QTL mapping of root and leaf traits associated with drought tolerance in a canola (Brassica napus l.) doubled haploid population
Date
2013
Authors
Mekonnen, Melaku Degefu, author
Byrne, Patrick, advisor
McKay, John, committee member
Seshadri, Arathi, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Drought stress is one of the major constraints to canola production in Colorado, therefore, improved understanding of the inheritance and genetic variation for drought tolerance will help to develop cultivars that are adapted to the state. To learn more about traits associated with drought tolerance in canola we focused on root pulling force and carbon isotope discrimination with the objectives of: • Detecting the location, number, and effects of quantitative trait loci (QTL) associated with root pulling force and carbon isotope discrimination • Understanding the association of root pulling force and carbon isotope discrimination with yield components in well watered and water limited environments We used 148 doubled haploid lines of the DHYB population developed from the cross of a black seeded (DH12075) and a yellow seeded (YN01-429) parent. The experiment was conducted as a split-plot design with three replications in the 2011 and 2012 summer seasons. Two moisture regimes (wet and dry) constituted the main plot factor, with genotype as the subplot factor. A single individual plant per replication represented each genotype. Days to flowering, leaf relative water content, δ13C (the ratio of 13C to 12C), plant height, lateral branch number, lateral root number, thousand seed weight, seed yield per plant, root pulling force, and proportion of aborted siliques were measured, though not every trait was evaluated in each treatment or year. Phenotypic correlation among all pairs of traits and heritability of the traits under both treatments were estimated. QTL analysis was conducted for each trait and environment with R/qtl software. Analysis of variance revealed significant differences (P<0.001) among genotypes for days to flowering, plant height, and δ13C in both treatments and years. Transgressive segregation was observed for root pulling force, δ13C, days to flowering and plant height in both treatments and years. Root pulling force was significantly correlated with plant height (r = 0.32 to 0.54, P<0.001), fresh biomass (r = 0.17 to 0.58, P<0.001), and lateral root number (r = 0.21 to 0.42, P<0.001) in both years and under both moisture treatments. The strong positive correlation of root pulling force with the branch number and fresh biomass suggests that it can be used to detect genotypes with higher yield potential in drought. δ13C was positively correlated with days to flowering in each experiment and negatively correlated with seed yield per plant and thousand seed weight. In 2011 QTL were detected for days to flowering on linkage group 1, 2, 12T, and 16, and for the interaction between loci on linkage groups 1 and 16; some of the same QTL were also detected in 2012. In 2011, QTL for root pulling force were detected on linkage groups 3, 5, 11, 14T, and 18 and for the interaction between QTL on linkage groups 3 and 18. In 2012, consistent QTL were detected on linkage groups 11 and 18. The QTL for root pulling force co-localized with a fresh biomass QTL on linkage group 11 and with plant height on linkage group 14T. Five QTL for δ13C were detected on linkage groups 2, 9, 18, and 19 in different environments. In general QTL for δ13C were associated with QTL for days to flowering. No epistatic interactions were detected for the QTL detected in 2011 and 2012 for δ13C, suggesting strong additive gene action for δ13C. We found high heritability and relatively low QTL x environment interaction for root pulling force and δ13C; therefore, we suggest these traits can be used to select genotypes with a higher yield and biomass in dry environments. The study provides insights about root pulling force, δ13C and their relationships with yield, and yield related traits in canola. In order to utilize these traits in breeding for drought tolerance and marker assisted breeding further research on the relationship among these traits is imperative.