Trichomes on Pigeonpea [Cajanus cajan (L.) Millsp.] and Two Wild Cajanus spp

Trichomes have been modified in a number of crops to develop insect‐tolerant genotypes. Pigeonpea, Cajanus cajan (L.) Millsp., is often heavily damaged by insect pests, and trichomes provide a potential insect resistance mechanism. The following study was conducted to identify and characterize the distribution of trichomes on pigeonpea and two wild species, C. platycarpus (Bentham) van der Maesen and C. scarabueoides (L.) Thours. Three glandular (Types A, B, and E) and two nonglandular (Types C and D) trichome types were identified with light and electron microscopy. Types A, B, C, and D were found on leaves, pods, and calyxes of all three Cajanus spp., except for Type A, which was not found on pods and calyxes of most C. scarabaeoides accessions examined. Because of their small size and rarity, Type E trichomes were not considered in this study. Pods of C. scarabueoides were the most densely pubescent, followed by pods of C. cajan and C. platycarpus. Trichome density on pods varied significantly among pigeonpea genotypes and different accessions of C. scarabaeoides. Differences across seasons and in greenhouse versus field‐grown plants were also significant. Leaves of C. platycarpus possessed the fewest trichomes, while C. cajan and C. scarabaeoides had highly pubescent leaves. The resistance of C. scarabaeoides pods to Helicoverpa armigera (Hübner) larvae reported in an earlier study is due to the high density of nonglandular trichomes. This wild species may thus be an important source for developing insect resistant pigeonpea.