Reaping the Potential of Wild Cajanus Species through Pre-Breeding for Improving Resistance to Pod Borer, Helicoverpa armigera, in Cultivated Pigeonpea (Cajanus cajan (L.) Millsp.).

Abstract

Simple SummaryPigeonpea is an important legume crop that is severely affected by various insect pests, especially pod borer. Because there are low resistance levels to pod borers in the cultivated pigeonpea gene pool, it is necessary to introduce resistance-related traits from its wild relatives. In this study, we conducted a series of crosses to introduce traits related to pod borer resistance from two wild relatives of pigeonpea into two popular cultivated varieties. We generated populations from four different crosses and screened these populations for traits related to pod borer resistance: i.e., low levels of insect damage, high concentrations of insect-deterring compounds in the seeds, and the presence of trichomes on the leaves. The most promising lines were tested across seasons and locations. Ultimately, we identified 21 lines with excellent traits related to pod borer resistance. These lines will be useful for breeding new insect-resistant pigeonpea cultivars. The availability of such cultivars will reduce the use of pesticides to control pests on pigeonpea crop.Pod borer (Helicoverpa armigera) causes the highest yield losses in pigeonpea, followed by pod fly (Melanagromyza obtusa). High levels of resistance to pod borer are not available in the cultivated genepool. Several accessions of wild Cajanus species with strong resistance, and different resistance mechanisms (antixenosis and antibiosis) to pod borer have been identified. These accessions can be utilized to improve the pod borer resistance of cultivated pigeonpea. Using pod borer resistant Cajanus scarabaeoides and Cajanus acutifolius as pollen donors and popular pigeonpea varieties as recipients, pre-breeding populations were developed following simple- and complex-cross approaches. Preliminary evaluation of four backcross populations consisting of >2300 introgression lines (ILs) under un-sprayed field conditions resulted in identifying 156 ILs with low visual damage rating scores (5.0–6.0) and low pod borer damage (<50%). Precise re-screening of these ILs over different locations and years resulted in the identification of 21 ILs having improved resistance to pod borer. Because these ILs were derived from wild Cajanus species, they may contain different alleles for different resistance components to pod borer. Hence, these ILs are ready-to-use novel and diverse sources of pod borer resistance that can be utilized for improving the pod borer resistance of cultivated pigeonpea.