Visual identification of small oilseeds and weed seed contaminants - Visual identification
Visual identification of small oilseeds
Small oilseeds, as defined in the Canadian Grain Commission Official Grain Grading Guide, include flaxseed, canola and domestic mustard seed. For the purposes of this manual, identification of flaxseed is not included and small oilseeds will refer to domestic mustard seeds and canola/rapeseed.
A high level of proficiency in identification of classes of small oilseeds and the weed seeds that occur in them is essential for grain inspectors engaged in commercial grading of these seeds. This proficiency can be attained only by a concentrated study of the seeds under suitable magnification and in conjunction with accurate descriptions of seed characteristics and identification techniques.
Some seed characteristics are reasonably apparent to the naked eye but, in some instances, the most important characteristics must be discovered under a microscope. A careful examination of the seeds and the recognition of individual characteristics and combinations of characteristics are essential to proper identification. Initially, grain inspectors use a small 10-power hand lens to examine samples. Final determinations are made using a binocular microscope at the magnification best suited for the specific analysis.
Characteristics and terminology used to describe the various classes and types of small oilseeds are intended to provide a description of appearance that can be readily interpreted, particularly when used in conjunction with physical examination of the seeds. The ability to distinguish pure classes of domestic mustard seed can be attained quite easily, but recognition and segregation of mixtures of these classes from wild mustard seed and canola or rapeseed are much more difficult.
The small oilseeds described in this manual include domestic mustard seed and canola/rapeseed indigenous to western Canada. There are different varieties grown for each class but these are virtually indistinguishable within a given class. As there are no official standards of varietal purity established for small oilseeds for grading purposes this manual has not attempted to classify varieties according to visual distinguishability.
Domestic Mustard Seed
Classes include yellow mustard, oriental mustard and brown mustard.
Canola and Rapeseed
Canola and rapeseed are differentiated based on their end-use purposes as defined by the term "canola".
Canola - The term canola applies to varieties of Brassica napus and Brassica rapa that meet the canola standards for low levels of erucic acid and glucosinolates. Canola grain is a mixture of the two species in varying proportions. The production of canola varieties is widespread in western Canada.
Rapeseed – Rapeseed varieties do not meet the standards for canola quality. They are generally of high erucic acid content (H.E.A.R.). Both Brassica rapa and Brassica napus could potentially have rapeseed quality varieties. Rapeseed is produced in small volumes and usually under contract.
The seeds of canola and rapeseed may not be visually distinguishable.
Brassica napus - The seed of the two quality types of Brassica napus are not visually distinguishable.
Brassica rapa - The two types of seeds of Brassica rapa are not always distinguishable from each other as they are the same species and therefore have many similar features. However, seeds of older varieties of rapeseed quality Brassica rapa may be visually different than canola quality varieties of Brassica rapa. Occasionally seeds of rapeseed quality Brassica rapa are found in canola and these seeds must be recognized as Brassica rapa. They are not regarded as weed seeds. (See "Descriptions and Drawings for Individual Species" for more details.)
Some weed seeds commonly found as impurities in small oilseeds are also described in this manual. One noteworthy weed seed is wild mustard which is classed as a primary noxious weed seed in Canada. Wild mustard belongs to the same botanical family as the small oilseeds described in this manual. Wild mustard seed is included in established tolerances for Inconspicuous Admixtures in the official definitions for grading small oilseeds. It is sufficiently different in characteristics from domestic mustard seed to be readily distinguishable, but it is more difficult to recognize and segregate when mixed in samples of canola or rapeseed.
Identification procedure for grain inspectors
The procedure followed in identifying small oilseeds is different from the grading of wheat and barley. This is because oilseeds are much smaller and most results are determined with the aid of a microscope. However, the basic principles of identification are maintained.
Through experience most samples consisting mainly of one class of oilseed can be recognized as such. A closer examination for purity is made using a small 10-power hand magnifying lens. When samples contain mixtures of other classes, a more precise examination is carried out under higher magnification using a binocular microscope.
The sample is thoroughly mixed and divided to a portion of a prescribed weight. This portion is then placed in a rectangular plastic tray having two shallow depressed channels. The seeds are placed in one layer along the two channels and then passed through an illuminated area directly under the lens of the microscope. The inspector then picks out the admixture with a hand or electric tweezer and weighs the amount finally segregated to determine the percentage. The size of the sample analyzed will be determined by the class or type of seed being analyzed and the apparent level of admixture.
While the visual features of seeds are relatively unchanged over time, there are situations that could impact on small oilseeds' seed identification and grading.
Plants are living organisms, which may evolve and adapt to changes in their environment. Breeding programs produce new varieties of plants and the seeds of these new varieties may be similar to other existing seeds.
Domestic mustard breeding programs are selecting for canola quality Brassica juncea. It is possible that these new varieties will have no additional distinctive external seed characteristics. Seeds of mustard quality Brassica juncea may therefore be visually indistinguishable from canola quality Brassica juncea.
The impact of the development of GMO (genetically modified) canola and mustards is presently unknown. Modification of the genetic content of the seed is not usually marked by distinctive changes in the external visual features of the seed. Therefore, GMO and non-GMO seeds currently are visually the same in appearance.
An existing problem is the evolution of herbicide tolerant weed seeds. Tolerances to chemicals allow weeds to flourish in the field and this could cause an increase the number of weed seeds found in harvested crops. Weed seeds that are specified as detrimental in graded grain, according to the Official Grain Grading Guide or by the contract specifications of customers, are then likely to increase. This will have an impact on the grades applied.
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