Alteração estomatal e respostas bioquímicas em cafeeiro resistente e suscetível à ferrugem

Abstract

Coffee is widely consumed worldwide, with production concentrated in a few countries, among which Brazil is the largest producer. However, coffee cultivation is severely affected by coffee leaf rust, caused by Hemileia vastatrix, which is responsible for severe defoliation and significant yield losses. The high dispersal capacity of the pathogen, combined with the complexity of the host–pathogen interaction and the high cost of disease management, highlights the need for a better understanding of coffee resistance mechanisms. Therefore, the objective of this study was to characterize the interaction between coffee plants and Hemileia vastatrix through an integrated analysis of stomatal and biochemical responses throughout the infection process in a resistant cultivar (Arara) and a susceptible cultivar (Catuaí Vermelho IAC 144). Two greenhouse experiments were conducted. In the first experiment, a randomized complete block design with split plots over time was used to evaluate stomatal aperture, the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POX), chitinase (CHI), and β1,3-glucanase (GLU), as well as total soluble phenolic compounds, soluble lignin, and lipid peroxidation (quantified as malondialdehyde, MDA). The second experiment confirmed the resistance and susceptibility of the cultivars using the area under the disease progress curve (AUDPC). The Arara cultivar exhibited early activation of defense mechanisms, evidenced by increased PAL, POX, and CHI activities at 5 days after inoculation, with relative activities compared with the control treatment (non-inoculated plants) that were 1.37-, 1.80-, 5.31-, and 1.80-fold higher for PAL, POX, CHI, and GLU, respectively. During the same period, increases in total phenolic compounds and soluble lignin contents were also observed, indicating activation of the phenylpropanoid pathway and enhanced lignification. Furthermore, the Arara cultivar showed an initial increase in MDA levels at 1 day after inoculation, followed by a reduction, indicating effective control of oxidative damage. In contrast, the Catuaí Vermelho IAC 144 cultivar exhibited increased MDA levels from 5 days after inoculation onward, which remained elevated throughout the evaluation period, suggesting progressive oxidative damage. The results demonstrate that the resistance of the Arara cultivar is associated with the early and coordinated activation of biochemical defense mechanisms, characterized by increased activity of defense-related enzymes, accumulation of phenolic compounds, and lignification, as well as more efficient control of oxidative damage.