Canola and mustard response to short periods of high temperature and drought stresses at different growth stages
Brassica crops grown on the semiarid Canadian prairie are often subject to heat and water stress during the period of flowering. A growth chamber study was conducted at Swift Current to understand the effects of short periods of high temperature stress and/or water stress at different developmental stages on the seed yield formation of different Brassica species. Two advanced breeding lines of canola quality Brassica juncea (PC98-44 and PC98-45) along with a canola cv. Quantum (B. napus L.) and a mustard cv. Cutlass (B. juncea L.) were grown under 20/18 °C day/night temperature. High (35/18 °C) and low (28/18 °C) temperature stresses were imposed for 10 days at bolting, flowering or pod formation stages in two separate growth cabinets. At the same time, low (90% available water) or high (50% available water) water stress was imposed on half of the plants in each of the temperature treatments. All yield components were affected by temperature stress, while water stress had no effect on most yield components. The severe reduction of pods main shoot-1 (75%), seeds pod-1 (25%), and seed weight (22%) by 35/18 °C, reduced main stem seed yield of by 87% in all Brassica cultivars. However, seed yield reduction per plant by the same stress was 51%, indicating recovery from the stress treatments by Brassica species. Delaying exposure to stress to pod development stage reduced the chance of the plant to recover from the stress. The low water stress was to encouraging better recovery at 28/18 °C stress. In the controlled growth chamber, B. juncea cultivars responded to heat stress by increasing pod production but ignoring filling pods, while B. napus maintained a better seed fill. Under field conditions where plant-to-plant competition is strong, B. juncea may produce more pods with higher seed yield than canola; this needs to be confirmed with further field trials.
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