Sweet, sweet corn

I met Kevin Montgomery of Montgomery Consulting at NCCC167 at Allerton Park, Illinois back in March. He specializes in native trait development, such as herbicide tolerance, enhanced nutritional quality, high yield, improved germination, and good stand establishment.

One of the most interesting of these native traits is what Kevin calls FACE (fall armyworm corn earworm). This trait, which confers resistance to armyworm and earworm, originates in tropical germplasm. Kevin is hoping to provide an alternative to Bt. One benefit of using a non-biotech trait is reduced cost. However, even native traits are not without added cost. This isn’t a single gene trait, so it’s extremely difficult to move out of the tropical lines. While the trait isn’t ready for licensing and distribution, it is very promising so far. Plants with the trait survived the entire growing season without damage from worms and without insecticide in Puerto Rico. This has great potential for the organic sweet corn market.

Currently, Kevin has a client asking for hybrid sweet corn varieties suitable for the fresh market, such as roadside stands and farmers’ markets. He breeds with his own genetic resources, but grows commercial hybrids like Vision alongside his experimental hybrids as checks. In the breeding program, he crosses promising (read: tasty) inbred lines to many other inbred lines, looking for the best hybrids. Just as in any other hybrid breeding program for any species, some inbreds combine better than others. He is also developing some improved open pollinated varieties for specialty markets.
The two most important traits in the selection program are taste and regional adaptability. He’s planted the same trial in at least three locations across the US to see how the hybrids fare with different weather and soil conditions.
The first round of taste testing is done in the field. This may seem strange, because most people eat sweet corn after it’s been cooked at least a little, but field tasting saves a lot of time and effort. Kevin can eliminate hybrids that just aren’t worth the bother of harvesting and cooking. Also, cooking can introduce a lot of variability – the time from harvest to pot, the temperature of the water, cooking time, and characteristics of the water such as sulfur content. However, there are some drawbacks to raw tasting. Cooking denatures some proteins and deactivates some enzymes. Leaving these intact can affect the flavor of the corn – positively, in my opinion. The enzymes, however, can cause severe digestive discomfort. My iron stomach did not fail me – perhaps I have resistance due to all of the raw veggies that I eat?

The tasting process starts with benchmarks. Kevin gave the tasters a range of samples from very sweet to not sweet so we knew where to place the unknown samples on a scale from 1 to 9 (with 9 being the sweetest). The sweetness isn’t just due to sugar; it can also be affected by molecules that taste sweet like the amino acid proline. Some of these molecules can be degraded through cooking, which is why it’s so important to avoid overcooking sweet corn.
The sweet flavor of sweet corn is primarily caused by mutations in one of two genes: sugary1 and shrunken2. Both genes affect how sugar and starch are metabolized in the kernels. Their effects are different enough that you can taste it. Sweetness conferred by shrunken lasts well into the season, but sweetness conferred by sugary will quickly disappear as sugars are converted into starch. There is a third gene affecting sweetness that is found in some tropical germplasm called brittle, but it’s not yet made the rounds into non-tropical lines. All of the mutations are recessive, which means that both of the inbred parents need to be homozygous for at least one of the sweetness conferring mutations in order to have the sweet phenotype appear in the hybrid. Finally, some lines carry a mutation in the gene sugary enhancer that improves tenderness and extends the length of time that sweetness lasts when it is present in the same line as sugary.
All of these genes interact with each other and with other genes to provide an endless range of sweetness from sickly sweet to barely sweet at all. Also, the combinations of mutant alleles have different effects on traits like germination rate and seed development. I’m not that familiar with the biochemical workings of sweetness in sweet corn – so if you’d like to learn more, you might want to visit Karl, who works with sugary enhancer, over at Inoculated Mind.
The appearance of the ears is very important to the success of any particular sweet corn hybrid, because that’s what people first see at the farm stand. One part of appearance is color. People in some areas of the US, Latin America, and Africa prefer white corn. They associate yellow corn with animal feed. People in other areas prefer bi-color corn with white and yellow kernels.

Another aspect of appearance is how the leaves envelop the ear. Ideally, the leaves will cover the end of the ear, which looks nice as well as being a deterrent to insects trying to get to the kernels. The leaves and silks must come off easily in shucking, and the leaves must have just the right length of “flags” at the tips. Susceptibility to insects and smut is another very important part of appearance. Nothing turns customers away more than worms in the ears. Smut can damage ears and is very unattractive as well (except in particular markets where smut, or cuitlacoche, is actually desired in its own right).
We also graded the tenderness and texture/creaminess of the corn. Tenderness includes how difficult it is to separate the kernels from the cob and how hard it is to bite into the pericarp, or outer layers, of the kernels. Texture includes the fat and water content of the kernels, which leads to a creamy or watery feeling as the kernels burst in your mouth. These traits can be affected by cooking but testing them raw still provides valuable information. Kevin tests many other traits on his own.

I was amazed at how different each ear could be, even within the same line. Differences within lines can be due to the age of each ear and the type of pollen that happened to fertilize a particular ear, among other factors.
All in all, tasting sweet corn with Kevin was a great experience, and not just because I got to have some delicious corn. This experience helped me to appreciate all the work and knowledge that goes into breeding a new crop line. I hope that reading this post helps you to appreciate it as well.
A few more incidental tidbits that came up (you never know what you’ll learn when you’re around a plant breeder):
Golden Cross Bantam, a hybrid resistant to Stewart’s wilt and containing the sugary mutation, has been around since the 1940s (but wasn’t part of the taste test). Illini super sweet was the first hybrid sweet corn to contain the shrunken mutation, and has been around since the early 1970s. Commercial sweet corn hybrids remain popular and in use for a long time, much longer than field corn hybrids, which last about 4 years before being replaced by hybrids with additional improvements. This may be because people, once they find a hybrid they love, will continue to seek out the same sweet corn year after year.
Each species has a different heirloom state, depending on their natural state of fertilization – open pollinated, obligate selfing, etc. Heirloom varieties of corn are open pollinated because that’s the natural state of the species. Inbred lines and the hybrids that are produced by crossing them remain constant, but open pollinated lines are always changing.
Talk of Kevin’s FACE (fall armyworm corn earworm) lines led to an interesting discussion of Bt. I need to research this a bit, but wanted to share the information and get comments. Instead of planting separate non-Bt refuges alongside Bt corn fields to guard against insect resistance, seed companies can mix the non-Bt seed right in. If there is one Bt gene in the seed, they are supposed to provide for 25% non-Bt seed. If there are two or more Bt genes in the seed, the seed companies argue that 5% is enough because it is less likely that insects could become resistant to two types of Bt. The problem is that seed with the Bt trait can get mixed into the non-Bt seed, so that the final percentage of non-Bt seed in the mix is lower than it should be. Seems to me that the solution is easy: conduct tests to see what is the lowest effective percentage, then mandate a slightly higher percentage, and conduct spot checks on lots of seed to be sure that seed companies comply.
In maize, % leaf area infected by fungus at mid silking = ½ % yield loss for grey leaf spot because damage is internal to the leaf. For example, if 20% of leaf area is infected at time when plants are at mid silk, the yield will be approximately 10% lower than if it was not infected. However, rust causes eruptions at the leaf surface, so there is water loss, thus a greater yield loss.
Many thanks to Kevin for the experience and for proofing this post, to Tina Paque for taking photos of the tasting, and to the other tasters for making this a fun and educational experience!