Hybrid Vigor; is it a thing?

[gilbert]

I've heard that hybrid vigor is part of the Landrace advantage.

At the same time, I've heard other people saying that hybrid vigor only applies to corn, and other extreme out breeders, and that hybrid tomatoes, peppers, eggplant, and even squash are just gimmicks employed by the seed companies to scare us away from seed saving.

Is hybrid vigor a thing?

Is it a thing in all plants?

Why is it a thing? (What causes it?)

In wild populations, does it have an effect? I thought it only operated because the two plants crossed were quite different. In a wild population, diversity is low in any given area compared to a bunch of cultivated varieties.

I know some people on here think inbreeding is a disadvantage for a crop. Is it a disadvantage for a wild plant? How many wild plants are inbreeders versus outbreeders? (And I know that those terms are relative.)

Interestingly, standard seed savers think inbreeding is a very good thing in a plant, since it makes it so much easier to save. Thus, lots of heirloom tomatoes and beans, very few cabbages and broccoli. Folks on here have the opposite view.

[billw]

I mostly just think of heterosis as the absence of inbreeding depression. If you are dealing with highly inbred lines, then hybridization can help to fix that and restore normal performance. If you don't have inbreeding depression to fix, then the results of hybridization may not be any better than what you started with.

I don't think that hybrids are gimmicks. I think that they are a useful way to quickly restore performance to highly inbred lines that exhibit desirable traits.

I don't think that there is a "right" approach. Plants give us the opportunity to use different techniques. They are all valuable and appropriate for different pursuits.

[Joseph Lofthouse]

I agree on principle with the notion that "hybrid vigor" is mostly about getting rid of the effects of inbreeding depression. The conventional wisdom is that tomatoes don't suffer from inbreeding depression, but when it is actually measured in a laboratory, the magnitude of inbreeding depression in tomatoes is around a 50% decrease in yield. Which goes a long ways to explaining why heirlooms are not favored by farmers who want great productivity from their tomatoes, and why hybrid tomatoes have such huge market share. Tomatoes are one of the most genetically fragile crops that we grow. They suffered a severe inbreeding bottleneck during domestication and dissemination. In recent decades, tomatoes acquired a strong phenotype towards self-pollination, which contributes to even stronger inbreeding depression.

As far as I can tell, diversity is much lower in typical domesticated populations than in the corresponding wild population from which it is derived. One of my favorite crops to work with has been okra... Because it seems wild to me, and hasn't been subjected to a lot of inbreeding.

I really like working with tomatillos. As mandatory out-crossers, the diversity of phenotypes available in even a single packet of seeds really pleases me.

Some people like to split things apart, and make them separate, and put labels on them. Things like inbreeders and outcrossers are discussed intellectually. But in the real world things are messy. Modern industrialized tomatoes might only be 95% inbreeders and 5% outcrossers on average. Older cultivars might be 70% inbreeders and 30% outcrossers. And it varies from garden to garden, and cultivar to cultivar. Many species are on a sliding scale like that... Even self-incompatible species don't always get it done right, and sometimes pollinate themselves. So it's a big mess that doesn't really fit an easy label, but people still try to impose order on things that are inherently chaotic.

[reed]

I also hold to the notion that hybrid vigor is just the absence absence of inbreeding. Getting rid of inbreeding is highest priority for me because I'm trying to make seed saving doable in populations much smaller than recommended. Some people would frown I suppose, at the thought of crops that might never stabilize to produce exactly the same every year but for my purposes that is a goal.

If I held to the "pure" variety restraints I would mostly have to give up on saving seeds, I just don't have enough space to meet the requisite isolation and population size guides, not that I'd want too anyway.

[castanea]

How you use the terms "hybrid vigor" and "inbreeding depression" depends to a great extent on how you define those terms and what plants (or animals) you are working with. "Hybrid" can refer to either crosses between varieties within a species, or to crosses between different species. Hybrid vigor is quite real, especially if you are dealing with inter-species crosses. Of course inter-species crosses can also result in some really lousy offspring. If you're working with intra-species varieties you may be seeing some significant inbreeding issues. If you are working with different species you will probably see a lot less of that. Many of the people here work with tomatoes and corn which usually involves intra-species breeding so there's a tendency to analyze breeding in terms of intra-species issues.

Here's an inter-species hybrid that definitely shows hybrid vigor:

www.youtube.com/watch?v=DM9cV1fF518