Insights into the effect of microgravity on phytopathogens and plant-associated microbes

With the evolving circumstances on Earth and the burgeoning scientific interest in space, space exploration is experiencing significant growth. As human presence in space increases, the necessity for cultivating fresh food becomes a critical consideration for astronauts' health and psychological well-being. Consequently, 'space farming' emerges as a vital area of research for the future. However, the conditions in space differ markedly from those on Earth, exposing plants and humans to various abiotic stressors, one of which is microgravity. Microgravity refers to the diminished gravitational force experienced by objects in Low Earth Orbit (LEO). This microgravity stress adversely impacts plant physiology, compromising their immune systems to varying degrees. Despite rigorous sanitation protocols, microbial contamination has been documented aboard the International Space Station (ISS), with some of these microbes identified as plant pathogens, exemplified by the infection of Zinnia hybrida by Fusarium oxysporum. Prior research indicates that the pathogenicity of these plant pathogens is exacerbated under microgravity conditions. Furthermore, microbes may undergo previously unobserved morphological changes, such as the formation of microcolonies in Ulocladium chartarum. Exposure to microgravity also facilitates alterations in the endophytic communities within crops and expands the potential for cross-kingdom interactions, including the stomatal entry of the human pathogen Salmonella species. This review discusses the implications of microgravity on plants, plant pathogens/plant growth-promoting microbes, their interactions with one another and the need for understanding these interactions for future space missions.