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United States Department of Agriculture

Agricultural Research Service

Title: Alternate Bearing of Pecan

item Wood, Bruce

Submitted to: Southeastern Pecan Growers Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 20, 2003
Publication Date: August 20, 2003

Interpretive Summary: Alternate bearing is the economically most important biological problem of the U.S. pecan industry. An understanding of alternate bearing is important to the development of short- and long-term solutions. It was determined that the absence of alternate bearing by individual trees is most closely linked to late fruit ripening, canopy retention, and good canopy health. Alternate bearing was also shown to likely involve at least two key steps, first involving floral initiation and developmental processes during the previous growing season; and secondly, energy reserves at bud break. This information will allow pecan farmers to make management decisions that will minimize alternate bearing and will help researchers to develop methods to control alternate bearing via regulation of flower development during the previous growing season.

Technical Abstract: The fundamental cause of alternate bearing in pecan [Carya illinoinensis (Wangenh.) K. Koch] is unknown, but is closely linked to the size of the dormant season carbohydrate pool. Nut yields (over a period of up to 78 years) were evaluated, for 66 cultivars, in regards to alternate bearing intensity (I). Best-fit regression analysis indicates no association between I and fruit ripening date (FRD) or nut volume; although, there was moderate association with post-ripening foliation periods (PRFP) in that I tends to decrease as the length of the PRFP decreases. Multiple regression models indicated that FRD and nut volume were poor predictors of I, however PRFP possessed significant inverse predictive power. Late-season canopy health, as measured by percentage of leaflet retention, decreased as FRD approached early-season ripening. Late-season photoassimilation rate was higher on foliage of trees with late FRDs than those with mid- or early-season ripening dates. Sprays of either Alar or ProGibb to the canopy of either "On" or "Off" trees altered return bloom the following year. These data provide new insight into the complex nature of alternate bearing in pecan and are interpreted to indicate that alternate bearing in pecan is regulated by; a) gibberellins during the time of fruit development, and b) the size of the carbohydrate pool at about the time of bud break.

Last Modified: 4/22/2015
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