Author
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Preece, John |
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MCGRANAHAN, G - University Of California |
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Submitted to: HortScience
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/27/2014 Publication Date: 2/1/2015 Publication URL: http://www.arw-grin.gov/dav Citation: Preece, J.E., Mcgranahan, G. 2015. Luther Burbank's contributions to walnuts. HortScience. 50:201-204. Interpretive Summary: Luther Burbank began making controlled crosses between walnut species in the late nineteenth century after hearing about a “supposed natural European hybrid walnut.” He crossed Juglans hindsii (northern California black walnut) × J. regia (Persian walnut) and produced progeny that he named ‘Paradox’ because of its extremely fast growth and other “anomalies.” He also crossed two American species, J. hindsii × J. nigra (eastern black walnut), producing ‘Royal’ walnut progeny that were fast growing and prolific nut producers. A third interspecific hybrid was a cross between J. ailantifolia (Japanese walnut) × J. regia that resulted in extremely vigorous progeny, but was not named. He observed segregation in the F2 populations and described giants and dwarfs as reversions to ancestral forms. Luther Burbank also made selections for walnut scion cultivars and was especially interested in thin shelled nuts. He collected seeds from a J. regia growing in San Francisco because it produced regularly and had very high quality nuts with relatively thin, but poorly sealed shells. He selected one of its seedlings as ‘Santa Rosa Soft-Shell’ and described it as bearing large crops of nuts that were nearly white with thin shells and delicious white meat. Burbank’s contributions to the walnut industry endure to this day, especially through the widespread use of seedling and clonal ‘Paradox’ walnut rootstocks. Luther Burbank’s field notes published in a 12 volume monographic series (Whitson et al. 1914, 1915) covers 40 years of his plant breeding work. Based on the changes in Burbank’s writings about Mendelian genetics in the walnut chapters in Vol. 2 and Vol. 11, the notes were likely published consecutively. He wrote that the paper by Mendel (1865) was forgotten for over 30 years (Whitson et al., 1915). By that time he had been breeding plants in California for more than 20 years. His understanding of Mendelian concepts although murky developed somewhat and he ultimately found it useful to explain the performance of his F1 and F2 generations. In his field notes about walnuts published in 1914, Burbank showed that he was aware of Mendel’s findings and mentioned “prepotency or dominance” when describing traits of one parent manifesting itself over those of the other in the walnut F1 interspecific hybrids. When describing the segregation in the F2 generations, he did not use the term “segregation,” rather he called this a “mixture of racial strains.” After describing dwarf walnuts in F2 populations generated from J. hindsii × J. regia (or J. hindsii × J. nigra) F1 hybrids, Burbank mentioned that Mendel would call them “pure recessives” or homozygous. He followed this with: “The reader may or may not feel that the new terminology adds to our comprehension of the phenomena” (Whitson et al., 1914, p. 160). However on page 150, Luther Burbank described the “dwarfs” in the F2 generation as a “reversion to dwarfed ancestral strains.” For the “giants” in the F1 and F2 generations, he wrote: “These, then are the remote ancestors (“colossal plants of the Carboniferous Era”) that may be invoked in explanation of the rapid growth and relatively gigantic stature of our hybrid walnuts” (p. 164). By the time that he wrote the field notes published in Vol. 11 of the same series (Whitson et al., 1915), Luther Burbank was applying Mendelian terminology to his walnut populations. At this time, he was using the term “segregation” and wrote: “It will be noted also that the distribution of these characters in the second generation was essentially that which has come to be familiar everywhere within recent years as the typical distribution of characters among second generation hybrids in what is now known as Mendelian heredity” (Whitson et al., 1915. p. 195). The segregation that he observed in the F2 generation from ‘Paradox’ was first described in his 1898 suppleme Technical Abstract: Luther Burbank began making controlled crosses between walnut species in the late nineteenth century after hearing about a “supposed natural European hybrid walnut.” He crossed Juglans hindsii (northern California black walnut) × J. regia (Persian walnut) and produced progeny that he named ‘Paradox’ because of its extremely fast growth and other “anomalies.” He also crossed two American species, J. hindsii × J. nigra (eastern black walnut), producing ‘Royal’ walnut progeny that were fast growing and prolific nut producers. A third interspecific hybrid was a cross between J. ailantifolia (Japanese walnut) × J. regia that resulted in extremely vigorous progeny, but was not named. He observed segregation in the F2 populations and described giants and dwarfs as reversions to ancestral forms. Luther Burbank also made selections for walnut scion cultivars and was especially interested in thin shelled nuts. He collected seeds from a J. regia growing in San Francisco because it produced regularly and had very high quality nuts with relatively thin, but poorly sealed shells. He selected one of its seedlings as ‘Santa Rosa Soft-Shell’ and described it as bearing large crops of nuts that were nearly white with thin shells and delicious white meat. Burbank’s contributions to the walnut industry endure to this day, especially through the widespread use of seedling and clonal ‘Paradox’ walnut rootstocks. Luther Burbank’s field notes published in a 12 volume monographic series (Whitson et al. 1914, 1915) covers 40 years of his plant breeding work. Based on the changes in Burbank’s writings about Mendelian genetics in the walnut chapters in Vol. 2 and Vol. 11, the notes were likely published consecutively. He wrote that the paper by Mendel (1865) was forgotten for over 30 years (Whitson et al., 1915). By that time he had been breeding plants in California for more than 20 years. His understanding of Mendelian concepts although murky developed somewhat and he ultimately found it useful to explain the performance of his F1 and F2 generations. In his field notes about walnuts published in 1914, Burbank showed that he was aware of Mendel’s findings and mentioned “prepotency or dominance” when describing traits of one parent manifesting itself over those of the other in the walnut F1 interspecific hybrids. When describing the segregation in the F2 generations, he did not use the term “segregation,” rather he called this a “mixture of racial strains.” After describing dwarf walnuts in F2 populations generated from J. hindsii × J. regia (or J. hindsii × J. nigra) F1 hybrids, Burbank mentioned that Mendel would call them “pure recessives” or homozygous. He followed this with: “The reader may or may not feel that the new terminology adds to our comprehension of the phenomena” (Whitson et al., 1914, p. 160). However on page 150, Luther Burbank described the “dwarfs” in the F2 generation as a “reversion to dwarfed ancestral strains.” For the “giants” in the F1 and F2 generations, he wrote: “These, then are the remote ancestors (“colossal plants of the Carboniferous Era”) that may be invoked in explanation of the rapid growth and relatively gigantic stature of our hybrid walnuts” (p. 164). By the time that he wrote the field notes published in Vol. 11 of the same series (Whitson et al., 1915), Luther Burbank was applying Mendelian terminology to his walnut populations. At this time, he was using the term “segregation” and wrote: “It will be noted also that the distribution of these characters in the second generation was essentially that which has come to be familiar everywhere within recent years as the typical distribution of characters among second generation hybrids in what is now known as Mendelian heredity” (Whitson et al., 1915. p. 195). The segregation that he observed in the F2 generation from ‘Paradox’ was first described in his 1898 suppleme |
