Agronomy Den Insights > Canola Genetics Explained

Canola Genetics Explained

Nov 03, 2021

Written By: Kerry Gerein

When it comes to canola choices and planning on your farm, there are multiple different genetic traits involved to make up individual canola varieties. The herbicide tolerant system will determine what herbicides may be used for in-season weed control with varieties available featuring multiple different disease resistance packages to help mitigate yield loss from the major diseases; sclerotinia, blackleg and clubroot. Additional agronomic traits that may be included within a canola variety are pod shatter and improved standability as well as variation in plant height and days to maturity when comparing different varieties. Lastly, yield potential is a very important trait in canola genetics.

Herbicide Tolerant System

There are multiple different herbicide tolerant systems of canola which include Roundup Ready®, Truflex™, LibertyLink®, Roundup®/Liberty® Stack, and Clearfield®. In Roundup Ready and Truflex canola, glyphosate is used in crop with the difference being that the Truflex trait allows for higher rates of glyphosate to be used and applied at a later stage, therefore resulting in improved weed control. In LibertyLink canola, glufosinate is used in crop,and with the Roundup/Liberty stack, both glyphosate and glufosinate can be applied but it must be done in separate passes. In Clearfield canola, options include imazamox, imazethapyr, and sethoxydim for in crop herbicides. Some additional herbicides for all systems include clethodim, quinclorac, and clopyralid. It is important to determine what herbicide system is the best fit on the farm with consideration of crop rotation and weed species and pressure.

Disease Resistance

Blackleg


Blackleg is also known as a stem canker and is caused by a fungus called Leptosphaeria maculans which overwinters on the canola stubble. In the spring when it warms and there is enough moisture, spores are released and infect the plants starting at the seedling stage. The cotyledons and young leaves will show lesions with black specs called pycnidia which release new spores to further infect more leaves. Blackleg will cause girdled stems which will restrict the uptake of moisture and nutrients, eventually leading to yield loss. It can best be identified at swath timing by clipping the base of the stems and looking for black pigment on the interior of the stem.

Genetic resistance was first introduced into canola varieties in the early 1990’s. Major gene resistance works by killing the cells around the point of infection on the cotyledon of the leaf in order to stop the fungus from advancing further. Minor gene resistance works by slowing and/or preventing the formation of stem cankers. Genetic resistance along with crop rotation are the best management practices to significantly reduce yield and quality losses.

Sclerotinia

Sclerotinia stem rot is a disease caused by a fungus called Sclerotinia sclerotiorum. The fungus overwinters in the soil or canola stubble as sclerotia bodies which may remain in the soil for up to 5 or more years. With warm (15 to 25ºC) and moist conditions for at least 10 days, the sclerotia germinate and produce apothecia. The apothecia produce ascospores which move by the wind and adhere to the flower petals. They then germinate and infect the petal, falling onto the leaves where lesions form and progress up and down the stem which become bleached and brittle. New sclerotia are formed in the stems and they can overwinter in the soil. Currently, there are limited canola varieties with tolerance or resistance to sclerotinia. Implementing a good crop rotation and applying a fungicide when conditions are favourable for disease development are very successful management practices.

Clubroot

Clubroot is a soil borne disease caused by a protist called Plasmodiophora brassicae. This pathogen overwinters in the soil as resting spores which can survive in the soil for up to 20 years. However, they may become inactive after a two year break from a host crop. In the spring when it is warm and moist, these resting spores germinate into zoospores and swim to find root hairs to infect. Once inside the root hair, more zoospores are developed from the pathogen which are released to infect more roots. Genetic resistance will prevent the secondary flush of zoospores which are the ones that initiate the root symptoms and cause yield loss. The pathogen causes cell division and cell growth which is the formation of galls. The galls limit water and nutrient uptake which then results in premature death of the plant. Resting spores are released back into the soil as these clubroot galls decay.

The potential yield loss of clubroot will depend on many different factors, some of which include time of infection, soil moisture, soil temperature, spore load, and soil pH. If all conditions are met and the infection happens early on, there could be complete yield loss in the canola crop. There are many canola varieties available with clubroot resistance. For a canola variety to be classified as resistant to clubroot, it must be resistant to the 5 most predominant clubroot strains in Western Canada which are named as 2F, 3H, 5I, 6M, and 8N. Additional ratings may be added to the label for new clubroot strains including 2B, 3A, 3D, and 5X. These varieties provide a high amount of clubroot control when it is used within a proper crop rotation. Rotation of clubroot resistant varieties is very important as well to minimize the chance of the pathotype overcoming the resistant traits. Besides growing clubroot resistant varieties, other important management practices against clubroot include minimizing soil movement, scouting fields to identify infection, controlling host weeds, and extending the crop rotation.

Pod Shatter

Pod shatter tolerance is a very important trait if delayed swathing or straight cut is a common practice on the farm. All canola varieties can be straight cut; however, those with pod shatter tolerance have the ability to out-yield those varieties without when straight cutting is done. The delayed swathing is a very useful strategy when there are elevation changes throughout the field.

Standability

Canola varieties with excellent standability can increase harvest efficiency. They tend to be easier to swath or straight cut and decreased lodging helps mitigate disease development.

Plant Height

Canola varieties can vary greatly when it comes to plant height. Height differences tend to be more of a grower preference. Canola can range anywhere from 2 to 6 ft tall, however environmental conditions have a large impact on plant height.

Days to Maturity

Days to maturity can be a very important variety selection factor. If canola is grown in a shorter growing season or if harvest always seems to occur late on the farm, it can be very important to choose earlier maturing varieties. However, if these are not concerns, then it may be preferable to select later maturing varieties.

Yield Potential

Yield potential can be viewed as the most important trait in canola. Nevertheless, it is more important to consider the important agronomic traits listed above that will improve quality, harvestability and disease management on the farm. Once those traits are selected, then it will narrow down the selection of varieties. From there the variety with the highest yield potential in that growing area should be chosen. If you are looking for additional information about canola seed genetics or would like to discuss canola varieties, please get in touch with your local G-Mac’s AgTeam Agronomist or Agronomy Consulting Expert (ACE).

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