Inheritance of trichomes and resistance to pod borer (Helicoverpa armigera) and their association in interspecific crosses between cultivated pigeonpea (Cajanus cajan) and its wild relative C. scarabaeoides

The legume pod borer, Helicoverpa armigera, is one of the most devastating pests of pigeonpea. High levels of resistance to pod borer have been reported in the wild relative of pigeonpea, Cajanus scarabaeoides. Trichomes (their type, orientation, density and length) and their exudates on pod wall surface play an important role in the ovipositional behavior and host selection process of insect herbivores. They have been widely exploited as an insect defense mechanism in number of crops. In the present investigation, inheritance of resistance to pod borer and different types of trichomes (A, B, C and D) on the pod wall surface in the parents (C. cajan and C. scarabaeoides) and their F₁, F₂, BC₁ (C. cajan × F₁), and F₃ generations has been studied. Trichomes of the wild parents (high density of the non-glandular trichomes C and D, and glandular trichome B and low density of glandular trichome A) were dominant over the trichome features of C. cajan. A single dominant gene as indicated by the segregation patterns individually will govern each trait in the F₂ and backcross generation. Segregation ratio of 3 (resistant): 1 (susceptible) for resistance to pod borer in the F₂ generation under field conditions was corroborated with a ratio of 1:1 in the backcross generation, and the ratio of 1 non-segregating (resistant): 2 segregating (3 resistant: 1 susceptible): 1 non-segregating (susceptible) in F₃ generation. Similar results were obtained for pod borer resistance under no-choice conditions. Resistance to pod borer and trichomes associated with it (low density of type A trichome and high density of type C) are governed individually by a dominant allele of a single gene in C. scarabaeoides. Following backcrossing, these traits can be transferred from C. scarabaeoides into the cultivated background.