Rootstock × Site Interaction and Stability Analysis of Apple Rootstocks Across Sites in Two NC-140 Multilocation Apple Rootstock Trials

Abstract

The NC-140 technical committee performs multisite rootstock trials to quickly expose rootstocks to a wide range of biotic and abiotic stresses. The site × rootstock interaction is almost always significant for every response variable measured in multisite rootstock trials, indicating that rootstock performance varies with site. Stable rootstocks are those that perform similar across sites. The ideal rootstock is one that has high potential and is stable over sites. Data for trunk cross-sectional area (TCA), cumulative yield (CY), cumulative yield efficiency (CYE) and root suckers per tree from the 1994 and the 2003 NC-140 apple rootstock trials were subjected to five stability analyses (Findlay-Wilkinson joint regression, Shukla’s stability variance, environmental variance, AMMI variance and Kang’s yield-stability statistic) to evaluate the stability of the tested rootstocks. As expected, results varied depending on the trial and the stability statistic being considered. For the 1994 trial, M.26, B.9 and B.491 had above-average stability for all response variables. For the 2003 trial, M.9 NAKBT337 and B.62396 had above average stability for TCA and CY, and G.41 and G.935 had above stability for CYE. M.26 had above average stability for root suckers in both trials because it had fewer than average root suckers at most sites. These results can be useful while making rootstock recommendations for sites not included in these trials.