Early Differences in the Intensity of Alternate Bearing Among Selected Pistachio Genotypes

Abstract

Alternate bearing (alternating years with high and low yields) is a prominent characteristic of ‘Kerman’ pistachio (Pistacia vera L.), the primary California cultivar. The degree of alternate bearing is described by alternate bearing index values from 0 (identical yields every year) to 1 (complete alternate bearing). Two separate and replicated trials designed to evaluate selections from a breeding program were conducted in the southwest (Kern County) and northeast (Madera County) areas of the San Joaquin Valley of California. Yields from the scion genotypes ‘Kerman’, ‘Golden Hills’, ‘Lost Hills’, ‘B5-8’, and ‘B19-1’ on PG1 rootstock were measured from 5- to 9-year-old trees in Kern County and from 5- to 7-year-old ‘Kerman’, ‘Golden Hills’, ‘Lost Hills’, and ‘B5-8’ trees on PG1 and UCB1 rootstock in Madera County. In Kern County, average annual yields among genotypes varied from a low of 208 to a high of 5273 kg·ha−1. Differences in the alternate bearing indices among genotypes were significant and ranged from 0.10 for ‘Lost Hills’ to 0.80 for ‘B19-1’. A similar pattern was observed for alternate bearing indices at the Madera County trial. In this younger trial, scion genotype had more influence on alternate bearing indices than did rootstock. Marked differences in the intensity of alternate bearing of young trees in these two trials suggest that alternate bearing might be amenable to selection in breeding programs. However, the observation that ‘B5-8’, with an alternate bearing index of 0.74, varied significantly from its female parent ‘Kerman’ at 0.36 suggests that inheritance is complex.