HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Carlone, M. R. Articles by Russell, W. A. Search for Related Content PubMed Articles by Carlone, M. R., Jr. Articles by Russell, W. A. Agricola Articles by Carlone, M. R. Articles by Russell, W. A.

Evaluation of S₂ Maize Lines Reproduced for Several Generations by Random Mating within Lines. I. Comparisons between the Original and Maintained S₂ Lines

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

^* Corresponding author.

Most parents used in single-cross maize (Zea mays L.) hybrid seed production are highly inbred lines that have been developed through many generations of selfing and evaluation. Many times, lines with good combining ability are identified in the first few generations of inbreeding, but after additional generations of selfing they become less vigorous and too weak (Le., reduced seed yield and pollen production) to be economically used. One way to overcome the problem of severe inbreeding depression and reduced vigor is to use lines that have been only partly inbred and are maintained by random-mating within lines (sib-mating). The primary objective of this study was to compare original S₂ lines with their maintained S₂-line counterparts to determine if the genetic integrity was maintained after several generations of sib-mating. We evaluated the performance of 14 original S₂ maize lines and their progenies reproduced by sib-mating for several generations There were 14 original S₂ lines, each S₂ line maintained by using 10 plants per generation for six generations, each S₂ line maintained by using 20 plants per generation for six generations, and four lines were maintained by using mild selection for five generations. The S₂ lines were evaluated in a randomized complete-block design in four environments. Significant (P < 0.05) or highly significant (P < 0.01) differences were found among S₂-line groups for all traits except kernel row number and ear length. When compared as groups, the S₂ lines maintained by using 10 and 20 plants yielded 3.66 and 3.63 Mg ha^–1, respectively, significantly less than did the original S₂ lines (3.83 Mg ha^–1). Conversely, the S₂ lines maintained by using mild selection yielded the same as their original S₂-line group. Individual comparisons between each original SI line and its maintained S₂-line counterpart showed that significant changes in the maintained S₂ lines occurred in both the positive and negative directions for 50% of the traits. The S₂ lines maintained by using 10 plants per generation tended to be less stable than if they were maintained by using 20 plants when compared with their original S₂-line counterparts. Also, data from electrophoretic assays showed results similar to those observed in field evaluation. It was concluded that the genetic integrity of the original S₂ lines was not maintained by using sample sizes of 10 or 20 plants for grain yield. The changes in the lines' performances were small, however, compared with changes that would have occurred if the lines had been further inbred by conventional pedigree methods.

Received for publication February 25, 1988.