Survival, growth and yield of 'Carogem' peach on an interstem and two dwarfing rootstocks

Size controlling rootstocks for intensive orchard systems, and interstems to delay phenology to reduce frost risk, were evaluated for peach in South Carolina. A high-density 'Carogem' peach orchard was established on heavy clay soil in February 1998 at the Musser Fruit Research Center, near Clemson, South Carolina. The orchard had 4-tree plots of four treatments consisting of 'Carogem' budded to a 30-40 cm Prunus sp. interstem (=PKI) on 'Lovell' rootstock, and to three other non-peach rootstocks, 'Jaspi', 'Pumiselect (R)' and 'Micronette'. Trees were spaced at 2.2 x 6.1 in and trained to a Kearney perpendicular-V system. Full bloom date, fruit maturity date, fruit yield, fruit size, trunk cross-sectional area, bacterial canker (Pseudomonas syringae) resistance and survival were recorded annually through 2003. All 'Carogem' on 'Jaspi' trees died in the springs of 1999 and 2000 from bacterial canker. After 6 years, PKI interstem trees had a lower survival percentage (68%) than trees on P. pumila rootstocks (81-88%). The majority of these dead trees died from waterlogging and Phytophthora spp. Some trees on P. pumila rootstocks were leaning. PKI interstem trees delayed full bloom by an average of 8 days for 4 years when compared to the two P. pumila rootstocks. Scion trunk cross-sectional area was significantly reduced by 18% on 'Pumiselect (R)' rootstock. Pruning times and pruning weights for P. pumila rootstocks in January 2004 were reduced by an average of 20% and 45%, respectively, compared to PK1 trees. The PK1 interstem delayed fruit maturity an average of similar to 2 days and had the highest cumulative fruit yields, followed by 'Micronette' and then 'Pumiselect (R)'. PKI trees also had the highest cumulative yield efficiency and fruit size was similar to 25% larger than with P. pumila trees. 'Jaspi' was highly susceptible to bacterial canker, but the P. pumila rootstocks survived as well as or better than 'Lovell' rootstock.