2019 ASHS Annual Conference

Yield is a key measurement of interest in field evaluations of novel rootstocks for tree fruit and nut production. However, key non-yield measurements help differentiate test rootstocks. Replicated and randomized field evaluations have been performed at two sites for novel rootstocks for prune (Prunus domestica) production in California’s northern Sacramento Valley. Measurements of trunk cross-sectional area and ratings of tree anchorage, rootstock suckering, and tree survival were evaluated at the two prune rootstock trial sites. Phenological monitoring of bloom density and timing at one prune rootstock trial site (2016, 2017 and 2018), as well as midday stem water potential readings with the pressure chamber have been conducted. Trunk cross-sectional area measurements differentiated a significant range in the vigor conferred from the rootstock to the prune (cv. ‘Improved French’) scion. Survival of prune rootstocks ranged from 97% (‘Atlas’) to 30% (‘Empyrean 2’) at one trial site and from 100% (‘Atlas’, ‘Viking’ and ‘Krymsk 86’) to 45% (‘HBOK 50’) at the second trial site. Higher vigor (trunk-cross sectional area) rootstocks tended to be less water stressed (less negative) at a midday stem water potential pressure chamber reading. ‘Krymsk 86’ and ‘Viking’ were among the rootstocks evaluated at two prune trials that had both few rootstock suckers and the least degree of lean. Finally, some consistent year-to-year relative differences in bloom timing by rootstock treatment were evident at the evaluated trial site. Although yield is of key interest to researchers and growers alike, numerous non-yield measurements can help differentiate the merits and disadvantages of evaluated rootstocks. This is particularly the case for non-yield measurements of direct horticultural value to growers.