Grain yield and associated physiological traits of rapeseed (<em>Brassica napus L.</em>) cultivars under different planting dates and drought stress at the flowering stage

Abstract

The adverse effects of abiotic stresses have always restricted oilseed crop production, particularly in arid and semi-arid regions. On the other side, global climate change has led us to adapt planting dates and select tolerant cultivars to encounter the new climatic conditions. To evaluate the effect of late-season drought stress under different planting dates on rapeseed cultivars, an experiment was conducted as a factorial split-plot based on randomized complete block design in Karaj region- Iran, during 2015-2017. Planting date and irrigation treatments were considered in the main plots as factorial and cultivars were placed in subplots. Two planting dates were regular date (October 7) (PD1) and late planting date (November 6) (PD2). Irrigation was also carried out at two levels of normal irrigation (NI) and irrigation interruption from flowering stage onwards (II). Experimental cultivars included ES Hydromel, ES Alonso, ES Darko, ES Lauren, and Ahmadi. According to the results, late-season drought stress and delayed planting date reduced leaf relative water content (LRWC), total chlorophyll content (TCC), proline (LPC), and grain yield (GY), and increased stomatal resistance (SR), canopy temperature (CT), and leaf soluble carbohydrates (CLS) in rapeseed cultivars. The highest grain yield (4505.6 kg ha-1) was obtained in NI conditions and PD1. Significant interactions of planting date, irrigation, and cultivar on LRWC, SR, and CLS traits indicated that the ES Hydromel was the most tolerant hybrid cultivar with the highest LRWC and the lowest SR and CLS levels compared to other ones in unfavorable conditions of late-season drought stress and delayed planting. To confirm these results, cluster analysis led to the formation of two clusters, where ES Darko, Ahmadi, and ES Lauren cultivars were placed in the sensitive cluster and ES Hydromel and ES Alonso cultivars were assigned to the tolerant cluster. Therefore, ES Hydromel can be introduced as a superior cultivar to be selected as a genotype that presents acceptable resistance under drought stress and late sowing in arid and semi-arid regions.

Integrated Analysis of Metabolome and Transcriptome Reveals Insights for Cold Tolerance in Rapeseed (Brassica napus L.)

“…Furthermore, the late sowing of winter rapeseed reduced the rapeseed yield, and early flowering was also significantly affected by CS. Moreover, intracellular ice crystals are formed due to CS, distorting the sensitive plant organs (Lardon and Triboi-Blondel, 1995;Raza, 2020a;Shafighi et al, 2020). New seedlings, flowering, and seed formation are also mainly affected by CS (Lardon and Triboi-Blondel, 1995;Shafighi et al, 2020).…”

“…Moreover, intracellular ice crystals are formed due to CS, distorting the sensitive plant organs (Lardon and Triboi-Blondel, 1995;Raza, 2020a;Shafighi et al, 2020). New seedlings, flowering, and seed formation are also mainly affected by CS (Lardon and Triboi-Blondel, 1995;Shafighi et al, 2020). In recent studies, it was found that CS significantly reduced survival rate by impairing different physiobiochemical (reduced antioxidant enzyme activities, osmolyte content, and phytohormone levels) and molecular (reduced transcript levels of CS-responsive marker and antioxidant genes) mechanisms (Yan et al, 2019;He et al, 2021).…”

High plant density increases sunlight interception and yield of direct-seeded winter canola in China

“…Canola plants at low densities produced more floral branches and were less efficient in producing seeds per unit of invested pod wall (non-seed reproductive biomass) compared with plants at relatively high densities (Figure 1d). Biomass allocation to seed and pod wall was higher in the main floral raceme than in floral branches (Shafighi et al, 2021;Wang et al, 2021).…”

“…Canola growth and biomass yield were sensitive to plant population density and environmental conditions (Behrens and Diepenbrock, 2006;Li et al, 2018). Although more resources were used by each canola plant under low plant densities, such resources would be applied to luxury vegetative growth at an individual level without increasing above-ground dry matter and hence seed yield per unit area (Shafighi et al, 2021;Zhang et al, 2020). Therefore, a reasonable increase in plant density can curtail such luxurious vegetative growth of individuals (Rathke et al, 2006;Ren et al, 2017).…”

“…However, all densities reached the highest IS (about 92%) for both cultivars at the flowering stage (Figure 3). The IS increase was associated with the reduced ratio of red light and far-red light, which was induced by slow leaf senescence and high pod area derived from the increasing floral branches during the canola maturity period (Rondanini et al, 2017(Rondanini et al, , 2014Shafighi et al, 2021).…”