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0109 FG: Why every alfalfa seed is different

Published on 09 February 2009

In this Forage Forum article, Pioneer alfalfa research director, Dave Miller, discusses how the genetics of alfalfa varieties are different than the other major crops and how they are tested.

Alfalfa genetics are different from other crops because in other crops we’re able to manipulate the plant to bring about genetic uniformity. So when you buy a particular grain hybrid or variety, every seed in that bag is considered to be genetically the same. Alfalfa is not able to achieve that same degree of uniformity. So when you have a bag of an alfalfa variety, every seed in that bag is different.

These genetic differences mean these varieties have a range of types within them. For example, a farmer goes out and plants maybe 16 pounds of seed to the acre. And that 16 pounds translates to approximately 100 seeds per square foot. As the stand grows, the plants are subjected to different diseases, different insects and different weather factors, including heat, drought and cold.

What you expect is a natural decline in the stands from those 100 seeds that were sown. In the first year, it will go down to somewhere between 30 and 50 plants per square foot. As the stand goes into its second, third and fourth year, you might be down to 10 to 12 plants per square foot. And you’ll see differences in their ability to survive the winter and diseases, even sometimes in the vigor of the regrowth seen after cuts.

Variety testing
When we speak about corn or soybeans, we say every seed in a bag of a hybrid or a variety is the same. What that means, then, is if one seed has the trait, every seed would have the trait. In alfalfa, when we say something is resistant to say, Phytophthora root rot, what we’re saying there is that a certain percentage of the seeds in that bag are resistant to Phytophthora. And we have resistant classes, such as highly resistant, which means that greater than 50 percent of the seeds in that bag have genetic resistance for Phytophthora. If it says resistant, there are 31 to 50 percent of the seeds in that bag that are resistant. So for alfalfa we characterize based on percentages when it comes to disease and insect resistance.

Fall dormancy is a little bit different. In fall dormancy, we actually plant 100 individual plants out in the field and cut them off during normal cutting times in the growing season, with the last cutting being approximately September 1. Then we come back the first of October, measure the height of each of those 100 plants and take an average of the heights. That average height gives us the dormancy for that variety. We characterize things based on a population, not based on an individual as would be done with other crop seeds.

The varieties are also tested for winter hardiness. There’s an industry standard test similar to what I described in fall dormancy where we plant 100 individual plants. We actually try to cut those at times in the fall to induce a winter injury.Then we come back in the spring and rate those 100 plants for their ability to survive. You’ll get a score based on the average severity that those 100 plants have for winter injury.

We also look at how these varieties perform in our standard yield plots where we cut them three, four or five times a year. Based on how those plots grow back, we give a combined score, combining the plot rating in the spring with the average severity of those 100 individual plants we put out. That gives a more accurate representation of winter hardiness than just the individual plant test.

Growers who are faced with the hundreds of variety options available should check out the developer of the seed and the type of testing done.  FG

—Submitted by Pioneer Forage

For more information, contact
Dave Miller
Research Director Pioneer Forage