Differential expression of CsWRKY genes reduced damage in Soy protein hydrolysate-treated cucumber plants infected with Fusarium oxysporum

The biostimulant activity of soy protein hydrolysate on Fusarium oxysporum-inoculated cucumber plants was investigated in comparison with salicylic acid (SA). Cucumber seedlings were treated with trypsin-digested soybean (PrH) and SA followed by F. oxysporum inoculation, and were assessed for gene expression pattern, disease incidence (DI%), growth rate and biochemical responses. Results showed that F. oxysporum infection in PrH-treated plants decreased shoot and root dry weights by 4 and 18.2%, respectively, while these parameters were decreased 45 and 66.5% in SA-treated, and 42 and 65.9% in control plants. Glutathione peroxidase (GPx) activity was decreased in PrH-treated plants upon infection with higher rate compared to control plants while it was increased in SA-treated plants. Gene expression analysis revealed that, compared to other treatments, CsWRKY2 was expressed earlier and in higher rate in PrH-treated plants, and was negatively correlated with disease incidence leading to lowest disease infection (11.3 %) among treatments. These results suggest that PrH activates defense responses in cucumber plants against infection at the expense of reduced plant growth. Although the increase in CsWRKY2 expression enhances plant defense, but its over-expression higher than a threshold will negatively affect plant growth. By contrast, CsWRKY35 expression was negatively correlated with plant growth and its resistance against pathogen. The findings of the present study may pave the road for exploration of WRKY genes in cucumber breeding programs.