Techniques to screen for resistance to insects.We have developed efficient techniques for artificial rearing of spotted stem borer, Chilo partellus, cotton bollworm/legume pod borer, Helicoverpa armigera, tobacco caterpillar, Spodoptera litura, and oriental armyworm, Mythimna separata to screen germplasm, breeding materials, mapping populations, and transgenic plants for resistance to insects. Infester row, artificial infestation, no-choice cage, detached leaf assay, and diet impregnation assay have been standardized to screen for resistance to shoot fly, Atherigona soccata; stem borer, Chilo partellu;, midge, Stenodiplosis sorghicola; and head bug, Calocoris angustatus in sorghum; and Helicoverpa armigera and Maruca vitrata in pigeonpea; Helicoverpa armigera in chickpea; Spodoptera litura in groundnut; and Mythimna separata in pearl millet under field, greenhouse, and laboratory conditions. Current research activities are focused on:

• Refining field screening techniques to evaluate mapping populations and genetically modified plants for resistance to insects.
• Standardize detached leaf assay and diet impregnation assay to assess antibiosis components of resistance to insects.

Identification and utilization of insect resistance. Several thousand germplasm lines have screened for insect resistance, and sources of resistance have been identified for shoot fly, A. soccata, stem borer, C. partellus, aphid, Melanaphis sacchari, midge, Stenodiplosis sorghicola, and head bugs, Calocoris angustatus and Eurystylus oldi in sorghum; H. armigera in chickpea; pod borers, H. armigera and M. vitrata, and pod fly, Melanagromyza obtusa in pigeonpea; leaf miner, Aproerema modicella, and leaf caterpillar, S. litura in groundnut; and shoot fly, Atherigona approximata, mite, Tetranychus sp., and Oriental armyworm, M. separata in peal millet. In collaboration with breeders, resistance to shoot fly, stem borer, midge and head bugs has been transferred into high-yielding cultivars in sorghum. ICSV 197 and ICSV 745 have been released for cultivation. ICSV 745 has been distributed to farmers in India and Sudan. Midge-resistant varieties ICSV 735, ICSV 758, and ICSV 804 have been released in Myanmar. Malisor 84-7, resistant to head bugs, has been released in Mali, and extensively used in sorghum improvement in Asia, West Africa, and USA. Resistance to sorghum midge, shoot fly, and stem borer has been transferred into cytoplasmic male-sterile (CMS) lines, and these lines have been made available to the scientists in public and private institutions. Several lines have been identified/developed with resistance to insects, of which IS 2123, ICSV 705, ICSV 708, SPSFR 94019, SPSFR 94006, SPSFR 94007, SPSFR 94011, SPSFR 94034, ICSV 93127, SPSFR 96069, SPSFR 86065, PS 23585, ICSR 89058 - resistant to shoot fly; and IS 5448, IS 5470, IS 2205, IS 18573, ICSV 700 and ICSV 93046 (sweet stalk) -resistant to stem borer, have been used in crop improvement in Asia, Africa, USA, and Australia. Several lines with resistance to Helicoverpa in pigeonpea (ICPL 332, ICPL 84060, and ICPL 187-1) and chickpea (ICC 506EB, ICSV 10, and ICCL 86111) have been identified, and distributed to the NARS. Present research focus is on:

• Transferring shoot fly resistance into male-sterile and restorer lines of sorghum.
• Identify sorghum lines with multiple resistance to insects, and sources of resistance to shoot bug and aphids, and sweet sorghums for resistance to shoot fly and stem borer.
• Develop chickpea and pigeonpea cultivars with resistance to Helicoverpa .

Wild relatives as sources of resistance to insects. Wild relatives of sorghum, groundnut, chickpea , and pigeonpea have been screened for resistance to insects pests, both under field and greenhouse conditions. High levels of resistance have been identified in the wild relatives of sorghum (Sorghum dimidiatum, S. australiense, S. purpeosericeum, S. nitidum, and S. angustum) for shoot fly, stem borer, and midge; and for leaf miner, Spodoptera, and jassids in groundnut (Arachis cardenasii, A. duranensis, A. kempff-mercadoi, A. monticola, A. stenosperma, A. paraguariensis, A. pusilla, and A. triseminata), Helicoverpa in pigeonpea (Cajanus scarabaeoides, C. sericeus, and C. acutifolius), and chickpea (Cicer bijugum, C. pinnatifidum, and C. judaicum). Resistance genes from the wild relatives can be or are being used for increasing the levels, and diversifying the bases of resistance to target pests in different crops. The current research effort is on:

• Characterizing the resistant accessions for different components of resistance.
• Quantifying the contribution of morphological traits and the biochemical constituents in genotypic resistance to insects.
• Introgressing resistance genes from wild relatives into the cultigen.

Mechanisms and inheritance of resistance to insects. Extensive studies have been carried out on mechanisms and inheritance of resistance to shoot fly, stem borer, head bugs, and sugarcane aphid in sorghum; leaf miner and leaf caterpillar in groundnut; Helicoverpa Maruca, and pod fly in pigeonpea, and Helicoverpa and aphids in chickpea. Oviposition non-preference, antibiosis, and tolerance are the principle components of resistance to sorghum midge. Resistance to midge breaks down under the constant day length at the Equator in Kenya. Resistance to shoot fly and midge is influenced by factors in the cytoplasm of B-lines or their interaction with the nuclear genes. Short and tight glumes can be used to select for resistance to sorghum midge. Longer covering of the grain by the glumes, and quicker grain hardening contribute to head bug resistance. Resistance is governed by additive gene action, and is needed in both the parents to produce insect-resistant hybrids. Leaf glossiness, faster seedling growth, trichomes, ligular hairs, and chemicals in the leaf surface wax (benzaldehyde, p-OH benzoate, -CN-ion metabolites) contribute to shoot fly and stem borer resistance. These traits can be used as markers to select for resistance to these pests.

Pigeonpea genotypes with indeterminate growth habit and non-clustered pods are less susceptible to pod borers (Helicoverpa and Maruca). Quercetin, iso-quercetin, quercetin-3-methyl ether, stilbene, and caryophyllene play an important role in host plant resistance to Helicoverpa. Non-glandular trichomes contribute to Helicoverpa resistance in wild relatives of pigeonpea, which is inherited as a simple dominant trait. The leaf surface exudates (oxalic acid, malic acid, citric acid, and formic acid) and flavonoids are the major components of resistance to Helicoverpa in chickpea. Information on mechanisms and inheritance of resistance is vital for planning appropriate strategies to develop crop cultivars with resistance to insects. Present studies are focused on:

Physico-chemical mechanisms of resistance to shoot fly and stem borer in sorghum, and Helicoverpa in chickpea and pigeonpea.

Inheritance of resistance to shoot fly, stem borer in sorghum, and Helicoverpa in chickpea. Effect of cytoplasmic male-sterility on expression of resistance to insects in sorghum.

Evaluation of mapping populations for insect resistance. To identify molecular markers associated with insect resistance, mapping populations have been evaluated for resistance to pod borer, Helicoverpa armigera in chickpea; and shoot fly, Atherigona soccata and spotted stem borer, Chilo partellus in sorghum. Genetic linkage maps for these crops have been developed, and the quantitative trait loci (QTLs) associated with resistance to the target pests are being identified. The identified QTLs are being used to develop cultivars for resistance to the target pests. Studies are in progress on:

• Identification of QTLs associated with shoot fly and stem borer resistance in sorghum.
• Development on intra- and interspecific mapping populations for mapping resistance to Helicoverpa in chickpea and pigeonpea.
• Identification of molecular markers associated with pod borer resistance in chickpea and pigeonpea.

Bioassay of transgene products and transgenic plants for insect resistance. We have evaluated Bacillus thuringiensis, trypsin inhibitor, and plant lectins for their effectiveness against Atherigona, Chilo, and Helicoverpa. Toxin proteins from Bt, Cry1a, Cry1Ac and CryIIa are effective against Helicoverpa, and a native strain against the shoot fly. In collaboration with molecular biologists, transformed tobacco, sorghum, chickpea, and pigeonpea plants have been evaluated for resistance to the target pests under greenhouse and contained field conditions. Studies are in progress on:

• Evaluation of transgene products for their bioefficacy against different insect pests.
• Evaluation of transgenic events of chickpea and pigeonpea for resistance to Helicoverpa under greenhouse and contained field conditions.
• Effectiveness of transgenic hybrids in pest management in cotton.