Abstract. Heat stress can frequently limit the yield of Brassica napus L. grown in Canada because of the often unavoidable concurrence of high temperatures and flowering. Ten B. napus inbred genotypes, an open-pollinated B. napus commercial cultivar and a B. juncea genotype were grown in a greenhouse and subjected to two temperature regimes in a growth chamber for 14 days during flowering: control 228C/108C and high 318C/148C (day/night). Floral buds were sampled at the end of the 14-day treatments, and an untargeted metabolomic assessment was completed using gas chromatography-mass spectrometry. Flower duration, number of flowers, number of pods, biomass, number of seeds and seed weight were recorded. Yield was reduced by 55% in the heat treatment during winter and by 41% during the subsequent autumn experimental run. Of the 12 genotypes, five were classified as heat-tolerant and four as heat-susceptible based on the calculated heat susceptibility index across two experiments. In total, 25 metabolic markers were identified that discriminated between the heat-tolerant and -susceptible genotypes exposed to the heat treatment. The variation identified within this set of germplasm has provided evidence that variation exists within B. napus to enable genetic gain for heat tolerance.

Koscielny C. B. and Gulden R. H. 2012. Seedling root length in Brassica napus L. is indicative of seed yield. Can. J. Plant Sci. 92: 1229–1237. Recent studies have shown relationships between root growth and development and seed production potential in some crops; however, little is known about this relationship in Brassica napus. Field and growth room experiments were conducted to determine the relationship between root parameters up to the four-leaf stage and seed yield among a group of four open-pollinated and four hybrid B. napus genotypes with different yield potential. In the field studies, root length was the best indicator of seed yield at the one- to two-leaf and the three- to four-leaf stages of development, and was one of the most consistent parameters among sites and years. Poor ability to recover fine roots from field soils at the cotyledon stage contributed to the relatively poor relationships between root parameters and seed yield compared with shoot parameters at this developmental stage. The growth room study clearly showed that root length is an excellent measure of seedling vigour and an indicator of seed yield as early as 7 d after imbibition. These studies demonstrate the importance of early root development in canola and its potential as a screening trait for seed yield in breeding programs.

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Canola (Brassica napus L.) is grown on >8 Mha in Canada and is sensitive to high temperatures; therefore, research on breeding methodologies to improve heat-stress tolerance is warranted. This study utilised a doubled-haploid population created from two parents (PB36 and PB56) that differed in their ability to set seed following growth at high temperatures. The experiment was designed to identify potential quantitative trait loci (QTLs) responsible for conferring tolerance to increased temperatures, and to utilise this population as a test case for evaluating the prospects of whole-genome prediction. The population was phenotyped in a split-plot, randomised complete block experimental design at three locations with two planting-date treatments. The first planting date was during the normal planting period (control), and the second planting was timed to experience increased average temperatures (1.7°C, 2.0°C and 1.2°C) and increased number of days with maximum temperatures above the critical temperature of 29.5°C (4, 12 and 3 days). The stress treatment reduced yield on average by 16.7%. There were 66 QTLs discovered across the nine traits collected. Given the quantitative nature of the traits collected, the ability to use whole-genome prediction was investigated. The prediction accuracies ranged from 0.14 (yield) to 0.66 (1000-seed weight). Prediction had higher accuracy within the stress treatment than within the control treatment for seven of the nine traits, demonstrating that phenotyping within a stress environment can provide valuable data for whole-genome predictions.