Evaluation of late planting date effects on agronomical traits and grain yield reduction of rapeseed genotypes in Mazandaran

Determining suitable planting date has important role in conformation of plant growth stages with desirable environmental conditions which results in maximum yield. Planting date has a considerable effect on seed yield by influencing the yield components so that late planting decreases the most important traits i.e. days to flowering, duration of flowering, plant height and pods per plant which cause a remarkable reduction in seed yield. Sowing time is also one of the most important factors for maximizing rapeseed yield especially in those areas where temperature, day length, rainfall and humidity vary throughout the year (Kurmi & Kalta, 1992; Gan et al., 2004). Late planting of canola delayed flowering and reduced reflection of radiation during flowering which were important factors leading to the highest yields achieved by normal sowing (Coffelt & Adamsen, 2005).
Material & Ten rapeseed genotypes were studied based on randomized complete block design in two separate experiments at two planting dates including normal (16 Oct.) and late (15 Nov.) planting dates conditions during 2011-13 years at Baykola Agriculture Research Station. The data were recorded on ten randomly selected plants of each entry of each replication for including phonological stages, plant height, number of pods per plant, 1000-seed weight and grain yield. Seed yield (adjusted to kg ha-1) was recorded based on two middle rows of each plot. All statistical analyses were carried out using SAS software.
The genotypes had significant genetic difference for all the traits except 1000-seed weight. Among the phonological stages, the most and least reduction effects of late planting date were detected for duration of flowering and days to maturity, respectively. Significant mean squares of interaction effects of planting dates and genotypes were exhibited for phenological traits, plant height, pods per plant and seed yield, indicating the different trend variations of the mentioned traits of the genotypes in different planting dates. The percentage of losing of pods per plant and grain yield due to late planting, were 0.23 and 0.38, respectively. Significant positive correlation of grain yield with days to flowering and number of pods per plant in both planting dates indicated that any variation for these traits had considerable effects on grain yield. In this study, Zafar (G10), Zabol-0 (G2) and Safi6 (G5) with grain yield of 3142.3, 2979.4 and 2967.3 kg ha-1, respectively in normal planting date and also with 1890.2, 1905.7 and 1784.7 kg ha-1, respectively in late planting date had high mean values of grain yield and were classified the same statistical group in both planting dates conditions.
The results showed that the one-month delay in planting resulted in a significant decrease for all the traits except 1000-seed weight. Among yield components, pods per plant were correlated with grain yield in both planting dates condition and was considered as superior criterion for improving grain yield. Due to decrease of plant height and most yield components in late planting condition, grain yield was high significantly deceased and its mean values for normal and late planting were 2726 and 1599.3 kg ha-1, respectively.
Acknowledgements: The author wish to thank Agricultural and Natural Resources Research and Education Center of Mazandaran and Seed and Plant Improvement Institute (SPII) for providing genetic materials and facilities for conducting the experiment.