In subtropical or tropical conditions, the insufficient winter chill accumulation is often a limiting factor to break the dormancy of temperate-climate species such as the blackberry, which requires using products to help break dormancy. This study evaluates the efficacy of compounds in breaking dormancy of blackberry and its consequent influence on phenology and crop yields. The experiment was conducted in S ?o Manuel, State of S ?o Paulo, Brazil, in the 2011/2012 production cycle. The plants used were two-year-old “Tupy” blackberry ( Rubus spp.), with 0.6 × 4.0 m spacing (4.166 plants·ha -1). Pruning was performed in August, followed by the application of these treatments: control (water); hydrogen cyanamide (Dormex ?); nitrogen fertilizer (Erger ?) and mineral oil (Assist ?). The concentrations of each compound used were: 2.0%, 4.0%, 6.0% and 8.0%. The compounds used influenced the budding, flowering and fruit harvest stages, in addition to providing increased yields depending on the concentration used. For hydrogen cyanamide the recommended concentration is of 4.2% and 5.4% for nitrogen fertilizer; doses above these concentrations may cause phytotoxic effects. For mineral oil the dose recommended is of 8.0%.
The increase of cultivated areas and the production of temperate fruits have grown in Brazil. On account of the high market prices, health benefits and high antioxidant content of this fruit, the cultivation of blackberry has caught the interest of both producers and consumers in recent years [
One of the obstacles to the advancement of these temperate fruits in subtropical and tropical climate regions regards the insufficient chilling hours. However, rustic varieties of peach, plum, pear, persimmon, fig and loquat have been successfully grown in warmer regions, with heat indices ranging between 40 and 80 hours (NHF < 7˚C) or 600 and 800 hours (NHF < 13˚C) in the state of São Paulo [
According to Takeda [
The natural break of dormancy of temperate species, such as blackberry, involves internal factors such as the balance between growth promoters and inhibitors, and external factors such as temperature, photoperiod, solar radiation, and other factors [
Among the plant growth regulators to stimulate and standardize the budding and flowering of temperate- climate species, hydrogen cyanamide is one of the most widely used due to its high efficiency. Although this product is extremely effective for breaking dormancy of fruit plants, it is highly toxic and hazardous to the workers exposed to this substance, and a series of safety measures should be taken when applying this product. The U.S. Environmental Protection Agency (EPA) classifies Dormex® (490 g・L−1 of H2CN2) at the highest toxicity category (category I). This high toxicity risk due to exposure to hydrogen cyanamide resulted in the temporary suspension of sales of the commercial product Dormex® in 2002 in Italy, and a regulatory review by European Union authorities [
According to Pérez [
The experiment was conducted at the São Manuel Experimental Farm, UNESP State University, Faculty of Agricultural Sciences, in the municipality of São Manuel, State of São Paulo, Brazil, SP, situated at 22˚44'28"S and 48˚34'37"W, 740 m of altitude. According to the Köppen methodology the climate is Cfa (subtropical), with an average temperature above 22˚C in the warmest month, small water deficiency in the months of April, July, and August, with annual potential evapotranspiration of 994.21 mm, of which 33% was concentrated in the summer [
The two-year-old “Tupy” blackberry plants used were grown in a non-irrigated experimental area, conducted on four rods using the T trellis system, with 4 wires, and 1.2 m in height. The spacing used was 0.6 m between plants × 4.0 m rows (4.166 plants・ha−1).
The experimental design used was a 3 × 5 factorial scheme consisting of four compounds (Hydrogen Cyanamide, Nitrogen Fertilizer and Mineral Oil) in five concentrations (control, 2.0%, 4.0%, 6.0% and 8 0%) in 4 replicates in blocks, with the experimental plot consisting of five plants.
The commercial brands and the composition of each compound were as follows: Dormex®: hydrogen cyanamide (490 g∙L−1 H2CN2); Erger® (monosaccharides and polysaccharides, 15% total nitrogen, 5.8% nitric nitrogen, 3.1% ammonia nitrogen, 6.1% amidic nitrogen and 6.5% calcium oxide, accompanied by 7% calcium sulfate) and Assist® (mineral oil 756 g∙L−1).
The nitrogen fertilizer doses were composed of nitrogen fertilizer and calcium nitrate in their respective concentrations: control (water), 2.0% nitrogen fertilizer + 2.0% calcium nitrate, 4.0% nitrogen fertilizer + 4.0% calcium nitrate, 6.0% nitrogen fertilizer + 6.0% calcium nitrate and 8.0% nitrogen fertilizer + 8.0% calcium nitrate.
After pruning, on 08/17/2011, an average 250 mL of solution per plant were used in the application of different compounds to promote the breaking dormancy, which were painted one by one to prevent the solution from drifting.
The phenological phases were identified based on budding and flowering onset, respectively, 5% of vegetative buds were in the green tip stage and 5% were open and producing flowering. The full budding and full bloom, respectively, when 50% or more of the vegetative buds were in the green tip stage, and when 50% of flowering buds were open. The end of each phenological stage was determined when there was no budding and vegetative buds or open flowers. The buds were counted in two stems of each plant, previously marked. The sprouting percentage was obtained using the following formula:
The yield was determined by the kilos of fruit produced per plant and the stand of 4.166 pl∙ha−1.
The data were subjected to analysis of variance using the SAS Program SAS (1999). The average results of the different compounds were compared by the Tukey test at 5% probability, and the polynomial regression analysis was performed for the concentrations of each compound.
At pruning-date (08/17/2011), the sum of the number of chilling hours below 7.2 and 13˚C recorded in São Manuel―SP was 51.91 and 347.83 hours (
The plants treated with hydrogen cyanamide started sprouting 15 days after breaking dormancy, and 22 days after with foliar nitrogen fertilizer, regardless of the dose applied (
The flowering and harvesting peaks of plants treated with hydrogen cyanamide occurred, respectively, at 63 and 91 days after breaking dormancy, anticipating by 22 days the flowering peak and 52 days the harvest peak, compared with the control, independent of the concentration used (
In plants treated with foliar nitrogen fertilizer (Erger®) the flowering peaks and harvest occurred, respectively, at 70 and 99 days after breaking dormancy, anticipating by 15 days the flowering peak and 44 days the harvest peak, compared with the control, independent of the concentration used. The mineral oil at concentrations of 6.0% and 8.0% provided higher anticipation of flowering and harvest peaks, when compared with the control (
As for the harvest period, hydrogen cyanamide and nitrogen fertilizer were the most effective to standardize the collection period, reducing its interval from 74 to 50 days with cyanamide applied at 4.0%; 6.0% and 8.0% and from 74 to 50 days with nitrogen fertilizer applied at 8.0% and 6.0% (
The results presented in this study are in agreement with Antunes [
Months | Chill hours accumulated | Temperatures (˚C) | Rainfall (mm) | |||
---|---|---|---|---|---|---|
<7.2˚C | <13˚C | Minimum | Maximum | Averages | ||
January | 0.00 | 0.00 | 21.34 | 32.34 | 25.94 | 329.0 |
February | 0.00 | 0.00 | 21.40 | 32.74 | 26.17 | 289.0 |
March | 0.00 | 0.00 | 20.41 | 28.47 | 23.89 | 129.5 |
April | 0.00 | 0.00 | 19.59 | 29.56 | 23.76 | 43.5 |
May | 0.00 | 29.58 | 16.58 | 25.88 | 20.17 | 20.0 |
June | 39.58 | 156.58 | 14.91 | 24.42 | 18.67 | 50.0 |
July | 0.00 | 60.42 | 16.78 | 27.31 | 21.20 | 0.0 |
August | 12.33 | 101.25 | 16.63 | 28.70 | 21.79 | 4.0 |
September | 0.00 | 32.17 | 16.50 | 31.05 | 22.25 | 0.0 |
October | 0.00 | 147.08 | 18.48 | 29.53 | 23.05 | 16.5 |
November | 11.08 | 55.50 | 20.50 | 20.68 | 20.59 | 47.0 |
December | 0.00 | 0.00 | 22.46 | 22.66 | 22.56 | 121.0 |
Data collected at the São Manuel experimental farm―SP, 2011.
Treatments | Budding (days after pruning) | Flowering (days after pruning) | Harvest (days after pruning) | Harvest time | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Hydrogen cyanamide | Begin | Peak | End | Begin | Peak | End | Begin | Peak | End | (Days) |
Control | 36 | 56 | 69 | 59 | 85 | 121 | 99 | 143 | 163 | 74 |
2.0% | 15 | 36 | 49 | 45 | 63 | 91 | 76 | 91 | 143 | 71 |
4.0% | 15 | 36 | 49 | 45 | 63 | 91 | 76 | 91 | 123 | 50 |
6.0% | 15 | 36 | 49 | 45 | 63 | 91 | 76 | 91 | 123 | 50 |
8.0% | 15 | 36 | 49 | 45 | 63 | 91 | 76 | 91 | 123 | 50 |
Foliar nitrogen fertilizer | Onset | Peak | End | Onset | Peak | End | Onset | Peak | End | (Dias) |
Control | 36 | 56 | 69 | 59 | 85 | 125 | 99 | 143 | 163 | 74 |
2.0% | 22 | 36 | 49 | 45 | 70 | 91 | 85 | 99 | 143 | 71 |
4.0% | 22 | 36 | 49 | 45 | 70 | 91 | 76 | 99 | 123 | 71 |
6.0% | 22 | 36 | 49 | 45 | 70 | 91 | 76 | 99 | 123 | 50 |
8.0% | 22 | 36 | 49 | 45 | 70 | 91 | 76 | 99 | 123 | 50 |
Mineral oil | Onset | Peak | End | Onset | Peak | End | Onset | Peak | End | (Dias) |
Control | 36 | 56 | 69 | 59 | 85 | 125 | 99 | 143 | 163 | 74 |
2.0% | 36 | 56 | 69 | 59 | 85 | 125 | 81 | 143 | 163 | 71 |
4.0% | 29 | 56 | 69 | 59 | 85 | 125 | 80 | 143 | 163 | 71 |
6.0% | 22 | 36 | 49 | 49 | 76 | 104 | 80 | 102 | 143 | 71 |
8.0% | 22 | 36 | 49 | 49 | 76 | 104 | 80 | 102 | 143 | 71 |
Mean values, based on the experimental design proposed in this paper.
With the increasing concentrations of hydrogen cyanamide and nitrogen fertilizer there was a quadratic increase in the percentage of sprouting buds, with maximum points, respectively, of 4.4% (93.1% sprouted buds) and 6.8% (92.4% sprouted buds). It was found that concentrations above 4.4% and 6.8% reduced the percentage of sprouted buds, which could indicate phytotoxic effect of very high concentrations of CH2N2 and nitrogen fertilizer (
The results of this study highlight the need for using compounds to break dormancy of the “Tupy” blackberry cultivated in subtropical region and agree with reports found in the literature for temperate fruit trees grown in areas with low occurrences of cold temperatures.
In “Eva” apple trees an increase in budding percentages was observed up to a certain level, cyanamide at concentrations above 0.50% did not increase the sprouting percentage [
In the “Superior Seedless” grapevines, subjected to 2/3 of cold requirements (300 h below 5.0˚C), the hydrogen cyanamide application at 2.0% provided sprouting of 85% of buds, while the branches that did not receive the compound applications had only 40% of sprouted buds [
The effect of cyanamide on grapevine appears to be associated to respiratory stress conditions under oxygen deprivation conditions, given that soon after the hydrogen cyanamide application the activation of genes related to fermentative pathway was verified, and this indicates that respiratory stress caused by respiration inhibitors can activate the breaking of dormancy [
The linear regression model was adapted to express the increase in the percentage of sprouting buds using mineral oil, and using 8.0% concentration resulted in 79.15% of budding (
For the variables number of fruits per∙plant−1 and yield (t∙ha−1), the quadratic regression models were adapted for the hydrogen cyanamide and nitrogen fertilizer, with maximum points of 4.2% (541 fruits∙pl−1 and 14.7 t∙ha−1) and 5.4% (521 fruits∙pl−1 and 14.2 t∙ha−1) respectively. Higher concentrations than those mentioned above reduced the fruit production per∙plant−1 and hence yields. With hydrogen cyanamide concentrations of 6.0% and 8.0%, the yields were, respectively, 476.6 and 335.5 fruit∙plant−1, and the same nitrogen fertilizer concentrations provided 478.8 fruits and 506 pl−1 respectively, showing a phytotoxic effect from using high concentrations of these compounds (
Several authors have reported a decrease in the number of fruits in temperate-climate fruit trees due to the use of plant growth regulators at high concentrations. For “Imperial Gala” apple trees a dose of 7% of nitrogen fertilizer (Erger®) is recommended because above this threshold a decrease in fruit yields can occur due to phyto-
toxic effects [
The yield values verified in this study are similar to or higher than those found in the literature. Without the compound application the yields ranged from 5.9 to 7.3 t∙ha−1 (controls―0.0% concentration), and with the application the yields ranged from 6.7 to 14.4 t∙ha−1 (2.0% mineral oil and 4.0% hydrogen cyanamide) (
The application of mineral oil at different concentrations influenced the fruit yields per plant and the yields of blackberry, with the concentrations used the linear regression model was adapted, indicating that in the concentrations used, as the concentration is increased there are increased yields, which was the highest yields achieved (12.0 t∙ha−1) when 8% mineral oil was used (
According to Antunes [
Under the conditions of Santa Helena-PR, subtropical climate region (Cfa), similar as in São Manuel, the yields of the “Tupy” blackberry, under different pruning times but without the application of plant growth regulators, ranged from 3.44 to 6.48 t∙ha−1 in 2008 and 0.86 to 6.25 t∙ha−1 in 2009 [
The results presented in this study demonstrate the yield potential of the blackberry in subtropical conditions in the state of São Paulo, as well as the importance of using the adequate compound concentrations for breaking bud dormancy in these regions, since the temperate-climate plants do not have their required temperature fully satisfied, which affects their physiological processes and as a result affects their phenological phases and yields.
For hydrogen cyanamide the dose of 4.2% is recommended and for nitrogen fertilizer of 5.4%, concentrations above these thresholds may have phytotoxic effects, resulting in lower fruit yields. For mineral oil a dose of 8.0% is recommended.
Nitrogen fertilizer showed similar results to hydrogen cyanamide and could be an alternative to this compound, since this product presented low risk to the workers applying this solution.
The use of adequate compounds to break dormancy of blackberry cultivars in areas with insufficient winter cold temperatures improves crop performance and increases yields.
The authors are grateful to FAPESP-State of São Paulo Research Foundation. Process No. 2010/52140-2, and to the agronomist Vitor Hugo Artigiani for kindly providing the Erger® product of Valagro.
Daniela MotaSegantini,SaritaLeonel,Ana Karolina daSilva Ripardo,Marco AntonioTecchio,Manoel Euzebiode Souza, (2015) Breaking Dormancy of “Tupy” Blackberry in Subtropical Conditions. American Journal of Plant Sciences,06,1760-1767. doi: 10.4236/ajps.2015.611176