## Measuring varietal purity## Why do we measure varietal purity?For seed to be classified as “good or certified,” it must be able to pass a seed certification standard that determines whether the seed is true to varietal type. ## How do we measure varietal purity?The measurements needed to determine varietal purity are grain size and shape, 1000-grain weight, and number of red grains in the sample. ## Grain size and shapeGrain size and shape (length-width ratio) is a very stable varietal property that can be used to measure the varietal purity of a sample. Comparing the length-width ratio of the sample with a published ratio for the variety will give an indication of varietal purity of the grain sample. A significant deviation means that the sample is impure – that is, it is either a different variety or a mixture of varieties. - Obtain a random sample from the seed batch.
- Collect 20 grains at random from this sample of seed.
- Use a Vernier caliper or photographic enlarger to measure the dimensions of each grain.
## 1000 grain weightEach variety has a published weight for 1000 grains. If the 1000-grain weight calculated from the sample departs from this, it may be an indication that the sample contains a mixture of varieties. - Select a random sample from the seed batch
- Count 1,000 whole grains from the sample.
- Weigh the 1,000 grains.
## Number of red grainsA grain is considered “red” if more than 25% of its surface area is red-colored or streaked. - Select a random sample of the milled rice. 25 g is a good sample size.
- Weigh the sample.
- Select and separate the red grains from the sample. The red kernels are those that have 25% or more of the grain colored red.
- Weigh the red grains separated from the sample.
- Calculate the percentage of red grains in the sample.
Prepare by M Gummert with inputs from JF Rickman (2004); updated by M Gummert (2010) |