Hormonal seed-priming improves tomato resistance against broomrape infection

Although it is well known that parasitic weeds such as Orobanche (broomrape) significantly reduce the yield of economically important crops, their infection-induced oxidative changes need more exploration in their host plants. Moreover, applying an eco-friendly approach to minimize the infection is not yet available. This study was conducted to understand the effect of Orobanche ramosa infection on oxidative and redox status of tomato plants and the impact of hormonal (indole acetic acid (IAA); 0.09 mM and salicylic acid (SA); 1.0 mM) seed-priming upon mitigating the infection threats. Although Orobanche invades tomato roots, its inhibitory effects on shoot biomass were also indicted. Orobanche infection usually induces oxidative damage i.e., high lipid peroxidation, lipoxygenase activity and H₂O₂ levels, particularly for roots. Interestingly, hormonal seed-priming significantly enhanced tomato shoots and roots growth under both healthy and infected conditions. Also, IAA and SA treatment significantly reduced Orobanche infection-induced oxidative damage. The protective effect of seed-priming was explained by increasing the antioxidant defense markers including the antioxidant metabolites (i.e., total antioxidant capacity, carotenoids, phenolics, flavonoids, ASC, GSH, tocopherols) and enzymes (CAT, POX, GPX, SOD, GR, APX, MDHAR, DHAR), particularly in infected tomato seedlings. Additionally, cluster analysis indicated the differential impact of IAA- and SA-seed-priming, whereas lower oxidative damage and higher antioxidant enzymes' activities in tomato root were particularly reported for IAA treatment. The principal component analysis (PCA) also proclaimed an organ specificity depending on their response to Orobanche infection. Collectively, here and for the first time, we shed the light on the potential of seed-priming with either IAA or SA to mitigate the adverse effect of O. ramosa stress in tomato plants, especially at oxidative stress levels.