Evergreen stalks are associated with robust root systems. These are the product, at least in part, of auxiliary root systems provided by the development of adventitious roots, commonly called "brace" or "prop" roots. We washed out the root systems of several plants with prominent adventitious roots. One of these had fourteen such roots, all of which had penetrated the soil to a considerable depth. All of these auxiliary roots comprised a single long fleshy root, similar to the tap root of some species, plus a number of lateral fibrous roots. We estimated that the total auxiliary root system was at least three times that of the remaining roots, the seminal and permanent.
Evergreen plants with auxiliary root systems are more resistant to drought than plants lacking such systems. Whether they contribute to higher yields is not certain. On this point we have only cursory observations. Of the 95 plants grown in our 3-point-test population in Raleigh, 74 were heterozygous perennial and 21 were annual. The heterozygotes consistently bore better developed ears than the annuals. It also remains to be determined whether plants with evergreen stalks will be practically useful. Grown in the South they might prolong the growing season and increase production for silage.
One more interesting observation: In its stiff stalks and prominent adventitious roots, our heterozygous perennials are quite similar to the widely used commercial inbred B73. Could these traits in B73 have been derived from Zea diploperennis? Major Goodman tells us that hybrids involving B73, although usually highly productive, are notoriously drought susceptible. Is this actually true or do they only exhibit wilting, another trait derived from Zea diploperennis? Wilting in some species, the aggressive vine kudzu for example, is a device imparting drought resistance rather than a symptom of drought susceptibility.
Although the practical possibilities of breeding perennial corns may have been greatly overstated, it may be that certain traits derived from Zea diploperennis can be usefully employed in corn breeding.
Paul C. Mangelsdorf and Mary Eubanks Dunn
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