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Selection Reversal in Strains of Corn Previously Long‐Term Selected for Chemical Composition 1
Author(s) -
Leng Earl R.
Publication year - 1962
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1962.0011183x000200020027x
Subject(s) - citation , library science , selection (genetic algorithm) , term (time) , biology , computer science , physics , artificial intelligence , quantum mechanics
V ERY few plant-breeding experiments have been conducted for enough generations to allow satisfactory comparisons between theoretical expectations and actual results. This problem has come into sharper focus in recent years as new systems, such as the various methods of recurrent selection, have been proposed. Prediction problems, involving expectations of genetic gain rates and final levels of performance, are acutely important when long-term, expensive breeding experiments must be conducted to obtain factual evidence of response to selection. Therefore, any information which bears on these problems may be of assistance in evaluating proposed new breeding methods. The long-term selection experiment with oil and protein content in corn (4), conducted for over generations at the Illinois Agricultural Experiment Station, offers unique material for studying problems such as the retention of genetic variability under selection. Progress toward desired objectives, as a result of selection, conventionally is explained either by assuming accumulation of "favorable" genes, or by assuming that desirable gone combinations have been attained. Unless the breeding system is specifically designed to maintain heterozygosity, it is usually assumed that the degree of homozygosity will increase under selection. Eventually, genetic variability is expected to be so far diminished that further selection becomes ineffective, and a "selection limit" (2) is reached. In evaluating the results of long-term selection for oil and protein content in corn, Winter (7), Woodworth al. (8) and Leng (3, 4) have called attention to the degree of variability retained in all four long-selected strains. The experiments reported in the present paper were undertaken to determine if any significant part of this variability was genetic in nature. Reverse selection was begun in all four strains, on the assumption that it would be effective only if a reasonable level of genetic variability existed in the source material.