Forcing Treatment and Rootstock Affect Budbreak and Growth of Containerized Citrus Nursery Trees

Abstract

Two experiments were conducted to determine the effects of rootstock and bud-forcing treatment on scion budbreak and nursery tree growth of `Hamlin' orange. In Expt. 1, `Carrizo' citrange, `Swingle' citrumelo, and `Cleopatra' mandarin were budded with `Hamlin' orange and forced by one of the following methods: cutting off (purning away the rootstock top about 2 cm above the inserted scion bud); lopping (cutting half to two-thirds of the way through the rootstock stem 2 cm above the bud union, and breaking over the stem but leaving it attached); or bending (bending the rootstock shoot above the inserted scion bud and tying it to the base of the plant). For `Swingle' only, percent budbreak was less for bending or lopping compared to cutting off. For `Carrizo' and `Swingle', scion dry weights were less when plants were forced by cutting off compared to bending or lopping. For all rootstocks, whole-plant dry weights were greater for plants forced by bending and lopping than for plants forced by cutting off. In Expt. 2, scion buds on `Swingle' and `Cleopatra' plants were forced by the three methods in Expt. 1 plus combinations of bending with notching (making an inverted V incision through the bark and into the wood on the rootstock stem directly above the scion bud) and/or topping (removing the teminal 2 cm of rootstock shoot tips of plants forced by bending). Percent scion budbreak was high for `Cleopatra' plants regardless of forcing treatment. For `Swingle', scion budbreak was greater when bending was combined with notching than for bending alone. For `Cleopatra', plant dry weight was greatest for plants forced by lopping. When bending was combined with notching, or notching with topping, `Swingle' scion budbreak was comparable to cutting off, but plant dry weights were greater with these combination treatments than when cutting off was used.