Jim's Thoughts (posted May 2008)
I became interested in the energy relationships in corn when studying stalk rot of corn. Most of my thoughts then and now were built upon the research concerning photosynthesis in corn and the translocation of its products in corn. Current interests in biofuels brings the concepts related to corn’s capacity to convert light energy to stored energy to the front.

Stalk rot of corn is the result of predisposition of roots to destruction by soil microorganisms and eventual invasion of wilted stalk tissue by fungi (most notably species of the genera Fusarium, Gibberella, Diplodia and Colletotrichum). Predisposition was caused by the lack of carbohydrate in the root tissue to maintain metabolic defense to the multiples of organisms ready to invade root tissue. Plants with predisposition did not produce enough carbohydrate to meet the storage commitments in the grain and the metabolic needs of the roots and the rests of the plant.

As this interaction became apparent in the mid 70’s, it was necessary to contemplate how to achieve both higher grain yields and acceptable stalk quality. During that time frame, there were studies done showing that corn varieties varied for the photosynthetic rate per square centimeter of leaf space, leaf area per plant and architectural differences affecting number of leaves exposed to maximum light. My conclusion from some private studies was that corn breeders were accomplishing gains in total photosynthesis by simply testing many hybrids for both standability and yield, and not worrying about how they got the photosynthetic gain. The other conclusion that I reached was that there remained plenty of variability for each of the factors (photosynthetic rate, leaf area and architecture) and that gains should continue. In fact, the gains have continued probably mostly through increased leaf area per acre as plant density increases for the past 25 years have been dramatic.

It is easy to imagine that other physiological and structural differences between corn genotypes also affect the plants ability to capture and store energy. Efficiencies of moving carbohydrates from the leaves to grain and plant structures must be complex; size of vascular bundles, hormone concentrations, number of ovules in ears come to mind. How about the energy requirements for movement of molecules across membranes, tissue development, whole plant growth, avoidance of senescence?

What we do know is that corn is wonderfully diverse. Even among genotypes that are currently adapted to a geographic area, every corn breeder is amazed with the diversity that is visible in the breeding nursery. And that is only what we see!

The future of food and fuel use of corn will be met by identifying the genotypes with best ability to capture the most energy per acre in a form that we can efficiently convert to our use. Biotech will help but a lot will come from effort to identifying those varieties with the combinations of complex factors (some unknown to us) that give us more food and fuel. For the most part I think the method of measurement is called yield testing.