A reevaluation of alternate bearing in pistachio

Studies documenting pistachio fruiting patterns (Pistacia vera L.) conclude this species shows evidence of alternate bearing; fruit production fluctuates between an ‘on’ year of high yields and an ‘off’ year of low yields. However, alternate bearing in pistachio has never been statistically tested. We collected yields of 4288 trees over six years to test for alternate bearing in a mature orchard planted with ‘Kerman’ scions grafted onto P. integerrima rootstock – the combination planted on the bulk of the acreage in California. A majority (58%) of the trees exhibited statistically significant alternate bearing patterns. Yet 42% showed yield patterns that were indistinguishable from random fluctuations, the standard measure of alternate bearing (I) was only modest (mean I = 0.48), and I varied considerably among trees (range = 0.04–0.83). These findings support that pistachio shows alternate bearing behavior but suggest alternate bearing is less ubiquitous and fruiting patterns are more complex than previously suspected. The presence of such a diversity of yield dynamics creates considerable challenges for crop management and research.