SARAH BROWNING For the Lincoln Journal Star
The growing season is in full swing and there are many gardening questions to ask! Including questions about pollination and its effects in the vegetable garden, so here’s a quick look at pollination and how it affects – or doesn’t affect – the plants in your garden.
Can pumpkins be planted near cucumbers or will they pollinate each other and cause problems with this summer’s fruit? Every summer, Extension’s offices receive calls from customers wondering if their plants have crossed with something else to create a weird hybrid. In this particular case, the answers are yes and no.
What is pollination?
Pollination occurs when a grain of pollen, which contains half of the genetic material needed to create a new seed, is transferred into a flower’s ovule, the egg-containing part of a flower that contains the second half of the DNA needed for a viable seed delivers forms. Pollen is the male parent’s contribution and the female parent provides the ovum.
Self-pollinating crops such as beans and peas have evolved strategies to ensure self-pollination. Often their flower structure prevents the easy movement of pollen outside of the flower, or flowers can be pollinated before they even open! Self-pollination often results in plant lines with very consistent DNA, ensuring that new plants raised from thrifty seeds are almost identical to the parent plants.
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Cross-pollination occurs when pollen from one plant fertilizes the ova of another plant. Some plants cannot produce viable seeds without cross-pollination, as is the case with broccoli and many varieties of apples.
Cross-pollination occurs through the actions of pollinators such as insects and other animals, or through the wind blowing pollen from plant to plant. In the home vegetable garden, tomatoes, watermelons, and cucumbers are cross-pollinated by insects, and sweetcorn is wind-pollinated.
Which plants can pollinate each other?
With very few exceptions, only plants of the same genus can pollinate each other. Within the Cucurbita genus, only plants of the same species can pollinate each other. Pumpkins belong to the genus Cucurbita and the species pepo, while cucumbers belong to the genus Cucumis and the species sativus.
As you can see below, squashes and cucumbers are not in the same genus, so they cannot pollinate each other. This means they can be planted right next to each other and gardeners won’t see any odd effects in the fruit. However, squashes and some squash species can pollinate each other because they belong to the same species.
• Cucurbita pepo – summer squash (both zucchini and yellow summer squash); Acorn, Delicata, Patty Pan and Spaghetti Squash; Pumpkins and gourds are all in the same style.
• Cucurbita maxima – Winter squash, such as buttercup, banana, Hubbard, and turbanum squash
• Cucurbita moschata – Winter squash, such as butternut, cushaw, and winter squash
• Citrullus lanatus – watermelon
• Cucumis melo – melon, honeydew melon
• Cucumis sativus – Cucumber
Pollen action on plants
Fruits – The source of pollen does not affect the appearance or taste of a new fruit, such as a new fruit. The part of the fruit that we eat comes from the ovum of the female plant and has the genetic traits of the female plant, regardless of the male pollen source. However, seed obtained from cross-pollinated plants will result in a variety of fruit traits in the next generation due to the mixing of female and male genetic traits.
Vegetative Plant Parts – When the plant part we eat is a vegetative structure – like broccoli, lettuce, beets, or potatoes – the plant’s characteristics are determined by the genetics of both the male and female parents that the plant received last year Seeds have been fertilized. Gardeners will only see the impact of the pollen source if they conserve seeds from year to year. No effects of the pollen source are seen in the first year of sowing, but in subsequent years, plants grown from stored seed obtained by cross-pollination will not reliably have the same traits as the original parents.
Seed – In some cases, the part of the plant that we eat is actually the seed, such as beans, peas, or sweetcorn kernels. Seed traits – size, color, texture, flavor – are affected by the pollen source since seeds are the result of a mix of female and male genetic traits. Beans and peas are self-pollinating, so the introduction of a new male pollen source is uncommon.
However, sweetcorn that is cross-pollinated by wind is very susceptible to changes caused by the pollen source. All maize varieties are easily cross-pollinated. Sweetcorn must be isolated from field corn, popcorn, and Indian ornamental corn either by location or flowering time, or the ears harvested will have kernels of different types. A spacing of 400 yards or a planting with ripening dates a month apart is necessary to insure isolation and to prevent cross-pollination between varieties.
White and yellow sweetcorn varieties also cross-pollinate, but the effects are minimal when they all share the same sweetness gene (sh2 – supersweet or shriveled, SE – sugary, or su – sugary). Maize varieties with the SE gene may benefit from isolation from other sweet corn varieties, but this is not essential.
So what about those odd shaped pumpkins, squashes or squashes appearing in the garden this year? They weren’t caused by some weird pollen source. These fruits are usually either 1) the result of plants grown from seed obtained from last year’s fruit, 2) the product of volunteer plants from fruit (possibly diseased or broken) left in the garden the previous year , 3) infected with a virus, or 4) rarely an off-type seed that is mixed into a seed packet.
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Sarah Browning is an extension educator at Nebraska Extension. To ask a question or reach her, call 402-441-7180 or email firstname.lastname@example.org or 444 Cherrycreek Road, Lincoln, NE 68528.