Plant a whole fruit or only seeds?

Question

I'm trying to figure out whether it is better for the plant to reproduce by planting its whole fruits with seeds inside them, or picking the seeds out and planting them without the fruit. In my case it's chili pepper, but I'm also interested in other plants that reproduce through fruits.

I heard that the whole fruit concept is about providing the seeds with some energy in form of their shell (the fruit) to give them a head start in terms of initial growth into a seedling. Is that true? Do all seeds benefit from growing from inside its fruit, or is it not very significant?

Answer 1

I'd argue that this relates to species-specific strategies of seed dispersal, so the answer depends on which species you're asking about. Here's an answer for chili peppers, which I think illustrates how complex and idiosyncratic these strategies can be.

As I mentioned in this answer, the seedsavers' manual Seed to Seed has great info on most plants, including the genus Capsicum (chili peppers). They say to clean the seeds from the peppers, and then dry them thoroughly but not in direct sun.

The Tewksbury lab has done someone amazing work on Capsicum evolution and seed dispersal from a biological standpoint. As published in Tewksbury and Nabhan 2001 (behind paywall, but described well in this Science in the News article) Capsicum fruits have evolved specifically to be eaten by birds, who do not have the receptors that make the fruits taste spicy to us and other mammals.

Essentially then, what you're trying to do when you hand-germinate seeds is to mimic the process of the fruit being eaten and passing through a bird gut. Tewksbury and Nabhan found that seeds from fruits eaten by birds actually germinated at a slightly higher rate than their control group of hand-processed seeds. In contrast, seeds eaten by mammals (who in normal settings totally avoid these spicy chilis) were destroyed and did not germinate.

Seed dispersal mediated by birds and other animals is one way that plants can be motile.

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• Tewksbury JJJ, Nabhan GPG. 2001. Seed dispersal. Directed deterrence by capsaicin in chilies. Nature 412: 403–404.

• Whealy K. 2012. Seed to Seed. Chelsea Green Publishing (p. 152)

Answer 2

I'm not aware of any plants where the fruit provisions energy to the developing embryo. Generally this type of energy and nutrient storage would be done within the seed. Think of an avocado: both the large pit and the flesh contain a lot of energy, but flesh only serves to attract animals for dispersal, while the developing embryo only gets energy from the pit.

Generally, if you have a big fleshy fruit, it's because there was an adaptation to attract an animal to eat the fruit and disperse the seeds (plus extra breeding by humans to make our common edible fruits). Rather than the flesh of the fruit serving as a fertilizer, the scat associated with that dispersal may serve that purpose.

However, there is an astonishing array of fruits and fruit strategies, and many species do have their seeds dispersed along with their fruits. For example, all grass "seeds" are essentially tiny fruits, where the fruit part is reduced to some protective layers. Sunflower seeds are another example, where the hard shell will protect the seed until it can germinate. Many fruits aid in dispersal by the environment, such as wind or water, or by animals without being eaten, as in burrs.