Alternate bearing is a major economic problem for producers of pecan nuts [Carya illinoinensis (Wangenh.) K. Koch], yet a fundamental understanding of alternate bearing remains elusive. Nut yields (over a period of up to 78 years) from a commercial-like orchard of 66 cultivars was used to calculate 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 high er on foliage of trees with late FRDs than those with mid- or early-season ripening dates. These data provide new insight into the complex nature of alternate bearing in pecan and provide evidence for modifying the existing theories of alternate bearing of pecan.
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