Progress report for GS22-265
Project Information
One of the main grower's concerns every year is the completion of the chilling hour requirement for peach cultivars. The understanding of winter dormancy and dormancy/growth cycle transitions in peaches is key for crop management practices. During the spring season, peach growers face the challenge of making decisions about the occurrence of freeze events and the possibility of potential damage to the growing peach crops. The goal of this study was to support peach growers with a phenological approach to best management practices. The understanding of the physiological aspects of the crops and the interaction with events such as dormancy, growth cycle transitions, phenology, and growth development is a key determinant for planning and executing management practices. To determine the time required to reach bud break, and to determine the connection between cold and heat accumulation for peach development three peach cultivars (Prunus persica (L.), including Harvester, Redglobe, and Rubyprince were evaluated. Five samples of branch segments with base, mid-section, and Apex buds were collected for every cultivar on different dates, to follow the progression of chill accumulation- dormancy, bud break, and transitions of phenological stages. We evaluated under laboratory conditions the progression and development of floral and vegetative buds, coming from Chilton Alabama for different dates starting from September 2022 until March 2023. Among the cultivars evaluated, Harvester was the earliest cultivar in bud breaks followed by Rubyprince and Redglobe respectively. Results of this study will provide valuable information to one of the implicit research priorities for peach producers, which is the understanding of the impact of climate variability on dormancy, phenology, crop production, and best management practices.
- To determine the timing in dormancy and phenological stages transitions in selected peach cultivars for management practices recommendations.
- To analyze the influence of climate variability on phenological stages for selected peach cultivars under Alabama conditions.
Cooperators
- (Educator and Researcher)
- (Educator and Researcher)
- (Educator)
- (Educator and Researcher)
Research
Materials and methods:
Phenological stages transition
Five samples of dormant shoots of three commercial peach cultivars (Harvester, Redglobe, and Rubyprince) were collected weekly starting - late fall September 23, 2022, to early Spring March 3, 2023. Samples were taken from Chilton Regional Research & Extension Center located at 120 County Road 756 Clanton, Alabama (32°55’14” N; 86°40’20” W) at 204 meters a.s.l. Samples were placed in plastic Ziploc bags to prevent drying out and transported in an ice cooler. Once in the laboratory, shoots were placed in beakers with 200 ml of water and activated carbon to prevent bacterial growth. The experiment took place under laboratory conditions. Observations were done daily to identify the time necessary in the transition between the stages to identify the transition among phenological stages (From Green Calyx until petal fall). Data were recorded in an Excel database for later analysis using the S.A.S program version 9.4.
Influence of climate variability on phenological stages
Data collected included the number of days to bud break as well as climate information such as air temperature. We used temperature records that include 2022, and 2023 years from the Chilton Regional Research & Extension Center as well as previous records for 2021 and 2022. Hourly and daily temperatures have been used to calculate chilling accumulation using the simple accumulated hours <7.2 °C model. Growing Degree Days will be calculated as the total accumulation of the difference between daily temperature and temperature base (4.5°C) (Citadin et al., 2001).
Results and discussion
Phenological stages transition
We evaluated a total of 1,258 buds including floral and vegetative buds through daily observations from three commercial peach cultivars, which come from 23 sampling dates from Chilton AL, starting on September 2022 until March 2023. In total, it was observed that only 884 bud breaks occurred distributed as 584 floral bud breaks, and 300 vegetative bud breaks. Harvester was the earliest cultivar in bud breaks followed by Rubyprince and Redglobe respectively (Table 1). For the season 2022 - 2023 bud breaks started on January 2, 2023, and finished on March 20, 2023.
Table 1. Total bud breaks per cultivar and the early, late, and average date of bud breaks (BB).
|
Cultivars |
Vegetative BB |
Floral BB |
E. Date |
L. Date |
A. Date |
|
Harvester |
109 |
251 |
1/2/2023 |
3/20/2023 |
3/1/2023 |
|
Redglobe |
118 |
161 |
1/17/2023 |
3/19/2023 |
2/26/2023 |
|
Rubyprince |
73 |
172 |
1/9/2023 |
3/19/2023 |
2/26/2022 |
|
Total Veg. & Floral BB |
300 584 |
||||
We used statistical procedures to establish correlations between variables such as bud position, bud type, and the days to reach the dormancy release among cultivars. Regarding the dormancy releases in floral buds, there were significant differences between the Harvester and Redglobe cultivars (p < 0.05), but there were no differences between Harvester-Rubyprince and Redglobe-Rubyprince as shown in Table 2.
Table 2. P-values for the comparison among peach cultivars.
|
Differences of Cultivar Least Squares Means |
|||||||
|
Cultivar |
Cultivar |
Estimate |
Standard Error |
DF |
t Value |
Pr > |t| |
Adj P |
|
Harvester |
Redglobe |
-5.9658 |
1.8312 |
579 |
-3.26 |
0.0012 |
0.0034 |
|
Harvester |
Rubyprince |
-1.4584 |
1.7818 |
579 |
-0.82 |
0.4134 |
0.6917 |
|
Redglobe |
Rubyprince |
4.5074 |
1.9846 |
579 |
2.27 |
0.0235 |
0.0607 |
Significant differences between the Apex and Base positions in floral bud breaks were found (p < 0.05), while Apex-Mid and Base-Mid positions were not significant Table 3.
Table 3. P -values for the comparison between bud positions (A: Apex, M: Mid, and B: Base).
|
Differences of Bud_position Least Squares Means |
|||||||
|
Bud_position |
Bud_position |
Estimate |
Standard Error |
DF |
t Value |
Pr > |t| |
Adj P |
|
A |
B |
-7.5366 |
2.0236 |
579 |
-3.72 |
0.0002 |
0.0006 |
|
A |
M |
-3.2902 |
1.6825 |
579 |
-1.96 |
0.0510 |
0.1243 |
|
B |
M |
4.2464 |
2.0091 |
579 |
2.11 |
0.0350 |
0.0880 |
Furthermore, the interaction between Cultivar and bud type was significant as Table 4 shows.
Table 4. P values for cultivars, bud position, bud type, and the interaction between cultivars and bud type.
|
Type III Tests of Fixed Effects |
||||
|
Effect |
Num DF |
Den DF |
F Value |
Pr > F |
|
Cultivar |
2 |
876 |
8.63 |
0.0002 |
|
Bud_position |
2 |
876 |
14.52 |
<.0001 |
|
Type_bud |
1 |
876 |
38.58 |
<.0001 |
|
Cultivar*Type_bud |
2 |
876 |
3.12 |
0.0446 |
The frequency of floral and vegetative bud breaks was determined as the number of dormancy releases through time for each cultivar (Fig. 1).
Harvester was the cultivar with the highest frequency of floral breaks followed by Redglobe and Rubyprince. Most of the floral and vegetative bud breaks were observed during late February and early March 2023, considering that the initial date of the experiment was September 1, 2022. The days with the highest frequency of bud breaks are shown in Table 5.
Table 5. Summary of the days (From September 1 until bud break date) with the highest frequency of dormancy releases.
|
Cultivars |
Most frequent day in floral bud breaks |
Most frequent day in vegetative bud breaks |
|
Harvester |
181 |
175 |
|
Redglobe |
178 |
192 |
|
Rubyprince |
178 |
181 |
The remains phenological stages (Pink, First Bloom, Full Bloom, and Petal Fall) are still under analysis. Since this is the first year of observations these are preliminary results, and analysis of data is still in progress.
Influence of climate variability on phenological stages
The average, maximum, and minimum temperature was recorded for Chilton AL (Fig. 2), to calculate chilling accumulation for dormancy release.
The total chilling hours were calculated for each of the cultivars during the earliest, late and average floral dormancy release period (Table 6).
A minimum of 466 and a maximum of 864 chilling hours were accumulated for all the cultivars evaluated, ranging from the earliest until the latest bud breaks. The calculation of heat requirements for all stages is still in progress.
Table 6. Total chilling hours accumulated during the dormancy release.
|
Floral bud breaks and chilling accumulation |
||||
|
Cultivar |
Bud break date |
Days bud break |
Chilling hours |
|
|
Harvester |
Early |
1/2/2023 |
123 |
466 |
|
Mean |
3/1/2023 |
181 |
816 |
|
|
Late |
3/10/2023 |
190 |
816 |
|
|
Redglobe |
Early |
1/17/2023 |
138 |
580 |
|
Mean |
2/26/2023 |
178 |
816 |
|
|
Late |
3/16/2023 |
196 |
864 |
|
|
Rubyprince |
Early |
1/15/2023 |
136 |
571 |
|
Mean |
2/26/2023 |
178 |
816 |
|
|
Late |
3/6/2023 |
186 |
816 |
|
Educational & Outreach Activities
Participation Summary:
EDUCATIONAL AND OUTREACH ACTIVITIES
As part of the educational development and dissemination of the present project participation in several academic events, has been taking place. An oral presentation titled “ End of dormancy determination, bud break, and the transition of floral bud progression for three peach cultivars Prunus persica (L)” was given at the Southeastern Professional Fruit Workers Conference, on November 14-16, 2022, hosted by the UF/IFAS Research and Education Center, University of Florida. The audience consists of undergraduate, Master, and Ph.D. students as well as, USDA scientists and stakeholders, staff from Clemson, Florida, Georgia, Rutgers, and Auburn Universities were part of the audience.
Every year Auburn University promotes the dissemination of student research projects where the research based on sciences, arts, and other professional programs is presented through a symposium of Student and Faculty Research on March 28, 2023. A poster presentation titled “Understanding dormancy release in peach flower buds (Prunus persica L.)” was performed.
In the same way, we took part in the Alabama Peach Growers meetings for this year hosted by the extension team at Chilton Regional Research & Extension Center, where growers and researchers were gathered around the different production challenges. Attendance and participation for the “Peach Production Meeting” on January 18, 2023, and on March 22, 2023, this last was about “Mating Disruption Pheromones for Control of Peach Tree Borer.
As a future academic activity, we have an oral and poster presentation programmed already at the 2023 ASHS (American Society for Horticultural Science) Annual Conference.
Project Outcomes
Supporting decision-making for farmers at the local level, this project has allowed the evaluation under laboratory conditions of three commercial peach cultivars, understanding the transition of phenological states from dormancy to petal fall, as an initial stage of fruit development. This is associated with the weather conditions of Chilton Alabama as the largest producer of peaches in Alabama. Both preliminary information and the final results will be used for future model development for peach dormancy and bud break prediction.
The development of the different phases of the project has allowed the learning of peach physiology with a focus on production, the needs, and challenges of the growers as well as the requirements of the consumer. Also, the articulation of knowledge between different disciplines and stakeholders. As part of a fruit physiology laboratory, this project has brought knowledge and development of skills in sampling collection, experimental design, statistical analysis, phenological transition monitoring, and the analysis of climate information. One of the major challenges for the execution of this project has been the construction, processing, and analysis of databases and mathematical models that have been used as a methodology. Also, it is important to mention the pedagogical skills acquired in information dissemination as well as the writing of results and technical documents.