Heat Stress in Strawberry Production: Effects, Cultivar Variability, and Solutions

Co-author: Ishaya Gadzama

Summary

Heat stress is a significant challenge in strawberry production, impacting various aspects of plant growth, development, and fruit quality. High temperatures, generally above 30°C (86°F), can reduce yields, fruit size, and overall plant health. Understanding the mechanisms of heat stress and implementing effective mitigation strategies are critical for sustainable strawberry production. This article reviews the impact of heat stress on strawberry plants, exploring its effects on various physiological processes, gene expression, and fruit quality. 

Introduction 

Strawberry (Fragaria × ananassa) production faces numerous challenges, with heat stress emerging as a significant factor that can negatively impact      vegetative growth and fruit quality (Kadir et al., 2006). High temperatures, especially those above 30°C (86°F), are common during the growing season (Sorkel et al., 2006) and are particularly detrimental for strawberries, which are typically grown in temperate climates with ideal temperatures between 18 and 26°C (64.4 to 78.8°F) (Strik, 1985). The challenge is exacerbated by climate change and global warming, which are causing an increase in average temperatures worldwide, along with more frequent and intense heat waves. 

Heat treatment, while a well-established method for eliminating systemic infections in plants, can also cause adverse effects on plant health. A key challenge in employing heat treatment is identifying temperatures that can kill pathogens without harming the plant. High temperatures not only affect growth and yield but also negatively impact plant reproductive development, reducing fruit size and weight. Specifically, high air temperatures for strawberries     , especially in early spring, can negatively affect fruit coloration, causing inferior fruit color (Fushihara and Takao, 1991). This makes understanding how strawberry plants respond to heat stress critical for developing effective strategies to reduce its adverse effects. 

Researchers are exploring lower-temperature pre-treatments to induce the heat shock response, which helps protect plants from subsequent higher-temperature treatments (Brown et al., 2016; Dash et al., 2022; Creative BioMart, 2024). Understanding how strawberry plants adapt to heat stress involves examining their complex molecular and physiological responses. A key aspect of this adaptation is the role of heat shock proteins (Creative BioMart, 2024), which help plants tolerate high temperatures. Additionally, the reduction in anthocyanin concentration in strawberries, which affects fruit color and quality, is thought to be controlled by gene expression      in anthocyanin synthesis (Lv et al., 2022). These insights are fundamental for breeding programs focused on developing heat-tolerant strawberry varieties (Brown et al., 2016). Understanding how different strawberry cultivars respond to heat stress is necessary for optimizing crop production in varying climates (Ledesma et al., 2008). Furthermore, it is important to consider the effect of heat stress on stored fruit and how storage temperatures impact fruit quality (Menzel, 2021). Overall, these challenges highlight the need for comprehensive strategies to sustain strawberry production in the face of changing environmental conditions. 

Diversity and Heat Stress Responses of Strawberry Cultivars

Strawberry cultivation involves a wide variety of cultivars, each with unique responses to environmental stressors, especially heat. Understanding these differences is necessary for optimizing crop production across different climates and for breeding resilient varieties. 

'Festival' and 'Ventana'

The cultivars 'Festival' and 'Ventana' are frequently used in studies examining the genetic basis of heat tolerance in strawberries (Brown et al., 2016). 'Festival' demonstrates a higher heat tolerance compared to 'Ventana'. This difference is associated with the differential expression of heat shock proteins (HSPs) and heat shock factors (HSFs). Specifically:

• 'Festival' shows significantly higher up-regulation of five HSPs compared to 'Ventana', including HSP90, HSP70, and three small HSPs (sHSP16, sHSP17.4, and sHSP25.1). These five genes may contribute to the higher heat tolerance in 'Festival'.
• 'Ventana', in contrast, exhibits significantly higher transcript levels of a Class I cytoplasmically localized small HSP gene, sHSP15.96, which may compensate for the lower abundance of other HSPs.

This suggests that different cultivars employ distinct molecular strategies to cope with heat stress, which could be crucial in breeding programs.

'Chandler' and 'Sweet Charlie'

The cultivars 'Chandler' and 'Sweet Charlie' exhibit contrasting physiological responses to high temperatures (Kadir et al., 2006). Key differences include:

• Transpiration Rate: 'Sweet Charlie' shows a negative relationship between transpiration rate and leaf temperature, whereas 'Chandler' does not, suggesting different heat resistance mechanisms.
• Vegetative Growth: The optimal temperature for vegetative growth is 30 °C day/25°C night, as plants maintain the highest total leaf area at this temperature. High temperatures, however, lead to reduced total leaf area, shoot, root, and leaf biomasses. Strawberry roots are more responsive to temperatures above 20°C day/15°C night than shoot growth, with the greatest root growth occurring at 20°C day/15°C night (Kadir et al., 2006).
• Fruit Production: 'Chandler' fruit size and yield are more affected by high temperatures than 'Sweet Charlie'. Chandler's skin redness is temperature-dependent, with the greatest redness at 20°C day/15°C night, while no significant temperature impact on fruit soluble solids concentration (SSC) was observed for either cultivar (Kadir et al., 2006).
• Flower Development: At 30°C day/25°C night, 'Chandler' has a maximum number of open flowers at 2 weeks of exposure, while 'Sweet Charlie' reaches its peak at 1 week. High temperatures (40°C day/35°C night) are most detrimental to flower initiation, with 20/15°C being the least harmful. The effect of 30°C day/25°C night on flower initiation and survival is cultivar-dependent (Kadir et al., 2006). These differences highlight the importance of selecting cultivars based on their regional climate.

'Nyoho' and 'Toyonoka'

The cultivars 'Nyoho' and 'Toyonoka' demonstrate contrasting responses in their reproductive development under high-temperature stress (Ledesma et al., 2008).

• Heat Tolerance: 'Nyoho' maintains a consistent fruit set percentage across different temperature treatments, suggesting a higher degree of heat tolerance compared to 'Toyonoka'.
• Fruit Malformation: There is a higher incidence of fruit malformation in plants grown at 30°C day/25°C night, particularly in 'Toyonoka', which is related to reduced pollen viability and germination.
• HSP Synthesis: 'Nyoho' synthesizes unique heat shock proteins (HSPs) in flowers under heat stress and exhibits a more robust heat shock response, especially in the flowers, compared to 'Toyonoka'. These findings emphasize the need for cultivar-specific strategies for strawberry cultivation under varying climatic conditions.

'Florida Beauty', 'Florida Radiance', and 'Florida127'

The Florida cultivars 'Florida Beauty', 'Florida Radiance', and 'Florida127' show varied responses to heat stress mitigation techniques like white mulch and kaolin applications (Deschamps and Agehara, 2018). 

• 'Florida Beauty' Shows increased early-season yields with early September planting regardless of mulch color, though vigor differed between black and white mulch depending on the season.
• 'Florida Radiance': Exhibits more vegetative growth when planted early, with higher early yields on white mulch in the first season and higher yields on September 20th in the second season. It also has more leaves per plant on white mulch than black mulch, suggesting higher sensitivity to heat stress.
• 'Florida127': Displays increased vegetative growth when planted early, higher runner production on white mulch in September, and larger crown diameters than 'Florida Beauty', with more leaves per plant on both white and black mulches. These results emphasize that cultivars should be chosen based on their responses to specific heat-stress mitigation strategies.

Other Cultivars

• 'Camarosa' was used in a study comparing gradual and shock heat stress, demonstrating that gradual stress leads to higher heat tolerance due to heat-stable protein accumulation (Gulen and Eris, 2003). 
• 'Sachinoka' was used to study the impact of high temperatures on anthocyanin biosynthesis, showing reduced coloration due to suppressed gene expression (Aharoni et al., 2001).
• 'Brilliance', 'Red Rhapsody', 'Scarlet Rose', and 'Sundrench': Studied in subtropical Queensland, revealed that higher temperatures reduce fruit size, which increases harvesting costs and could reduce profits for growers (Menzel, 2021). The findings highlight the need for heat-tolerant cultivars or new management strategies to mitigate the negative impact of global warming on strawberry production.

Conclusion

The detailed analysis of various strawberry cultivars presented in this review reveals a complex interplay between genetics, physiology, and environmental conditions. Different cultivars exhibit varying degrees of heat tolerance and employ distinct mechanisms to cope with high-temperature stress. These studies emphasize the importance of cultivar-specific management strategies and highlight the need for continued research to develop more heat-tolerant and resilient strawberry varieties. Combining this detailed scientific information with practical farming techniques makes it possible to improve strawberry production in the face of increasing global temperatures, ensuring a stable supply of high-quality fruit.

References

• Aharoni, A., De Vos, C. R., Wein, M., Sun, Z., Greco, R., Kroon, A., ... & O'Connell, A. P. (2001). The strawberry FaMYB1 transcription factor suppresses anthocyanin and flavonol accumulation in transgenic tobacco. The Plant Journal, 28(3), 319-332.
• Brown, R., Wang, H., Dennis, M., Slovin, J., & Turechek, W. W. (2016). The Effects of Heat Treatment on the Gene Expression of Several Heat Shock Protein Genes in Two Cultivars of Strawberry. International Journal of Fruit Science, 16(sup1), 239-248. https://doi.org/10.1080/15538362.2016.1199996
• Creative BioMart. (2024). Heat Shock Proteins: The Cellular Guardians. Retrieved from https://www.creativebiomart.net/blog/heat-shock-proteins-the-cellular-guardians/
• Dash, P. K., Chase, C. A., Agehara, S., & Zotarelli, L. (2022). Alleviating heat stress during early-season establishment of containerized strawberry transplants. Journal of Berry Research, 12(1), 19-40. https://doi.org/10.3233/JBR-210702
• Deschamps, S. S., & Agehara, S. (2019). Metalized-striped plastic mulch reduces root-zone temperatures during establishment and increases early-season yields of annual winter strawberry. HortScience, 54(1), 110-116.
• Fushihara, H., & Takao, M. (1991). Studies on inferior color of strawberry fruit. (2) Effects of air temperature and air humidity on the occurrence of inferior-color fruit. Bulletin of Fukuoka Agricultural Research Center B, 11, 1-4.
• Gulen, H., & Eris, A. (2003). Some physiological changes in strawberry (Fragaria× ananassa ‘Camarosa’) plants under heat stress. The Journal of Horticultural Science and Biotechnology, 78(6), 894-898.
• Kadir, S., Sidhu, G., & Al-Khatib, K. (2006). Strawberry (Fragaria xananassa Duch.) growth and productivity as affected by temperature. HortScience, 41(6), 1423.
• Ledesma, N. A., Nakata, M., & Sugiyama, N. (2008). Effect of high temperature stress on the reproductive growth of strawberry cvs.‘Nyoho’and ‘Toyonoka’. Scientia Horticulturae, 116(2), 186-193.
• Lv, J., Zheng, T., Song, Z., Pervaiz, T., Dong, T., Zhang, Y., Jia, H., & Fang, J. (2022). Strawberry Proteome Responses to Controlled Hot and Cold Stress Partly Mimic Post-harvest Storage Temperature Effects on Fruit Quality. Frontiers in Nutrition, 8, 812666. https://doi.org/10.3389/fnut.2021.812666
• Menzel, C. (2021). Higher temperatures decrease fruit size in strawberry growing in the subtropics. Horticulturae, 7(2), 34.
• Kadir, S., Sidhu, G., & Al-Khatib, K. (2006). Strawberry (Fragaria xananassa Duch.) growth and productivity as affected by temperature. HortScience, 41(6), 1423.
• Strik, B. C. (1985). Flower bud initiation in strawberry cultivars. Fruit Varieties Journal, 39(1), 5-9.

Further reading

• 10 Health Benefits of Strawberries
• 15 Interesting facts about strawberries
• History, Global Production, and Key Varieties of Strawberries
• How to Grow Strawberries in Your Garden or Balcony
• Strawberry Soil Requirements, Cultivation Systems, and Plant Density
• How and Why to cultivate Strawberries in a Hydroponic system
• Strawberry Propagation Methods
• When and How to Irrigate Strawberries
• Heat Stress in Strawberry Production: Effects, Cultivar Variability, and Solutions
• How to Fertilize Strawberry Plants
• How to Prune Strawberries
• The Most Important Strawberry Pests & Diseases and Management Strategies
• Strawberry Yield, Harvest, and Storage