Quantitative trait loci mapping in maize (Zea Mays L.) using a novel mapping population approach

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Singh, Asheesh Kumar

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University of Guelph

Abstract

The overall objectives of this study were to investigate the feasibility of a novel mapping population approach, Identity-by-Descent limited Recombinant Inbred Line (IBD-limited-RIL) for quantitative trait loci (QTL) mapping in maize ('Zea mays' L.) and to develop a better understanding of grain yield and its underlying physiological mechanisms. Three families of six sister-lines (SL) each were evaluated in a multi-environment trial. The IBD estimates of SL were developed using simple sequence repeat (SSR) markers. Results showed that despite high IBD levels, genetic variation exists between SLs. IBD-limited-RIL population can be used for QTL mapping and offers many advantages compared to currently available mapping populations. IBD-limited-RIL population from a SL cross of CG60 and CG108 were developed to identify grain yield QTL. The multi-environment trial clustered into three distinct environmental groups based on additive main effect and multiplicative interactions (AMMI) analysis. Significant QTLs with large effect were identified within the three environmental groups; however, no common QTL was detected in the three groups. Physiological experiments were conducted to develop a better genetic understanding of grain yield and its underlying physiological mechanisms. Genotypes were a significant source of variation for all tested traits, except dry matter at silking (DMS). Dry matter at maturity (DMM) and dry matter accumulated during the grain filling period (GFP) had significant positive correlation with grain yield. Harvest index (HI) also was significantly positively correlated with grain yield. The parental genotypes CG60 and CG108 did not differ for grain yield (GY), DMS, DMM, HI and GFP. However, transgressive segregation was observed for all traits studied. The majority (62%) of the dry matter was accumulated during the grain filling period. Significant QTLs were detected for GY, DMM, GFP, and HI. Significant GY QTL were not the same QTLs for any other trait QTL, except one GY QTL was a HI QTL. These experiments are the first attempt at linking grain yield with underlying physiological processes at a genetic level using segregating populations. Linking of genetic and physiological information will be useful for plant breeders, physiologist and geneticist as we try to better understand the processes governing grain yield and develop higher yielding hybrids.

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maize, quantitative traint loci mapping, novel mapping population approach, grain yield, higher yield hybrids

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