Morphological characterization and surface classification of chili pepper leaves considering trichomes and domatia

The knowledge of morphological characteristics of plant leaves is important to study the interactions among plants, herbivores and natural enemies. Variations on such characteristics are determinant on the occurrence, abundance and diversity of organisms that exploit that habitat. The leaf surface of four Capsicum pepper species was characterized, focusing on the presence of trichomes and domatia. The objective is to identify possible mite resistance mechanisms on these plants. The classification key of pepper leaves was based on presence/absence, density and distribution of trichomes. The counting of trichomes was done in an area of 5 cm², from the medium third of each leaf. We assessed the trichomes from the limb, ribs and domatia. The pepper species significantly differed on the density of domatia and trichomes present on the ribs and limbs of their leaves. A significant difference was observed on the total density of trichomes/cm² and on the number of trichomes/domatia. From the five Capsicum species evaluated, only C. baccatum var. pendulum (hot pepper, variety girl finger pepper) does not have domatia neither trichomes in any part of its leaves. The highest domatia density was found on C. baccatum var. praetermissum, which has the highest trichome density in all leaf parts and the only one with significant density of limb trichomes. The variation of the presence, distribution and density of trichomes and domatia may be determinant on the occurrence of herbivorous and predatory mites on plants. Such structures can act as a resistance mechanism against herbivore mites or may favor the presence of predatory and fungivorous mites due to provision of shelter sites. We propose here a surface classification scale of chili pepper leaves varying from 1 to 5 taking into account the number and density of observed trichomes and domatia.

Capsicum spp.; trichomes density; domatia; plant defense