Research hotspots and frontiers of heat stress in maize

Maize is the largest food crop in the world, and it plays a vital role in maintaining global food security. However, global warming, which has led to frequent high-temperature weather events, has severely limited the growth and yield of maize. Therefore, an in-depth exploration of research hotspots and frontiers in the field of high-temperature stress in maize worldwide will help to cope with the challenges brought about by climate change and promote the sustainable development of maize industry. In this study, CiteSpace software was used to analyze the keyword co-occurrence, clustering, and brust of 4255 papers related to high-temperature stress in maize included in the Web of Science core database from 1990 to 2023. The results showed that the research hotspots mainly focused on four aspects: growth and yield changes, physiological responses, molecular mechanisms, and coping strategies of maize under high-temperature stress. Through an in-depth exploration of the research progress in these four aspects, it was found that high-temperature stress at different growth stages caused different degrees of damage to maize, and the yield reduction ranged from high to low as follows: flowering stage>filling stage>heading stage>seedling stage. High-temperature stress caused changes in multiple physiological and biochemical characteristics of maize, such as impaired photosynthesis, increased biofilm permeability, excessive accumulation of reactive oxygen species, and hormonal imbalance. The molecular mechanism of maize in response to high-temperature stress was mainly on gene expression and heat shock protein operation, but the specific heat tolerance mechanism is still unclear. Through the comprehensive application of agronomic measures and breeding techniques, such as sowing date adjustment, scientific water and fertilizer management, rational application of growth regulators, and cultivation of heat-tolerant varieties, high-temperature stress can be effectively alleviated and a high and stable yield of maize can be obtained. In addition, the transcriptional regulation mechanism of maize in response to high-temperature stress is a current research frontier and will be an important topic for future research. This study comprehensively reviewed the literatures on high-temperature stress in maize in the past 34 years and provides a useful reference for the study of high-temperature resistance of maize and formulation of mitigation measures.