ARS | Publication request: Insight into Alternate Bearing of Pecan

Submitted to: Acta Horticulturae
Publication Acceptance Date: February 15, 2004
Publication Date: August 1, 2004
Citation: Wood, B.W., Conner, P.J., Worley, R.E. 2004. Insight Into Alternate Bearing Of Pecan. Acta Horticulturae. V.636. P.617-629.

Interpretive Summary: Alternate bearing is the economically most important biological problem of pecan, adversely impacting producers, processors, and consumers in many different ways. Management tools need to be developed to reduce or prevent alternate bearing. It was discovered that gibberellins play an important role in the alternate bearing process in pecan in regards to the early stages of flower development during the growing season prior to fruiting. A new theory is therefore presented that better explains the alternate bearing mechanisms. The theory can be used to develop better approaches to the mitigation of alternate bearing through new varieties, improved management strategies, and development of risk management tools.

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 predicators of I, however, PREP 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.