Biostimulating effects of silicon on the tolerance of fenugreek (Trigonella foenum-graecum L.) to salt stress under biological nitrogen fixation: Agrophysiological and biochemical responses

Abstract

Although, aromatic and medicinal plants have a crucial role in the world’s health, but their growth and production are drastically affected by various abiotic stresses such as salinity and water deficit. In this context, the present work aimed at improving the tolerance of fenugreek (Trigonella foenum graecum L.) and its rhizobial symbiosis to salt stress by using exogenous silicon (Si). The experiments were carried out at different plant development stages. Results showed that salt stress reduced seed germination and embryo viability and altered seed reserve mobilization. The reduction in seed germination was significantly correlated with the induction of oxidative stress, reflected by high levels of malonyldialdehyde (MDA) and hydrogen peroxide (H2O2). However, Si supply induced a significant accumulation of compatible osmolytes and improved seed germination, embryo viability and seed reserve mobilization process. Si also triggered high activity of both enzymatic and non-enzymatic antioxidant systems, reducing as a result MDA and H2O2 contents in seedling. During vegetative stage, salinity also reduced plant growth and nodulation. This reduction was accompanied with a significant decrease in leaf chlorophyll content, relative water content, nutrient uptake and photosynthesis machinery in terms of the activity of photosystems. However, the exogenous supply of Si resulted in a considerable accumulation of some compatible solutes together with enhanced antioxidant systems, reflected by a significant accumulation of polyphenols and flavonoids and a high activity of antioxidant enzymes, such as superoxide dismutase, catalase, polyphenol oxidase and guaiacol peroxidase. These latter improved leaf relative water content and reduced oxidative stress and therefore restored growth and photosynthetic activity in saltstressed fenugreek plants. Similarly, under field conditions, the obtained results showed that seed priming with Si significantly improved seed germination, plant biomass and yield related parameters, such as number of pods per plant, hundred seed weight, and harvest index, in salt stressed fenugreek. More interestingly, Si priming not only enhances plant biomass and yield parameters but also was able to improve the nutritional quality and antioxidant activity of harvested seeds under salt stress. Taken together, treatment with exogenous Si could be a promising and ecofriendly technic to alleviate the drastic effects of salinity on germination, growth and yield of fenugreek