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Heterosis What Have We Learned? What Have We Done? Where Are We Headed?
| Content Provider | Semantic Scholar |
|---|---|
| Author | Hallauer, Arnel R. |
| Copyright Year | 1999 |
| Abstract | Observations on the effects crossbreeding and inbreeding have been reported for several centuries in different plant and animal species (Zirkle, 1952). Although the genetic basis of crossbreeding and inbreeding was not understood until the 20th century, it was observed that inbreeding tended to be injurious and crossbreeding tended to be beneficial. Experimental methods of making direct comparisons of either individuals or progenies developed by crossbreeding and inbreeding were not used, but the observations were generally consistent that vigor and productivity were greater in crosses, particularly in crosses produced after some level of inbreeding. Koelreuter, Knight, and Burbank observed greater vigor in crosses, but the concept of using inbreeding and crossbreeding on a consistent basis for crop improvement was not proposed (see Zirkle, 1952). The observations reported by the early hybridizers were not based on a concept of heterosis and how heterosis could be exploited to increase crop productivity. The potential of hybrids to increase maize (Zea mays L.) production was first suggested by Beal (1880). Crosses were produced between cultivars of maize, and the crosses tended to have greater yields than either of the parent cultivars. Sanborn (1890) and McClure (1892) reported similar results in maize. Although Beal (1880), Sanborn (1890), and McClure (1892) did not have an understanding of Mendelian genetics, their interpretations of the necessity of reproducing the hybrid seed for each growing season were correct. The potential of cultivar crosses for increasing maize production in the USA continued to be studied, but the use of cultivar crosses and their impact on U.S. maize production were not important factors for future maize production. Because maize is a cross-pollinated species, a maize cultivar is a heterogeneous mixture of genotypes. Isolation of maize cultivars was not strickly adhered to, and, consequently, the hybrid vigor observed in cultivar crosses may not have been consistent among growing seasons because of possible contamination. Appropriate experimental techniques for making valid comparisons among crosses and between crosses and parents were either not available or used to make definitive conclusions. Richey (1922) summarized data for 244 variety crosses, and he emphasized that the greatest hybrid vigor was expressed in cultivar crosses of extreme types; i.e., in crosses that probably had the greatest differences in allele frequencies of the parent cultivars. Richey (1922) concluded that the chances were about equal to have a cultivar cross that was or was not better than the better parent. The future course of crossbreeding and inbreeding changed dramatically after the rediscovery of Mendel's paper in 1900. |
| Starting Page | 483 |
| Ending Page | 492 |
| Page Count | 10 |
| File Format | PDF HTM / HTML |
| DOI | 10.2134/1999.geneticsandexploitation.c45 |
| Alternate Webpage(s) | https://dl.sciencesocieties.org/publications/books/abstracts/acsesspublicati/thegeneticsande/483/preview/pdf |
| Alternate Webpage(s) | https://doi.org/10.2134/1999.geneticsandexploitation.c45 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
