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 United States there were no commercially available rootstocks for peach with proven resistance to ARR pathogen. Available chemical controls are not considered to be cost effective. ‘Guardian’ is currently the dominant rootstock for the southeastern peach industry primarily due to its superior resistance to PTSL. However, ‘Guardian’ is highly susceptible to the widespread ARR pathogen. ‘MP-29’ is recently released clonal plum-peach hybrid rootstock, developed by Dr. Beckman, USDA, which provide superior resistance to ARR, PTSL, and root-knot nematodes. ‘MP-29’ offers the benefits of ARR resistance without the adverse effect on scion fruit size and productivity.
In a previous multistate peach rootstock study, 14 Prunus rootstocks budded with ‘Redhaven’ peach were planted at 16 locations in North America in 2009. Nine-year rootstock performance from 13 states showed significant differences among rootstocks and sites for tree survival, number of root suckers, tree 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, due to 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:
- 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)
Control rootstock cultivars include ‘Lovell’ and ‘Guardian.’ Scion cultivar used is virus indexed ‘Cresthaven.’ The experiment is designed as a replicated study. Supplemental irrigation system was build 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 and the training system used is the perpendicular V training system.
Data was collected during 2017-2019 to determine the tree vigor. Trees were de-fruited after planting to promote better root system establishment. The first cropping occurred in 2019 and trees were harvested four times between July 12th and July 23rd. Our preliminary results on trunk cross sectional area (TCSA) indicate that ‘MP-29’ grafted trees were the smallest, while trees on ‘Guardian’ were the largest (Table 1; Figure 2). Trees on ‘Guardian’ produced the highest total yield per tree, while trees on ‘MP-29’ had the highest yield efficiency. Trees grafted on ‘Controller 6’ produced the largest fruit size of 276 g on average (Figure 1 B), and only ‘Rootpac 20’ trees had fruit size smaller than the ‘Cresthaven’ fruit size on ‘Guardian.’ Our data also suggests all tested rootstocks advanced crop maturity of ‘Cresthaven’ peach in comparison with ‘Guardian’ and ‘Lovell’ grafted trees. Studies will continue to evaluate the yield efficiency, profitability and overall rootstock feasibility for establishment of higher-density peach orchards in Alabama.
Table 1. Rootstock Effect on Yield Efficiency and Vigor of 'Cresthaven' Peach
|Rootstock||Mean fruit weight (g)||Total yield/tree (kg)||TCSA (cm2)||Yield efficiency (kg/cm2)||Number of suckers/tree|
|Controller 6||276.0 a||7.1 cd||36.0 cd||0.2 b||0.0 b|
|Controller 7||225.2 bc||5.2 d||35.9 cd||0.1 c||0.1 b|
|Controller 8||238.2 b||7.8 cd||40.7 c||0.2 b||0.1 b|
|Guardian||212.4 bc||15.6 a||70.5 a||0.2 b||2.8 b|
|Lovell||229.9 bc||14.6 ab||58.7 ab||0.2 b||0.8 b|
|MP-29||222.8 bc||10.2 bc||25.0 e||0.4 a||0.6 b|
|Rootpac 20||203.0 c||10.1 bc||47.3 bc||0.2 b||8.8 a|
|Rootpac 40||233.0 bc||3.0 d||27.0 de||0.1 c||0.1 b|
Study Will Provide Useful Information
Knowledge generated through this study can help Alabama producers to establish higher density peach orchards utilizing semi-dwarf and dwarf rootstocks that provide higher yield efficiency combined with improved fruit quality and pest resistance.
The maximum light interception provided by the perpendicular V training system allows for crop precocity and improved fruit quality. The tree uniformity provided by the training system also helps to facilitate dormant pruning, fruit thinning practices, and fruit harvest. We predict there will be labor savings by utilizing the system due to less time needed to prune a single tree, easy access to the fruit at harvest, and to the flowers at thinning. We are planning to collect additional measurements to compare reductions in labor requirements provided by the rootstock. Disease resistant rootstocks tested in this study can significantly improve production sustainability by increasing the longevity of the orchard and reducing the need for the grower to replace dead and sick unproductive trees or to replace the entire orchard prematurely.
The long terms impacts of this study to our fruit producers will include facilitation of mechanization of multiple orchard operations, including pruning, thinning for crop load adjustment, and harvesting of the crop.