PERFORMANCE POTENTIAL AND STABILITY OF 15 APPLE ROOTSTOCKS AS AFFECTED BY NORTH-AMERICAN GROWING SITES OVER THE PERIOD 1984-1993

Stability analysis models were developed by the method of joint linear regression for the cumulative performance of 15 apple rootstocks eval uated in replicated trials in 29 sites located across North America ov er a period of 10 years. Stability analysis provides a simple graphica l basis to compare rootstocks based both on mean performance and on th e stability, or consistency, of that performance across sites for a gi ven trait. Models were developed for cumulative tree growth (based on trunk cross-sectionalarea), cumulative yield per tree, and cumulative yield efficiency (yield per trunk cross sectional-area). Rootstocks fo llowed a trend varying from low mean potential with high stability acr oss sites, to high mean potential with low stability across sites for all three performance variables. However, no rootstock demonstrated a simultaneous improvement in both mean potential and stability of tree performance in contrast to models developed previously for the 1980-19 89 NC-140 apple rootstock trial.