Development of a dense genetic map and QTL analysis for pod borer Helicoverpa armigera (Hübner) resistance component traits in chickpea (Cicer arietinum L.).

Genetic enhancement for resistance against the pod borer, Helicoverpa armigera is crucial for enhancing production and productivity of chickpea. Here we provide some novel insights into the genetic architecture of natural variation in H. armigera resistance in chickpea, an important legume, which plays a major role in food and nutritional security. An interspecific recombinant inbred line (RIL) population developed from a cross between H. armigera susceptible accession ICC 4958 (Cicer arietinum) and resistant accession PI 489777 (Cicer reticulatum) was evaluated for H. armigera resistance component traits using detached leaf assay and under field conditions. A high-throughput AxiomCicerSNP array was utilized to construct a dense linkage map comprising of 3,873 loci and spanning a distance of 949.27 cM. Comprehensive analyses of extensive genotyping and phenotyping data identified nine main-effect QTLs and 955 epistatic QTLs explaining up to 42.49% and 38.05% phenotypic variance, respectively, for H. armigera resistance component traits. The main-effect QTLs identified in this RIL population were linked with previously described genes, known to modulate resistance against lepidopteran insects in crop plants. One QTL cluster harbouring main-effect QTLs for three H. armigera resistance component traits and explaining up to 42.49% of the phenotypic variance, was identified on CaLG03. This genomic region, after validation, may be useful to improve H. armigera resistance component traits in elite chickpea cultivars.

Proteolytic Activity in the Midgut of Helicoverpa armigera (Noctuidae: Lepidoptera) Larvae Fed on Wild Relatives of Chickpea, Cicer arietinum.

Wild relatives of crops are an important source of resistance genes against insect pests. However, it is important to identify the accessions of wild relatives with different mechanisms of resistance to broaden the basis and increase the levels of resistance to insect pests. Therefore, we evaluated 15 accessions of wild relatives of chickpea belonging to seven species and five genotypes of cultivated chickpea for their resistance to pod borer, Helicoverpa armigera, which is the most damaging pest of chickpea. The test genotypes were evaluated for resistance to H. armigera using detached pod assay. Data were also recorded on activity of the digestive enzymes in the midgut of the larvae fed on different wild relatives of chickpea. All the wild chickpea genotypes suffered lower pod damage and weight gained by the third-instar larvae of H. armigera was lower when fed on them compared with the cultivated chickpea. The accessions, IG 69979 (Cicer cuneatum), PI 599066, IG 70006, IG 70018, IG 70022 (Cicer bijugum), IG 599076 (Cicer chrossanicum), and IG 72933, IG 72953 (Cicer reticulatum), showed high levels of resistance to H. armigera. There were significant differences in protease activity in larval gut of H. armigera fed on different wild relatives of chickpea. Total protease, trypsin, and chymotrypsin activities were lowest in larva fed on PI 599066 (C. bijugum) compared with that in the larvae fed IG 69979 (C. cuneatum) and IG 70022 (C. bijugum). Aminopeptidase activity was highest in the larvae fed on IG 70022 (C. bijugum) and IG 599076 (C. chrossanicum), whereas lowest activity was recorded in the larvae fed on ICC 3137 and KAK 2 (susceptible checks). The variation in protease activities may be due to the presence of protease inhibitors in the wild relatives or hyperproduction of enzymes by the larvae as result of protease inhibitor activity of the wild relatives, resulting in low weight gain by larvae. The results suggested that wild relatives of chickpea with diverse mechanisms of resistance can be exploited to increase the levels and diversify the basis of resistance to H. armigera in cultivated chickpea.

Double-Stranded RNA-Mediated Suppression of Trypsin-Like Serine Protease (t-SP) Triggers Over-Expression of Another t-SP Isoform in Helicoverpa armigera.

High diversity of digestive proteases is considered to be the key factor in the evolution of polyphagy in Helicoverpa armigera. Serine proteases (SPs) contribute ~85% of the dietary protein digestion in H. armigera. We investigated the dynamics of SP regulation in the polyphagous pest, H. armigera using RNA interference (RNAi). HaTry1, an isoform of SP, expressed irrespective of the composition of the diet, and its expression levels were directly proportional to the larval growth rate. Therefore, HaTry1 was silenced by delivering 10 and 20 µg concentrations of double-stranded RNA through semi-synthetic diet. This led to a drastic reduction in the target gene transcript levels that manifested in a significant reduction in the larval weight initially, but the larvae recovered in later stages despite continuous dsRNA treatment. This was probably due to the compensatory effect by over-expression of HaTry13 (31-folds), another isoform of SP. Phylogenetic analysis of H. armigera SPs revealed that the over-expressed isoform was closely related to the target gene as compared to the other tested isoforms. Further, silencing of both the isoforms (HaTry1 and HaTry13) caused the highest reduction in the larval weight and there was no larval growth recovery. These findings provide a new evidence of the existence of compensatory effect to overcome the effect of silencing individual gene with RNAi. Hence, the study emphasizes the need for simultaneous silencing of multiple isoforms.

Influence of CO2 and Temperature on Metabolism and Development of Helicoverpa armigera (Noctuidae: Lepidoptera).

Climate change will have a major bearing on survival and development of insects as a result of increase in CO2 and temperature. Therefore, we studied the direct effects of CO2 and temperature on larval development and metabolism in cotton bollworm, Helicoverpa armigera (Hübner). The larvae were reared under a range of CO2 (350, 550, and 750 ppm) and temperature (15, 25, 35, and 45°C) regimes on artificial diet. Elevated CO2 negatively affected the larval survival, larval weight, larval period, pupation, and adult emergence, but showed a positive effect on pupal weight, pupal period, and fecundity. Increase in temperature exhibited a negative effect on larval survival, larval period, pupal weights, and pupal period, but a positive effect on larval growth. Pupation and adult emergence were optimum at 25°C. Elevated CO2 and temperature increased food consumption and metabolism of larvae by enhancing the activity of midgut proteases, carbohydrases (amylase and cellulase), and mitochondrial enzymes and therefore may cause more damage to crop production. Elevated CO2 and global warming will affect insect growth and development, which will change the interactions between the insect pests and their crop hosts. Therefore, there is need to gain an understanding of these interactions to develop strategies for mitigating the effects of climate change.

Elimination of Gut Microbes with Antibiotics Confers Resistance to Bacillus thuringiensis Toxin Proteins in Helicoverpa armigera (Hubner).

Helicoverpa armigera is one of the most important pests worldwide. Transgenic crops with toxin genes from Bacillus thuringiensis (Bt) have been deployed on a large scale to control this pest. The insecticidal activity of Bt is probably influenced by the insect midgut microbes, which vary across crop hosts and locations. Therefore, we examined the role of gut microbes in pathogenicity of Bt toxins in the H. armigera. Antibiotic cocktail was used for the complete elimination of the H. armigera gut microbes. Activated Cry1Ac, Bt formulation, and transgenic cotton resulted in larval weight loss and increase in mortality, but pretreatment of larvae with antibiotic cocktail significantly decreased larval mortality and increased the larval weight gain. Activated Cry1Ac and Bt formulation inhibited the activity of proteases in midgut of H. armigera larvae but showed no such effect in the larvae pretreated with antibiotic cocktail. Five protease bands in activated Cry1Ac and two in Bt formulation-treated larvae were inhibited but no such effect in the larvae pretreated with antibiotic cocktail. Cry1Ac protein was detected in Bt/Cry1Ac protoxin-fed larval gut extract in the absence of antibiotic cocktail, but fewer in larvae pretreated with antibiotic cocktail. The activity of antioxidant enzymes and aminopeptidases increased in larvae fed on Bt toxin, but there was no significant increase in antioxidant enzymes in larvae reared on toxin protein in combination with antibiotic cocktail. The results suggest that gut microbes exercise a significant influence on the toxicity of Cry1Ac and Bt formulation in H. armigera larvae. The implications of these results have been discussed in relation to development of insect resistance to Bt transgenic crops deployed for pest management.

Mitochondrial P-glycoprotein ATPase contributes to insecticide resistance in the cotton bollworm, Helicoverpa armigera (Noctuidae: Lepidoptera).

Cotton bollworm, Helicoverpa armigera, is one of the most damaging polyphagous pests worldwide, which has developed high levels of resistance to commonly applied insecticides. Mitochondrial P-glycoprotein (Pgp) was detected in the insecticide-resistant strain of H. armigera using C219 antibodies, and its possible role was demonstrated in the efflux of xenobiotic compounds using spectrofluorometer. The TMR accumulated in mitochondria in the absence of ATP, and effluxed out in presence of ATP; the process of efflux was inhibited in the presence of ortho-vandate, an inhibitor of Pgp, in insecticide-resistant larvae of H. armigera. The mitochondria isolated from insecticide-resistant larvae were resistant to insecticide-induced inhibition of oxygen consumption and cytochrome c release. Membrane potential decreased in a dose-dependent manner in the presence of higher concentration of insecticides (>50 µM) in mitochondria of insecticide-resistant larvae. In conclusion, mitochondrial Pgp ATPase detected in the insecticide-resistant larvae influenced the efflux of xenobiotic compounds. Pgp might be involved in protecting the mitochondrial DNA and the components of the electron transport chain from damage due to insecticides, and contributing to the resistance to the deleterious effects of insecticides on the growth of insecticide-resistant H. armigera larvae.

Comparative studies on the effects of Bt-transgenic and nontransgenic cotton on arthropod diversity, seedcotton yield and bollworms control.

The effectiveness of commercial Bt-cotton in pest management, influence on arthropod diversity, natural enemies, and toxin flow in the insect fauna under field conditions were studied keeping in view the need to assess bioefficacy and biosafety of Bt-transgenic cotton. There were no significant differences in oviposition by Helicoverpa armigera on Bt-transgenic and non-transgenic cottons (9.2 versus 9.6 eggs plants(-100)), while the numbers of H. armigera larvae were significantly more on non-transgenic than on Bt-transgenic (10.4 versus 4.0 larvae plants(-100)) cotton. The Bt-cotton had significantly more number of mature opened bolls (9.6 versus 4.4 bolls plant(-1)), lower bollworm damage (12.8 versus 40.2% bolls damaged), and higher seedcotton yield (667.7 versus 231.7 kg ha 1). Population of cotton leafhopper, Amrasca biguttula biguttula was lower (582.2 versus 732.2 leafhoppers plants(-100)), while that of whitefly, Bemisia tabaci was higher on Bt-transgenic (65.2 versus 45.6 whiteflies plants(-100)) than on non-transgenic cotton. There was no significant influence of Bt-transgenic cotton on abundance of natural enemies of crop pests - chrysopids (9.6 versus 8.4 chrysopids plants(-100), ladybird beetles (16.0 versus 10.8 ladybirds plants(-100)), and spiders (128.4 versus 142.8 spiders plants(-100)). There were no significant differences in H. ormigera egg (19.8 versus 20.9%), larval (7.4 versus 9.6%), and larval-pupal (1.3 versus 2.9%) parasitism on Bt-transgenic and non-transgenic cottons in the farmer's fields. The parasitism in larvae of H. armigera was far lower than that of the eggs, which might be because of early mortality of H. armigera prior to parasitoid development in the host larvae. Although, Cry1Ac Bt toxin was detected in Cheilomenes sexmoculatus, chrysopids, A. bigutulla bigutulla, Thrips taboci, Myllocerus sp., Oxycarenus laetus, Dysdercus koenigii, spiders, bugs, and grasshoppers, no significant differences were observed in their abundance on Bt-transgenic and non-transgenic cottons, suggesting that there were no adverse effects of Bt-cotton on the arthropod diversity under field conditions.

Interaction of plant cell signaling molecules, salicylic acid and jasmonic acid, with the mitochondria of Helicoverpa armigera.

The cotton bollworm, Helicoverpa armigera is a polyphagous pest in Asia, Africa, and the Mediterranean Europe. Salicylic acid (SA) and jasmonic acid (JA) are the cell signaling molecules produced in response to insect attack in plants. The effect of these signaling molecules was investigated on the oxidative phosphorylation and oxidative stress of H. armigera. SA significantly inhibited the state III and state IV respiration, respiratory control index (RCI), respiratory complexes I and II, induced mitochondrial swelling, and cytochrome c release in vitro. Under in vivo conditions, SA induced state IV respiration as well as oxidative stress in time- and dose-dependent manner, and also inhibited the larval growth. In contrast, JA did not affect the mitochondrial respiration and oxidative stress. SA affected the growth and development of H. armigera, in addition to its function as signaling molecules involved in both local defense reactions at feeding sites and the induction of systemic acquired resistance in plants.

Effect of mating and parasitism regimes on progeny production and sex-ratio of Campoletis chlorideae Uchida.

The ichneumonid parasitoid, C. chlorideae is an important natural enemy of pod borer/bollworm, Helicoverpa armigera (Hubner) in different agro-ecosystems. The sex-ratio of parasitoids has an important bearing on the population build up of the natural enemies for biological control of insect pests. Therefore, the present studies were conducted to gain an understanding of the influence of mating behaviour and abundance of the insect host on fecundity and sex-ratio of the parasitoid, C. chlorideae. There was no significant influence of number of matings and abundance of the insect host on cocoon formation, adult emergence, and larval and pupal periods of C. chlorideae. However, fecundity and female longevity were significantly influenced by mating and abundance of the insect host. There was a significant and positive correlation (r = 0.84**) between longevity and fecundity of C. chlorideae females. The unmated C. chlorideae females produced only males. Nearly 20% of the females that had mated twice were able to parasitize the H. armigera larvae successfully. The sex-ratio of the progeny from females that had mated twice was male biased. Females mated with males from the unmated females produced significantly less numbers of females than those mated with males from the fertilized females, indicating genetic regulation of sex-ratio in C. chlorideae.

Degradation of the insecticidal toxin produced by Bacillus thuringiensis var. kurstaki by extracellular proteases produced by Chrysosporium sp.

AIMS: Some Cry proteins produced by the soil bacterium Bacillus thuringiensis (Bt) or by transgenic Bt plants persist in agricultural soils for an extended period of time, which may pose a hazard for nontarget soil organisms. The aims of our study were to screen for soil fungi capable of degrading the Cry1Ac toxin and to identify the mechanisms that lead to the inactivation of this protein. METHODS AND RESULTS: Of the eight fungal strains screened, only one, Chrysosporium sp., was found to produce extracellular proteases capable of degrading the 66-kDa Cry1Ac at the N-terminal end of amino acid 125 (alanine). The proteolytic products of the Cry1Ac toxin did not exhibit any insecticidal activity against Helicoverpa armigera, in contrast to its high toxicity exhibited in the native form. CONCLUSIONS: Proteases elaborated by the Chrysosporium sp. degrade the Cry1Ac toxin in a way that it looses its insecticidal activity against H. armigera. SIGNIFICANCE AND IMPACT OF THE STUDY: Chrysosporium sp., a specific soil micro-organism capable of producing proteases that degrade the Cry1Ac toxin into inactive products under controlled conditions is being reported for the first time. Application of this observation needs to be further tested in field conditions.

Effect of storage temperature and duration on viability of eggs of Helicoverpa armigera (Lepidoptera: Noctuidae).

The ability to store different insect stadia for prolonged periods provides considerable flexibility and ability to conduct experiments properly. Therefore, studies were undertaken to determine the effect of storage temperature and duration on viability of eggs of Helicoverpa armigera (Hübner). The percentage egg hatch and incubation period were significantly (P=0.01) influenced by egg age, storage temperature, and storage duration. Egg hatch ranged from 0.0 to 96.8% across temperatures and storage durations. None of the eggs hatched when stored at -20 and 0 degrees C. The regression model with the optimum Mallow Cp statistic for any of the identified linear and quadratic terms did not improve the precision of prediction in egg hatch beyond 67.0%. Forecasting of incubation period based on egg age, storage duration, and durationxtemperature was quite effective (R2=84.2%). Day degrees required for egg hatching decreased with an increase in temperature from 10 to 27 degrees C, and egg age from 0 to 3 days. The day degree requirements were highest for 0-day-old eggs at 10 degrees C, and lowest at 27 degrees C. Although the incubation period was higher, the hatchability was lower for 0- and 1-day-old eggs stored at constant 10 degrees C, these eggs can be stored for 10 days at 10 degrees C, with a hatchability of >75.0%. It was safer to store the H. armigera eggs for 10 days at 10 degrees C, which will hatch within 1.6 to 2.0 days after restoration at 27 degrees C with a hatchability of >75.0%. This information will be useful in planning and execution of experiments involving H. armigera on various aspects of research in entomology.

Development of transgenic sorghum for insect resistance against the spotted stem borer (Chilo partellus).

Transgenic sorghum plants expressing a synthetic cry1Ac gene from Bacillus thuringiensis (Bt) under the control of a wound-inducible promoter from the maize protease inhibitor gene (mpiC1) were produced via particle bombardment of shoot apices. Plants were regenerated from the transformed shoot apices via direct somatic embryogenesis with an intermittent three-step selection strategy using the herbicide Basta. Molecular characterisation based on polymerase chain reaction and Southern blot analysis revealed multiple insertions of the cry1Ac gene in five plants from three independent transformation events. Inheritance and expression of the Bt gene was confirmed in T(1) plants. Enzyme-linked immunosorbant assay indicated that Cry1Ac protein accumulated at levels of 1-8 ng per gram of fresh tissue in leaves that were mechanically wounded. Transgenic sorghum plants were evaluated for resistance against the spotted stem borer (Chilo partellus Swinhoe) in insect bioassays, which indicated partial resistance to damage by the neonate larvae of the spotted stem borer. Reduction in leaf damage 5 days after infestation was up to 60%; larval mortality was 40%, with the surviving larvae showing a 36% reduction in weight over those fed on control plants. Despite the low levels of expression of Bt delta-endotoxin under the control of the wound-inducible promoter, the transgenic plants showed partial tolerance against first instar larvae of the spotted stem borer.

Standardization of cage techniques to screen chickpeas for resistance to Helicoverpa armigera (Lepidoptera: Noctuidae) in greenhouse and field conditions.

Because of variations in insect populations and staggered flowering of chickpea, Cicer arietinum L., genotypes, it is difficult to compare the genotypic performance across seasons and locations. We standardized a cage technique to screen chickpeas for resistance to Helicoverpa armigera (Hübner). Leaf feeding by the larvae was significantly lower on ICC 506 than on ICCC 37 when the seedlings were infested with 20 neonates per five plants at 15 d after seedling emergence or 10 neonates per three plants at the flowering stage. Maximum differences in pod damage were observed when the plants were infested with six third-instar larvae per three plants in the greenhouse, and with eight larvae per plant under field conditions. Larval weights were significantly lower on ICC 506 than on ICCC 37 across growth stages and infestation levels. At the podding stage, percentage of reduction in grain yield was significantly greater on ICCC 37 and Annigeri than on ICCV 2 and ICC 506. The no-choice test can be used to screen segregating breeding material and mapping populations for resistance to H. armigera. It also provides useful information on antibiosis mechanism of resistance to H. armigera.

The melon fruit fly, Bactrocera cucurbitae: a review of its biology and management.

The melon fruit fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) is distributed widely in temperate, tropical, and sub-tropical regions of the world. It has been reported to damage 81 host plants and is a major pest of cucurbitaceous vegetables, particularly the bitter gourd (Momordica charantia), muskmelon (Cucumis melo), snap melon (C. melo var. momordica), and snake gourd (Trichosanthes anguina). The extent of losses vary between 30 to 100%, depending on the cucurbit species and the season. Its abundance increases when the temperatures fall below 32 degrees C, and the relative humidity ranges between 60 to 70%. It prefers to infest young, green, soft-skinned fruits. It inserts the eggs 2 to 4 mm deep in the fruit tissues, and the maggots feed inside the fruit. Pupation occurs in the soil at 0.5 to 15 cm below the soil surface. Keeping in view the importance of the pest and crop, melon fruit fly management could be done using local area management and wide area management. The melon fruit fly can successfully be managed over a local area by bagging fruits, field sanitation, protein baits, cue-lure traps, growing fruit fly-resistant genotypes, augmentation of biocontrol agents, and soft insecticides. The wide area management program involves the coordination of different characteristics of an insect eradication program (including local area options) over an entire area within a defensible perimeter, and subsequently protected against reinvasion by quarantine controls. Although, the sterile insect technique has been successfully used in wide area approaches, this approach needs to use more sophisticated and powerful technologies in eradication programs such as insect transgenesis and geographical information systems, which could be deployed over a wide area. Various other options for the management of fruit fly are also discussed in relation to their bio-efficacy and economics for effective management of this pest.

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.

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 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, Puccnia arachidis Speg., and late leaf spot, Cercosporidium personatum (Berk. et Curt.). 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.

Can larvae of the pod-borer, Helicoverpa armigera (Lepidoptera: Noctuidae), select between wild and cultivated pigeonpea Cajanus sp. (Fabaceae)?

Experiments were conducted to observe the feeding and food selection-behaviour of different instars of the pod-borer Helicoverpa armigera (Hübner) in response to choices between the cultivated and a wild species of Cajanus. First and second instars fed upon a cultivated variety of Cajanus cajan in preference to a wild species, C. scarabaeoides and on flowers of C. cajan, rather than pods or leaves of C. cajan. First and second instars preferred pods of C. scarabaeoides with trichomes removed to pods with trichomes present. All instars fed upon pods of C. cajan rather than those of C. scarabaeoides. Solvent extraction of the pod surfaces affected the feeding of larvae, in some instances. They preferred the unextracted pods of C. cajan; the extracted pod of C. scarabaeoides (first and second instars) or the unextracted pod of C. scarabaeoides (fourth and fifth instars). Glass-fibre disc bioassays showed that the methanol, hexane and water extracts from the pod-surface of C. cajan stimulated the feeding of fifth instars. The experiments have shown that characteristics of C. cajan, such as either the compounds present or the type and distribution of trichomes on the plant surfaces, can determine the susceptibility of C. cajan to pod-borer larvae.

Host plant resistance to insects: an eco-friendly approach for pest management and environment conservation.

Host plant resistance (HPR) to insects is an effective, economical, and environment friendly method of pest control. The most attractive feature of HPR is that farmers virtually do not need any skill in application techniques, and there is no cash investment by the resource poor farmers. Considerable progress has been made in identification and development of crop cultivars with resistance to the major pests in different crops. There is a need to transfer resistance genes into high-yielding cultivars with adaptation to different agro-ecosystems. Resistance to insects should form one of the criteria to release varieties and hybrids for cultivation by the farmers. Genes from the wild relatives of crops, and novel genes, such as those from Bacillus thuringiensis can also be deployed in different crops to make HPR an effective weapon to minimize the losses due to insect pests. HPR will not only cause a major reduction in pesticide use and slowdown the rate of development of resistance to insecticides in insect populations, but also lead to increased activity of beneficial organisms and reduction in pesticide residues in food and food products.

Identification and characterization of wheat-wheatgrass translocation lines and localization of barley yellow dwarf virus resistance.

Stable introgression of agronomically important traits into crop plants through wide crossing often requires the generation and identification of translocation lines. However, the low efficiency of identifying lines containing translocations is a significant limitation in utilizing valuable alien chromatin-derived traits. Selection of putative wheatgrass-wheat translocation lines based on segregation ratios of progeny from gamma-irradiated seed using a standard phenotypic analysis resulted in a low 4% success rate of identifying barley yellow dwarf virus (BYDV) resistant and susceptible translocation lines. However, 58% of the susceptible progeny of this irradiated seed contained a Thinopyrum intermedium chromosome-specific repetitive sequence, which indicated that gamma-irradiation-induced translocations occurred at high rate. Restriction fragment length polymorphism (RFLP) analysis of susceptible lines containing alien chromatin, their resistant sister lines and other resistant lines showed that more than one third of the progeny of gamma-irradiated double monosomic seeds contained wheatgrass-wheat translocations. Genomic in situ hybridization (GISH) analysis of selected lines confirmed that these were wheatgrass-wheat translocation lines. This approach of initially identifying BYDV susceptible deletion lines using an alien chromosome-specific repetitive sequence followed by RFLP analysis of their resistant sister lines efficiently identified resistant translocation lines and localized the BYDV resistance to the distal end of the introgressed Th. intermedium chromosome.