Later this summer, many of us will enjoy the bursting flavor of sweet corn. Approximately 70% of the world supply of hybrid, temperate, sweet corn seed is grown in Idaho’s Treasure Valley. Growing conditions there are ideal for seed production and sweet corn isn’t the only seed crop they grow.
Seed production basics
While the sweet corn grown in gardens requires self-pollination, the production of sweet corn seed relies on both self-pollination and cross-pollination.
Self-pollination is when the pollen from a plant lands on the female part of the flower of the same plant or a plant of the same cultivar. In order for self-pollinated plants to produce consistent offspring, there needs to be a consistent genetic foundation.
Cross-pollination is when the pollen from a plant lands on the female part of the flower of a plant of a different cultivar. If you have a squash fruit that looks weird, it is a result of cross-pollination in a previous year. Cross-pollination of squash this year will not affect the fruit of the plant this year. This is true for all plants where fruit production is the key and not the seed— for example cucumbers, melons, squash, tomatoes, peppers, apples and peaches. Sweet corn is different because it is the seed that is being eaten and not the “fruit”.
Intentionally cross-pollinated, first generation, corn seeds are called hybrids—usually indicated by “hybrid” or “F1” included in the name. This is the corn that is planted in gardens. While these first generation seeds produce delicious corn if they are self-pollinated, seeds kept from these first generation plants will not — there is too much genetic variation in the seeds. This is why gardeners with a favorite cultivar need to purchase new corn seed rather than save their own.
Sweet corn seed production
Sweet corn seed production is a two-step process. The pure strains of the two parent plants must be maintained. The parent plants are each considered a ‘pure line’ that has been developed over many years of breeding and selection, and they will contain one of several recessive genes that affect the sweetness of the corn.
Sweet corn seed hybridization is the crossing of these two ‘pure line’ parents. Corn is monoecious—has male flowers (tassels) and female flowers (ears) on the same plant. In order to avoid self-pollination in sweet corn production, one of the ‘pure line’ parents needs to be a female parent plant and the other one a male parent plant. Rows of female plants are often referred to as cow rows, and the male plant rows are referred to as bull rows.
Cow rows are created by removing the tassel off the plants in the cow rows. That way, only the pollen from the bull row will pollinate the cow rows. The cow row seeds are then harvested and packaged as the sweet corn seed grown in gardens. The bull row seeds may be harvested for the next year’s ‘pure line’ bull rows.
In order to have the tassels of the bull rows shed pollen when the cow row silks are ready to receive the pollen, they may have to be planted at different times. All the fields in the seed production process, the ‘pure line’ production as well as the F1 production, need to be isolated to avoid the introduction of undesirable traits. In addition, there are crews who rogue the fields to remove off-types.
There is a lot that goes into the great sweet corn cultivar you love so much. Next week’s article will discuss growing sweet corn in the garden.