Figure 6. Chlorophyll (Chl) content in leaf (A) 1, (B) 3, (C) 5 and (D) 10 or more for control (18°C night and day) (red) and cold treatments (5°C night and 18°C day) (blue) in a growth chamber. Asterisks indicate the significance of the Student’s t-test between the cold and control treatments: ***: p < 0.001, **: p < 0.01, *: p < 0.05, NS: non-significant. Corresponding experimentations was 20HP01.
Along with measuring growth, chlorophyll was measured in leaves 1, 3, and 5 and the leaf ranked at 2/3 of the total number of leaves (i.e., leaf 10 or more). Chlorophyll content was higher in stressed plants than in control plants after being transferred outside. Chlorophyll content was higher on day 1 in leaf 1 in the control treatment than in the cold treatment, which reflected the influence of the recent cold treatment in the growth chamber (Fig. 6A). Seven days after transfer outside, the chlorophyll content became higher in the cold treatment than in the control treatment. This result was observed for all measurements for leaves 3, 5 and 10 or more, with a high level of significance for leaves 3 and 5 (Fig. 6B and C).

Impacts of early sowing on yield and yield-related traits

We studied impacts of ES date on late development and yield in the 2022 experiments (22TE01-02). We measured morphology, yield, number of seeds, thousand kernel weight, seed weight, oil content and seed lipid composition (Table 2). ES did not influence plant height but did result in later flowering (111 days) than that of normal sowing (79-86 days) (i.e., 9-16 d later). Flowering occurred earlier with ES (20 June 2022) and was more synchronized for its three replicates than those of normal sowing, which flowered from 29 June-6 July 2022. ES increased the seed yield and the oil yield (770 kg/ha) compared to that of normal sowing (430 kg/ha) (i.e., +80%) due to a slightly higher oil content. ES decreased the oleic acid content in seeds significantly and increased the contents of linoleic and palmitic acids.
Impacts of night chilling at early stages on final yield-related traits
To study impacts of early chilling stress on final traits, plants were stressed in the cold and control treatments described previously. After three weeks in growth chambers, the cold treatment was stopped, and plants were transferred outside to the high-throughput phenotyping platform Heliaphen.