“Plum” of a Rootstock May Boost a Premium Almond

Almond growers who today can't grow Nonpareil--America's premium almond variety--might be able to do so in a few years, thanks to a plum rootstock called Deep Purple.

Almonds and plums are both members of the Prunus plant family, along with prune, apricot, plumcot, cherry and peach. U.S. almond growers typically produce new almond-bearing trees by grafting an almond scion--the tree’s upper, fruit-bearing part--onto a peach rootstock, the rooted portion.

Unfortunately, the premium Nonpareil variety scions can't be grafted successfully onto certain choice plum rootstocks. So, some growers now have to settle for less popular almond varieties that can be grafted to other rootstocks. Nonpareil almonds might, however, graft well to Deep Purple rootstock. That’s according to preliminary tests at USDA’s Agricultural Research Service. Deep Purple, a hardy plum introduced by the University of Minnesota in 1965, hasn't been tried for this job until now.

In the ARS experiments, 24 Deep Purple grafts of scions of other Prunus relatives of almond--prune, apricot and plumcot--were still strong after 4 years.

This spring, several dozen Nonpareil scions will be grafted onto Deep Purple rootstock, then readied for ARS test-planting in commercial orchards next year.

Like most other plum rootstocks, and unlike peach, Deep Purple can thrive in orchard sites where water tends to accumulate. It shows tolerance to bacterial canker. It also resists two kinds of destructive, microscopic worms--called nematodes--better than some other candidate rootstocks. Growers today rely on a soon-to-be-banned soil fumigant, methyl bromide, to fend off these orchard pests.

Scientific contact: Craig A. Ledbetter, USDA-ARS Horticultural Crops Research Laboratory, Fresno, Calif., phone (209) 453-3064, jlitster@qnis.net.