Grain yield, root growth habit and lodging of eight oilseed rape genotypes in response to a short period of heat stress during flowering

Under nearly all scenarios, the global mean temperature is predicted to intensify by at least 1°C within the twenty–first century. Elevated temperature stress is the increase in air temperature above a threshold level, for a duration long enough to lead to a negative effect on plant growth. This phenomenon has become a serious concern particularly in light of the changing climate. Recent research has focused on potential consequences of climate change on crop production via in–situ trials and global climate models. Effective acclimation and adaptation strategies can be developed to coping with climate change. Canola (Brassica napus L.) is among the leading oilseed crops in Canada. Canola is susceptible to elevated temperatures, compared to C4 plants, for example, corn, and some other C3 crops, such as wheat. Daily mean air temperatures above 32°C and lasting for one week or longer during a particular growing season are very common in the semiarid prairie and eastern Canada. Such elevated temperatures can influence the rate of metabolism of a crop which can consequently minimize the buildup of biomass and seed formation. As much as a 40% reduction in yield due to elevated temperature has been witnessed under field conditions in eastern Canada.

We designed a controlled growth chamber study with the following main objectives to (i) examine the responses of different B. napus genotypes to a short period of elevated temperature stress during early flowering and the resulting impact on root traits and seed yield, (ii) assess the reliability of EC and EI techniques to determine morphological attributes of roots and genotypic differences in reaction to acute exposure to heat stress, and (iii) evaluate the impact of short period exposure of canola to high temperature on its stem and root lodging and the underlying mechanisms.

We demonstrated large genotypic differences in terms of seed yield, root growth and lodging resistance in response to heat stress. Heat–tolerant genotypes, such as Invigor 5440 consistently showed higher seed yield, better root traits and larger electrical capacitance (EC) values. These B. napus genotypes exhibited a limited response to high temperature stress in terms of negative impact on important parameters. Conversely, heat–sensitive genotypes had lower seed yield, inferior root growth, and smaller EC values. Pearson’s simple correlation and PCA analysis revealed a stronger relationship of EC with root traits and seed yield. This study implies that EC could be reliably used as a non–destructive indicator for evaluating B. napus genotypic responses to heat and other abiotic stresses. Heat stress increased the risk of stem lodging significantly, as shown by reduced bending strength of stem and smaller stem safety factor against stem lodging; whereas it did not affect the severity of root lodging with respect to root safety factor and anchorage strength consistently, since the taproot was not affected by the short–term high temperature stress.