Efficiency of S2 recurrent selection for improvement of exotic and semi-exotic populations in maize (Zea mays L.)

Abstract

Iglesias, Carlos Ariel, "Efficiency of S2 recurrent selection for improvement of exotic and semi-exotic populations in maize (Zea mays L.) " (1989). Retrospective Theses and Dissertations. 9199. https://lib.dr.iastate.edu/rtd/9199 INFORMATION TO USERSThe most advanced technology has been used to photo graph and reproduce this manuscript from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer.The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction.In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.Oversize materials (e.g., maps, drawings, charts) are re produced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. These are also available as one exposure on a standard 35mm slide or as a 17" x 23" black and white photographic print for an additional charge.Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. University Microfilms International 1989Signature was redacted for privacy.Signature was redacted for privacy.Signature was redacted for privacy.ii (Russell, 1986). Even if the most sophisticated and efficient breeding method is developed, the efforts of the breeder will be futile if the genes are not present in the original population. Choosing the initial germplasm and the breeding procedure are two equally important decisions that maize breeders have to make .The restricted genetic base of maize production and breeding in the U.S. Corn Belt region has two main consequences: an increased vulnerability of biological and environmental stresses; and a reduction in the genetic variability available to the breeder for selection. The emergence of many effective seed companies with extensive testing programs led to the identification of elite, widely adapted hybrids, from which both farmers and seed companies benefit (Bradley et al., 1988). Genetic vulnerability can be reduced if a measurement of genetic diversity for commercial hybrids could influence the farmer's choice among top performing hybrids, prompting seed companies to broaden the genetic base of their hybrids . 2When gerraplasm from a wild species or an exotic race contributes to a breeding program, it...

Testcross Response to Four Cycles of Half‐sib and S2 Recurrent Selection in the BS13 Maize (Zea mays L.) Population

“…Inbred‐progeny selection was approximately equal in effectiveness or inferior to noninbred‐progeny selection in every case except S 2 –selection in the study by Weyhrich et al (1998) and S 1 –selection in cycles zero through four in Tanner and Smith (1987) were superior to noninbred forms of selection. Similar to the observation by Tanner and Smith (1987) in which greater response to inbred progeny selection was observed in early cycles, Iglesias and Hallauer (1991, 1989) and Lamkey (1992) evaluated responses to inbred‐progeny recurrent selection in which responses appeared to be greater in early cycles (less than five) than in later cycles or combined across more than four cycles of selection.…”

“…Linkage disequilibrium would be expected to be low in relatively broad‐based populations, such as the populations in the studies reviewed here, in early cycles of selection. At small population sizes, linkage disequilibrium could be expected to increase rapidly causing pseudo‐overdominance which limits response to inbred‐progeny recurrent selection in later cycles, as observed by Lamkey (1992), Tanner and Smith (1987), and Iglesias and Hallauer (1991, 1989).…”

Conversion of elite subtropical maize germplasm to temperate environments

“…Albrecht and Dudley (1987) concluded when considering yield alone, 25% exotic is the preferred starting material, which agrees with Wellhausen's (1965) recommendation 25 years earlier. Field studies support the use of backcross introgression to introduce exotic germplasm into temperate populations (Albrecht and Dudley, 1987;Crossa and Gardner, 1987;Iglesias and Hallauer, 1991). Studies indicate 25 and 50% semi-exotic populations did not differ significantly for yield, and have greater genetic variability than the adapted recurrent populations (Albrecht and Dudley, 1987;Crossa and Gardner, 1987;Michelini and Hallauer, 1993).…”

“…Introgression of exotic germplasm into adapted photop>eriod insensitive maize sources has been reported to increase genetic variation relative to adapted sources (Albrecht and Dudley, 1987;Crossa and Gardner, 1987;Hoffbeck et al, 1995). Most authors have observed greater genetic variability when introgressing exotic germplasm into adapted maize in temperate environments (Hallauer, 1980;Iglesias and Hallauer, 1991;Hainzelin, 1998).…”

Inbreeding Depression and Other Genetic Effects in Populations of Maize Containing Highland Tropical Germplasm

“…Populations from crosses involving highland Peruvian germplasm have shown less potential (EAGLES 1990), and will not be considered in detail, although most of the following comments on the utilization of populations containing highland Mexican germplasm would also be applicable to them. S] or S2 line recurrent selection has been effective for reducing inbreeding depression, especially during early cycles of recurrent selection (TANNER and SMITH 1987, HORNER et al 1989, WALTERS et al 1991, and has been effective for reducing root lodging (IGLESIAS and HALLAUER 1991). A feasible system would be to grow the So population at a moderate plant density and self-pollinate plants with strong roots.…”