Improvement of Medicago sativa Crops Productivity by the Co-inoculation of Sinorhizobium meliloti–Actinobacteria Under Salt Stress

Abstract

Biotic and abiotic stresses are severely limiting plant production and productivity. Of notable importance is salt stress that not only limits plant growth and survival, but affects the soil fertility and threatens agricultural ecosystems sustainability. The problem is exacerbated in fragile arid and semi-arid areas where high evaporation, low precipitation and the use of salty water for irrigation is accelerating soil salinization. Legumes, considered very nutritious foods for people and providing essential nutrients for ecosystems are a fundamental element of sustainable agriculture. They can restore soil health by their ability to fix nitrogen in a symbiotic interaction with the rhizobia of the soil. However, salt stress is severely limiting productivity and nitrogen fixation ability in legumes. Plant growth-promoting rhizobacteria (PGPR) and mainly actinobacteria promote plant growth by producing phytohormones, siderophores, antibiotics and antifungal compounds, solubilizing phosphate and providing antagonism to phytopathogenic microorganisms. In addition, actinobacteria have beneficial effects on nodulation and growth of legumes. In this study, actinobacteria isolated from different niches and having PGP activities were used in co-inoculation experiments with rhizobia in Medicago sativa plants rhizosphere submitted to salt stress. The results indicate that drought- and salinity-tolerant Actinobacteria with multiple PGP traits can potentially increase alfalfa growth under saline conditions, in the presence or absence of symbiotic rhizobial bacteria. Actinobacteria discovered in this study can, therefore, be suitable biofertilizers in the formulation of agricultural products improving plant development, health and productivity in saline soils, a necessary alternative for modern agriculture and sustainable development.

Plant Beneficial Deep-Sea Actinobacterium, Dermacoccus abyssi MT1.1T Promote Growth of Tomato (Solanum lycopersicum) under Salinity Stress

“…strain UW4 [ 109 ]. Similar observations were recorded in soybean inoculated with Arthrobacter woluwensis AK1 [ 18 ], Bacillus aryabhattai ALT29 [ 19 ] and Arthrobacter woluwensis ALT43 [ 19 ], and alfalfa co-inoculated of Arthrobacter strain M1, M2, and Nocardiopsis Ag-1 with rhizobium Sinorhizobium meliloti R1 and R2 [ 22 ].…”

“…PGPA39 [ 14 ], maize inoculated with Azotobacter sp. C5 and C5 [ 97 ], and alfalfa inoculated and co-inoculated with Arthrobacter strains MS-1, MS-2, and symbiotic bacteria ( Sinorhizobium meliloti strains R1 and R2) [ 22 ]. Interestingly, plants inoculated with these actinobacteria showed growth performance that was not impaired by salt stress, in particular the dry weight and chlorophyll content.…”

“…Plant growth promoting bacteria, in particular actinobacteria, have been adopted to enhance crop production and alleviate salt stress in several plant species. Actinobacteria have been reported to promote plant growth under salt stress in tomato [ 14 , 15 , 16 , 17 ], soybean [ 18 , 19 ], wheat [ 20 , 21 ], alfalfa [ 22 ], and dwarf glasswort [ 23 ]. Recently, actinobacteria with plant growth promoting potential dwell in extreme saline environments such as marine sediments, mangrove, and halophyte are attracting research attention due to their adaptive features in such environments which are beneficial to plants under salinity stress.…”

Deep-Sea Actinobacteria Mitigate Salinity Stress in Tomato Seedlings and Their Biosafety Testing

“…PGPA39 contained lower proline content than non-inoculated tomatoes but exhibited higher dry biomass and chlorophyll content under salinity stress (180 mM NaCl). Similarity, inoculation and co-inoculation of Arthrobacter strain MS-1 and MS-2 with symbiotic bacteria (Sinorhizobium meliloti strains R1 and R2) decreased proline content in leaves and improved growth rate, number of nodules, and salt tolerance in alfalfa under salinity stress (100 mM NaCl) [39]. Therefore, our results suggested that D. barathri MT2.1 T may use another alternative approach in combination with proline accumulation to alleviate salinity stress.…”

Soil Bacteria to Regulate Phoebe bournei Seedling Growth and Sustainable Soil Utilization under NPK Fertilization

“…Urea, as the N source in our experiment, was conducive to increasing P. bournei seedlings' nitrite absorption and reducing the nitrite content in the soil, thus decreasing Chloroflexi abundance, which oxidizes nitrites into nitrates, increasing autotrophic nitrite bacteria growth (e.g., the best Chloroflexi growth was in T2, which did not include N fertilizer) [41,42]. Actinobacteria are known to be beneficial bacteria that produce agricultural antibiotics and fight plant diseases [43]. Similar to most NPK fertilization results, high N levels resulted in reduced Actinobacteria abundance; however, an appropriate NPK ratio can promote Actinobacteria growth, reaching maximum abundance in T14 (N 2 P 1 K 1 ), probably because NPK fertilizer provides material and energy in relatively arid red soil [40,44].…”