Maternal traits vs. biparental traits

A plant breeder or seed producer is concerned with maintaining genetic purity in seed. They are concerned with the seed genotype. Their customers are more concerned with seed phenotype. When the grain trait in question is influenced entirely or primarily by the female parent that is producing the seed, the trait is referred to as a maternal trait. When both parents contribute to the seed trait, the influence is biparental. This distinction can be very important for the producer who plans to sell grain based on quality.

The red pigment in red wheat is deposited in a layer of cells in the seed that is actually a part of the female plant. Therefore, this grain color trait is maternal. If the plant producing seeds has only the recessive alleles for white, the seed will be white even if the pollen came from a red plant to produce that seed. Maternal traits may also occur when the metabolic status of the mother plant dictates the amounts of seed components. Producers who grow white wheat have only one thing to worry about to maintain purity in their fields: the genotype of the seeds they plant. As long as they are white seeds, they will produce white offspring. Maternal traits are thus easier for producers to work with.

In contrast to white wheat is white corn. For two reasons, white corn provides purity challenges to the producer. First, the trait is not maternal. The yellow color in corn kernels is formed in a layer of cells that is produced by the seed and thus contains genes from both the male and female parent. The white trait is recessive to yellow so a pollen grain carrying the yellow allele will produce a yellow seed in the ear made by a white mother plant. Secondly, corn is an outcrossing species and cross-pollination events between distant plants are not uncommon. Therefore, the combination of situations makes the white corn producer earn their premium for maintaining high levels of seed color purity.

Fig. 8 Yellow and white kernels on a white corn hybrid.