This work reports the reaction of Capsicum genotypes to the powdery mildew pathogen with variables of the stomatal complex, from samples of five to 15 Capsicum genotypes in a complete randomized experiments. Ostiolum size, stomatal morphometry (length, width and surface area), the number of stomata.mm-2, and the frequency of stomata (stomatal units per unit of epidermal cells) were evaluated on both leaf epidermal surfaces of plants growing in greenhouse. The variable ostiolum size did not explain the genotype reaction to the mildew, neither in the upper (R²=0.16) or lower leaf surfaces (R²=0.13). Nevertheless, the number of stomata.mm-2, on the upper or lower leaf surfaces, explained 84 % to 74 % of the genotype reaction, respectively. For the relation between stomatal frequency and host reaction, a better fit was found with the number of stoma in the upper leaf surface (R²=0.76), than with number in the lower leaf surface (R²=0.48). Sweet pepper 'Magali' (highly susceptible) had the largest numbers and frequency of stomata on both leaf surfaces at both experiments, which were significantly higher than in 'HV-12' (highly resistant). We suggest that the susceptibility of Capsicum to O. haplophylli may be partially related to pre-formed structural defense mechanisms, such as number of stomata, which relates to the number of infection sites. However, the low correlation of the disease and variables of the stomatal complex among some genotypes, indicates that other mechanisms might be involved with the expression of resistance in Capsicum to powdery mildew.
Leveillula taurica; stoma; resistance groups; hot pepper; chili; sweet pepper
