Submitted to: Southeastern Pecan Growers Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 25, 2006
Publication Date: July 1, 2006
Citation: Wood, B.W. 2006. Improving fruit-set. Proceedings of Southeastern Pecan Growers Association. p. 11-21. Interpretive Summary: Major causes of revenue losses in pecan farming enterprises are crop losses due either to nutrition related fruit-drop or to poor pollination. This communication identifies nickel nutrition as a factor affecting fruit abortion. It also identifies pollination associated factors that can used to determine if pollination associated yield losses are occurring and how orchard management can be altered to minimize losses. This information provides pecan farmers with the knowledge needed to improve pecan orchards yields.
Technical Abstract: Fruit-drop in pecan can occur due to insufficient nickel nutrition. Timely foliar sprays of Ni can prevent loss. Nut yield loss to pollination related factors is likely far more significant in many orchards than commonly recognized. Pollination studies in the southeastern U.S. pecan belt, where there is a relative abundance of pollen from many sources, shows that in certain years many orchards experience pollination associated yield loss. A similar loss has been documented in southwestern orchards where it was thought that there was good flowering complementarity between cultivars. Use of both a “Type I” and a “Type II” cultivar does not guarantee adequate cross-pollination. Pollination affects orchard profitability at several levels. In addition to the harmful and straightforward effect of the absence of pollen at stigma receptivity, there are also subtle secondary aspects of pollination that limit revenue via egg fertilization, fruit-set, and seed development. This talk addresses the pollination/fertilization/seed development process, how pollen and different pollen sources affect these processes, and how growers can determine if there is a pollination problem in a particular orchard. Key to successful pollination management is the ability to recognize pollination associated problems. These pollination associated problems can be detected by the asking the following questions: 1) Is there a fruit-set gradient among main crop trees surrounding “off-variety”, “seedling”, or “pollinator” trees? A gradient is most apparent when one compares the fruit-set of the side of the canopy facing the aberrant trees to fruit-set in canopies 4-5 trees further away, but is often apparent only 1-2 trees away. Note that such a gradient will not occur around all aberrant trees, even if there is a pollination problem, because the timing of pollen dispersal by aberrant trees will not always overlap with surrounding trees. 2) Is there a fruit-set gradient, or kernel quality gradient, or yield gradient, across the orchard as one traverses from one pollinator row to the next? Note that tree canopies, especially noticeable as orchard canopies crowd, are a substantial barrier to across-orchard pollen movement. 3) Is there a fruit-set, June-drop, kernel quality, or yield gradient across the orchard from the 2nd -3rd row to the center of the orchard? Note that fruit-set is generally good on the perimeters rows of all orchards, but drops off substantially from about the 4th-5th row inward if pollen is limiting fertilization. 4) Is there heavy, or excessive, June-drop accompanied by “fruit-tip senescence”? Fruit-tip senescence is when the shuck of aborted fruit is just beginning to separate from the shell, a physiological process requiring 2+ weeks. Fruit drops due to insect feeding do not exhibit this “shuck separation zone” as such drop occurs about 5-7 days after being damaged; thus there has not been sufficient time for senescent processes to produce a shuck separation zone. Note that fruit will drop due to lack of egg fertilization; thus this drop can be due either to lack of pollination or to genetic incompatibilities with the pollen parent. Thus, selfing, or self fertilization, can cause June-drop, with the problem ranging from nil to severe depending upon the cultivar. 5) Is there a gradient in kernel quality, especially percentage kernel, as distance from the pollinator variety increases? Such a loss is due to self-fertilization, with the degree of loss varying among cultivars. A variety of factors will be discussed that causes annual variation in complementary pollination. Guidelines will be provided that can be implemented to correct or prevent significant pollination related yield losses.