Characterization of drought stress response at early plant development stages in Panicum miliaceum and Pennisetum glaucum

Drought has been the leading cause of yield losses for crop productivity in the last decade, and current climate trends show an increase in the frequency and intensity of drought events for the near future (1). Traditional crops like wheat, rice and maize are unable to ensure productivity while withstanding the effects of drought stress, as it alters the quality of agricultural land and disrupts many key plant metabolic and physiological processes. Millets are promising climate-resilient alternatives to achieve nutritional security in challenging environments. They are a group of small-grain cereals that exhibit agronomic traits suitable for managing drought conditions and many other environmental stresses, such as short life cycles, dense root systems and C4 metabolism (2). Although millets are known to be highly stress-tolerant crops, they remain relatively understudied and underutilized due to the high genotypic variability within species. Consequently, the mechanisms underlying drought tolerance in millets have not yet been fully elucidated. Early growth stages are among the most susceptible to drought stress. During germination, seeds need water to break out of dormancy and reactivate their enzymatic metabolism to allow stored nutrient utilization and embryo development (3). Moreover, this stressful condition requires immediate adaptation by the plant’s root system in order to maintain plant water balance and nutrient acquisition in arid environments. This research aims to identify drought-tolerant and drought-sensitive genotypes of two key and unexplored millet species, namely Pennisetum glaucum and Panicum miliaceum through the identification of early markers of drought tolerance. Six genotypes per species (IP8210, IP8949, IP9406, IP17486, IP4862, IP6769 for Pennisetum glaucum and IPm2758, IPm2784, IPm2621, IPm381, IPm2004, IPm2812 for Panicum miliaceum) were used for the initial screening of tolerance. The seeds were placed on filter paper soaked in water and solutions of increasing concentrations (0%, 10%, 20% and 25%) of PEG-6000 to simulate drought stress. The drought stress response during the early stages (6 days after sowing) of plant development was characterized by evaluating germination rate and root system morphology. The preliminary screening shows a sensitive response to drought stress by some of the tested genotypes, with a decline in germination rate and root system development in increasing stress levels, compared with unstressed controls. Other genotypes have exhibited lower sensitivity, even under severe drought conditions, and therefore have been selected and further characterized through anatomical analyses of the root system. Moreover, the production of reactive oxygen species and their cellular localization in drought-stressed roots were also analysed by fluorescence microscopy. These initial results, combined with quantification of proline content, will provide the necessary information for the identification of early markers of sensitivity or tolerance to water stress in Pennisetum glaucum and Panicum miliaceum genotypes. However, further molecular and biochemical analyses will be needed to confirm the response of these genotypes to water stress. 1) FAO. 2023. The Impact of Disasters on Agriculture and Food Security 2023 – Avoiding and reducing losses through investment in resilience. Rome. https://doi.org/10.4060/cc7900en 2) FAO. (2023). Unleashing the potential of millets – International Year of Millets 2023. Background paper. Rome. https://doi.org/10.4060/cc7484en 3) Ghadirnezhad Shiade, S. R., Fathi, A., Taghavi Ghasemkheili, F., Amiri, E., & Pessarakli, M. (2023). Plants’ responses under drought stress conditions: Effects of strategic management approaches—a review. Journal of Plant Nutrition, 46(9), 2198–2230. https://doi.org/10.1080/01904167.2022.2105720