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Seeds rapidly take on water and must be in contact with moist soil in the presence of oxygen. Seeds swell with water, splitting the seed coat, and the root tip emerges. Canola is sensitive to soil salinity, and germination can be impaired in saline soils. Temperature will also affect seed germination. This stage lasts roughly four to 10 days, depending on planting depth, soil temperature, and moisture.
Seedling roots continue to develop, and leaf development begins. After emergence, the cotyledons open and supply the seedling with energy. The seedling is vulnerable to soil-borne pathogens and flea beetle injury. The canola plant growing point is between two cotyledons, where damage can kill the seedling. As the tap root system expands, secondary roots emerge from the taproot. The first true leaves appear about four to eight days after emergence.
First true leaves begin to expand forming the “rosette”, a cluster of leaves forming around the main stem with older leaves at the base and smaller, younger leaves at the center. The stem has not yet begun to elongate yet continues to grow thicker. Canola growth rate is dependent on sunlight exposure. This stage can be characterized by an increase in leaf area index.
Bolting (stem elongation) and flower bud development are triggered by lengthening daylight and rising temperatures. Flower buds become visible around the center of the rosette. Secondary branches form from buds and develop in the axils of the upper leaves. The canola plant reaches maximum leaf area index during this stage. Stem elongation overlaps with leaf and flower development. Most of the photosynthesis occurs in the leaves; loss of leaves means potential yield loss.
During flowering, the lowest buds in the main stem begin to open, continuing for 14-21 days. Three to five flowers or more will open per day and 40-55 percent of open flowers will develop pods. During this stage, heat and moisture stress and nutrient deficiencies can cause flowers to abort resulting in potential yield loss. Full plant height is reached at peak flowering.
Seed development occurs during mid-flowering. The location of the pod will determine the nutrient access and seed size, and number of seeds per pod. During the first couple weeks of seed development, the seed coats expand until the seed is almost full size. Plant stress during this stage can cause pod abortion. When seed expansion is complete, plants will be more resistant to pod and yield loss.
Ripening begins when the petals fall from the last flower and plant leaves begin to yellow. Seeds begin to fill about 35-45 days after flowering begins. When they are fully mature, seeds are yellow. Seeds in the last formed pods are in the last stages of filling when 30-40 percent of the seeds on the main stem of a plant have changed seed coat color. During this stage, the crop is considered ripe and is ready to be swathed when 30-40 percent of the seeds on the main stem have turned brown. If growers are using a contact herbicide to desiccate, the recommended application timing is when 60-70 percent of the seed has turned brown, more than the typical swathing stage.