Maturation in corn

Four inbred lines of corn and two of their hybrids of contrasting relative maturity, vary in rate of moisture depletion and in rate of deposition of dry matter in the grain. In general, strains that flower early tend to mature more rapidly than those that flower late. However, the rate of kernel maturation may be relatively slow in some early strains and relatively rapid in some late ones. The quick-maturing strains of each maturity class, early and late respectively, were characterized by a slower rate of dry matter increase in the later phase of kernel development, whereas the slow-maturing strains were characterized by a somewhat more rapid and longer rate of moisture depletion and dry matter translocation. Moisture depletion was hastened by cross-pollination. The use of pollen from quick-maturing inbreds tends somewhat to hasten the rate of moisture depletion. The early, quick-maturing line 9 pollinated by the late, slow-maturing line WF9 was an exception to this rule. Heterosis for the most part seems to be responsible for the more rapid rate of moisture depletion in the kernels after cross-pollination. The action of heterosis appears to be specific and perhaps interacts with the xenia effect. The two effects are difficult to separate. Stalk rot infection tends to hasten the rate of moisture depletion, to decrease the rate of dry matter increase, to shorten its duration, and to reduce seed size, especially in the earlier more susceptible strains. In resistant material the rate of dry matter increase is not thus retarded and continues much longer. The rate of maturation in corn appears to result from the complex interaction of genetical and pathological factors. For an adequate measure of maturity, not only time of flowering and kernel moisture content, but also the time at which the dry matter increase is completed and the degree of susceptibility to stalk rot infections need to be considered.