My type of work explained (with an example).

As a species, the vast majority of corn is a tropical plant. The types grown in the higher latitudes of Argentina-Chile, the US-Canada, Europe, and Asia are a small and very peculiar fraction of the overall genepool in that they will grow and yield regularly under long days. In contrast, most tropical corn grows abnormally tall, sheds pollen very late, and frequently makes no grain when moved out of low latitudes. A local landrace or variety may grow to 6 feet tall and bloom after 65 days in Guatemala, Puerto Rico, Brazil, Thailand, or Nigeria. The same populations moved to Tennessee, New Zealand, France, or South Korea may hit 15 feet and bloom in 110 days. The main difference: longer days. (Temperature plays a role too but less so than daylength.)

As one might imagine, such rank growth and late blooming makes it quite difficult to grow and preserve tropical corn outside of tropical latitudes. This is where my interests come in.

Despite the moderate to extreme growth changes that tropical corn shows under long days, the actual number of genes controlling this behavior is surprisingly small. Temperate zone corns (and a few tropical-subtropical landraces) carry different versions of these genes that don’t react as strongly to changing light duration. Some have no reaction.

What farmer-breeders of the past did was gradually eliminate the highly sensitive gene variants that prevented corn plants from ripening a crop on time – or blooming at all. After many generations, only the moderate (South), weak (Corn Belt), and insensitive (New England, northern Plains) genetic variants were present in adapted corn. Modern breeders have substantially sped up the process by mass selecting only the least daylength sensitive plants within a population. 5 – 6 generations are usually all that one needs to breed a long day adapted strain from a sensitive original.

The downsides of this mass selection approach are: 1) reduced genetic diversity and 2) potential lack of variation in the original corn. It makes sense that if one only saves – say – the earliest 5% of their plants for seed, then the great majority don’t actually get to pass down any of their genetics. This “bottleneck” can lead to a loss of useful traits that may be rare in the starting batch of plants. Furthermore, some corn populations have little or no variation in them for blooming habit. A breeder can’t select for something that isn’t present or expressed. πŸ˜‰

The next approach – and my preferred choice – is to crossbreed daylength insensitive, adapted types with sensitive, exotic types. This gives a 50-50 mix, and a breeder can reselect faster bloomers as early as the second generation. Granted, said person has now eliminated 50% of the exotic genetics that he / she wanted to adapt in the first place. The solution? Cross back to the foreign corn and select again. This cuts the unwanted type’s genetics by half each time, while keeping the long day adaptation from the “donor” corn. So, the crosses go: 1/2 local –> 1/4 local –> 1/8 –> 1/16 –> 1/32 and so on. Eventually, one will have a “conversion” that is functionally identical to the pure variety…but without all the abnormal behavior. One can use backcrossing like this to convert all kinds of plants (and animals) to any number of traits.

Now, after the torrent of text above, let me show some pictures that demonstrate what substituting a (relatively) low number of gene variants can change.

pure Interlocked Amazon corn in Tennessee (original)
94% Interlocked Amazon corn in Tennessee (Cargill Coroico conversion)

Big difference, right? πŸ™‚ In 2021, I’m gonna (try to) breed these two populations together so that I can cut the non-Amazon genetics down to 1/32 (96.9%). And I’ll be using landraces different from those that went into Cargill Coroico for more thorough sampling of the breed. Ideally, I’d want to backcross up to 127/128 (>99%) Amazonian genetics. The hypothetical end result would give growers representation from the Interlocked corn’s full range.

I’m working on converted populations like this for many different sources: Andean, Mexican highland, mesoamerican-Caribbean lowland, and South American lowland floury.

We’ll see what happens.

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