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Early performance of newly released blueberry cultivars with improved fruit quality characteristics

Elina Coneva1, Ebrahiem Babiker2, Eric Stafne3, Sushan Ru1, Melba Salazar-Gutierrez1, Camila Rodrigues1, and Edgar Vinson1, 1Auburn University, 2USDA-ARS, 3MSU


‘Titan’ and ‘Krewer’ (Fig. 1 A,B) are two new blueberry cultivar releases from the University of Georgia breeding program are reported to produce large berries. Their fruit size is reported to be twice as large as the berry size of most rabbiteye blueberry cultivars. ‘Pink Lemonade’ (recommended as a backyard cultivar, Fig. 1C) possesses unique pink fruit color and ripens late. ‘Pink Lemonade’ has a very attractive and unusual appearance and draws consumers’ curiosity and attention in the marketplace. ‘Alapaha’ is known for its very early ripening, surpassing ‘Climax’, while its blooming season is about 7 to 10 days after that of ‘Climax’, which reduces the risk of late spring frost and freeze damage to the crop. ‘Vernon’ is another early-season cultivar that has not been evaluated for production in Alabama conditions. ‘Ochlockonee’ is reported to mature about a week after ‘Tifblue’ and can extend the harvest season. These blueberry cultivars with improved quality traits have not been previously tested for their performance in Alabama conditions where the interest of blueberry production is currently increasing. Thus, an experimental plot was established to evaluate cultivar vegetative growth, production potential and fruit quality characteristics in order to develop cultivar recommendations to specialty crop producers in the Southeast. Traditionally grown cultivars such as the early season ‘Climax’, ‘Premier’, and the late ripening ‘Powderblue’ and ‘Tifblue’ were included as controls.


Figure 1: Newly released rabbiteye blueberry cultivars ‘Titan’, ‘Krewer’, and ‘Pink Lemonade’ with improved characteristics grown at the CREC, Alabama, 2021.

A: ‘Titan’
B: ‘Krewer’
C: ‘Newly ‘Pink Lemonade’

Results

The above mentioned newly released and established blueberry cultivars were planted as a randomized complete block design experiment with 4 single plant replications at the Chilton Research and Extension Center (CREC), Clanton in Central Alabama. Each cultivar had a single plant on each of the four rows in the experiment. Data to determine each cultivar bud break and flowering phenology were collected periodically starting in January 2022 until mid-March. A late spring freeze event occurred on March 12-13 when temperatures fall to 24 degrees F. Row covers (Figure 2) were used to protect the experimental bushes every time critically low temperatures were expected starting as early as January 2022 until last freeze in mid-March. The early row cover application was due to the fact that low chill cultivars such as ‘Krewer’ and ‘Pink Lemonade’ had fulfilled their chill requirements at the end of December and had some open flowers in early January (Figure 3).

Row covers used to protect the blueberry cultivar experiment at the CREC, AL during January-March 2022
Figure 2. Row covers used to protect the blueberry cultivar experiment at the CREC, AL during January-March 2022.

Application of row covers increased the temperature under the cover by as much as 8°F and successfully protected the plants through mid-March when the strong winds of over 35 miles/hr. blew away the row covers from two of the experimental rows (half of the experiment) and exposed the plants to the freezing temperatures. At this time the blueberry cultivars had between 20% (‘Tifblue’), and 100% (‘Krewer’) open flowers due to the warming trend in the beginning of March. Since blueberry plants can tolerate temperatures of 23-24°F during the early pink bud stage, but are susceptible to cold injury at 28°F at the full bloom stage, all cultivars sustained cold injury and the most advanced blueberries had a complete crop lost, especially on the two rows where the wind damage caused the row covers to be removed from the plants (Figures 3, 4, and 5).

'Krewer' rabbiteye bush flowering stage on January 11, 2022, CREC, AL
Figure 3-A: ‘Krewer’ rabbiteye bush flowering stage on January 11, 2022, CREC, AL.
‘Climax’ rabbiteye bush flowering stage on January 11, 2022, CREC, AL
Figure 3-B: ‘Climax’ rabbiteye bush flowering stage on January 11, 2022, CREC, AL.
Figure 4. Phenogram of flowering (percent open flowers) of selected rabbiteye blueberry cultivars grown at the CREC, AL, 2022.
Figure 4. Phenogram of flowering (percent open flowers) of selected rabbiteye blueberry cultivars grown at the CREC, AL, 2022.
Figure 5-A. Cold damage to uncovered ‘Krewer’ rabbiteye blueberry plants after the freeze event on the evening of March 12, 2022.
Figure 5-A. Cold damage to uncovered ‘Krewer’ rabbiteye blueberry plants after the freeze event on the evening of March 12, 2022.
Figure 5-B. Cold damage to row covered ‘Krewer’ rabbiteye blueberry plants after the freeze event on the evening of March 12, 2022.
Figure 6. Percent cold damaged flowers for selected blueberry cultivars based on row cover protection after the March 12 freeze event, 2022.
Figure 6. Percent cold damaged flowers for selected blueberry cultivars based on row cover protection after the March 12 freeze event, 2022.

Visual rating of the degree of cold injury was conducted for each blueberry plant shortly after the freeze event on March 12. The results (Figure 6) suggest the two covered rows had between 20 and 90% damaged flowers, while the damage on uncovered/unprotected rows representing the other half of the experimental plants varied between 85 and 100%.


Table 1. Yield and fruit quality attributes at each harvest period of selected rabbiteye blueberry cultivars grown in Central Alabama CREC, 2022.

Yield, g/plant

Cultivar7-Jun14-Jun23-Jun
Alapaha92.0123.012.0
Climax33.568.032.0
Krewer133.0156.037.0
Vernon427.3143.3129.0
Titan110.3116.0
Tifblue194.0226.0
Ocholocknee139.0188.0
Powderblue83.095.5
Premier56.0

Berry wt, g

Cultivar7-Jun14-Jun23-Jun
Alapaha2.21.61.2
Climax2.32.11.8
Krewer4.03.32.3
Vernon3.01.92.4
Titan4.53.5
Tifblue1.41.7
Ocholocknee2.32.3
Powderblue1.41.8
Premier1.6

°Brix

Cultivar7-Jun14-Jun23-Jun
Alapaha14.915.514.4
Climax16.116.118.7
Krewer14.815.116.4
Vernon14.914.415.5
Titan12.116.6
Tifblue13.516.1
Ocholocknee13.215.9
Powderblue14.315.5
Premier15.5

Season of ripening and the number of harvests were recorded on bushes with some fruit produced. First blueberry harvest occurred on June 7, followed by harvesting on June 14 and 23rd, 2022. Individual harvest yield was measured for each bush (Table 1). To determine fruit quality characteristics, a 10-berry sample was collected at each harvest event when berry size and SSC were measured. Due to the spring freeze crop loss, no sufficient berry samples were available to measure berry pH, total phenolic, total sugar, glucose, fructose, and total acids.


Figure 7. Total yield/plant (g) of selected blueberry cultivars grown at the CREC, AL, 2022.

Our results for total yield/plant (Figure 7) suggest ‘Vernon’ produced the highest yield of 699.3 g/plant (mainly the protected bushed produced fruit), while no crop was harvested from any of the ‘Pink Lemonade’ plants.


Table 2. Fruit quality attributes of selected rabbiteye blueberry cultivars grown in Central Alabama CREC, 2022.

Mean berry weight, g°Brix
Alapaha2.015.5
Climax2.116.5
Krewer3.515.2
Ochlocknee2.315.0
Powderblue1.715.3
Premier1.615.5
Tifblue1.615.3
Titan4.014.4
Vernon2.515.0

Due to the significant freeze, crop loss fruit quality attributes were determined on a small berry sample (10 fruit) and should be considered with caution. The results on seasonal mean berry weight and total soluble solids expressed as degree Brix are presented in Table 2. ‘Titan’ berries were the largest (4.0g) among all cultivars tested and were followed by ‘Krewer’ fruit with an average size of 3.5g. ‘Climax’ berries were the sweetest during 2022 season, but all blueberry cultivars produced crop with relatively sweeter fruit, likely an effect of the low crop load.