Plant protein hydrolysate and arbuscular mycorrhizal fungi synergistically orchestrate eggplant tolerance to iodine supply: A two-year study

Biofortification is a promising strategy to overcome iodine (I) deficiencies in the world population. However, since iodine is not essential for plants, its administration may cause phytotoxicity issues. The objective of this work was to evaluate the effects of two biostimulants [arbuscular mycorrhizal fungi (AM) and plant protein hydrolysates (PH)], used alone or in combination, on eggplant plants treated with three different I doses (0, 300 or 600 mg L−1). Results underlined that the highest I dosage significantly reduced plant growth, yield, fruit dry matter content, chlorophylls and stomatal conductance compared to the control. Whereas, I increased total anthocyanins, chlorogenic acid, antioxidant activity, fruit I concentration, proline, H2O2 and malondialdehyde of the biofortified plants compared to non-biofortified plants. The biostimulants enhanced eggplant growth and yield, fruit dry matter content, chlorophylls, total anthocyanins and chlorogenic acid compared to the control, especially when both biostimulants were supplied. Interestingly, it was often recorded an interaction between I and biostimulants, suggesting that PH and AM had a buffer effect on I toxicity, specifically when combined (PH+AM). Overall, our study pointed out that the mutual use of microbial (AM) and non-microbial (PH) biostimulants and the application of 300 mg I L−1 might be an helpful approach to relieve the detrimental effects of high I dosages and, simultaneously, to increase crop yield and fruit quality of eggplant.