Extreme weather events, including heat waves caused by large-scale climate change, are one of the major threats to global agricultural production and food security. Since 75% of the world's poor live in rural areas and nearly 50% of people in developing countries depend on agriculture for livelihood, these people are most likely to be severely affected by climate change. The challenge is therefore to create sustainable agricultural production systems through the use of varieties that are more tolerant to heat stress (heat tolerance) than those currently in use. To develop heat-tolerant tomato varieties, JIRCAS is collaborating with the World Veg (World Vegetable Center) to select heat-tolerant tomato varieties from tomato genetic resources and conduct genetic verification and other research.

Tomato (Solanum lycopersicum) is one of the most popular fruit vegetable crops produced worldwide and of great importance to the global economy and food culture. Tomatoes are rich in nutrients such as vitamin C, beta-carotene, and lycopene, which are known to have significant health-promoting effects (Bergougnoux, 2014).
 
Heat stress significantly impacts on tomato growth and fertilization, leading to a decrease in quantity and quality of harvested fruit (Sato et al., 2000). In response to heat stress, morphological and physiological changes in tomatoes vary among entries and accessions, at various growth stages, and during the heat stress period. These changes can be seen not only in vegetative organs such as leaves (Zhou et al., 2017), but also in reproductive organs such as flowers and gametophytes (Firon et al., 2006). Furthermore, changes in flower bud structure, such as stigma exertion, under heat stress conditions are associated with jasmonate signaling and other plant hormone pathways, which are known to reduce fruit set (Pan et al., 2019).
 
As described above, heat stress caused by rising temperatures due to climate change can adversely affect all stages of crop growth. In the case of fruit vegetables such as tomatoes, even moderate heat stress can reduce fruit set and fruit quality. Therefore, increasing crop heat stress tolerance is one of the best ways to adapt to climate change. In a review article recently published in Frontiers in Plant Science, entitled Genetic and molecular mechanisms conferring heat stress tolerance in tomato plants, the authors described the molecular, morphological and physiological mechanisms that contribute to heat stress tolerance, and the challenges in developing heat-tolerant vegetable varieties. Understanding plant tolerance mechanisms to heat stress require an understanding of the tolerance mechanisms at each growth stage and type of heat stress (short or long term). While there are numerous reports on gene regulatory networks for short-term heat stress, which are essential for exerting tolerance mechanisms, there are few reports on long-term heat stress. Considering the need to develop heat-tolerant tomato varieties, it is important to understand how heat stress affects each growth stage and organ, to select genetic resources for screening heat-tolerant materials, and to understand gene regulatory networks. The nutritional and functional properties of vegetables, including tomatoes, are valuable from a global food and nutritional safety assurance perspective. Research on the development of heat stress-tolerant and heat-tolerant vegetable varieties, for which demand is rapidly increasing, is expected to contribute to climate change adaptation and the establishment of sustainable food systems.
 
Utilizing the findings summarized in this review, JIRCAS is promoting research on heat stress tolerance and nutrition using tomato genetic resources, and addressing issues related to climate change and human nutrition in developing countries in Africa and Asia.

References

Bergougnoux, V., 2014. The history of tomato: from domestication to biopharming. Biotechnol. Adv. 32, 170-189. doi: 10.1016/j.biotechadv.2013.11.003

Firon, N., Shaked, R., Peet, M., Pharr, D., Zamski, E., Rosenfeld, K., Althan, L., Pressman, E., 2006. Pollen grains of heat tolerant tomato cultivars retain higher carbohydrate concentration under heat stress conditions. Sci. Hortic. 109, 212-217. doi: 10.1016/j.scienta.2006.03.007

Hoshikawa K, Pham D, Ezura H, Schafleitner R and Nakashima K (2021) Genetic and Molecular Mechanisms Conferring Heat Stress Tolerance in Tomato Plants. Front. Plant Sci. 12:786688. doi: 10.3389/fpls.2021.786688

Pan, C., Yang, D., Zhao, X., Jiao, C., Yan, Y., Lamin‐Samu, A.T., Wang, Q., Xu, X., Fei, Z., Lu, G., 2019. Tomato stigma exsertion induced by high temperature is associated with the jasmonate signalling pathway. Plant, Cell Environ. 42, 1205-1221. doi: 10.1111/pce.13444

Sato, S., Peet, M., Thomas, J., 2000. Physiological factors limit fruit set of tomato (Lycopersicon esculentum Mill.) under chronic, mild heat stress. Plant, Cell Environ. 23, 719-726. doi: 10.1046/j.1365-3040.2000.00589.x

Zhou, R., Kjaer, K., Rosenqvist, E., Yu, X., Wu, Z., Ottosen, C.O., 2017. Physiological response to heat stress during seedling and anthesis stage in tomato genotypes differing in heat tolerance. J. Agron. Crop Sci. 203, 68-80. doi: 10.1111/jac.12166

490. Vegetable Research ― Towards Improving Global Nutrition 

402. Contribution of Fruits and Vegetables to Improved Nutrition and Challenges in the Food System

Fruits and Vegetables – Research and Action Opportunities for Human and Planetary Health 

Photo: Heat tolerant (left) and susceptible (right) tomatoes grown at the World Vegetable Center in Taiwan.

Contributors: HOSHIKAWA Ken (Biological Resources and Post-harvest Division), NAKASHIMA Kazuo (Director, Food Program)