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There is evidence of the negative effects on canola seed yield caused by shading (SH) and high temperature stress (HT) separately, but the combined effect of both stresses has not been studied. This work aimed to (i) evaluate the effects of SH and HT stresses, alone and combined, on floral development, seed yield and quality, (ii) quantify the resulting effect (additive, synergistic, antagonistic) of combined stresses, and (iii) examine the utility of the photothermal quotient (PTQ, solar radiation/temperature ratio) to predict seed yield in stressed canola crops. Two field experiments were performed in Buenos Aires (Argentina) applying HT daytime temperature stress (25–30 °C from 1000 to 1500 h), SH (−80% irradiance), and SH + HT combined stresses, with C unstressed (20 °C and 100% irradiance) crops. Long and short duration SH and HT strongly affected floral development (fewer flowers and pods, with smaller ovules) and seed yield (reduction from −40 to −90% respect to C). Combined SH + HT exhibited detrimental synergistic effects on seed yield and oil concentration for long duration stresses, whereas antagonistic effects were mainly observed for short stresses. We conclude that the PTQ (cumulative from 100 to 500 °Cd after flowering) summarizes adequately the detrimental effects of combined post-flowering abiotic stresses on canola seed productivity. [ABSTRACT FROM AUTHOR]

Sunlight is a crucial environmental factor for photosynthesis. Plant density affects both quality and quantity at light penetration into the canopy. The effects of plant density on the expression of photomorphogenic traits in cultivated spring rapeseed ( Brassica napus L.), and their consequences on seed production per unit area are unknown. The aims of this work were to: i) analyze the magnitude of shade avoidance responses to plant densities in five spring rapeseed genotypes, ii) describe the dynamics of floral branching in response to genotype and plant density, and iii) study yield and its components and seed quality in field-cultivated plants with contrasting plant densities (15 and 240 pl m −2 ). Rosette diameter was the main attribute of vegetative plasticity modified by plant density, without significant changes in petiole length. Plant density changed the relationship between intercepted solar radiation (ISR) and red/far red ratio (R/FR) during crop development, but at flowering all densities reached ISR = 95% and R/FR ratio <0.1. From flowering to maturity, the lower the plant density, the lower the R/FR, associated to increased silique area by a promotion of floral branching. Growth dynamics of floral branches at first, second and third orders were strongly affected by plant density and genotype. Seed yield per plant could be described by a negative power-law function as a function of plant density at harvest, exhibiting a high reproductive plasticity capable of compensating grain yield per unit area. Fruiting efficiency per plant was around 100–160 seeds g −1 , regardless of plant density. Seed oil and protein content were not responsive to plant density. We concluded that plant density could be reduced without significant penalty for seed production per area, because short-cycle spring rapeseed genotypes expressed a strong vegetative and reproductive plasticity at individual level when plants were grow under well- watered and fertilized conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Seed growth dynamics were followed across floral positions, cultivars and crop population plant densities. • Bi-linear functions provided good fits to seed dry weight/water concentration relationships. • Physiological maturity (PM) was reached at 45–46% seed water concentration (SWC). • The water concentration of whole pod was 70% at PM but decreased drastically before pod shattering. • At crop level, 46% SWC corresponded to 90% of the maximum simulated seed yield. Abstract Determining the optimum time for rapeseed harvest is challenging due to non-uniform seed maturity resulting from asynchronous flowering and pod dehiscence from sequential racemes. Identifying physiological maturity (PM) by visual methods is subjective and results can be affected by environmental conditions. PM can be determined using a quantitative model based on seed water concentration (SWC) as previously demonstrated for several other crops, although not yet developed for rapeseed crop. The objective of this work was to study the relationship between the dynamics of seed dry weight and water concentration in seven spring rapeseed cultivars grown at two contrasting densities (15 and 60 pl m−2) in three experiments at one location in Buenos Aires (Argentina). We evaluated the timing of PM on the basis of SWC in seeds located in the main raceme, second and fourth floral branches. The evolution of seed fresh and dry weight was followed bi-weekly from the beginning of flowering to harvest maturity. In Exp. 1, the grain-filling duration ranged from 39 to 57 days (700–1100 °C d) and the growth of seeds from floral branches finished 3–8 days later than those from the main raceme. Seed dry weight at PM ranged from 2.4 to 2.7 and from 3.0 to 3.2 mg for Lynx and Monty cultivars, respectively, without significant effects of floral position or plant density. Bi-linear functions were used to fit the relationship between relative seed dry weight (RSDW) and SWC relationships (R2 from 0.85 to 0.95). Across cultivars and floral positions, PM was attained when seeds exhibited 46.3 ± 0.7% SWC (R2 = 0.90, P < 0.001, n = 441). This model was validated against independent data from Exps. 2 and 3, successfully simulating the dynamics of relative seed dry weight based on fruit WC (r = 0.88; P < 0.001, n = 275). At PM, the water content (WC) of whole pod was about 70% and the pod shattering began after this point, when the WC of the pod dropped drastically. We conclude that under non-stressful conditions, PM in rapeseed occurs at 46% SWC. Swathing can be conducted from SWC < 46%, instead of the currently recommended 35%, advancing the harvest and leaving the land available for sowing the next crop, which would represent an advantage for double cropping in intensified agricultural systems. [ABSTRACT FROM AUTHOR]