Plums on the Prairies

Information from Literature Much has been published about pollination, pollinators, pollinizers, fertilization and fruit set in text books and periodicals. The definitions are not difficult. Pollination is the movement of pollen among compatible flowering plants (cross-pollination) or from anthers to stigmas on the same plant or different plants of the same clone (self-pollination). Many plants will self-pollinate but set very few fruit; some authors consider them selfpollinating but they are definitely not self-fruitful. Self-fruitful plants (and clones) set a crop of fruit after self-pollination; some of these plants bear fruit with no seeds (parthenocarpy); others develop seeds with embryos that are genetically identical to the parent plant (apomixis); and others produce haploid seeds that develop from an unfertilized egg cell. (When haploid seeds germinate they are very weak seedlings with only half the chromosomes of normal seedlings.) Regarding temperate zone tree fruits, self-pollination and fruit set does not mean self-fertility and the development of normal seeds. Many temperate zone small fruit species (e.g. strawberries and raspberries) are self-fertile and develop maximum yields of fruit with normal seeds as the result of self-pollination by insects. Pollinators, usually insects, are vectors of pollen movement. Pollinizers are plants which provide the appropriate pollen for other plants. Fertilization is the process in which gametes from the pollen unite with egg cells in the ovary of the flower. Normal seeds are usually the result of this process. Also, the principles are easily understood. Poor fertilization in plums and other Prunus species results in a poor fruit set. Poor fertilization in apples and pears results in fewer fruit with fewer seeds and smaller, misshapen fruit. Most writers have overlooked or significantly understated the pollination requirements for growing good plum crops. The exception is George F. Chipman who edited the Prairie Gardener for many years and who wrote about plum pollination in 1934. He summarized a study done by Prof. W. H. Alderman at the University of Minnesota by saying, “...very few hybrid plums would accept pollen freely from other hybrids, but they would all accept pollen from native plums”.