Everbearing Cultivars Research Articles

Local CO2 Application within Strawberry Plant Canopy Increased Dry Matter Production and Fruit Yield in Summer and Autumn Culture

ABSTRACT June-bearing strawberry cultivars have been widely grown in Japan. Since they are harvested in winter and spring, little produce is available in summer and autumn. To achieve stable year-round supply, we need to expand the production area of ever-bearing cultivars. Here, we examined whether it is possible to increase dry matter (DM) production and fruit yield by increasing the CO2 concentration within the plant canopy through local application to promote photosynthesis in summer and autumn protected culture. We investigated the CO2 concentration in the plant canopy, DM production characteristics, yield characteristics, fruit quality, projected leaf area, cumulative light interception, and light use efficiency. We confirmed that the CO2 concentration within the plant canopy could be increased in summer and autumn (Control; 398 ppm, CO2; 1280 ppm), significantly increasing DM production and total yield (Control; 349 g, CO2; 447.5 g). We consider that local application of CO2 increased the projected leaf area and thus cumulative light interception. This method may help to increase fruit yield in summer and autumn protected culture.

Impact of Nitrate and Ammonium Ratios on Flowering and Asexual Reproduction in the Everbearing Strawberry Cultivar Fragaria × ananassa Albion

Ever-bearing (EB) strawberries are long-day cultivars that show perpetual flowering behavior. Compared to June-bearing short-day cultivars, EB cultivars can initiate flowers with less dependency on light and temperature levels. This leads to a more consistent flowering and fruiting pattern, making EB cultivars favorable for areas with long growing seasons. However, this flowering pattern also brings significant challenges to open-field strawberry nurseries. Consistent flower development in EB cultivars frequently leads to increased labor cost for manual flower removal on nursery ground. The alteration of flowering behavior via fertilizer regimes could be a cost-effective tool for strawberry nurseries. However, while it is known that the source of nitrogen (N) impacts strawberry flowering, its effect on strawberry propagation rates needs further investigation. The objective of this study was to investigate the impact of nitrate (NO3−) to ammonium (NH4+) ratio on flower and daughter plant production in the EB strawberry cultivar ‘Albion’ (Fragaria × ananassa c.v. ‘Albion’). Strawberry plants were grown in a completely randomized design under greenhouse conditions (26.6 °C, 16 h photoperiod). Four treatments of NO3−:NH4+ were implemented: (1) 100%:0%; (2) 80%:20%; (3) 60%:40%; (4) 50%:50%. Strawberry plants fertilized with a 60%:40% NO3−:NH4+ ratio produced 17–31% fewer inflorescences than those fertilized with 100%:0% (8.8 ± 1.19) and 80%:20% (10.3 ± 1.85) ratios. The production of daughter plants remained similar in all four treatments. Our results show that increased ratios of ammonium in combination with decreased ratios of nitrate reduce flowering of EB strawberry cultivars, while propagation rates remain consistent. These results could potentially lead to the development of fertilizer regimes for strawberry nurseries to reduce flower production in EB cultivars.

Environmental regulation of dormancy, flowering and runnering in two genetically distant everbearing strawberry cultivars

The environmental control of dormancy and its relation to flowering and runner formation is poorly understood in everbearing (EB) strawberry cultivars. We studied the topic by growing plants of the seed-propagated F1-hybrid ‘Delizzimo’ and the runner-propagated ‘Favori’ cultivar in daylight phytotron compartments under short day (SD) and long day (LD) conditions at temperatures of 6, 16 or 26 °C for 5 and 10 weeks. This was followed by forcing at 20 °C and 20-h photoperiod for 10 weeks with and without preceding chilling at 2 °C for 6 weeks. The results showed that dormancy in EB strawberry is regulated by a complex interaction of temperature, photoperiod and chilling in much the same way as known for seasonal flowering (SF) cultivars. Surprisingly, the EB cultivars exhibited the same SD dormancy induction response as SF cultivars, despite their opposite photoperiodic flowering requirements. However, at 26 °C the EB cultivars developed partial dormancy also under LD conditions. As known for SF cultivars, none of the EB cultivars became dormant at 6 °C regardless of daylength conditions, whereas they were increasingly sensitive to SD dormancy induction at intermediate and high temperatures. Similar to SF cultivars, the EB cultivars needed exposure to SD and relatively high temperatures for at least 10 weeks for attainment of the semi-dormant state that is typical for strawberry in general. As reported for SF cultivars, there was a close interrelation between the control of flowering, runner formation and dormancy also in the EB cultivars. ‘Favori’ had an obligatory LD requirement for flowering at 26 °C and was almost day neutral at 16 °C, while ‘Delizzimo’ behaved as a quantitative LD plant at both temperatures, and both cultivars were completely day neutral at 6 °C. Except for the stricter LD control of flowering in ‘Favori’, the overall environmental responses were quite similar in the two genetically distant cultivars. Chilling for six weeks at 2 °C was adequate for complete reversal of the constrained elongation of leaf petioles and flower trusses in dormant plants, but had little or no effect on the degree of flowering and runner formation.

Extension of the strawberry (Fragaria×ananassaDuch.) season in Estonia using ever-bearing cultivars and covers during the winter

Extension of the strawberry (<i>Fragaria</i>×<i>ananassa</i>Duch.) season in Estonia using ever-bearing cultivars and covers during the winter

Sugar and organic acid contents of day-neutral and ever-bearing strawberry cultivars in high-elevation for summer and autumn fruit production in Korea

This study was conducted to evaluate the contents of sugars and organic acids in the fruits of day-neutral (DN) and ever-bearing (EB) cultivars grown in high-elevation in Korea. Six DN and five EB cultivars were established in bench-top substrate culture system in high tunnel. Plug transplants were planted on 5 May, 2011 and complete nutrition was supplied during the whole experimentation. Fruit harvest started in early June, and lasted until middle of November. The fruits of DN cultivars showed higher organic acid contents but lower sugar contents and total soluble solids than those of EB cultivars. ‘Albion’ showed the highest contents of total soluble solids and sugars, and sugars/acids ratio among DN cultivars. Among EB cultivars, ‘Goha’ possessed mediate contents of sugars, organic acids and total soluble solid without any extreme weakness in qualities. ‘Charlotte’ showed the highest contents of sugars and total soluble solid, and sugar/acid ratio, and the lowest contents of organic acids; the unique character of ‘Flamenco’ was its lowest contents of organic acids among EB cultivars. Fruit total soluble solid contents, sugars, organic acids, and sugar/acid ratio all significantly varied with the progressive seasons and an interactive effects between cultivars and harvest time on above fruit quality parameters were found. Integrated cultural strategy based on contents of sugars and organic acids was discussed according to fresh consumption and process purposes.

Flowering and fruiting of day-neutral and ever-bearing strawberry cultivars in high-elevation for summer and autumn fruit production in Korea

This study was conducted to evaluate the flowering and fruiting of day-neutral (DN) and ever-bearing (EB) cultivars in high-elevation in Korea. Six DN and five EB cultivars were established in bench-top substrate culture system in high tunnel. Plug transplants were planted on 5 May, 2011 and complete nutrition was supplied during the whole experimentation. Fruit harvest started in early June, and lasted until middle November. Fruit yield was significantly different among DN and EB, and individual cultivars. Generally, summer flower came out earlier and resulted in more summer yield for EB cultivars than for the DN cultivars. However, DN cultivars produced higher autumn yield than EB cultivars. Fruits of DN cultivars showed harder firmness, bigger size, less malformed fruits, deeper surface colors than those of EB cultivars. Fruit surface colors significantly varied with the progressive seasons and an interactive effect between cultivars and harvest time on fruit surface colors was found. Among DN cultivars, ‘San Andreas’ not only showed some typical DN characters such as big fruit and hard firmness, but also showed high values of color parameters. Among EB cultivars, ‘Charlotte’ and ‘Goha’ combination can realize even fruit supply in summer and autumn. Combination of DN cultivar and EN cultivar not only can realize even fruit supply but also can fulfill both fresh consumption and processing purposes in summer and autumn season.

Pre-Harvest Night-Interruption on Everbearing Cultivars in Out-of-Soil Strawberry Cultivation in Belgium

Trials were conducted in 2009 and 2010 to examine the relationship between photoperiod and temperature in commercial production of two everbearing strawberry cultivars. Specifically, two experiments were conducted to determine: 1) the extent of flowering and runnering in the everbearing strawberry cultivar Charlotte as influenced by night-interruption using incandescent lights, or no night-interruption; and 2) the influence of temperature and night-interruption on flowering and runnering of the everbearing cultivar Portola in 2010. The 2009 trial was conducted in a glasshouse, while the 2010 trial was conducted on a table-top system. In both trials, the influence of pre-harvest night-interruption lighting or night-interruption lighting + temperature on fruit yield, cropping pattern, and runnering were investigated. The results demonstrate that use of night-interruption can result in increased fruit production and earlier fruit production of the second fruit cycle and a reduced stolon development for both cultivars. Both cultivars were sensitive to long-day treatments. It appears that an appropriate lighting strategy is required for optimizing yields of everbearing cultivars in Northern European environments.

PERFORMANCE OF EVERBEARING STRAWBERRY CULTIVARS IN A NORDIC CLIMATE

In the Nordic strawberry industry only single-cropping cultivars are used. Several everbearing cultivars have been tried, but neither yield nor quality has been satisfactory. In 2005, new everbearing cultivars were collected and an experiment was established in a polyethylene tunnel. Yield and runnering capacity were recorded in two seasons. The cultivars were the English 'Flamenco' and 'Everest', the Dutch 'Elan' and the Norwegian 'Rita', 'Rondo', 'Ridder' and 'Rosa'. Plug plants were planted in double rows on low ridges mulched with plastic at a plant density equivalent to 50,000 plants per ha. A block design with 20 plants per plot and four replicates was used. The field was harvested two to three times a week during the whole season from June until the beginning of October in both years. Berry size was recorded at all harvests while taste and general performance were evaluated using a scale 1-9. In the first year, the everbearing cultivars had significantly higher yield than the single-cropping cultivars due to more inflorescences, but this was levelled out the second year. While the cropping season of the single-cropping cultivars is only about four weeks, the everbearing cultivars were picked from late June until beginning of October, in both years. The highest yields were obtained by 'Everest' (729 and 844 g) followed by 'Rita' and 'Ridder'. The cultivars 'Elan' and 'Rondo' scored highest both in taste and general performance. 'Everest' also performed well, but flavour was not acceptable.

MANIPULATION OF THE PRODUCTION PATTERN OF EVERBEARING CULTIVARS BY DEFOLIATION TREATMENTS

An experiment was performed in 2003 to determine the effect of defoliating plants on the production pattern of the everbearing cultivar 'Flamenco'. Defoliation was achieved by mowing-off the plants with a strimmer (a mechanical rotary cutter) on three different dates. All leaf material and emerged flowers were removed but the crown was left undamaged. Results showed that the total yield of 'Flamenco' remained largely unaffected in comparison to the non-defoliated control, provided the plants were defoliated before the second half of July. The cropping pattern was shifted so that the peak occurred two weeks later in comparison to the control, filling a trough in production. In a second experiment, in 2005, three defoliation treatments were compared on four everbearing cultivars. The defoliation treatments had no significant effect on the class 1 yield of 'Flamenco' and there was a shift in the peak of production but not as marked as in 2003. With the exception of one defoliation treatment with 'Everest', the overall yields of the other cultivars were significantly reduced. It is clear that everbearing cultivars respond differently to defoliation treatments and it is also likely that the response will vary between seasons, due to different weather patterns. Further studies are needed to determine if this practice would be a useful agronomic tool, particularly for avoiding periods of high temperatures that can reduce flowering in some everbearing cultivars.

Pattern of Growth and Development of the Strawberry Cultivars Elsanta, Bolero, and Everest

The differences in growth and yield in the Junebearing strawberry (Fragaria ×ananassa Duch.) `Elsanta' and the everbearing `Bolero' and `Everest' were evaluated under field conditions. The seasonal patterns of radiation use efficiency and assimilate partitioning were also studied. Growth, development and yield showed considerable differences among cultivars. `Elsanta' showed the highest and `Bolero' and `Everest' the lowest values for almost all the vegetative parameters (leaf area, leaf dry weight, runner number). `Elsanta' produced large leaves and few crowns per plant in contrast to the everbearing cultivars which had more but smaller leaves and a larger number of crowns per plant. The production of flowers by `Elsanta' was concentrated in June with fruit production following in July. `Bolero' and `Everest' produced more than one flush of flowers during the season and fruited until October. As a result, yields of `Bolero' and `Everest' were greater than `Elsanta'. The higher yields of `Bolero' and `Everest' also reflected the greater number of crowns produced by these cultivars. The maximum intercepted and absorbed photosynthetically active radiation (PAR) occurred between July and August when the three cultivars showed the greatest increase in vegetative growth. Harvest index clearly differed among cultivars and this was related to the duration of cropping. The greatest harvest indexes were found for `Bolero' and `Everest'.

Effect of temperature and daylength on flower initiation and runner formation in two everbearing strawberry cultivars

Plants of the everbearing cultivars ‘Revada’ and ‘Rabunda’ were placed at constant temperatures of 14, 20 and 26°C and daylengths of 8, 16 and 24 hours, consisting of 8 hours daylight prolonged with 0, 8 or 16 hours in can descent light, light intensity 0.8 W/m 2 visible radiation. Flower initiation and runner formation occurred irrespective of temperature and daylength. The duration of runner formation depended on temperature and daylength and was longer at 20 and 26°C than at 14°C and longer at 16 and 24 hours than at 8 hours. The results are discussed.