[OG bub]

Late in the nineteenth century and early in the twentieth century it was becoming increasingly apparent to corn breeders and farmers alike that traditional breeding methods (repeated mass selection for particular plant characteristics, especially selection for car conformation, such as was eagerly promoted in corn shows), as well as the newer car-to-row methods, were not producing satisfactory results in the form of improved yields (see Figure 5-1). The first hint of a way to solve the problem came with the reports by Beal (1876-1882) that hybrids between different varieties of corn intervarietal hybrids, were usually more productive than open-pollinated parental varieties. Although Beal did not provide detailed yield data, he asserted that the yields of intervarietal hybrids of corn were higher than those of their parents, sometimes by as much as 40%. But neither breeders nor farmers of the time were ready for such a considerable departure from established ways of corn breeding, with the result that Beal's underlying idea, to exploit "hybrid vigor" using controlled intervarietal crosses, was not accepted until more precise data on the effects of inbreeding, and the often favorable effects of crossing selected inbreds, became available as a result of the independent work of East (1908) and, particularly, of Shull (1909). The more important effects of continued self-fertilization reported by East and Shull can be summarized as follows: (1) A large number of lethal and subvital types appeared in early generations of selfing; (2) the progeny of original parental plants rapidly separated into distinctive lines that became, with continued inbreeding, increasingly uniform for various morphological and functional characteristics such as height, ear length, and maturity; (3) all inbred lines decreased in vigor and fecundity, until many could no longer be maintained even under the most favorable cultural conditions; and (4) all lines that survived showed a general decline in size and vigor; but (5), and by far most important, many unrelated inbred lines when intercrossed gave superior Fl hybrids.

From the earliest recorded history, inbreeding has been associated with lessened vigor, reduced fecundity, and the appearance of increased numbers of defective off-types in inbred populations. Among the consequences were pronouncements in many human societies that prohibited marriages between relatives of specified closeness (forbidden degrees) of kinship. Inbreeding has not, however, consistently been regarded as something to be avoided. For example, consanguineous marriages have been favored in some human societies, sometimes for the purpose of preventing "dilution of superior blood lines," but also for the nonbiological purpose of maintaining property and/or power within families.

The development of many modern breeds of livestock provides another example of the potential biological usefulness of inbreeding. Starting about 1700 it had become common practice for livestock breeders to mate the offspring of outstanding males with their offspring in particular lines of descent to preserve or to fix desirable characteristics and to eliminate undesirable characteristics. However, such "line-bred" stocks sooner or later "ran out", and it became necessary to cross outside the line to restore fecundity and productivity. The system thus became one of inbreeding (breeding within outstanding lines) to concentrate desirable qualities, coupled intermittently with crossbreeding to prevent degeneration. Darwin (1868), who described this process in detail, concluded that "although free crossing is a danger on one side which everyone can see, too close inbreeding is a hidden danger on the other." Scientific information concerning the effects of outcrossing in plants dates from the experiments of the plant hybridizes of the eighteenth century. Kolreuter is reported to have noted that hybrids are often remarkably luxuriant, whereas Sprengel is reported to have reached the conclusion from studies of the relationships between flowers and insects that nature usually "intended" that flowers should not be pollinated by their own pollen. Darwin (1876) recorded the results of his own observations and experiments; he reached the conclusion that self-fertilization is an unnatural and harmful process. Apparently, the first inbreeding experiments with corn were those of Darwin. Unfortunately his experiments with corn were continued for only a single generation and hence were not very informative. Darwin did, however, observe the dramatic negative effects of even a single generation of selfing and concluded that "nature abhors self-fertilization.'

Shull was also impressed by the obvious deleterious effects of inbreeding corn, especially the large numbers of lethals brought to light in the early generations of inbreeding, as well as the decrease in vigor and fecundity of longer-surviving lines. By 1908, however, after many years of observations, he wrote that a field of open-pollinated corn "contains" many complex hybrids and that corn breeders should strive to maintain the best "hybrid combination.' Earlier he had accepted the concept held by some corn breeders that selfing has "deleterious effects," but Shull did not recognize until 1907 or 1908 that crossing often had advantageous effects. When Shull began to make crosses among his inbred lines, he found that the degree to which vigor and productivity were restored on crossing were functions of the origin of the lines crossed. Crosses between sibs within a self-fertilized line showed little improvement over self-fertilization in the same family; however, the difference between selfing and sib-crossing became progressively greater as the numbers of generations of inbreeding increased. Still more important, when inbreds derived from different original open-pollinated plants were crossed at random, the average response was a return to the vigor and productivity of the original population before inbreeding had commenced. Some hybrid combinations showed greater improvement than the average, whereas others showed less improvement. But Shull emphasized that there was no overlapping of the hybrids as a group and the inbred parents as a group; the hybrids in all cases were superior to the inbred parents. By 1908 these experimental results forced Shull to a conclusion that had been unappreciated over the centuries: that it was crossing that had advantageous effects and that the breeding of corn must have as its objective the recovery of occasional, infrequent, but vigorous and productive plants, presumably rare fortuitous hybrid combinations, such as he had observed occasionally in his open-pollinated populations. Shull's insights and his experiments in the next few years adumbrated many of the intricate and complexly interrelated procedures that are used at present in breeding hybrid cultivars of corn and other crop species, as well as in breeding many domesticated animal species. However, before proceeding to discussion of hybrid varieties, it seems appropriate to introduce two opposing but widely accepted hypotheses advanced in the early decades of the 1900s to explain the apparently conversely related phenomena of "inbreeding depression" and "hybrid vigor" or "heterosis," the latter a term coined by Shull to express the advantageous effects of hybridity.

[ethereal]

everybody should read this

thanks OGB!

Awesome Bub, this kind of info is great to read. Agriculture as a whole is fascinating stuff.

good stuff bub.

[irieeyes808]

that was truly deep! Informative read

[maxima32]

That was informative OG . But i cant keep but thinking the "Holy Grail finding" is neither more apparent through art rather than science . For years the world has been at conflict with science and art. Conflict because there is a debate on what is more innovative . What will get us to uderstand more ? What can capture something unexplained and put it in plain view to understand or appreciate ?
Science does it with informative and descriptive theories, experiments and hypothesis'. Art does it with unexplained strokes, undefined characteristics, and in self understanding of what is being portrayed. Of course E=mc2 because of recorded results and proven testimony. But what does Mona Lisa equal ? Why is it regarded as one of the greatest pieces of all time that can potray emotion, anatomical exact and perfection through use of instruments? What will get us to the grail ? What will get us to the point were we have a plant that is unmistakenly regarded as the "one" ? In my opinion it will not be through experiments and recorded results from years of experiments. There is just to many factors and conclusions to determine. It will not be through the talent or hidden trait to tell what plant is better than the other. I think it will be from a mistake, an error, an uneducated account on what is great for certian individuals.
For centuries things have been found by mistake. Factors that have unfolded from a basic human nature to learn more and create things that make us more efficient . Hopefully that individual is a researchist, a scholar, a rock n roll follower, a hip hop producer, a dad, professor, a criminal and most importantly a level minded individual . For we cannot push the limits of this great plant with just research and recorded results. We will not find the limits of this plant with an eye for perfection or single minded happiness . The grail will come from a generation of realist and an individual or individual(s) that did not care about failure .