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 Volumes 2 and 11, the notes were likely published consecutively. He wrote that the paper by Mendel (1865) was forgotten for over 30 years (Whitson et al., 1914, 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, 1915, 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., 1914, 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., 1914, 1915, p. 195).
The segregation that he observed in the F2 generation from ‘Paradox’ was first described in his 1898 supplementary catalog (Whitson et al., 1914, 1915). In this catalog, he divided the offspring into three groups: one-third a new type of Persian walnut with broad leaflets, one-third a new type of California black walnut, and the remaining one-third had combined traits of J. hindsii and J. regia. Burbank wrote that these observations of segregation were obviously made before the catalog was published in 1898 “at a time, therefore, when no one living had the remotest knowledge of the discovery made by Mendel more than thirty years before” (Whitson et al., 1914, 1915, p. 196). At this point, he seemed defensive: “…the fact being quite overlooked that the essential principles involved had been discovered by me quite independently; exploited by me in connection with many hundreds of species; given publication by me prior to the rediscovery of Mendel’s forgotten paper: championed by me against the opposition of all the leading authorities of the world; and that therefore the aspect of heredity in question might with full propriety have been named “Burbankian” instead of “Mendelian,” were it not that Mendel’s discovery had priority because it was published so long ago as 1863, whereas my independent discovery of the principle was not made until almost twenty years later. Even at that, however, I had had full twenty years priority over any one else except Mendel in the recognition of the principle” (Whitson et al., 1914, 1915, p. 199).
However, Burbank still believed that there was a “misapprehension as to the real significance of ‘unit characters’, and who, misguided by a narrow range of experiments, and lacking the breadth of view that comes with wider experience, have supposed that all heritable characters might be classified as fixed and unvarying entities that are transmitted in accordance with the Mendelian formula” (Whitson et al., 1914, 1915, p. 200). In this, he seems to be making a point about polygenic traits “that do not Mendelize in any tangible or demonstrable way” (p. 200). He also thought that Mendel’s “unit characters” were composed of “subordinated characters” and that new “unit characters” appear at various times and that the old “unit characters” would then no longer follow Mendelian heredity. To follow this, he wrote: “So Darwinian heredity, which recognizes the heritability of whole coteries of characters that are too profoundly fixed to Mendelize, is again receiving recognition” (p. 202).
Howard, W.L. 1945 Luther Burbank’s plant contributions. Univ. Calif. College Agr. Agr. Exptl. Sta. Bull. 691
Lucker, P.C. 1996 Paradox solved: Determining the black walnut parent in hybrid rootstocks using restriction fragment length polymorphisms. MS thesis, Univ. California Davis, Davis, CA
Mendel, G. 1865 Versuche über Planzen-Hybriden. Berh. Naaturforsch. Ver. Brünn 4 3 47
Smith, R.E., Smith, C.O. & Ramsey, H.J. 1912 Walnut culture in California: Walnut blight (No. 231). Agricultural Experiment Station, Berkeley, CA
Whitson, J., John, R. & Williams, H.S. (eds.). 1914, 1915 Luther Burbank his methods and discoveries and their practical application prepared from his original field notes. Vol. 2 Luther Burbank Press, New York, NY (University of Wisconsin Digital Collections Center). 7 Jan. 2014. <http://uwdc.library.wisc.edu/collections/HistSciTech/LutherBurbank>
Wiesler, W. 2012 #8 ‘Royal’ hybrid black walnut (Juglans ‘Royal’). Walking tour of Luther Burbank’s Gold Ridge Experiment Farm. Western Sonoma County Historical Society. 7 Jan. 2014. <http://www.wschsgrf.org/farm-walking-tour/8>