By Peter Kevan Apples, pears, and some cherries need cross-pollination to set a crop. How does the pollen move from tree to tree so that cross-pollination takes place? On the bodies of insects, especially bees. For orchard pollination, honey bees make excellent pollinators. Managed orchard bees can be used but the technology is not well developed. Wild bees, including bumble bees, can be important. Honeybees are excellent pollinators of apples. If they are excluded from the flowers, as with bags (see Figure below), few flowers develop to give fruit. The few fruit that do devel- op may arise because of experimental contamination. The issue is not so simple as to be solved by just adding bees to the orchard. For apples and pears, cross-pollination must take place between cultivars. For efficient orchard harvesting, block plantings would seem most practical, but for pollination as a crucial process, the size of blocks becomes a real issue. How far can pollen move on the bodies of pollinating insects? Research results taken from commercially run orchards with high density trees grown on dwarfing rootstock show that pollen does not move far! How can one give that answer? It is next to impossible to determine how far a bee flies and how many different trees it visits on a foraging trip. Even if one could do that, the problem of how much cross-pollen the bee moves from tree to tree remains. Our team at the University of Guelph took a genetic approach to solving the problem. Flowers of apple bagged to prevent pollinators visiting and pollinating them. These flowers could then be used for various controlled pollinations by hand to investigate how important pollination and different pollinizers are in apple production. First, the genetic fingerprints of the main cultivars were determined. Each of the study cultivars had distinctive genotypes. With that information, it is possible to determine the paternity of the embryos in the apple seeds. Working within multiple rows of apple culti- vars, and divided rows with two cultivars, it was possible to determine how far away from the mother trees the nearest potential father (pollinizer) tree was. In other words, knowing the genotype of the mother trees in the rows (producing apples of a given cultivar), the paternity of the seeds, and the distance to the nearest potential father (pollinizer) tree (also a production cultivar), the paternity tests revealed how far cross-pollen could move. So, how far does pollen move in an apple orchard? Only about four to five trees! To place those findings into the context of a map of an orchard means that for pollina- tion to function at its best, cultivars need to be in close proximity to each other. Given the recommended tree densities for typical high-density orchards, most pollen travels only about 20 meters, indicating that four or, at most, five rows of a given cultivar should be grown together to allow cross-pollination to take place for proper pollination. The rows at the edges of orchards should be only two, or at most three trees wide of a single cultivar. Without pollinizer interplantings within rows, or pollinizer grafting onto trees within rows, cross-pol- lination takes place only from a few trees away on either side of the rows of any given cultivar. The results indicate that pollinizer interplantings should be such that every pro- duction cultivar tree is within two or three trees of the pollinizer. In a cultivar production block orchard (i.e. an orchard without differing groups of rows, but specializing in one cul- tivar) that means that within rows, pollinizers should be planted about every 8th to 12th tree, but about four - six trees out-of-step between rows. The exact geometry must be cal- culated depending on planting density, row spacing, and production vs. pollinizer cultivar. Not all pollinizers are equal! How to choose a pollinizer? The pollinizer must bloom synchronously, and produce viable pollen that is compatible, with the production trees it is there to service. Some orchards use crab apples as pollinizers, other use grafts of other cul- tivars or crabs on the production cultivar. Research is needed on the strategies that best fit the various ways of growing pome fruit and planning orchard design. Just from our limited studies on the interactions between pollen and fruit production, the results presented sur- prises. The pollen of some cultivars is better at fertilizing flowers than is that of others. Fuji and Granny Smith produce “stud” pollen. We dis- covered this by hand pollinating flowers with known mixtures of pollen that we had prepared. Moreover, some cultivars, such as Mutsu and Jon- agold, produce little or no viable pollen and are in essence eunuchs, use- less as pollinizers. Pollen from Fuji and Granny Smith were much more virile in fertilizing flowers of Empire, Golden Delicious, and McIntosh than were pollen from Ida Red, Northern Spy, and Vista Bella. The reasons for the differences are not understood, but “stud” pollinizers should be used in combination with production cultivars. Tests to determine which is the best “stud” for each production cultivar are needed because it cannot be assumed that the stud for one is also a stud for another. Even given the fact that some cultivars produce “stud” pollen, anoth- er surprise was in store. Multiple paternity helps apple set and quality. As part of studies on the effect of pollinizer pollen, we found that if pollen from several pollinizers reached the stigmas of the production cultivar, then the seediness of the apples and the size of the apples increased. The combination of pollinizer proximity, pollinizer diversity, and pol- lination translates into greater production. Continued on next page THE GROWER PAGE 20 –– APRIL 2010 Guy Anderson Kincardine 519-396-3529 Nicholas Bilinsky Simcoe 519-428-1560 Ann & Stefan Board Nipissing 705-729-2939 Tom Buckle Langton 519-875-2389 Jim Coneybeare Fergus 519-843-7328 Roger/Tom Congdon Cottam 519-839-4000 Dan Davidson Watford 519-849-5959 Joe DeVillers Penetang 705-533-3655 Jerry Dietrich Alma 519-846-5839 Dutchman's Gold/ John VanAlten Carlisle 905-689-6371 Tim Greer St Catharines 905-934-5904 Chris Hiemstra Aylmer 519-773-5503 Zenon Kohut Lynden 519-647-9796 Leonid Beekeeper Schomberg 647-381-3435 Bill Minnick Smithville 905-957-3667 Munro Honey Davis & John Bryans Alvinston 519-847-5333 Charlie Parker Beamsville 905-563-7285 Kelly Rogers Chatsworth 519-372-0141 Dirk Schapp Lasalette 519-879-6392 Michael Sounak Dundas 905-317-4140 Henry Van Lingen Belmont 519-269-3923 BEES FOR POLLINATION Please contact the beekeeper nearest you. Sponsored by Ontario Beekeepers’ Association Phone 905-636-0661, fax 905-636-0662 www.ontariobee.com The following Ontario Beekeepers offer Honey Bee Pollination Services: SUPPORT YOUR LOCAL BEES We help to bring you fruit and sweeten your day with honey. Using pollination research to boost orchard yields