What is combining ability?

Advanced Techniques GrowFAQ
#1

Certain inbred lines will display hybrid vigour when crossed. These vigorous lines are said to have favorable combining ability.

Certain inbreds have the ability to combine well with testers–these have general combining ability (GCA). When the inbred combines well only in certain crosses, it has specific combining ability (SCA). The only way to select for combining ability is to grow and examine the progeny. An astute breeder can recognize the potentital for hybrid vigour by identifying the dominant traits of the parents and deducing which lines may combine favorably.

Predicting the combining ability of recessive traits can only be determined through progeny testing.

The breeder is interested in single crosses (also known as F1 generations) that outperform other single crosses. If the breeder has multiple IBLs to work with, she could select first for GCA, then for SCA among the lines with GCA, then identify the best parental gene donors. In most cases with Cannabis you can go directly to selecting for specific combining ability between your IBL and your testers.

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How do I select a male?
What is hybrid vigour?
#2

So only ibl+ibl has the possibility of showing hybrid vigor? A ibl+f1 or f1+f1 won’t show hybrid vigor? Also when i think of ibl it’s f4+ is that the case here or can a f2+f2 cause this if combining ability is favorable?

#3

I may be wrong but from my understanding hybrid vigour can be achieved depending on genetic diversity. So if you have an ibl, trubred, or landrace and cross to a f1 hybrid, I believe you can still achieve hybrid vigour as long as the f1 hybrid doesn’t share a lot of common ancestry with the ibl/truebreeding mate.
The same can be said of two f1 hybrids as long as they don’t share common ancestry.
This is one reason why its important to try and preserve or create true breeding and landrace varieties.
Please though, someone correct me if I’m off base!

I do know however that a true breeding strain can be created from any combination of plants. Even polyhybrids can be bred true, though difficult and time consuming requiring many generations and a large pool of offspring.

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#4

Isn’t truebreed and ibl like saying the same thing? The purpose of an ibl is to get a truebreed plant. A landrace is an ibl that may or may not had human intervention of selective breeding but are still ibl but not necessarily truebreed.
Edit ohh duhh answered my own ? Just like a land race can be ibl but not necessarily truebreed

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#5

I’m not sure but I think true bred strains have “minimal” deviation or an occasional oddball.
All my info is based on veggies and breeding sunflowers and canola growing up, so take what I say with a grain of salt lol.
Again I welcome any correction, or constructive criticism.

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#6

Nah, you’re spot on. A cultivar needs only be true-breeding in a couple different traits really. Like if you’re advertising your seeds as a purple variety, it needs only be true-breeding in that trait. Or if you’re putting diesel in the name, the plant should true-breed for that smell. The rest can absolutely be as variable as you prefer.

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