Many seed corn companies classify their hybrids as to "ear type" using terms such as flexible, fixed, indeterminate, determinate, and prolific, among others, to characterize growth, size, and number of ears. Most corn hybrids grown in the Corn Belt have been developed to produce only one harvestable ear under normal production conditions. In contrast, prolific (multi-eared) corn hybrids have the capacity to produce more than one ear per plant. One-eared corn hybrids are often characterized as having an indeterminate or determinate ear growth habit. According to some seed companies, a hybrid's capacity to adjust ear size (i.e. length, girth) can play a significant role in determining its yield potential. The perception is that a "flexible" or "flex" ear hybrid has a more indeterminate ear size which can adjust to growing conditions by changing ear size. This supposedly allows flex hybrids to take advantage of optimum growing conditions and to compensate more for variation in plant population. A fixed ear hybrid is associated with a relatively determinate ear size which limits its capacity to adjust to growing conditions or to compensate for variation in plant density. Plant population is considered more important for a fixed ear hybrid than for a flex ear hybrid because the latter can increase ear size (and potential yield) whereas a fixed ear hybrid cannot. Prolific hybrids are less sensitive to variation in plant population than single ear types. At low plant densities, prolifics have the ability to average more than one ear per plant and at high densities, they exhibit resistance to barrenness. Although prolific corn hybrids have been used widely in the South, the breeding and development of prolific hybrids adapted to the Corn Belt has been limited.
There is surprisingly little published data to substantiate the various claims made with regard to different ear types. In a recent study conducted in Illinois and Wisconsin, two corn hybrids varying in degree of ear determinacy were evaluated across a range of plant populations and planting dates. Although the primary focus of this work was to investigate the effects of uneven emergence in corn, the results suggested little difference in yield response between hybrids to varying population despite differences in ear type. In contrast, preliminary results of an on-going study at Ohio State indicated that LH119 x LH51, a hybrid with a relatively indeterminate ear length, showed a greater capacity to adjust to low plant populations than B73 x LH38, a hybrid with a relatively determinate ear length. The inconsistencies between these studies may be explained in part by differences in hybrid maturity, genotype, and environment. The relative significance of ear type must be considered in conjunction with overall hybrid performance. Remember to select a hybrid for its performance not because it possesses a particular trait or characteristic like flex or fixed ear size.
Prepared by:
Peter R. Thomison
Extension Agronomist
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