Plant–insect interactions: resistance mechanisms of barley against Mayetiola hordei

This work aims to enhance our understanding of plant-defense mechanisms, which is crucial for developing resistant crops following pest attacks. Focusing on the susceptibility of Tunisian barley to the gall midge Mayetiola hordei, the current study explores how gall formation affects the structure of attacked organs, and how sensitive and resistant barley cultivars respond to infestations. Two barley cultivars, Kounouz and Rihane, were selected for this experiment in two semi-arid regions of North Tunisia, Zaghouan and Kef. Sampling was carried out at four stages of barley development (tillering, elongation, heading, and ripening). Kef region was identified as the most affected area, recording significant economic and severe infestations for Kounouz variety, particularly at the ripening stage (53% and 24%, respectively). While Rihane variety demonstrated the least susceptibility, with only 4% of tillers severely infested during the heading stage in Kef and 7% in Zaghouan. This study detected structural changes in the stem induced by gall formation, revealing cellular hypertrophy, tissue hyperplasia, and lignin accumulation. Furthermore, the findings demonstrated a significant increase in total polyphenol compounds and total peroxidase activity upon gall midge attack. Polyphenol, flavonoid, condensed tannins, and peroxidase activity concentrations after infestation reached 1.312 ± 0.056 mgGAE/gWF; 1.457 ± 0.079 mgRE/gWF; 0.237 ± 0.036 mgCE/gWF; and 4.160 U/g FW, respectively, for Rihane variety during the heading stage of barley in Kef. The study also highlighted a linear relationship between peroxidase activity and total phenolic content post-infestation, underscoring the role of phenolic compounds and peroxidase activity in plant resistance and defense in response to M. hordei-induced stress.