Growth and 14C-Photosynthate Allocation in Citrus Nursery Trees Subjected to One of Three Bud-forcing Methods

Abstract

Three commercially employed treatments to force scion bud growth were compared using greenhouse-grown `Carrizo' citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] seedlings budded with `Hamlin' orange [Citrus sinensis (L.) Osb.]. Scion buds were forced either by 1) cutting off (removing the rootstock shoot above the bud union); 2) lopping (cutting half-way through the rootstock shoot above the bud union and breaking over the rootstock stem); or 3) bending (bending the rootstock shoot to its base and tying it in position). Plants were harvested, dried, and weighed at various times after scion shoot emergence. Plants on which rootstock shoots remained attached (lopping or bending) had the largest scion leaf area and gained the most scion and whole-plant dry weight. Bending rootstock shoots also resulted in a longer scion, more leaves, and higher root dry weight than did removal of rootstock shoots by cutting off. Few differences in overall growth were observed among trees retaining their rootstock shoots after two scion growth flushes. Removal of rootstock shoots after the first scion growth flush reduced leaf area and dry weight gain of the second scion growth flush; however, it did not affect total scion leaf area or dry weight. Analysis of 14C-photosynthate transfer from labeled rootstock leaves showed that bending allowed the greatest movement of labeled assimilates to other plant parts during the 24 hours after 14CO2 fixation. Radiolabeled photosynthates from rootstock leaves were partitioned primarily to shoots during scion growth flushes and to roots during periods between growth flushes.