Understanding frost vulnerability in citrus crops: exploring the interplay of plant susceptibility and ice-nucleating bacteria

Abstract

International audienceDespite being mainly cultivated in subtropical and tropical regions, periodic freezing events have historically posed threats to citriculture in more temperate areas, as witnessed in historical events in Florida (1985) and Greece (2004). Global warming has extended the potential growing area including frost exposed area. Citrus sp are not frost-tolerant but are still able to survive mild freezing events by maintaining intracellular water in a supercooled state. This ability could be mitigated by the abundance of ice nucleation agents, among which Ice Nucleation Active (INA) bacteria are a critical factor. Indeed, epiphytic bacteria of the genus Pseudomonas could catalyze ice nucleation above and within plant tissues, increasing the ice nucleation temperature by several degrees. This study aimed to unravel the intricate relationship between plant response to temperature and INA bacteria, shedding light on the multifaceted factors influencing citrus frost damages. Notably, this study explored the susceptibility of evergreen citrus trees to intrinsic ice formation, with a focus on the acclimation to temperature, leaf morphological traits and the abundance of INA bacteria. We determined the relation between temperature and the ability to acclimate and deacclimate, predicting the sensitivity to freezing events. Although a critical threshold of -6°C was identified. Moreover, the presence of nucleating agents above the leaves could alter the pattern of freezing. This research provides crucial insights into the factors affecting Citrus frost vulnerability and contributes to our understanding of how changing climatic conditions may affect citriculture