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ISHS Acta Horticulturae 591: III International Symposium on Pistachios and Almonds


Authors:   L. Ferguson, R.H. Beede, H. Reyes, P. Metheney
Keywords:   Pistacia atlantica, Atlantica, P. integerrima, Pioneer Gold I, PGI, P. atlantica X P. integerrima, Pioneer Gold II, PGII, University of California Berkeley 1, UCB-1.
DOI:   10.17660/ActaHortic.2002.591.5
Currently, the California pistachio industry relies upon four rootstocks, two species and two interspecific hybrids, all members of the genus Pistacia. They are P. atlantica, P. integerrima (PGI), P. atlantica x P. integerrima (PGII and UCB-1). The first three are open pollinated, the last a result of closed pollination. These trials were established in 1989 in three microclimates representative of the major pistachio production regions in California’s Central San Joaquin Valley. Each plot consists of 400 trees, divided into 10, 40 tree replications containing 10 of each of the four rootstocks. All of the trees are budded with buds from the same female and male trees. With these locations, and this design, the behavior of the different rootstocks was observed under a range of climatic and soil conditions. The trees achieved mature bearing in the 10th year in the ground, 1998. The results given below are primarily the result of yields from 1998-2000.
Over the 11 years of this trial trees on the UCB-1 hybrid rootstocks have consistently produced significantly higher yields in all three microclimates. From most to least productive the cumulative average marketable dry weight yields of inshell split nuts from 1989 through 2000 are as follows. Trees on UCB-1 rootstocks produced a cumulative average of 10,645 kg/ha, trees on PGII, 8,658 kg/ha, trees on PGI, 9,197 kg/ha and trees on Atlantica, 7,328 kg/ha. In 2000 the average individual yields per tree on the four different rootstocks were as follows. Trees on UCB-1 rootstocks produced 15.1 kg/tree, or 4,182 kg/ha at 277 trees/ha. Trees on PGII rootstocks produced 13.3 kg/tree or 3,684 kg/ha. Trees on PGI rootstocks produced 12.8 kg/tree or 3,536 kg/ha. Trees on Atlantica rootstocks produced 10.9 kg/tree or 3,019 kg/ha. These differences in yield are the result of more clusters per tree not heavier nuts or more nuts per cluster.
With only three years of mature bearing it is not possible to calculate a reliable alternate bearing index. However, trees on all four rootstocks, in all three locations, had large crops in 1998 and 2000 with a low crop in 1999. This suggests trees on all three rootstocks alternate bear to the same degree, indicating alternate bearing is primarily a function of the scion, not the rootstock.

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