A damaging soilborne fungus causing Armillaria Root Rot (ARR) disease is the second leading cause of peach tree mortality after Peach Tree Short Life (PTSL) in the southeastern United States. Estimated lifetime production losses attributed to ARR average more than $5 million annually.
Research in Multistate Rootstock Study
Until recently, in the US there were no commercially available rootstocks for peaches with proven resistance to this pathogen. Available chemical controls are not considered to be cost effective. Guardian is currently the dominant rootstock for the southeastern peach industry primarily because of its superior resistance to PTSL. However, Guardian is highly susceptible to the widespread ARR pathogen. MP-29 is a recently released clonal plum-peach hybrid rootstock that was developed by Tom Beckman (USDA). This hybrid provides superior resistance to ARR, PTSL, and root-knot nematodes. It also offers the benefits of ARR resistance without the adverse effect on scion fruit size and productivity.
In a 2009 multistate peach rootstock study, 14 Prunus rootstocks budded with Redhaven peaches were planted at 16 locations across North America. Nine-year rootstock performance from 13 states showed significant differences among rootstocks and sites for tree survival, root suckers, growth, bloom date, fruit maturity date, fruit size, cumulative yield, and yield efficiency. The clonal P. persica rootstocks HBOK 10 (Controller™ 8) and HBOK 32 (Controller™ 7) appeared to be the most promising of the size-controlling rootstocks tested. Size controlling rootstocks are particularly valuable when high-density peach orchards are designed because of their potential to reduce management costs, provide economic sustainability by reducing chemical pesticide applications, and also improve environmental sustainability.
Thus, a new trial was established to compare the performance of recently released size-controlling and pest resistant rootstock cultivars that could provide improved economic and environmental sustainability in peach production in Alabama.
Experimental Block Established at CREC
A site with documented ARR history was selected in Clanton Alabama, at the Chilton Research and Extension Center (CREC) to establish the experimental block in 2017 (Figure 1). The rootstocks being test at the CREC include the following:
- UC Davis root-knot resistant peach hybrids: Controller 6, Controller 7, and Controller 8
- Spanish rootstocks: Rootpac 20 (plum X almond) and Rootpac 40 (peach X almond)
- USDA rootstocks: MP-29 (plum X peach interspecific hybrid)
Control rootstock cultivars include Lovell and Guardian (Clemson/USDA). Scion cultivar used is virus indexed Cresthaven from California. The experiment is designed as a replicated study. A supplemental irrigation system was built to aid in tree establishment and provide better plant development. The tree spacing used is 6’ X 18’ which provides a moderately high density of 405 trees per acre. The training system used is the perpendicular V training system.
Data was collected from 2017 to 2021 to determine the rootstock effect on tree vigor and productivity. The first cropping occurred in 2019 when Cresthaven trees were harvested four times between July 12 and July 23. Chilling insufficiency in 2019 and 2020 and early spring cold injury in 2020 and 2021 resulted in a prolific button formation and poor marketable yields of the experimental Cresthaven trees during the fourth and fifth season. The 2021 results on trunk cross sectional area (TCSA) indicate that MP-29 grafted Cresthaven trees were the smallest, with a TCSA of 41.9 cm2, while trees on Guardian grew about three times larger trunks of 110.7 cm2 (table 1). Trees on Guardian and Lovell also had the largest canopies as measured by tree height and canopy dimeters recorded within the row and across the row, while trees on MP-29 were the smallest.
Trees on Guardian produced the highest 2019 to 2021 cumulative yield per tree, while trees on MP-29 had the highest cumulative yield efficiency. Cresthaven trees on Rootpac 40 had the lowest cumulative yield efficiency during the reported period. Trees grafted on Controller 7 produced the largest fruit size (357.9 grams on average) in the 2021 season when all of the rootstocks produced larger fruit size in comparison with Guardian (297.4 grams) and Lovell (298.3 grams). However, this was likely an effect of the lower crop load produced on these rootstocks in comparison with the controls.
Table 1. Rootstock Effect on Cresthaven Tree Size, Yield, and Yield Efficiency
|Rootstock||TCSA (centimeter2)||Canopy Height (meter)||Within Row Diameter (meter)||Across Row Diameter (meter)||Mean Fruit Weight (gram)||Cumulative Yield (kilogram per tree)||Cumulative Yield Efficiency (kilogram per centimeter2)|
Study Will Provide Useful Information
These results indicate the semi-dwarf rootstocks have the potential to provide labor savings because between 48 and 52% less time is required to dormant prune and summer prune a single tree. Additional benefits of semi-dwarf rootstock utilization in peach production include an easy access to the fruit at harvest and to the flowers at thinning.
Studies continue to evaluate the yield efficiency, profitability, and overall rootstock feasibility for establishment of high-density peach orchards in Alabama. The long terms impacts of this study to our fruit producers will include facilitation of mechanization of multiple orchard operations, including pruning, thinning, crop load adjustment, and harvesting of the crop.