Chemically Synthesized AgNPs and <i>Piriformospora</i> <i>indica</i> Synergistically Augment Nutritional Quality in Black Rice

The use of biofertilizers has been the spotlight of research aiming to mitigate the food security threat as well as to restore the fertility of agricultural lands, for decades. Several studies are being conducted to unravel the role and mechanisms of plant growth-promoting microbes. In the present research, we evaluated the effect of silver nanoparticles (AgNPs) and <i>Piriformospora indica</i> on the growth and nutritional enhancement of black rice (<i>Oryzae sativa.</i> L.) individually and in combination. Among the different treatment conditions, the AgNPs + <i>P. indica</i> treatment led to a significant (<i>p</i> ≤ 0.05) increase in morphological and agronomic parameters. In comparison to the control, the percentage increase in plant height in AgNPs-treated black rice was 2.47%, while that for the treatment with only <i>P. indica</i> was 13.2% and that for the treatment with both AgNPs + <i>P. indica</i> was 30.9%. For the number of productive tillers, the effect of AgNPs in comparison to the control was non-significant; however, the effect of <i>P. indica</i> and AgNPs + <i>P. indica</i> showed a significant (<i>p</i> ≤ 0.05) increase of 13.2% and 30.9% in both the treatments, respectively. Gas chromatography mass spectrophotometry analysis of grains revealed that the contents of phenylalanine, tryptophan, and histidine (aromatic amino acids) were significantly (<i>p</i> ≤ 0.05) increased by 75%, 11.1%, and 50%, respectively, in <i>P. indica</i>-treated black rice. Nutrient profiling showed that macronutrients such as potassium, calcium, magnesium were found to be increased by 72.8%, 86.4% and 59.2%, respectively, in the treatment with AgNPs + <i>P. indica</i> in comparison to the control plants. Additionally, a significant (<i>p ≤</i> 0.05) increase of 51.9% in anthocyanin content was observed in AgNPs + <i>P. indica</i>-treated black rice. The <i>P. indica</i> treatment also showed improved growth and augmented nutrient contents. From this study, we were able to understand that AgNPs + <i>P. indica</i> treatment would be a better plant growth-promoting factor and further evaluation would enable us to obtain a clear picture of its mechanisms of action.