Indeterminate vs. determinate ears

Field corn breeders have generally appreciated the value of selection for ears with slightly barren or unfilled tips which have one or more non-functional spikelets near or at the growing point. Such indeterminate ears have a potential to elongate or continue growth under unusually favorable growing conditions. This capacity for continued elongation occurs in various grasses with indeterminate inflorescences such as the relatives of corn.

In contrast, the trait for determinate ears occurs in certain strains of corn, especially in sweet corn where consideration for "complete tip fill" with deep kernels tends to conflict with selection for increased ear length and increased yields. In the determinate ear type, continued differentiation is abruptly terminated resulting in a terminal functional spikelet. Sometimes the expression is semi-determinate in that the uppermost spikelet is male with a capacity to continue male differentiation. When the determinate or semi-determinate ear encounters unusually favorable growing conditions, it can't respond with growth in ear-length. Rather it has to take other options. The extra energy may be channeled toward the development of deeper kernels which is highly desirable. But it may also be wasted on the development of non-functional tassel tips on the ear or sometimes in the form of secondary and lower non-usable ears. Since the tip of the ear in sweet corn is frequently snapped off by man or destroyed by earworms anyway, it would seem more practical to select for the indeterminate type of ear. Then a potential for increased ear length could be realized in favorable years. Increased kernel depth is independent of ear type although it is common in high kernel-row number ears. It must be borne in mind that only a given amount of energy is available, regardless of what ear type or kernel size and shape it is packaged in.

The indeterminate ear is largely dominant in expression. Such a factor occurs on chromosome 9 in teosinte and apparently in the same position in corn.

Walton C. Galinat

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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