Effects of Nanoparticles (Zinc and Silicon) and Plant Growth Promoting Rhizobacteria on Yield, Photosynthetic Pigments and Grain Filling Components of Triticale under Salinity Stres

Salinity stands as a significant environmental stressor that profoundly curtails the growth and yield of crop plants. This adversity also extends to the impairment of pigments and plastids, leading to diminished chlorophyll indices, rates, and grain-filling durations. To counteract the deleterious impact of such stressors on plant growth, a spectrum of strategies has been devised. Prominent among these strategies are plant growth-promoting rhizobacteria, exemplified by azospirillum, and the utilization of nanoparticles like zinc and silicon. These factors play a pivotal role in elevating yield outcomes. Zinc's pivotal involvement spans protein metabolism, photosynthetic activities, and diverse physiological traits within plants. Particularly noteworthy is its contribution to rectifying zinc deficiency, a particularly critical concern in plants cultivated in high-pH soils. Notably, recent research has illuminated the potential of applying minute quantities of micronutrients, notably zinc via foliar spraying, in bolstering plant resilience against salt stress. Likewise, silicon emerges as a supplemental micronutrient that imparts heightened resistance to environmental stresses, fostering increased resilience within biological systems. Therefore, this study aimed to evaluate the effects of application of plant growth-promoting rhizobacteria and nanoparticles (zinc and silicon) on the yield, photosynthetic pigments, and filling components of triticale grain under salt stress.

This experiment was conducted as factorial based on a randomized complete block design with three replications in greenhouse research of the Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili in 2022. Factors experimental included salinity at three levels (no salinity as control, application of 60, 120 mM salinity) by NaCl, application of PGPR at two levels (no inoculation as control and seed inoculation with Azospirillium), and foliar application of nanoparticles at four levels (foliar application with water as control, foliar application of 0.8 g.L-1 nano zinc oxide, foliar application 50 mg.L-1 nano silicon, foliar application both of nano zinc oxide (0.4 g.L-1) and nano silicon (25 mg.L-1). The strains and cell densities of microorganisms used as PGPR in this experiment were 1×107 bacteria per milliliter (107 cfu.ml−1). A two-part linear model was used to quantify the grain-filling parameters. In this study, grain dry weight and number were used to calculate the average grain weight for each sample. Total duration of grain filling was determined for each treatment combination by fitting a bilinear model:    GW =where GW is the grain dry weight; a, the GW-intercept; b, the slope of grain weight indicating grain filling rate; t, the days after earring; and t0, physiological maturity. The effective grain filling period (EGFD) was calculated from the following equation:EGFD = the highest grain weight (g)/rate of grain filling (g day-1).

The results showed that application of Azospirillium and foliar application of nano zinc-silicon oxide under no salinity increased chlorophyll a (38.42%), chlorophyll b (41.76%), total chlorophyll (39.39%), carotenoids (53.99%), root weight (62.61%), grain filling rate (16.37%), grain filling period and effective grain filling period (21.28 and 29.78%) and grain yield (47.23%) in compared to no application of Azospirillium and nanoparticles under 120 mM salinity. Application of Azospirillium and foliar application nano zinc-silicon oxide under 60 mM salinity also increased chlorophyll a (31.4%), chlorophyll b (34.35%), total chlorophyll (32%), carotenoids (45.68%), root weight (57.14%), grain filling rate (15.21%), grain filling period and effective grain filling period (21.29 and 28.16%) and grain yield (35.67%) in compared to the application of Azospirillium and nanoparticles under 120 mM salinity. According to this study, application of Azospirillium and nanoparticles (zinc and silicon) can increase yield of triticale grain under salinity stress such as no salinity due to the improvement of photosynthetic pigments content and grain filling components.