ANALYSIS OF CLIMATIC FACTORS IN CONNECTION WITH STRAWBERRY GENERATIVE BUD DEVELOPMENT

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1 AGRICULTURAL SCIENCES (CROP SCIENCES, ANIMAL SCIENCES) ANALYSIS OF CLIMATIC FACTORS IN CONNECTION WITH STRAWBERRY GENERATIVE BUD DEVELOPMENT Ieva Kalniņa 1,, Sarmīte Strautiņa 1 Latvia University of Agriculture Latvia State Institute of Fruit-Growing ieva.kalnina@lvai.lv Abstract Strawberries (Fragaria Ananassa Duch.) are widely grown in Latvia, and it is the first berry crop that ripens in summer. In Latvia, climate conditions are very suitable for strawberry growing. Unfortunately, meteorological conditions have become very changeable in recent years. The short day (SD) strawberry cultivars are the most important ones for Latvia, as they initiate flower buds in autumn. For these cultivars it is important to initiate flower buds at the end of September till the end of October. The day length has to decrease less than 14 hours per day to begin this process. In Latvia, the day length below 14 hours per day is at the end of August. The second important limiting factor for initiation of flower buds is the average day temperature, which must be between 1 and 15 C. The studies on strawberry flower bud initiation in Latvia were done long time ago, on a very small scale and fragmentary. The current paper analyzes the temperature regime during the period of previous ten years (4 13) in autumn in Dobele in relation to suitability of this climatic factor to the flower bud initiation and strawberry yield next year. The soil surface temperatures during the last ten years in August were about + C, which means that the flower bud initiation could not occur as early as it was described in the previous study. Key words: temperature, day length, bud initiation. Introduction June-bearing strawberries (Fragaria Ananassa Duch.) are short-day plants and initiate their flowers in the fall of previous year as day length shortens until hours (Temperate zone., 93). The strong interaction between photoperiod and temperature on flower induction shows that a lower temperature is required to achieve successful induction at longer photoperiod. Moreover, each cultivar has its own specific photoperiod temperature interaction response curve for flower induction (Taylor, ). Only one study was found about strawberry plants flower bud initiation, which was carried out in Latvia 4 years ago by E. Muižarāja (Dūks, ). The research was carried out with cultivars bred in Russia. In this study it was concluded that the strawberry bud initiation for short day (SD) cultivars in weather conditions typical in Latvia for early cultivars begins in mid August but for late cultivars in mid September (Dūks, ). According to research about the Latvian climate change carried out during the period from 5 to 1, an increase in the number of warm nights and a decrease in the number of cold days and nights in the second half of the th century has been observed as well as a slightly increased number of summer days with daily maximum temperatures above 5 C (Avotniece et al., ), which could possibly affect the beginning of buds initiation since the year compared to the -ies when the only study was conducted. Mostly the research on strawberry flower buds initiation had been done under controlled climatic and day conditions (Heide, ; Opstad et al., 11), but only few studies in open field conditions (Opstad et al., 11).were found. The aim of the study was to evaluate the temperature regime from August to October during last ten years for strawberries in the open field to determine the potential of strawberry bud initiation time for short day s varieties. Materials and Methods Materials Soil surface temperature data from 4 till 13 was collected by the meteorological station in Dobele ( Soil surface temperature was recorded every hour, and average soil surface temperature was assessed, as well as determined maximum and minimum soil surface temperatures per decade (October I,II,III) and per month (August, September and October). Soil surface temperature was reviewed for 1-year period, but closer studied data from, when the first strawberry trial in the Latvia State Institute of Fruit-Growing in Dobele was planted. Day length was calculated from data Flower bud initiation was determined from literature studies. Yield per plant (g) was calculated for the cultivar Polka per year at the end of the harvest period. Data were collected for two planting periods and 1. Yield was harvested per two cycles 9-1 and 11-. Statistical analysis Data are expressed as mean ± standard deviation. For the statistical data analysis 95% probability was used to determine the significance of differences. Research for Rural Development 14, volume 1 51

2 Ieva Kalniņa, Sarmīte Strautiņa ANALYSIS OF CLIMATIC FACTORS IN CONNECTION WITH Results and Discussion Studies on the bud initiation for strawberries have not been conducted in Latvia during past 4 years. However, foreign studies have shown that the flower buds can do initiation only when the day length reduces to 14 hours. The day length observations show that the day length in Latvia above 14 hours falls after August 5, and hours achieves on September 5. If the day length achieves 14 hours at the end of August, cultivars flower bud initiation for SD strawberry can start at this time, not as it was mentioned in literature at the beginning of August (Dūks, ). Not only the day length is important to bud initiation, but also the adequate temperature is needed at this time. In contrast to research done by E. Muižarāja (Dūks, ), the flower bud initiation in Latvia can occur in August. The analyses of temperature and day length data shows that it could be impossible, because the day length was longer than 14 hours and average temperature in August was C (Fig. 1.). According to A. Sønsteby and O.M. Heide () and M. J. Verheul et al. (), it is not suitable for the flower bud initiation. Photoperiod and temperature are considered as two the most important environmental factors controlling the transition from vegetative to floral growth (Guttridge, 5; Durner and Poling, ). Greatly varying threshold photoperiods (11 1 h) and temperature (9 5 C) have been reported in various studies (Larson, 94; Taylor, ; Hytönen et al., 4). Temperature is also important for floral initiation under SD conditions. The optimum temperature for SD floral initiation is 15 1 C, while below 1 C and above 5 C SD induction is rather ineffective (Sønsteby and Heide, ). G.M. Darrow and G.F. Waldo (34) described the influence of temperature on flower initiation in strawberry, indicating the potential difficulty in photoperiodic classification of cultivars. Flower induction of SD types can occur under any photoperiod if the temperature is cool enough, generally <15 C (Guttridge, 5). The effects of temperature and photoperiod on flower and inflorescence initiation during the autumn for the strawberry cultivar Elsanta in the research carried out by P. Le Miere et al (9) were investigated. This study shows that photoperiod had no effect on the rate of flower initiation or final flower number in the primary, secondary or tertiary inflorescences. The temperature had a little effect on the final flower number in the primary inflorescence. However, the rate of flower initiation increased linearly with increasing temperature in the secondary and tertiary inflorescences, namely to an optimum of 1. C for the secondary and.9 C for the tertiary inflorescence, and declined at temperatures above these. The data analyses shows that in the years, 11 when autumn periods were relatively very warm, the next year berry yields, namely in 9 and, were much higher (for about 3 5%). The average soil surface temperature at the 1 st decade of October in was 9 C, in 11 it was C (Table). It can be concluded that enough high average air temperatures in October promoted better flower bud initiation in comparison to years when temperatures were lower (Fig.., Table) year average Figure 1. Average soil surface temerature in August years Research for Rural Development 14, volume 1

3 ANALYSIS OF CLIMATIC FACTORS IN CONNECTION WITH Ieva Kalniņa, Sarmīte Strautiņa Figure. Average soil surface temerature in September and October years 4 13: September October Table Temperature influence on the next year s strawberry yield Planting year s of harvesting Yield per plant, g Soil surface temperature in the I decade of October: In, 11 and 13 there were no significant (p>.5) differences in soil surface temperature among years. Data showed that only in October of both I and II decades average soil surface temperatures were similar, 9 C (Table, Fig. 3.). This taken together with a shorter day length may have prolonged bud initiation in the autumn as shown by higher yield next year. In, 11 and 13 were no significant (p>.5) difference between soil surface temperature among years. Description of temperatures in October showed that in the I and II decades average temperatures were similar (9 C) (Table, Fig. 3.). It can prolong bud initiation in the autumn Figure 3. Soil surface temperature decade II of October years 4 13: Average Minimum Maximum 1 Average 1 Minimum 1 Maximum author observation Research for Rural Development 14, volume 1 53

4 Ieva Kalniņa, Sarmīte Strautiņa ANALYSIS OF CLIMATIC FACTORS IN CONNECTION WITH Figure 4. Soil surface temperature decade III of October years 4 13: Average Minimum Maximum 1 Average 1 Minimum 1 Maximum author observation Temperature observations in the third October decade in the period of ten years show that in 4, and 13 temperatures did not decrease below. C. In other years temperature was lower and plant vegetative growth stopped (Fig. 4.). Conclusions 1. Strawberry flower bud initiation during the period of last ten years could not occur in August because of too high temperatures. It could be related to long-term trends in climate changes in Latvia.. According to meteorological observations in Latvia, strawberry bud initiation time could be in September when the day length becomes less than 14 hours, and temperatures are suitable, 1 15 C. 3. In, 11 and 13 average soil surface temperature was more suitable for strawberry bud initiation, because average temperature was above1 C till the beginning of October. References 1. Avotniece Z., Klavins M., Rodinovs V. () Changes of Extreme Climate Events in Latvia. Environmental and Climate Technologies, No. 9, pp Darrow G.M., Waldo G.F. (34) Responses of strawberry varieties and species to duration of the daily light period. United States Department of Agriculture Technical Bulletin, 453 p. 3. Durner E.F., Poling E.B. () Strawberry developmental response to photoperiod and temperature: a review, Advances in Strawberry Production., pp Dūks V. () Zemenes (Strawberries). Liesma, Rīga, 1. lpp. (in Latvian). 5. Guttridge G.C. (5) In Fragaria ananassa Duch., CRC handbook of flowering, 3 rd edition, Halevy A.H. (eds) CRC Press, Boca Raton, Florida, pp Heide O.M. () Photoperiod and temperature interactions in growth and flowering of strawberry, Physiology Plant, 4, pp... Hytönen T., Palonen P., Mouhu K., Junttila O. (4) Crown branching and cropping potential in strawberry (Fragaria ananassa Duch.) can be enhanced by day length treatments. The Journal of Horticultural Science and Biotechnology, 9, pp Larson K.D. (94) Strawberry. In: Schaffer B.and Anderson P.C. (eds) Handbook of environmental physiology of fruit crops. Vol. 1, Temperate Crops. CRC Press, Boca Raton, Florida, pp Le Miere P., Hadley P., Darby J., Battey N.H. (9) The Effect of Temperature and Photoperiod on the Rate of Flower Initiation and the Onset of Dormancy in The strawberry (Fragaria Ananassa Duch), The Journal of Horticultural Science and Biotechnology, Vol. 1, No: 3, pp Opstad N., Sønsteby A., Myrheim U., Heide O.M. (11) Seasonal timing of floral initiation in strawberry: Effects of cultivar and geographic location. Scientia Horticulturae, 9/1, pp Sønsteby A, Heide O.M. () Dormancy relations and flowering of the strawberry cultivars Korona and Elsanta as influenced by photoperiod and temperature. Scientia Horticulturae, 11, pp Research for Rural Development 14, volume 1

5 ANALYSIS OF CLIMATIC FACTORS IN CONNECTION WITH Ieva Kalniņa, Sarmīte Strautiņa. Taylor D.R. () The physiology of flowering in strawberry. In: Hietaranta T., Linna M.-M., Palonen P., Parikka P. (eds) The IV International Strawberry Symposium, Tampere, Finland, pp Temperate-zone pomology. Physiology and Culture. Third edition (93) Westwood M.N. (ed). Timber Press Portland, Oregon, pp Verheul M.J., Sønsteby A., Grimstad S.O. () Influences of day and night temperature on flowering of Fragaria ananassa Duch. cv. Korona and Elsanta. Scientia Horticulturae, 1, pp.. Research for Rural Development 14, volume 1 55