THE PRODUCTIVITY OF SOME BLUEBERRY CULTIVARS UNDER ESTONIAN CONDITIONS

Abstract

Success in the cultivation of half-high and lowbush blueberry has been achieved in Estonia. The objective of the experiment was to evaluate highbush blueberry (Vaccinium corymbosum L.) cultivation possibilities in northern conditions. The field trial with 15 highbush blueberry and three half-high blueberry cultivars was established in South Estonia (58°21' N, 26°31' E) in 2003. To select cultivars for experiment we took into consideration the winter hardiness of plants and harvest season of berries. The experimental plantation produced its first yield in 2007 and current data are based on this year. In 2007, ‘Blue Rose’, ‘Bluegold’, ‘Bruni’, ‘Caroline Blue’, ‘Chandler’, ‘Denise Blue’, ‘Nui’ and ‘Reka’ had more winter damage. The blueberry plants of all cultivars had winter damage, but none of the plants died for that reason. ‘Blue Rose’ and ‘Nui’ had smaller plants. The yields of highbush blueberries ‘Bluecrop’, ‘Denise Blue’ and ‘Hardyblue’ were the highest. The berry weight ranged from 1.1 to 4.2 g. ‘Bruni’ and ’Nui’ had the largest berries. The harvest season of ‘Caroline Blue’ was very late; therefore, some berries did not ripen. Results showed that highbush blueberry grew satisfactorily in Estonian conditions and we can recommend all of these cultivars for the home garden. ‘Bluecrop’, ‘Denise Blue’, ‘Hardyblue’ (syn. 1613A), ‘Olympia’ and ‘Reka’ are more suitable for commercial cultivation. INTRODUCTION About 10% of the world blueberry production area was situated in Europe in 2003. An estimated, 1,100 ha were situated in Poland, 1,350 ha in Germany, 410 ha in France, 300 ha in The Netherlands, 250 ha in Spain and Portugal, 65 ha in Italy and 15 ha in the United Kingdom (Strik, 2005). In northern Europe, several field experiments with blueberries have been carried out (Vestrheim et al., 1997; Heiberg and Stubhaug, 2006), also some greenhouse experiments have been conducted in Norway (Heiberg and Lunde, 2006). Research into possibilities for cultivating highbush blueberries have also been started in Latvia (Abolins and Gurtaja, 2006). In Finland, attention has been mainly paid to cultivation and breeding of half-high blueberries (Lehmushovi and Ylamaki, 1994; Hiirsalmi, 1989). The experimental work with blueberries in the department of Horticulture at the Estonian Agricultural University began in 1997. Experiments have shown that due to good winter resistance, lowbush and half-high blueberries could be prospective berry cultivars in Estonia (Starast et al., 1999; Karp et al., 2000). Highbush blueberries have higher yields than lowbush blueberries; in field conditions lowbush blueberries usually give 1.8 t ha, while highbush blueberries may yield at least 4.5 to 5.5 tons of berries per hectare. The berry weight of highbush blueberries may reach 3 to 4 g, whereas berry weight of lowbush blueberries is usually less than 1 g (Hancock and Draper, 1989). Since previous experiments with other blueberry species were successful, we presumed that northern highbush cultivars may possibly grow in Estonia. The objective of the experiment was to evaluate highbush blueberry (Vaccinium corymbosum L.) marge.starast@emu.ee Proc. IX IS on Vaccinium Eds.: K.E. Hummer et al. Acta Hort. 810, ISHS 2009 104 cultivation possibilities in northern conditions. MATERIALS AND METHODS The experiment was situated in South Estonia (58°21’ N, 26°31’ E) at the Research Centre of Estonian University of Life Sciences. Soil in the experimental area was sandy loam. The experimental plantation was established in 2003. Plant to plant spacing was 1.0 m and space between the rows was 2.5 m. Pine bark mulch was used in between the plants and turfgrass in between the rows. For each cultivar, five plants in each of four replications were planted randomly. The following cultivars were used in the experiment: half-high cultivars, ‘Northblue’ (control), ‘Northland’; lowbush cultivar, ‘Putte’; and highbush cultivars, ‘Ama’, ‘Blue Rose’, ‘Bluecrop’, ‘Bluegold, ‘Bluejay’, ‘Bruni’, ‘Caroline Blue’, ‘Chandler’, ‘Denise Blue’, ‘Hardyblue’ (syn. 1613A), ‘Nui’, ‘Olympia’, ‘Puru’, ‘Reka’ and ‘Toro’. In 2007 plants were fertilized by irrigation using Kemira blueberry fertilizer (7-3-18 + micronutrients), 0.8% solution. Plants were fertilized on 18 May, 29 May and 8 June. Winter damage was estimated at the beginning of the vegetative growth period on 15 May, 2007. A 9-point scale was used, where 1 = no damage; 9 = whole plant damaged (plant dieback to the soil level). The height of the bush (cm) was measured from the highest point of the plant. The width of the bush was measured along and across the row, and the average width of the plant was calculated. Plant height:width ratio was calculated in order to compare growth habit differences. The number of long shoots (more than 15 cm) was counted per each bush. Plants were measured at the end of the vegetation period on 13 September. At this time it was also estimated to what extent plants had finished their growth. This was done using a 9-point scale, where 1 = plant completely green and continuing to grow; 9 = growth completely finished, leaves yellow and dropped. Plants were harvested on 16 and 24 July, 1, 9, 16, 23 and 29 August, and 6 and 12 September. Yield from each plant was harvested separately. To find the berry weight (g), 10 fruits from each of four replications were picked, weighed, and the average calculated. Berry length (mm) (from stem to calyx end) and berry diameter (mm) (from side to side) of 10 fruits in four replications was measured with digital caliper. To detect differences in fruit shape berry, length:diameter ratio was calculated. Data were analyzed by one-way ANOVA table. The least significant difference (LSD) at the 95% confidence level was calculated. Significantly different values from control (‘Northblue’) are typed in bold letters in tables. In order to find correlations between different parameters, correlation coefficient (r) was calculated. RESULTS Winter damage was detected in all cultivars (Table 1). Winter damage ratings in ‘Northblue’ averaged 2.3 points. Compared to the control, ‘Blue Rose’, ‘Bluecrop’, ‘Bluegold’, ‘Bruni’, ‘Caroline Blue’, ‘Chandler’, ‘Denise Blue’, ‘Northland’, ‘Nui’, ‘Olympia’, ‘Reka’ and ‘Toro’ showed significantly more winter injury. Conversely, ‘Ama’, ‘Bluejay’, ‘Hardyblue’, ‘Puru’ and ‘Putte’ were as hardy the half-high ‘Northblue’. The height of the plants ranged from 42 to 80 cm and the width of the plants from 51 to 71 cm (Table 1). Heights of ‘Putte’, ‘Nui’ and ‘Blue Rose’ plants were similar to the height of ‘Northblue’ plants. Plants from other cultivars were significantly taller. ‘Ama’, ‘Bluecrop’, ‘Bluejay’, ‘Denise Blue’, ‘Northland’ and ‘Olympia’ had wider plants than others. The plant height:width ratio showed that growth habit of ‘Ama’, ‘Bluecrop’, ‘Bluegold’, ‘Bluejay’, ‘Bruni’, ‘Caroline Blue’, ‘Chandler’, ‘Hardyblue’, ‘Olympia’, ‘Puru’, ‘Putte’ and ‘Reka’ differed significantly from the control. The vertical growth of shoots was modest, since most of the plants had shoot damage by spring frost and had to be pruned back. The number of shoots per plant ranged from 0.9 to 8.8 per plant by autumn (Table 1). ‘Putte’ had the highest number of shoots, ‘Ama’ had a similar number and other cultivars had fewer shoots compared to the control