primers of known M. sativa genomic locations covering all 8 linkage groups [29][30][31]. Introgression of M. arborea-specific alleles was found from linkage groups 1, 6, and 7, with two hybrids showing introgression from all three linkage groups [32].…”

Section: Genomic Characterisationmentioning

confidence: 99%

“…Repeated pollination of M. arborea with M. sativa has failed to produce hybrids [21]. It has been established that alfalfa seed parents and their derivatives that produce hybrid also produce unreduced male and female gametes [23,34]. Alfalfa parent MB had a lower frequency of 2n eggs than the other parent M8; MB is a less efficient hybridiser than M8 [34].…”

Section: Importance Of Reproductive Abnormalities In Generating Inter...mentioning

confidence: 99%

“…It has been established that alfalfa seed parents and their derivatives that produce hybrid also produce unreduced male and female gametes [23,34]. Alfalfa parent MB had a lower frequency of 2n eggs than the other parent M8; MB is a less efficient hybridiser than M8 [34]. The production of 2n eggs, arising from second division restitution [39] by the MB or M8 parents, would appear to be integral to hybrid generation.…”

Section: Importance Of Reproductive Abnormalities In Generating Inter...mentioning

confidence: 99%

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Review of Partial Hybrids between Herbaceous Medicago sativa and Woody Medicago arborea and Their Potential Role in Alfalfa Improvement

Irwin

Bingham

2023

Applied Biosciences

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Medicago sativa (2n = 4x = 32) and M. arborea (2n = 4x = 32) were thought to be reproductively isolated until hybrids (Alborea) were produced by sexual reproduction for the first time in 2003 in Wisconsin. The hybrids were asymmetric, at or near 2n = 4x = 32, and with a predominance of the alfalfa genome. Only M. sativa seed parents with reproductive abnormalities, including unreduced eggs, have produced hybrids; where M. arborea has been used as the seed parent, no hybrids have resulted. Pedigree selection within derivatives of the two original M. sativa seed parents (MB and M8) has been successful in increasing the frequency of hybrids produced. While Alborea individuals more closely resemble M. sativa, a number of M. arborea-specific traits have been observed across different hybrid individuals. These include single-coil flat pods, large seeds, yellow flowers, indeterminate growth, a minimal crown, lodging, frost resistance, and anthracnose resistance. These M. arborea traits have the potential to restructure alfalfa to increase its versatility and utilisation. There is emerging evidence from North and South America and Australia that some Alborea selections have the capacity to complement adapted alfalfa cultivars for yield. Work is continuing to introgress M. arborea traits of value into alfalfa.

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Section: Similarities Between Alborea and Other Asymmetric Plant Hybridsmentioning

confidence: 98%

Section: Generation Of Alborea and Its Characteristicsmentioning

confidence: 99%

Section: Genomic Characterisationmentioning

confidence: 99%

Section: Importance Of Reproductive Abnormalities In Generating Inter...mentioning

confidence: 99%

Section: Importance Of Reproductive Abnormalities In Generating Inter...mentioning

confidence: 99%

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Review of Partial Hybrids between Herbaceous Medicago sativa and Woody Medicago arborea and Their Potential Role in Alfalfa Improvement

Irwin

Bingham

2023

Applied Biosciences

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The Hybridization Barrier between Herbaceous Medicago sativa and Woody M. arborea Is Weakened by Reproductive Abnormalities in M. sativa Seed Parents

Bingham¹,

Irwin

2023

Plants

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Historically, crosses between Medicago sativa (alfalfa) and M. arborea with alfalfa as the seed parent failed, as did crosses using M. arborea as the seed parent. Thus, a reproductive barrier kept the two species isolated until early in this century. The breakthrough came when alfalfa seed parents were identified in Wisconsin USA and Queensland AU that produced partial hybrids (hereafter hybrids). The hybrids were obtained by making large numbers of crosses on selected alfalfa parents. This was the first level of weakening the crossing barrier as reported in Plants in 2013. Further weakening of the barrier is reported herein whereby more hybrids were obtained with fewer crosses. This was accomplished by pedigree selection for new alfalfa seed parents and by using a product of the first hybrids called Alborea. New alfalfa seed parents were crossed with M. arborea, and Alborea parents were backcrossed to M. arborea. Hybrid plants were produced with fewer crosses in both cases. These hybrids, like the first hybrids, have mostly alfalfa traits but also have traits from M. arborea. It was theorized early on that the alfalfa component could be explained by 2n eggs in the alfalfa parents that were fertilized by normal n gametes from M. arborea. Evidence that the Wisconsin alfalfa and Alborea seed parents did in fact produce 2n eggs was reported in Plants in 2022. Moreover, they produced 2n eggs at approximately the same frequency that they produced hybrids. As reported herein, Alborea parents produced the highest frequency of hybrids and thus had the weakest barrier. Importantly, they also have the highest frequency of 2n eggs. It was determined that alfalfa and Alborea parents that produce 2n eggs and hybrids, also produce 2n pollen. In effect, an experiment was undertaken in reverse showing that 2n pollen could be used to screen for plants that produce hybrids. In the thousands of crosses made over the years, fertilization of normal n eggs in alfalfa parents always failed. Normal meiosis appears to be the main barrier to producing interspecific hybrids in our case. Fertilization of abnormal 2n eggs ensures sufficient alfalfa genetic material to continue embryogenesis. Evidently, the meiotic abnormality of 2n eggs is the major factor that weakens the crossing barrier.

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Inheritance and Response to Selection for Seed Weight Using the Large Seeded Landrace Oman 2 of Lucerne

Irwin,

Havey

2024

Seeds

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Seed weight in lucerne (Medicago sativa) may affect subsequent seedling vigour and stand establishment. A landrace of lucerne (Oman 2) from Oman has a 100-seed weight over 60% larger than the largest seeded parent used in previous studies. Crosses were made between Oman 2 and the smaller-seeded cultivar Titan 9, and segregating families were produced for genetic analysis and measurement of response to selection for seed size. There were significant differences in 100-seed weights between the parents (Oman 2 and Titan 9) and subsequent families. Regression of 100-seed weights of F2 families versus F1 parents was highly significant (p < 0.001), as well as 100-seed weights of the F3 families versus F1 parents. Analysis of diallel crossing among large and small-seeded F1 plants revealed highly significant general (GCAs) and specific (SCAs) combining abilities, as well as highly significant reciprocals. The GCA effect was much greater than the SCA effect with a GCA/SCA ratio of 15.9. This large ratio agrees with the significant regression coefficients and indicates that 100-seed weight in lucerne has high heritability. The significance of reciprocals was due to a large maternal effect in which large-seeded maternal parents produced progenies with significantly larger seeds relative to small-seeded parents. These results indicate that large-seeded plants should be used as the maternal parents in crosses and for recurrent selection to increase the seed size of progenies.

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Evidence That 2n Eggs Explain Partial Hybrids between Medicago sativa and Medicago arborea

Cited by 3 publications

References 10 publications

Review of Partial Hybrids between Herbaceous Medicago sativa and Woody Medicago arborea and Their Potential Role in Alfalfa Improvement

Review of Partial Hybrids between Herbaceous Medicago sativa and Woody Medicago arborea and Their Potential Role in Alfalfa Improvement

The Hybridization Barrier between Herbaceous Medicago sativa and Woody M. arborea Is Weakened by Reproductive Abnormalities in M. sativa Seed Parents

Inheritance and Response to Selection for Seed Weight Using the Large Seeded Landrace Oman 2 of Lucerne

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