Selected indigenous drought tolerant rhizobium strains as promising biostimulants for common bean in Northern Spain

Abstract

Drought is the most detrimental abiotic stress in agriculture, limiting crop growth and yield and, currently, its risk is increasing due to climate change. Thereby, ensuring food security will be one of the greatest challenges of the agriculture in the nearest future, accordingly it is essential to look for sustainable strategies to cope the negative impact of drought on crops. Inoculation of pulses with biostimulants such as rhizobium strains with high nitrogen fixation efficiency and drought-tolerance, has emerged as a promising and sustainable production strategy. However, some commercial inoculums are not effective under field conditions due to its lower effectiveness against indigenous rhizobium strains in the establishment of the symbiosis. Thus, in the present study, we evaluated the ability to improve drought tolerance in common bean plants of different indigenous rhizobia strains isolated from nearby crop fields in the Basque Country either affected by drought or salinity. The plants in this trial were grown in a climatic chamber under controlled conditions and exposed to values of 30% relative soil water content at the time of harvest, which is considered a severe drought. From the nine bacteria strains evaluated, three were found to be highly efficient under drought (namely 353, A12 and A13). These strains sustained high infectiveness (nodulation capacity) and effectiveness (shoot biomass production) under drought, even surpassing the plants inoculated with the CIAT899 reference strain, as well as the chemically N-fertilized plants. The tolerance mechanisms developed by plants inoculated with 353, A12 and A13 strains were a better adjustment of the cell wall elasticity that prevents mechanical damages in the plasma membrane, a higher WUE and an avoidance of the phenological delay caused by drought, developing a greater number of flowers. These results provide the basis for the development of efficient common bean inoculants able to increase the yield of this crop under drought conditions in the Northern Spain and, thus, to be used as biostimulants. In addition, the use of these efficient nitrogen fixation bacteria strains is a sustainable alternative to chemical fertilization, reducing cost and minimizing its negative impact on environment.

Farm management has a greater impact on common bean rhizobia diversity and abundance than rainfed treatment

“…Similar effects were described in soybean (Sharaf et al, 2019) and common bean (Cytryn et al, 2007). Therefore, the rhizobia isolated in this work, that were able to nodulate under rainfed conditions, are probably efficient inocula under water stress conditions, as was demonstrated with some of them (del-Canto et al 2023). Thus, it would be interesting to test their efficiency under field conditions, following successful formulations such as those described by Pastor-Bueis et al (2019).…”

“…However, the number of nodules gives an idea of the abundance and/ or the viability of the rhizobia present soils, and it has also been stated that more drought-tolerant strains show higher nodulation capacity under drought conditions (Aulakh et al, 2020;del-Canto et al, 2023;Omari et al, 2022).…”

“…In this sense, the establishment of symbiotic relationships with efficient rhizobia can alleviate the effects of stress in legumes (Igiehon et al, 2021;Omari et al 2022;Oviya, 2023). In common bean it has been reported that symbiosis with drought tolerant rhizobia, improves the stress tolerance of the plants against water scarcity, aside from improving legume yield and quality (del-Canto et al, 2023;Rodiño et al 2021;Steiner et al, 2020). In this sense, good results have been obtained by inoculating efficient rhizobia even under field conditions (Pastor-Bueis et al, 2019;Rodiño et al 2021).…”

Conventional management has a greater negative impact on Phaseolus vulgaris L. rhizobia diversity and abundance than water scarcity

“…Thus, the establishment of symbiotic relationships with efficient rhizobia can alleviate the effects of stress in legumes ( Igiehon et al., 2021 ; Omari et al., 2022 ; Oviya et al., 2023 ). This is the case of common bean, where it has been observed that symbiosis with drought-tolerant rhizobia improves plant tolerance to stress as well as legume yield and quality ( Steiner et al., 2020 ; Rodiño et al., 2021 ; del-Canto et al., 2023 ), even under field conditions ( Pastor-Bueis et al., 2019 ; Rodiño et al., 2021 ).…”

“…According to different authors, the conservation of soil rhizobial diversity in agrosystems is a sustainable strategy of great interest to improve crop tolerance to stress by favouring the establishment of efficient symbiotic relationships even under water scarcity conditions ( Wolff and Killebrew, 2010 ; Szparaga et al., 2019 ; Hossain and Bakhsh, 2020 ). In addition to this, there is interest in the search for indigenous inocula that are better adapted to local growing conditions and therefore more efficient in responding to stress conditions ( del-Canto et al., 2023 ).…”