Blackberry fruit is gaining popularity in the U.S. and overseas. New cultivars have been developed in recent years that provide more options for growers and homeowners alike. Although proven in major blackberry growing regions around the world, these cultivars have not been tested extensively in potential emerging areas. In Oklahoma, some growers noticed that canes were dying with ripening fruit still attached. The fruit would not reach maturity and thus be unharvestable. One potential cause is an unbalanced leaf-to-fruit ratio. In this study, six blackberry cultivars were used to assess the reproductive and vegetative growth ratios. Three plots with three canes per plot were individually harvested, had leaf counts, and leaf area measurements. Leaves were counted on canes in mid-June, during harvest, and mid-July, immediately after the final harvest. ‘Apache’ had the greatest number of leaves per berry in June (2.6) and July (2.0). In June, all other cultivars (Chickasaw, Natchez, Ouachita, Triple Crown, and Tupi) were not significantly different from each other, but ranged from 1.4 to 1.1 leaves per berry. In July, ‘Chickasaw’ was significantly different, having only 0.6 leaves per berry. ‘Natchez’ produced the most berries and the most leaves. These data may help give insight into the phenomenon of premature cane death.
Blackberries are gaining popularity in the U.S. and around the world as a healthy fruit crop. New cultivars provide more growing options for commercial growers and homeowners alike. These new cultivars have been proven in major blackberry growing regions around the world, but in emerging blackberry growing areas they may not have been extensively tested.
In Oklahoma and Mississippi, both states where blackberry production is small, some growers noticed ripening fruit that shriveled while still attached to the cane. This has occurred in other states as well. There was no evidence of usual pests that could cause that condition such as raspberry crown borer, red-necked cane borer, wind damage, etc. One potential theory is that an unbalanced leaf-to-fruit ratio could be to blame.
Fernandez (2012) reported that ‘Natchez’ had lots of red fruit, but few leaves on floricanes, and few primocanes during the 2012 growing season in North Carolina; whereas ‘Ouachita’ had abundant fruit, leaves, and primocanes. Borda (2012) in California also noticed this issue.
Materials and Methods
Six blackberry cultivars were used to assess the reproductive and vegetative growth ratios: ‘Apache’, ‘Chickasaw’, ‘Natchez’, ‘Ouachita’, ‘Triple Crown’, and ‘Tupi’. These were planted in 2009 at the Oklahoma State University Perkins Experiment Station in Perkins, Oklahoma. They were not pruned in the first growing season and the first harvest of any fruit took place in 2010. During the first harvest, noticeable premature fruit shrivel was apparent and it was not attributable to insect, disease, or abiotic causes.
Primocanes were pruned to 42 inches (107 cm) tall in June 2010. Spent floricanes were removed in fall and winter 2010-2011. The laterals on the remaining floricanes were pruned to 15 inches (38 cm). The plants were trellised with floricanes tied up to wires.
Data was taken during the 2011 season. Three plots of each cultivar were sampled, with three canes per plot used for yield, brix, leaf counts, and leaf area. Harvest periods were June 1 to July 15 for ‘Natchez’ and ‘Tupi’, June 8 to July 22 for ‘Chickasaw’, June 13 to July 28 for ‘Ouachita’, and June 20 to July 28 for ‘Apache’ and ‘Triple Crown’. Leaves were counted on canes in mid-June and mid-July. Means were separated by t-test (P<0.05).
‘Natchez’ had the most average leaves per floricane in both June (323) and July (416). ‘Tupi’ had the fewest in June and was equal to ‘Apache’, ‘Chickasaw’, and ‘Triple Crown’ in July (Table 1 and 2).
Table 1. Mid-June leaf number per floricane on 6 different blackberry cultivars.
|Cultivar||Mean # Leaves/Floricane||Mean Separation|
Table 2. Mid-July leaf number per floricane for six blackberry cultivars.
|Cultivar||Mean # Leaves/Floricane||Mean Separation|
‘Natchez’ produced the most berries and ‘Apache’ the fewest (Table 3).
Table 3. Total number of berries produced per floricane on six blackberry cultivars.
|Cultivar||# of berries/floricane||Mean separation|
‘Chickasaw’ had the fewest leaves per berry (0.6) with all others similar (Table 4).
Table 4. Number of leaves per berry for six blackberry cultivars.
The leaf area (cm2) to fruit (g) ration was highest for ‘Ouachita’ and lowest for ‘Chickasaw’, which was not statistically different from ‘Triple Crown’ and ‘Apache’ (Table 5).
Table 5. Leaf area to fruit ratio of six blackberry cultivars.
|Cultivar||cm2 of leaf area/g of fruit (July)||Mean Separation|
Canes with more leaves also produced fruit with higher brix (R2=0.21) (Fig. 1).
Figure 1. Effect of leaf number on fruit sugar content (brix) of six blackberry cultivars.
The issues with the fruit were not seen as prominently in 2011 as compared to 2010. Weather conditions were mild in 2010 when compared to 2011 when severe heat, drought, and cold were all experienced (Table 6).
Table 6. Extreme weather conditions in Oklahoma during 2011 compared to 2010.
|Jan 28||Jan 29||Feb 3||Feb 10||Feb 16||Feb 17|
‘Chickasaw’ had fewer overall leaves but this could have been caused by droughty conditions, suggesting that ‘Chickasaw’ may have a lower drought tolerance than the other cultivars. ‘Natchez’, the cultivar most prominently tied to the condition of on-cane shriveling fruit, did not display these characteristics during 2011.
Other crops have different leaf area to fruit ratios than what was found in this study. Apples are around 3 cm2/g, cherries are 22, grapes 8 to 12, and strawberries 15. From this one year of data, blackberries averaged around 7 cm2/g.
The results from this study lead to other questions that may be asked to fully reach the answer.
- Were the younger root systems not able to support fruit production in 2010?
- Did the fall and winter pruning help to balance the crop load for 2011?
- Did the heavy first year crop seen in 2010 reduce return bloom in 2011?
- Did the extreme weather in early 2011 play a role in reducing the overall crop later in 2011?
Bolda, M. 2012. Pruning of ‘Natchez’ blackberry. Strawberries and Caneberries. University of California Agriculture and Natural Resources blog http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7642
Fernandez, G. 2012. Natchez overcropping? Team Rubus blog. North Carolina State University Extension. http://teamrubus.blogspot.com/2012/06/natchez-overcropping.html
The original abstract for this study was published as noted below:
Stafne, E.T and B. Carroll. 2012. Ratios of Reproductive to Vegetative Growth in Six Blackberry Cultivars. HortScience 47(9):S105 (abstr.).