University of Massachusetts

The O2-CO2 cycle and the development of trait technology for yield enhancement in maize: Umbrella canopy adjacent to the ear sink
--Galinat, WC

We and our food plants are a small part of a general symbiotic balance within all of life on planet earth. It results from complementation between the hemoglobin of animals and the chlorophyll of plants that allows survival of both by mutually supplying each other's lack of raw materials. This mutual exchange is reflected in every breath of air we take. Simplistically, the hemoglobin in the lungs' capillaries captures the plants' O2 waste from the chlorophyllic photosynthesis of carbohydrates. The O2 now fixed in red blood cells then circulates with insulin into a sequence of known reactions involved in cellular metabolism. The animal's body wastes, CO2 and excrement, are released to planet earth where they then find a way back to the food plants as raw material to make more photosynthetic food.

Success of these symbiotic exchanges depends partly on a population balance between food plants and animals. When people invented agriculture and plant breeding, they allowed a great increase in human populations. In some areas now the symbiosis has become unbalanced as expanding human populations exceed the capacity of the fixed plant populations to feed them and this situation is expected to spread. By increasing the efficiency and productivity of the food plants, we may increase their carrying capacity for human populations.

Perhaps more like the architecture of banana, a new arrangement possibly effecting yield enhancement in maize might be to have the energy sink ear immediately below an umbrella canopy of broad, erect leaves together with a reduced tassel (Fig. 1). This combination of traits was constructed by recombination of umb (umbrella), which is an allele at the abp (abnormal phyllotaxy) locus with Bl (broad leaves) and es (eye stabber, erect leaves) together with ub (unbranched tassel). While all of these traits can behave as single genes, they do occur at compound loci, sometimes called QTL loci, and do interact with modifier genes (suppressors and enhancers). These genes must work together in perfect harmony to build the beautiful maize symphony of the future.

The story of yield enhancement starts with the identification of those precious traits within the total diversity that could contribute to yield. Especially non-agronomic or exotic races must be scrutinized. Such maize that survives, despite severe genetic and/or environmental handicaps and their interplay, would have filtered out some powerfully beautiful yield enhancers. The selected enhancers may then be put to important use in the elite backgrounds with the added power of their accumulation through recombination. All of this occurs rapidly under the guidance and direction of the most important people in the world, the plant breeders - the cultural descendants of those who converted the wild ancestor teosinte into the first maize many thousands of years ago in their gardens of more useful forms. Then as now, as each splendid new mutation comes along, the breeder-conductor must recombine it in exquisite harmony with the other melodious mutations in order for the yield of maize to maintain its symbiotic harmony with volume increases in human populations.

Evolution from either natural or domestic selection depends upon two kinds of raw material. First, selection and bringing together the special beautiful mutations that are carried in the total racial diversity and second, selection of the recombination harmonies from interactions between these mutations. Under domestication evolution is more rapid because both kinds of raw material are selected deliberately by the plant breeder from artificially controlled pollinations. The types selected by the breeder may be adapted "not to the plant's own good, but to man's use or fancy" (Darwin, C. 1859. The Origin of Species by Means of Natural Selection or the Preservation of Favored Races in the Struggle for Life.) In contrast, as Darwin described, in nature progress is slower but over vast expanses of time and the adaptation is to the wild plant's own good by means of selection for intricate specialization for specific natural environments.

The great evolutionary success of mindless, unplanned, trial and error in bringing order out of chaos by natural selection operating over immense vistas of geological time is obvious. But we humans are armed only with dubious, sporadic intelligence and communication skills, and we have only a little time left to conduct the symphony of evolution and the fate of our species on earth and in the universe. Therefore, let us use our minds to plan with the wisdom of forethought to create a beautiful future, a future in which our species smiles on for ever and ever.

Figure 1. On left, control normal maize. On right, yield enhanced maize with umb, Bl, es, ub, as described in the text.

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