Assessment of Cold and Heat Tolerance of Winter‐grown Canola (<i>Brassica napus</i> L.) Cultivars by Pollen‐based Parameters

Abstract

Abstract Winter‐grown canola ( Brassica napus L.) production is limited mostly by frost and winter kill in the southern canola‐growing regions of the United States. Tolerance to cold and heat were assessed by studying percentage of pollen viability (PV), in vitro pollen germination (PG) and pollen tube length (PTL) for 12 field‐grown cultivars. Freshly collected pollen from all cultivars were incubated on artificial solid growth media at a constant temperature ranging from 10 to 35 °C at 5 °C interval for 30 h to determine PG and PTL. A modified bilinear model best described the temperature response functions of PG and PTL. Canola cultivars showed significant variability (P &lt; 0.001) for PV (61.3 % to 89.7 %), PG (29.0 % to 48.2 %) and PTL (463 to 931 μm). The average cardinal temperatures, T min , T opt and T max , for PG and PTL were 6.4, 24.3 and 33.7 °C, respectively. Principal component analysis revealed that maximum PG, PTL, T min and T opt of both PG and PTL were the most important factors in determining cold tolerance, whereas T max of PG and PTL, and maximum PG and PTL were more responsible in separating the cultivars for heat tolerance. The canola cultivar, KS3077, was the most cold tolerant with the lowest T min and the widest temperature adaptability range, and the cultivar Kadore was the most heat tolerant with the highest T max for the PG. The identified cold‐ and heat‐tolerant cultivars may be useful in canola‐breeding programmes to develop cultivars suitable for a niche environment.