Role of cuticle thickness and wax composition in the resistance to Xanthomonas citri ssp. citri during mandarin leaf-development

FAVARO, M.A.; GARIGLIO, N.F.; MOLINA, C.; MARANO, M.R.; ROESCHLIN, R.A.; GADEA, J.

Lednice

Conferencia; 3rd Annual Conference of the EuroXanth COST Action, Integrating science on Xanthomonadaceae for integrated plant disease management in Europe; 2019

EuroXanth

Satsuma (C. unshiu) ´Okitsu´ is a mandarin presenting substantial resistance to X. citri ssp. citri (X. citri), causal agent of citrus canker disease. We have previously shown that ´Okitsu´ is more resistant to X. citri than mandarin ´Clemenules´ (C. clementine), particularly during early stages of leaf development and exclusively when the leaves are inoculated by a noninvasive spraying method, suggesting that the leaf surface could be contributing to this resistance. In this work, we study the structural-chemical properties of leaf surface barriers of both mandarin cultivars. Ultraestructural analysis showed a thicker cuticle covering epidermal surface and guard cells in young ´Okitsu´ leaves that was associated with a smaller stomatal aperture, reduced cuticle permeability and increased stomatal defense to X. citri infection. These findings were correlated with an early accumulation of cuticular wax components, including primary alcohols, alkanes and fatty acids. Expression of the major wax-associated genes confirmed these results. None of these differences described for young leaves were observed in mature leaves, where both cultivars are equally resistant to the bacterium. Remarkably, mechanical alteration of cuticular thickness of young ´Okitsu´ leaves allows X. citri colonization and canker development. Taken together, these data suggest that a faster cuticular wax development in ´Okitsu´ leaves play a central role in its resistance to X. citri.