QTL Analysis of Brassica Napus for Yield Components in Dryland and Irrigated Conditions.

Canola (Brassica napus) has potential as an oilseed crop in Colorado if its heat and drought tolerance were improved. We undertook this study to determine areas of the canola genome that influence maturity, yield, and yield components under both dryland and irrigated conditions through quantitative trait locus (QTL) analysis. Two doubled haploid canola mapping populations were grown in side-by-side irrigated and rainfed treatments near Fort Collins, Colorado: population SE1 (n=183) in 2010 and population DHYB (n=150) in 2011. Traits evaluated included days to flower, seed yield, siliques per main inflorescence, seeds per silique, and thousand seed weight. QTL mapping was conducted separately for each treatment in each population using R-QTL software to detect additive and epistatic effects.

In the 2010 study, three QTL for days to flower were detected that co-localized with QTL for most of the other traits, demonstrating the strong influence of flowering time on seed yield and yield components in this population. These QTL explained 73 and 65 percent of phenotypic variance for days to flower in the wet and dry treatments, respectively, in a multiple QTL model. In the 2011 study several novel QTL were detected, including a locus on LG 17 that explained 7.5% of phenotypic variation for seed yield in the dry treatment and a locus on LG 16 that explained 11.4% of variation for seed yield in the wet treatment. A novel QTL for seeds per silique was detected on LG 7 in both treatments. Two QTL reported for days to flower in the wet treatment on LGs 14 and 18 are novel, as are two QTL for siliques per main inflorescence in the dry treatment.

Of the yield components studied, seeds per silique had high heritability estimates and low genotype by treatment interaction in both populations. That trait also correlated positively and significantly (P<0.05) with seed yield in both years of the study. Additionally, the QTL detected for seeds per silique in the 2011 study were the same for the wet and dry treatments, indicating QTL stability. It is our conclusion that seeds per silique is a reliable trait for direct selection in a breeding program, and that the QTL reported for the trait could be useful for marker-assisted selection for improved yields in Colorado.