ANALYSIS OF POTENTIAL AND STABILITY ACROSS ENVIRONMENTS OF NINE APPLE ROOTSTOCKS IN THEIR INFLUENCE ON GROWTH AND YIELD

Abstract

Nine apple rootstocks grafted with `Starkspur Supreme Delicious' were evaluated in 19 states over 9 to 10 years by the NC 140 Regional Project as a randomized complete block with 10 replications in each site. Effects on trunk cross-sectional area (TA), cumulative yield per tree (Yc), and cumulative yield efficiency (YEc=Yc/TA) were evaluated. Rootstock differences in mean potential (mean performance at the mean site) and environmental stability (slope across sites) were compared by analysis of rootstock performance within a site linearly regressed on mean performance of all rootstock in that site. MAC 24 had the highest mean potential of Yc and TA with lowest stability, giving this rootstock the highest Yc and TA in best sites, and lowest in poor sites. M.27 EMLA was the opposite, having low potential and high stability in Yc and TA. In YEc, M.27 EMLA and MAC9 had high potential and low stability, while OAR1, M.7 EMLA, and especially MAC 24 were the opposite. YEc of Ott.3 and M.26 were average in both respects. M.9 had high potential YEc with average stability. M.9 EMLA was unique in having both high potential and high stability of YEc.