Off-season survival and life history of beet armyworm, Spodoptera exigua (Hubner) on various host plants.

The beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), has become a significant pest of chickpea in recent years. The polyphagous nature allows it to survive on various hosts during the off-season, creating a great menace to the crop in the following season. To assess the incidence and document the alternate hosts of S. exigua, a rapid roving survey was conducted in 11 chickpea-growing areas of Prakasam district, Andhra Pradesh, India. Additionally, the life history traits of S. exigua were studied on major alternate host plants under laboratory conditions (27 ± 1 °C and 70 ± 2% RH) to understand the survival, life expectancy and potential contribution to future populations. The results show that, among the different crops surveyed, the maximum larval incidence was noticed in maize (1.93 larvae/plant), cowpea (1.73 larvae/plant), and sunflower (1.68 larvae/plant) during the off-season. Life history studies of S. exigua showed that highest larval survival percentage was observed on chickpea (83.6%), while the lowest was on maize (44.5%). The mean developmental time for larvae was longest on maize (27.1 days) and shortest on chickpea (14.9 days). Larvae did not develop beyond the third instar when fed with chilli. The growth index statistics showed chickpea (9.2) was the most suitable host plant, whereas maize (0.9) was the least suitable host. The age-stage-specific survival rate (Sxj) varied across developmental stages, and the survival curves overlapped, indicating different growth rates among individuals. The life expectancy (exj) at age zero was highest on groundnut (37.06 days). The intrinsic rate of increase (r) of S. exigua was lowest on maize (0.10 ± 0.0013) and highest on chickpea (0.22 ± 0.0010). Similarly, the net reproductive rate (R0) was highest on chickpea (846.39 ± 18.22) and lowest on maize (59.50 ± 2.06). The population doubled every 3.08 ± 0.011 days on chickpea compared to 7.22 ± 0.80 days on maize. The study conclusively indicates that chickpea and sunflower, primarily cultivated during the rabi season in India, are the most preferred hosts for S. exigua. In contrast, maize and cotton, mainly grown during the kharif season, are less preferred and merely support the pest's survival. Consequently, S. exigua switches hosts between different crops growing seasons, so effective management of S. exigua during the kharif season can help prevent pest outbreaks during the rabi season.

Transcriptome analysis reveals key genes associated with root-lesion nematode Pratylenchus thornei resistance in chickpea.

The root-lesion nematode, Pratylenchus thornei, is one of the major plant-parasitic nematode species causing significant yield losses in chickpea (Cicer arietinum). In order to identify the underlying mechanisms of resistance to P. thornei, the transcriptomes of control and inoculated roots of three chickpea genotypes viz. D05253 > F3TMWR2AB001 (resistant advanced breeding line), PBA HatTrick (moderately resistant cultivar), and Kyabra (susceptible cultivar) were studied at 20 and 50 days post inoculation using the RNA-seq approach. On analyzing the 633.3 million reads generated, 962 differentially expressed genes (DEGs) were identified. Comparative analysis revealed that the majority of DEGs upregulated in the resistant genotype were downregulated in the moderately resistant and susceptible genotypes. Transcription factor families WRKY and bZIP were uniquely expressed in the resistant genotype. The genes Cysteine-rich receptor-like protein kinase 10, Protein lifeguard-like, Protein detoxification, Bidirectional sugar transporter Sugars Will Eventually be Exported Transporters1 (SWEET1), and Subtilisin-like protease were found to play cross-functional roles in the resistant chickpea genotype against P. thornei. The identified candidate genes for resistance to P. thornei in chickpea can be explored further to develop markers and accelerate the introgression of P. thornei resistance into elite chickpea cultivars.

Defense Response in Chickpea Pod Wall due to Simulated Herbivory Unfolds Differential Proteome Profile.

The pod wall of legumes is known to protect the developing seeds from pests and pathogens. However, the mechanism of conferring defense against insects has not yet been deciphered. Here, we have utilized 2-dimensional gel electrophoresis (2D-GE) coupled with mass spectrometry (MS/MS) to identify over expressed proteins in the pod wall of two different cultivars (commercial cultivar: JG 11 and tolerant cultivar: ICC 506-EB) of chickpea after 12 h of application of Helicoverpa armigera oral secretions (simulated herbivory). The assays were performed with a view that larvae are a voracious feeder and cause substantial damage to the pod within 12 h. A total of 600 reproducible protein spots were detected on gels, and the comparative analysis helped identify 35 (12 up-regulated, 23 down-regulated) and 20 (10 up-regulated, 10 down-regulated) differentially expressed proteins in JG 11 and ICC 506-EB, respectively. Functional classification of protein spots of each cultivar after MS/MS indicated that the differentially expressed proteins were associated with various metabolic activities. Also, stress-related proteins such as mannitol dehydrogenase (MADH), disease resistance-like protein-CSA1, serine/threonine kinase (D6PKL2), endoglucanase-19 etc. were up-regulated due to simulated herbivory. The proteins identified with a possible role in defense were further analyzed using the STRING database to advance our knowledge on their interacting partners. It decoded the involvement of several reactive oxygen species (ROS) scavengers and other proteins involved in cell wall reinforcement. The biochemical analysis also confirmed the active role of ROS scavengers during simulated herbivory. Thus, our study provides valuable new insights on chickpea-H.armigera interactions at the protein level.

Nematicidal activity of fluensulfone against some migratory nematodes under laboratory conditions.

BACKGROUND: The fluoroalkenyl fluensulfone, known to have strong nematicidal activity against Meloidogyne spp. (root-knot nematodes), was evaluated in vitro and in soil against the migratory nematodes Bursaphelenchus xylophilus, Aphelenchoides besseyi, Aphelenchoides fragariae, Ditylenchus dipsaci, Pratylenchus penetrans, Pratylenchus thornei and Xiphinema index. RESULTS: B. xylophilus and D. dipsaci were not immobilised by 48 h in vitro exposure to up to 16 mg L(-1) of fluensulfone. A. besseyi and A. fragariae were affected by 8 mg L(-1) , the highest concentration used for these nematodes. More than 60% of P. penetrans and P. thornei were immobilised by 4 mg L(-1) of fluensulfone; however, exposure of P. penetrans to the compound prior to inoculation did not affect their root penetration ability. The immobilisation rate of X. index was increased by 48 h exposure to even 1.0 mg L(-1) of fluensulfone. Incorporation of over 2 mg L(-1) of fluensulfone into the soil reduced populations of P. penetrans and P. thornei before and after planting lettuce and chickpea respectively. The efficacy of fluensulfone against the tested nematodes was the same or higher than that of fenamiphos in most cases. CONCLUSION: A. besseyi, A. fragariae, B. xylophilus and D. dipsaci were tolerant to fluensulfone and fenamiphos. P. penetrans, P. thornei and X. index were affected by fluensulfone, but nematicidal activity was much lower than that reported for root-knot nematodes.

Enhanced permeation, leaf retention, and plant protease inhibitor activity with bicontinuous microemulsions.

Bicontinuous microemulsions (BCMEs) have excellent solubulizing properties along with low interfacial tension and aqueous content that can be controlled. In this work, water soluble plant protease inhibitor (PI), well characterized for its activity against insect pests, was incorporated into a BCME system and explored for permeation on hydrophobic leaf surfaces and protease inhibition activity. The bicontinuous nature of the microemulsion containing water:2-propanol:1-butanol (55:35:10 w/w) was characterized using conductivity and self-diffusion coefficient measurements. The PI was soluble in the water-rich bicontinuous domains, stable in the microemulsions, and protease inhibition activity was retained for a prolonged duration. The microemulsions ensured greater wettability and a wider spread of the PI on hydrophobic leaf surfaces as revealed by contact angle measurements. Significantly, trypsin inhibition activity assays of the PI recovered from the leaves after delivery from the microemulsion indicated a significant increase in the PI retention on the leaf. This BCME enabled greater leaf permeation and retention of the PI can be attributed to a temporary disruption of the waxy leaf surface followed by self-repair without causing any long term damage to the plant.

Tissue specific expression of potent insecticidal, Allium sativum leaf agglutinin (ASAL) in important pulse crop, chickpea (Cicer arietinum L.) to resist the phloem feeding Aphis craccivora.

The phloem sap-sucking hemipteran insect, Aphis craccivora, commonly known as cowpea aphid, cause major yield loss of important food legume crop chickpea. Among different plant lectins Allium sativum leaf agglutinin (ASAL), a mannose binding lectin was found to be potent antifeedant for sap sucking insect A. craccivora. Present study describes expression of ASAL in chickpea through Agrobacterium-mediated transformation of "single cotyledon with half embryo" explant. ASAL was expressed under the control of CaMV35S promoter for constitutive expression and phloem specific rolC promoter for specifically targeting the toxin at feeding site, using pCAMBIA2301 vector containing plant selection marker nptII. Southern blot analysis demonstrated the integration and copy number of chimeric ASAL gene in chickpea and its inheritance in T(1) and T(2) progeny plants. Expression of ASAL in T(0) and T(1) plants was confirmed through northern and western blot analysis. The segregation pattern of ASAL transgene was observed in T(1) progenies, which followed the 3:1 Mendelian ratio. Enzyme linked immunosorbant assay (ELISA) determined the level of ASAL expression in different transgenic lines in the range of 0.08-0.38% of total soluble protein. The phloem tissue specific expression of ASAL gene driven by rolC promoter has been monitored by immunolocalization analysis of mature stem sections. Survival and fecundity of A. craccivora decreased to 11-26% and 22-42%, respectively when in planta bioassay conducted on T(1) plants compared to untransformed control plant which showed 85% survival. Thus, through unique approach of phloem specific expression of novel insecticidal lectin (ASAL), aphid resistance has been successfully achieved in chickpea.

Infection by Meloidogyne artiellia does not break down resistance to races 0, 1a, and 2 of Fusarium oxysporum f. sp. ciceris in chickpea genotypes.

Fusarium oxysporum f. sp. ciceris, and the root-knot nematode Meloidogyne artiellia, coinfect chickpea crops in several countries of the Mediterranean Basin. The influence of root infection by M. artiellia on the reactions of chickpea genotypes with different reaction to infection with F. oxysporum f. sp. ciceris races 0, 1A, and 2 was investigated under controlled environmental conditions. Results demonstrated that co-infection of chickpea genotypes resistant to specific fungal races by M. artiellia did not influence the Fusarium wilt reaction of the plant, irrespective of the F. oxysporum f. sp. ciceris race assayed. However, in some of the assayed combinations, coinfection by both pathogens significantly affected the level of colonization by the fungus or reproduction of the nematode in the root system. Thus, coinfection of chickpea plants with Foc-0 and M. artiellia significantly decreased the level of colonization of the root system by F. oxysporum f. sp. ciceris in genotypes 'CA 336.14.3.0' and 'PV 61', but not in 'ICC 14216 K' and 'UC 27'. Similarly, the nematode reproduction index was also significantly reduced by coinfection with Foc-0 in the four chickpea genotypes tested and inoculated with this race. Conversely, coinfection of chickpea plants with Foc-1A and M. artiellia significantly increased colonization of the root system by the fungus in all genotypes inoculated with this race, except for line BG 212. Altogether, we confirmed the complete resistance phenotype of 'UC 27' and 'ICC 14216 K' to Foc-0, and of 'ICC 14216 K' to Foc-1A and Foc-2, and demonstrated that this resistance was not modified by coinfection of the resistant plant with M. artiellia.

Evaluation of Cymbopogon martinii oil extract for control of postharvest insect deterioration in cereals and legumes.

The essential oil of Cymbopogon martinii was tested for its potency as a botanical pesticide to protect stored wheat (Triticum aestivum) and gram (garbanzo bean, Cicer arietinum) from insect infestation. The C. martinii oil was potent as a fumigant in stored gram. The oil was an effective repellent against the beetles Callosobruchus chinensis and Tribolium castaneum. Geraniol, the major component of the oil, was not as effective as the oil itself. C. martinii oil significantly affected oviposition, adult development, and mortality of C. chinensis in cow peas (Vigna unguiculata). The C. martinii oil when used as fumigant did not affect viability, germination, and seedling growth of gram. Because of its insecticidal and semiochemical nature, the oil could be used as an alternative to synthetic pesticides in an integrated pest management program to protect stored food commodities.

The expression of the homologue of the Caenorhabditis elegans lin-45 raf is regulated in the motile stages of the plant parasitic nematode Meloidogyne artiellia.

The Ras-MAPK signal transduction pathway controls multiple developmental events and is involved in the processing of olfactory information in the free living nematode Caenorhabditis elegans. We have studied the Ras-MAPK pathway in the plant parasitic nematode Meloidogyne artiellia. The genes Mt-let-60, Mt-lin-45, Mt-mek-2 and Mt-mpk-1 have been isolated and sequenced. Each of them shows a high level of sequence similarity to its presumed ortholog in C. elegans and key functional domains are structurally conserved. Furthermore, we show that the M. artiellia recombinant MEK-2 protein can phosphorylate and activate the M. artiellia recombinant MPK-1 and the recombinant MEK-2 itself can be phosphorylated and activated by immunoprecipitated mammalian Raf. Surprisingly, the Mt-lin-45 message is not detectable in freshly emerged juveniles or in male specimens, suggesting that it may be quickly degraded in these life stages.

Quantitative genetics of preference and performance on chickpeas in the noctuid moth, Helicoverpa armigera.

If a novel, resistant host-plant genotype arises in the environment, insect populations utilising that host must be able to overcome that resistance in order that they can maintain their ability to feed on that host. The ability to evolve resistance to host-plant defences depends upon additive genetic variation in larval performance and adult host-choice preference. To investigate the potential of a generalist herbivore to respond to a novel resistant host, we estimated the heritability of larval performance in the noctuid moth, Helicoverpa armigera, on a resistant and a susceptible variety of the chickpea, Cicer arietinum, at two different life stages. Heritability estimates were higher for neonates than for third-instar larvae, suggesting that their ability to establish on plants could be key to the evolution of resistance in this species; however, further information regarding the nature of selection in the field would be required to confirm this prediction. There was no genetic correlation between larval performance and oviposition preference, indicating that female moths do not choose the most suitable plant for their offspring. We also found significant genotype by environment interactions for neonates (but not third-instar larvae), suggesting that the larval response to different plant genotypes is stage-specific in this species.

Effect of different initial population densities of Meloidogyne incognita on the growth of Cicer arietinum.

Studies were undertaken to determine the effect of different initial population densities (Pi = 50, 100, 250, 500, 1000, 2500, 5000, 10,000 and 15,000 J2/Pot) of Meloidogyn incognita on chikpea cv. Bandal local in a pot experiment. Plant growth, flowering and pod bearing were influenced by all the initial population densities. Increase in Pi not only resulted in proportional decrease in plant lenght, fresh weight, dry weight and pod bearing but also delayed the flowering. The highest reduction was observed at the initial population of 15000 as compared to uninoculated control. It was noticed that reduction in root fresh weight was less than shoot especially at higher initial population. Reproduction of nematode was observed inversely proportional to intial population (on 50 J2/Pot, Rf = 196.64 and 15000 J2/Pot, Rf = 3.60).

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.