Apple Shoot and Trunk Growth as Affected by Rootstock

Abstract

Annual shoot and trunk xylem growth increment of `Starkspur Supreme' in the 1984 NC-140 uniform rootstock trial was studied of 10 selected rootstocks representing a range of tree sizes. Shoot growth was measured weekly from budbreak through harvest in each of four seasons. After 11 seasons of growth, whole trees were cut, placed in water containing diffuse fuschin dye for 30 to 60 min during mid-day. After that, a section of trunk (10 to 15 cm long) was excised at 25 cm above the graft union. Trunk xylem thickness and percent of water transport active xylem were measured. Shoot length during the study was related to both the duration and rate of growth; however, growth duration contributed more to variation among stocks. In all stocks, it appears that almost all xylem translocated water and that there was very little “plugged” or active xylem. There were no differences among stocks for the relative percentage of active xylem. Annual xylem increment width varied with stock. The vegetative growth of these trees will be discussed relative to the production efficiency of scions on these stocks.