Heterotic grouping of tropical early-maturing maize inbred lines based on combining ability in Striga-infested and Striga-free environments and the use of SSR markers for genotyping

Title 
Heterotic grouping of tropical early-maturing maize inbred lines based on combining ability in Striga-infested and Striga-free environments and the use of SSR markers for genotyping 
Publication Type 
Journal Article 
Authors 
O Akinwale R, Badu-Apraku B, Fakorede MAB, Vroh-Bi I 
Year of Publication 
2014 
Volume 
156 
Journal 
Field Crops Research 
Pagination 
48 - 62 
Date Published 
2/2014 
ISSN 
03784290 
URL 
http://www.sciencedirect.com/science/article/pii/S0378429013003663 
Keywords 
Combining ability, Heterotic groups, Maize, simple sequence repeat markers, Striga resistance 
DOI 
10.1016/j.fcr.2013.10.015 
Abstract 

Highlights

  • Both genetic and molecular analyses revealed that there was moderately high genetic diversity among the inbred lines, which facilitated identification of distinct heterotic groups and the best testers.
  • Results of the general and specific combining abilities suggest that a programme may be initiated to develop heterotic populations and pools from which more genetically diverse superior inbred lines could be synthesized through reciprocal recurrent selection.
  • Results also revealed that GD estimates among the Striga resistant inbreds were more associated with their combining abilities under Striga-free than under Striga-infested conditions.
  • Although, the molecular marker analysis showed wide variability among the inbreds, none of the 46 polymorphic SSR primer pairs could discriminate the different levels of Striga resistance present in the inbred lines.

Identification of heterotic groups among inbreds is crucial to the success of a maize (Zea mays L.) hybrid breeding program. The objectives of this study were to determine the combining ability of 28 early maturing inbreds, classify them into heterotic groups, identify suitable testers under Striga-infested and Striga free environments and to assess the efficiency of three heterotic grouping methods. Three hundred and seventy-eight hybrids derived from diallel crosses of 28 early inbreds along with two checks were evaluated in Striga-infested and Striga-free environments for 2 years at two locations in Nigeria. Twenty-seven of the 28 inbreds were genotyped with 46 polymorphic simple sequence repeats (SSR) markers previously mapped on the 10 maize chromosomes. Analysis of variance revealed highly significant (P < 0.01) general combining ability (GCA) and specific combining ability (SCA) mean squares for most traits under test conditions. Based on the SCA effects and heterotic group's specific and general combining ability (HSGCA) for grain yield, four and five heterotic groups were identified under Striga-infested and Striga-free environments, respectively. Two inbreds could not be classified into any of the four groups under Striga-infestation. The SSR markers revealed a wide genetic variability among the inbred lines as the genetic distance ranged between 0.21 and 0.68. Four heterotic groups were identified based on genetic distance (GD) derived from the SSR analysis. Correlation analyses showed that grouping using GD was more consistent with grouping based on SCA under Striga-free than under Striga-infested environments. The HSGCA method was the most effective in classifying early maturing maize inbreds under Striga-infested and Striga free environments. A total of 4 and 8 inbred testers were identified under Striga-infested and Striga-free environments, respectively. These inbred testers are invaluable resources for tropical maize breeding programs.

 
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