The effect of hydrolysis and protein source on the efficacy of protein hydrolysates as plant resistance inducers against powdery mildew

The substitution of synthetic pesticides has become a priority in agriculture and the induction of plant resistance by protein hydrolysates may offer a sustainable alternative. The protein source, method and degree of hydrolysis, as well as the amino acid and peptide composition may affect the efficacy of protein hydrolysates against plant diseases. The aim of our work was to clarify the effect of enzymatic and acid hydrolysis on various plant protein sources (soybean, rapeseed and guar protein meal), in term of efficacy against courgette powdery mildew. The enzymatic hydrolysates were produced using Alcalase or Flavourzyme at 1 and 50% enzyme/substrate ratio at 50°C for 24 h. The acid hydrolysates were obtained using 6N H2SO4 for 15 min at 121°C (6N A) or for 8 h at 100°C (6N B). Preventive foliar treatments with guar Alcalase 50% and 6N B hydrolysates significantly reduced disease symptoms compared to the non-hydrolysed protein source. A positive correlation was found between efficacy and the degree of hydrolysis of guar acid hydrolysates, suggesting that this hydrolysis method may enhance the functional properties of the original protein source. Moreover, our analysis revealed positive correlations between the efficacy of guar hydrolysates and concentrations of specific peptides and amino acids. Our results showed that the biocontrol effect of plant protein hydrolysates was related to the original protein source, and two specific hydrolysis processes improved the functional properties of guar, producing peptide fragments and free amino acids that may be involved in the regulation of innate immune response in plants.