Friday, October 25, 2013

Using Stress as a Selection Tool

Using Stress as a Selection Tool

In breeding any plant or animal, we often have the tendency to pamper our precious offspring, especially if we only have a few or they come from expensive and rare parents. There are instances where this may be warranted, but they are few and far between. If we are talking about a very rare parent or narrow gene pool, or if we only have a few offspring, we may pamper those few in order to get them to reproductive age and increase the rare stock. In time though, as numbers increase, our goals should shift toward selecting for the most vigorous and hardy individuals within the gene pool to continue increasing the numbers of that particular family line. In the vast majority of instances though, pampering does not help the family line nor is it helpful in gene pools that have large numbers of individuals. In fact, in those instances, it can be detrimental.

In breeding, we usually understand that the things we actively select become concentrated into our gene pools, but we often fail to realize that those things we ignore and do not actively select can become imbedded in our gene pools just as easily. I refer to this as passive selection, in order to contrast it to active selection. In active selection, we actively select for certain traits, generally seeking to increase them. With passive selection, we are not actively selecting for a trait or traits, but we accidentally select those traits through ignoring them or not creating conditions that reveal them.

An excellent example of this is crown rot. We know there is some genetic aspect involved with this deleterious trait, as crown rot is prominent in particular family lines. So when we use those family lines, we run the risk of creating more cultivars with the propensity for crown rot. In order to select against the crown rot trait, we would want to expose seedlings to the conditions that are conducive to crown rot, in order to select those seedlings for further evaluation that do not show the trait and then to also eliminate those seedlings that do show crown rot. 

I have found two techniques to test against crown rot. One is to grow seedlings in fairly moist conditions and the other is to divide and replant seedlings in hot, moist conditions. By doing these things you can identify those that have a high propensity to crown rot and eliminate them (if they don't actually eliminate themselves for you). 

This picture shows some of my seedling growing tubs. Note that the drainage holes are drilled 1/3rd of the way up on the sides, rather than on the bottom of the containers. This is done for two reasons, both involving the creation of a water reservoir. The first reason is that this reservoir ensures there is water retained there so that in very dry weather, supplemental watering is not necessary on a constant basis. The second is that in wet weather, and through much of the winter, the seedlings are kept constantly moist. In hot, wet weather this will activate rot in those families that are susceptible, while families that are not susceptible show no crown rot. This added water stress can eliminate rotters, but in those individuals that have no susceptibility, it actually increases the rate of growth, thus serving two purposes.

However, I frequently hear people talk about how they only move their seedlings late in the year when it is cool to "avoid rot". This is a way to avoid seeing rot, but by not seeing rot, you can not make selection against the trait. You are then passively selecting toward the propensity to rot because you are not actively selecting against it. There is always the chance that the seedlings you select for further breeding or introduction won't carry the rot trait, but there is just as high a chance that you will select the worst rotters and if you don't provide the conditions to reveal those traits, how will you know?

Rust is another excellent example. There are genes for resistance to rust in daylilies, but a great many breeders spray to suppress rust from going into the spore phase throughout the year so there is no way they can be selecting for those individual seedlings that show higher levels of resistance or immunity to rust.

In both instances, the breeders undoubtedly feel they are doing the right thing and taking the best possible care of their plants, but the "best possible care" of the individual plants is not always the best possible situation to select the best possible plants in the next generation, though it might allow you to select "the best" flowers, if that is your only focus. In short, the best interest of the entire gene pool is not always the same as the best interest of the individual plant.

In breeding it is very important to remember this. If we pamper our plants those individuals may flourish, but we may thus be compromising our gene pool by not having proper situations by which to select for important traits such as plant vigor or disease resistance. The only way we can really select for such traits is by creating (or allowing) the conditions that reveal the plants with the best concentration of genes for the desired traits.

So let's take a minute to think about some of these (rather obvious) points.

1. If you are concerned about drought tolerance, don't water your seedlings (and maybe your breeders too).
2. If you are concerned about disease resistance, expose your seedlings and breeders to the diseases that concern you and the conditions that accelerate the disease(s).
3. If you are concerned about flowers opening on cold mornings, grow your seedlings on the Northern side of your house or garden, or in a cold-pocket microclimate.
4. If you are concerned about water spotting, then overhead water when scapes are flowering.

While this area of my hybridizing garden may look lush, it is in fact very dry. A south facing slope, the soil is a mixture of sand and orange clay with a very thin layer of topsoil. I use this particular area to test out potential breeders and seedlings for drought tolerance. This area is too far away from the hose for convenient watering and I am highly unlikely to actually carry buckets of water very far. In the drought of 2012, I was able to produce over 7,000 seeds from this area because the cultivars I focused on there have proven themselves fertile in full sun and dry conditions over several years. Not surprisingly, the seedlings from those cultivars tend to also set seeds well in full sun and dry conditions...

These are just a few ideas. There are many, many more examples. Think of the traits (faults) that you want to work against and then think about the conditions that seem to bring out or accelerate these negatives and how you might expose your plants to these conditions in order to reveal those with the weakness, as well as, and most importantly, those that do not display the weakness. Select the later to move forward with!

I was recently watching a Youtube video where Dan Heims of Terra Nova Nurseries speaks about how new perennials enter the market. It is fascinating and I recommend you watch it, but I was particularly excited by one comment he made in regards to breeding new plants. He states that he starts all breeding projects by asking the question, "What is wrong with this plant". He says that he is looking at the problems in order to solve them through selection. His story about breeding pulmonaria for mildew resistance is fascinating and every daylily breeder should take head to the successful techniques of this master breeder. Below is the link to the Youtube video of his talk. Enjoy! 

Dan Heims, Perennials from Around the World