Trichomes on pigeonpea [Cajanus cajan (L.) Millsp.] and two wild Cajanus spp.

Trichomes have been modified in a number of crops to develop insect-toleran t genotypes. Pigeonpea, Cajanus cajan (L,) Millsp., is often heavily damage d by insect pests, and trichomes provide a potential insect resistance mech anism. The following study was conducted to identify and characterize the d istribution of trichomes on pigeonpea and two wild species, C. platycarpus (Bentham) van der Maesen and C. scarabaeoides (L,) Thours, Three glandular (Types A, B, and E) and two nonglandular (Types C and D) trichome types wer e 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 Ty pe Al which was not found on pods and calyxes of most C. scarabaeoides acce ssions examined. Because of their small size and rarity, Type E trichomes w ere not considered in this study. Pods of C. scarabaeoides were the most de nsely pubescent, followed by pods of C. cajan and C. platycarpus. Trichome density on pods varied significantly among pigeonpea genotypes and differen t accessions of C. scarabaeoides, Differences across seasons and in greenho use versus field-grown plants were also significant. Leaves of C. platycarp us possessed the fewest trichomes, while C. cajan and C. scarabaeoides had highly pubescent leaves. The resistance of C. scarabaeoides pods to Helicov erpa armigera (Hubner) larvae reported in an earlier study is due to the hi gh density of nonglandular trichomes. This wild species may thus he an impo rtant source for developing insect resistant pigeonpea.