Field evaluation of rootstocks for 'Improved French' prune production in California grower trials

Historically, the California dried prune industry uses five rootstocks, ‘Myrobalan seedling’, ‘Myrobalan 29C’, ‘Marianna 2624’, ‘Marianna 40’, and ‘Lovell’ peaching seedling. Alternative rootstocks for prune have been identified but not tested under California conditions since the last California prune rootstock experiments were planted in the 1980s. Two rootstock trials were planted in 2011 to evaluate the potential of 10 alternative rootstocks for use in California prune production along with the five historical industry standards, all with ‘Improved French’ as the scion. Evaluating survival, trunk circumference, survival, yield (dry kg tree^‑1), fresh:dry fruit ratio, and dry fruit size. Both trials were planted on commercial farms using randomized complete block designs with 14 rootstock treatments and 5 replicates with 6 trees plot^‑1. Rootstocks include the five standards, as well as ‘Marianna 30’, ‘Marianna 58’, ‘HBOK 50’, ‘Krymsk 1’, ‘Krymsk 86’, ‘Citation’, ‘Rootpac R’, ‘Viking’, ‘Atlas’, and ‘Empyrean 2’. ‘Viking’, ‘Atlas’, and ‘Krymsk 86’ had generally high survival and have consistently been among the highest yielding rootstocks at both sites. At both sites ‘Myrobalan 29C’, ‘Atlas’, ‘Viking’, and ‘Lovell’ had among the largest trunk cross sectional areas while trees on ‘Marianna 58’ and ‘Krymsk 1’ were among the smallest. Additional years of evaluation will more clearly define survival and yield of the rootstocks.