Influence of transgenic cotton on the relative abundance and damage by target and non-target insect pests under different protection regimes in India

Effectiveness of transgenic cottons with Bacillus thuringiensis (Bt) cry1Ac gene along with non-transgenic commercial cultivars of Gossypium hirsutum and G. arboreum for the management of cotton bollworm, Helicoverpa armigera was evaluated at the research farm, International Crops Research Institute for the Semi-Arid Tropics, Patancheru, Andhra Pradesh, India. In general, there were no significant differences in oviposition between the transgenic and the non-transgenic cultivars under protected and unprotected conditions. The larval numbers were significantly lower on the transgenic hybrids during the 2004 rainy season under high infestation, but the differences in larval density between the transgenic and non-transgenic hybrids during 2002 and 2003 seasons under low levels of infestation were quite small. Bollworm damage in squares and bolls was significantly lower in the transgenic hybrids than in the non-transgenic ones, although there were a few exceptions. Differences in seed cotton yield between the transgenic and the non-transgenic hybrids were not significant under unprotected conditions at moderate levels of infestation during the 2002 and 2003 cropping seasons (except in the case of Mech 184). However, significant differences in seed cotton yield were observed during the 2004 cropping season under heavy bollworm infestation. Seed cotton yield of the first picking in transgenic hybrids was significantly greater than that of the non-transgenic counterparts. Transgenic hybrids suffered low shoot damage by spotted bollworm, Earias vittella. However, there were no differences between the transgenic and non-transgenic hybrids in their relative susceptibility to cotton jassid, Amrasca biguttula biguttula and serpentine leaf miner, Liriomyza trifolii, white fly, Bemisia tabaci, green bug, Nezara viridula, ash weevil, Myllocerus undecimpustulatus, and red cotton bug, Dysdercus koenigii. With a few exceptions, the bollworm damage and seed cotton yield of the G. arboreum varieties Aravinda and MDL 2450, and the G. hirsutum variety L 604 was not significantly different than that of the transgenic hybrids, and these varieties were also resistant to cotton jassid. The results suggested that it would be useful to combine transgenic resistance to H. armigera with plant characteristics conferring resistance to the target or non-target insect pests in the region in order to realize the full potential of transgenic plants for sustainable crop production

Influence of transgenic cottons with Bacillus thuringiensis cry1Ac gene on the natural enemies of Helicoverpa armigera

Transgenic cotton has been released for cultivation in several parts of the world to increase crop productivity. However, concerns have been raised regarding the possible undesirable effects of genetically modified crops on non-target organisms in the eco-system. Therefore, we studied the effects of transgenic cottons with cry1Ac gene from Bacillus thuringiensis Berliner (Bt) on the natural enemies of cotton bollworm/legume pod borer, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) under field and laboratory conditions. There was no apparent effect of transgenic cotton on the relative abundance of predatory spiders (Clubiona sp. and Neoscona sp.), coccinellid (Cheilomenes sexmaculatus Fab.), and the chrysopid (Chrysoperla carnea Stephens). However, the abundance of spiders, coccinellids, and chrysopids was quite low in insecticide protected plots towards end of the cropping season. There was a significant reduction in cocoon formation and adult emergence of the ichneumonid parasitoid, Campoletis chlorideae Uchnida reared on H. armigera larvae fed on the leaves of transgenic cottons before and after parasitization. However, no Bt toxins were detected in H. armigera larvae and the parasitoid cocoons with enzyme linked immunosorbent assay. Reduction in cocoon formation was because of early mortality of the H. armigera larvae due to Bt toxins in the leaves of transgenic cotton. There was a slight reduction in adult weight and fecundity, and prolongation of the larval period when the parasitoid was raised on H. armigera larvae fed on the leaves of transgenic cotton before and after parasitization. Survival and development of C. chlorideae was also poor when H. armigera larvae were fed on the leaves of cotton hybrid Mech 184. The adverse effects of transgenic cotton on survival and development of C. chlorideae were largely due to early mortality, and possibly poor nutritional quality of H. armigera larvae due to toxic effects of the transgene

Wild relatives of pigeonpea as a source of resistance to the pod fly (Melanagromyza obtusa Malloch) and pod wasp (Tanaostigmodes cajaninae La Salle)

Pigeonpea [Cajanus cajan (L.) Millsp.] is an important legume crop in South Asia, East and southern Africa, and the Caribbean. Pod fly (Melanagromyza obtusa Malloch) and pod wasp (Tanaostigmodes cajaninae La Salle) are important constraints to increase the production and productivity of pigeonpea under subsistence farming conditions. Host plant-resistance can be used as an important component for the management of these pests, and therefore, we evaluated 28 accessions of wild relatives of pigeonpea for resistance to these pests. There were significant inter- and intra-species differences in the relative susceptibility to pod fly and pod wasp damage. Accessions belonging to Cajanus scarabaeoides (L.) Thouars, C. sericeus (Benth. ex Bak.) van der Maesen, Rhynchosia bracteata Benth. ex Bak., C. acutifolius (F.v. Muell.) van der Maesen, C. lineatus (W. & A.) van der Maesen, and C. albicans (W. & A.) van der Maesen showed resistance to pod fly damage, while those from C. platycarpus (Benth.) van der Maesen, C. cajanifolius (Haines) van der Maesen and R. aurea DC. were susceptible. For the pod wasp, some of the accessions from C. scarabaeoides, C. albicans, Flemingia stricta Roxb., and R. bracteata (Roxb.) Wight showed a resistant reaction, while ICPW 83 belonging to C. scarabaeoides showed a susceptible reaction. ICPW 141, ICPW 278, and ICPW 280 (C. scarabaeoides), ICPW 214 (R. bracteata), ICPW 14 (C. albicans), and ICPW 202 (F. stricta) showed resistance to both pod fly and pod wasp damage. There was considerable variation in accessions belonging to different species for their susceptibility to pod fly and pod wasp, which can be exploited to breed for resistance to these pests. There was a negative association between pod wasp and pod borer damage, and therefore, it is important to keep track of the relative susceptibility of pigeonpea genotypes to pod wasp, while breeding for resistance to pod borers

Multiple-resistance to sorghum shoot fly, spotted stemborer and sugarcane aphid in sorghum

Sorghum is one of the most important cereal crops in the semi-arid tropics. Several insect pests damage it. The possibility of identifying genotypes with multiple resistance to these pests and transferring the relevant genes into high-yielding varieties and hybrids has been considered as an attractive approach to reducing yield losses. A set of 12 cytoplasmic male-sterile and maintainer lines, 12 restorer lines and their F1 hybrids were evaluated for resistance to sorghum shoot fly Atherigona soccata Rondani, spotted stemborer Chilo partellus (Swinhoe) and sugarcane aphid Melanaphis sacchari (Zehntner) under field conditions. There were significant differences among the genotypes tested. A total of 50% of male-sterile lines, 41.7% maintainers, 58.3% restorers and 35.4% of the hybrids tested showed moderate to high level of resistance to the three pests. The male-sterile and restorer lines showing resistance to different insects can be exploited for developing hybrids with multiple insect resistance for cultivation by the resource-poor farmers in the semi-arid tropics

Antibiosis mechanism of resistance to pod borer, Helicoverpa armigera in wild relatives of chickpea.

The pod borer, Helicoverpa armigera, is one of the major constraints to chickpea production worldwide. The levels of resistance to pod borer in the cultivated chickpea germplasm are moderate, and therefore, we studied the reaction of 32 accessions of wild relatives of chickpea for resistance to H. armigera under greenhouse conditions. Accessions ICC 17257, IG 70002, IG 70003, IG 70012, (Cicer bijugum), IG 69948 (C. pinnatifidum), IG 69979 (C. cuneatum), IG 70032, IG 70033, IG 70038, and IG 72931 (C. judaicum) showed lower leaf feeding, a drastic reduction in larval weight, and poor host suitability index at the vegetative and/or flowering stages of crop growth as compared to the cultivated chickpeas. Based on percentage pods damaged by 5th day (<52% pods damaged compared to 90% pods damaged in Annigeri), and percentage weight gain by the larvae (<35% weight gain compared to 366% weight gain on ICCV 2); accessions IG 69979 (C. cuneatum), IG 70003, IG 70022, IG 70016, IG 70013, IG 70012, IG 70010, IG 70001, IG 70018, and IG 70002 (C. bijugum), and IG 72953 (C. reticulatum) showed high levels of resistance to H. armigera. Larvae of H. armigera weighed <50 mg when reared on C. pinnatifidum (IG6 9948 and IG 70039), and C. judaicum (IG 72931) compared to 301.95 mg on C. arietinum (ICCC 37 - the cultivated chickpea). Larval weights on many accessions of the wild relatives of chickpea were much lower than those on the cultivated chickpeas, indicating the existence of different mechanisms of resistance to H. armigera. There was no pupation and adult emergence when the larvae were reared on accessions of C. pinnatifidum (IG 69948 and IG 70039), and C. judaicum (IG 69980, IG 70032, IG 70033 and IG 72931). The wild relatives of chickpea showing high levels of antibiosis to H. armigera can be used to introgress diverse resistance genes into cultivated chickpea to increase the levels and diversify the basis of resistance to this insec

Impact of Bt transgenic cottons and insecticides on target and non-target insect pests, natural enemies and seedcotton yield in India

Genetically engineered cottons expressing ä-endotoxins from Bacillus thuringiensis have been adopted on a largescale worldwide. Therefore, we studied the efficacy of Bt cottons for the management of bollworms, their effects on nontarget insects, and seedcotton yield under insecticide protected and unprotected conditions. Helicoverpa armigera and Earias vittella damage was significantly lower in Bt than in non-Bt cottons, while no significant differences were observed in egg-laying by H. armigera. The populations of major non-target sucking insect pests such as Amrasca biguttula biguttula, Bemisia tabaci, Aphis gossypii, Oxycarenus laetus, Dysdercus koenigii and Nezara viridula and the generalist predators, viz Cheilomenes sexmaculatus, Chrysopa spp., and spiders did not differ significantly between Bt and non-Bt cottons. Insecticide application resulted in resurgence of cotton aphid and whitefly, possibly because of elimination of natural enemies or better growth of plants uder protected conditions. Abundance of bollworms, non-target pests, and generalist predators was significantly greater before insecticide sprays than after insecticide application, except in a few cases. Bollworm damage was lower and seedcotton yields higher in Bt than in non-Bt cottons. The present studies indicated that Bt cotton hybrids are effective for the management of bollworms and yield more, and do not have any adverse effects on the abundance of generalist predators

Mechanisms and diversity of resistance to insect pests in wild relatives of groundnut

The levels of resistance to insect pests in cultivated groundnut (Arachis hypogaea) germplasm are quite low, and therefore, we screened 30 accessions of Arachis spp. and 12 derived lines for resistance to insect pests under field (Andhra Pradesh, India) and greenhouse conditions. Accessions belonging to Arachis cardenasii, Arachis duranensis, Arachis kempff-mercadoi, Arachis monticola, Arachis stenosperma, Arachis paraguariensis, Arachis pusilla and Arachis triseminata showed multiple resistance to the leaf miner Aproaerema modicella, Helicoverpa armigera, Empoasca kerri and to rust, Puccinia arachidis, and late leaf spot, Cercosporidium personatum [Mycosphaerella berkeleyi]. Arachis cardenasii (ICG 8216), Arachis ipaensis (ICG 8206), A. paraguariensis (ICG 8130) and Arachis appressipila (ICG 8946) showed resistance to leaf feeding and antibiosis to Spodoptera litura under no-choice conditions. Six lines, derived from wild relatives, showed resistance to H. armigera and S. litura, and/or leaf miner. Plant morphological characteristics such as main stem thickness, hypanthium length, leaflet shape and length, leaf hairiness, standard petal length and petal markings, basal leaflet width, main stem thickness and hairiness, stipule adnation length and width, and peg length showed significant correlation and/or regression coefficients with damage by H. armigera, S. litura, and leafhoppers, and these traits can possibly be used as markers to select for resistance to these insect pests. Principal component analysis placed the Arachis spp. accessions into five groups, and these differences can be exploited to diversify resistance to the target insect pests in groundnut

Exploitation of Wild Cicer reticulatum Germplasm for Resistance to Helicoverpa armigera

In the absence of high levels of resistance to Helicoverpa armigera (Hübner) in the cultivated germplasm of chickpea, we evaluated accessions of Cicer spp. mostly Cicer reticulatum Ladzinsky, for resistance to this important pest. Under multichoice conditions in the field, 10 accessions showed lower leaf damage and lower numbers of eggs, larvae, or both of H. armigera. Of these, IG 69960, IG 72934, and IG 72936 showed significantly lower leaf feeding than the cultivated genotypes or other accessions at the vegetative and reproductive stages. Larval weight was lower or comparable with that on C. bijugum (IG 70019) and C. judaicum (IG 70032) in C. reticulatum accessions IG 72933, IG 72934, IG 72936, and IG 72953 at the seedling stage and on IG 69960 and IG 72934 at the flowering stage. The accessions showing resistance to H. armigera in the field and laboratory conditions were placed in different groups, indicating the presence of diversity in C. reticulatum accessions for resistance to this pest. Less than seven larvae survived on IG 70020, IG 72940, IG 72948, and IG 72949, and IG 72964 compared with 12 on ICC 506. Larval and total developmental periods were prolonged by 6-15 and 3-8 d, respectively, on C. reticultatum accessions compared with those on ICCC 37. Less than five larvae pupated on the C. reticulatum accessions (except IG 72958 and ICC 17163) compared with 11 in ICCC 37. Accessions showing lower leaf feeding and adverse effects on the survival and development can be used in increasing the levels and diversifying the basis of resistance to H. armigera in chickpea

Inheritance of resistance to spotted stem borer, Chilo partellus, in sorghum, Sorghum bicolor

The spotted stem borer, Chilo partellus, is one of the most important pests of sorghum, and host plant resistance is an important component for the management of this pest. Most of the sorghum hybrids currently under cultivation are based on cytoplasmic male-sterility (CMS). In order to develop a strategy for resistance to stem borer, we studied the traits associated with resistance, and their nature of gene action in F1 hybrids derived from resistant, moderately resistant, and susceptible CMS and restorer lines. The hybrids based on stem borer-resistant, moderately resistant, or susceptible CMS and restorer lines were equally resistant or susceptible as the parents for leaf feeding [Damage rating (DR) 5.8 to 6.6 vs. 5.9 to 6.6], and had significant and decreasing trend in deadheart formation (resistant CMS × resistant restorer lines < moderately resistant CMS × moderately resistant restorer lines < susceptible CMS × susceptible restorer lines), respectively. Proportional contributions of restorer lines were greater than those of the CMS lines for leaf feeding, deadhearts, recovery and overall resistance, stalk length, nodes per plant, stem borer holes per plant, and peduncle tunneling. The general (GCA) and specific combining ability (SCA) estimates suggested that leaf feeding score, number of nodes, overall resistance score, panicle initiation, recovery score, and stalk length (dominance type of gene action) have been found to be associated with resistance to spotted stem borer, governed by additive type of gene action, their correlation and direct effects in the same direction, and explained 65.3% of the variation in deadhearts, and thus could be used as marker traits to select and breed for resistance to C. partellus in sorghum. The parents having significant SCA effects for two or more resistance traits for either or more parents have also been discussed for their use in the stem borer resistance breeding

Evaluation of Wild Relatives of Chickpea (Cicer spp.) for Resistance to Pod Borer, Helicoverpa armigera (Hubner)

The legume pod borer, Helicoverpa armigera, is a major constraint to chickpea production worldwide. The levels of resistance in the cultivated chickpea germplasm are moderate, and therefore, we evaluated 93 accessions of annual wild relatives of chickpea in the field, and 141 accessions under greenhouse conditions for resistance to H. armigera. Under field conditions, 24 accessions showed a leaf feeding score of <2.0 compared to 6.0 to 6.5 of the Cicer reticulatum accession IG 69975. These accessions also had less than 2 eggs and/or larvae of H. armigera and <2 larvae of Spodoptera exigua per plant at the flowering/podding stages. Based on leaf feeding, larval survival, and larval weights in the detached leaf assay, 41 accessions showed low leaf feeding, reduced larval weights, and/or low larval survival. Accessions IG 69947, IG 70002, IG 70003, IG 70009, IG 70019, IG 70022, ICC 17125, IG 69979 ICC 17122, ICC 17156, IG 70006, and ICC 17187 (C. bijugum), IG 69995 and IG 70030 (C. judaicum), and IG 69988, IG 69999 IG 70021, IG 70025, and IG 70028 (C. pinnatifidum) showed low leaf feeding, low larval weights, and low host suitability index. These accessions can be exploited for introgressing resistance genes from the wild relatives into the cultivated chickpeas to increase the levels and diversify the basis of resistance to H. armigera