Impact of Variegated Temperature, CO2 and Relative Humidity on Survival and Development of Beet Armyworm Spodoptera exigua(Hubner) under Controlled Growth Chamber

Climate change will have a noteworthy bearing on survival, development, and population dynamics of insect pests. Therefore, we contemplated the survival and development of beet army worm, Spodoptera exigua under different temperatures, (15˚C, 25˚C, 35˚C, and 45˚C), CO2 (350, 550, 750 ppm) and relative humidity (55%, 65%, 75% and 85%) regimes. Maximum larval and pupal weights were recorded in insects reared at 25˚C. The growth of S. exigua was faster at 35˚C (larval period 7.4 days and pupal period 4.5 days) than at lower temperatures. At 15˚C, the larval period was extended for 61.4 days and there was no adult emergence from the pupae till 90 days. The S. exigua hatchling was absent at 45˚C. The larval survival ranged from 31.6% - 57.2%, maximum survival was recorded at 25˚C, and minimum at 45˚C. The maximum (84.27%) and minimum adult emergence were recorded in insects reared at 25˚C and 35˚C respectively. Maximum fecundity (384.3 eggs/female) and egg viability (51.97%) were recorded in insects reared at 25˚C. Larval and pupal periods increased with an increase in CO2 concentration. The highest pupal weights (128.6 mg/larva) were recorded at 550 ppm. The highest larval survival (73.50%) was recorded at 550 ppm and minimum (37.00%) at 750 ppm CO2. Fecundity was the highest in insects reared at 550 ppm CO2 (657.4 eggs/female), and the lowest at 750 ppm. Maximum larval and pupal weights were recorded in insects reared at 75% relative humidity (RH). The growth rate of S. exigua was faster at 85% RH than at lower RH. The larval survival ranged between 40.0% - 58.5%. Maximum adult emergence (88.91%) was recorded in insects reared at 75% RH and minimum at 85% RH. Maximum fecundity (447.6 eggs/female) and the highest egg viability (72.95%) were recorded in insects reared at 75% and 65% RH respectively. Elevated temperatures and relative moistness will diminish the life cycle, while hoisted CO2 will drag the life expectancy. Therefore, there is a need for thorough assessment of the impact of climatic factors on the population dynamics of insect pests, crop losses, and sustainability of crop production

Expression of different mechanisms of resistance to insects in groundnut under field conditions

Host plant resistance is an important component of pest management, and information on contribution of different mechanisms of resistance is important for developing cultivars with resistance to the target pests. Therfore, we studied the contribution of different components of resistance in five groundnut genotypes to three insect species occurring in India under field conditions. Plant damage by the larvae of Helicoverpa armigera, Spodoptera litura, and leafhoppers (Empoasca kerri) was evaluated visually on a 1 – 9 damage rating (DR) scale (1 being 80 % leaf damage). Further, the activities of various plant defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD), ascorbate peroxidase (APX), lipoxygenase (LOX) and catalase (CAT)], and the amounts of total phenols, condensed tannins, hydrogen peroxide (H2O2), malondialdehyde (MDA) and proteins were also recorded. The genotypes ICGV 86699, ICGV 86031, ICG 2271 and ICG 1697 suffered lower leaf damage by H. armigera and S. litura (DR 2.6 – 3.2) and E. kerri (DR 2.0 - 3.2) as compared to JL 24 (DR 7.2 and 6.0, respectively). ICGV 86699, ICGV 86031, ICG 2271 and ICG 1697 exhibited greater enzymatic activity, and had more amounts of phenols, condensed tannins, hydrogen peroxide and proteins than the susceptible check, JL 24. There was a positive association between leaf damage and the activity of the defensive enzymes, and the amounts of phenols, condensed tannins and H2O2. These results suggested that the plant defensive enzymes such as POD, PPO, LOX, PAL, SOD, APX and CAT were involved in genotypic resistance to insects, and the resistant genotypes accumulated phenols, condensed tannins, and H2O2 to impart resistance to insects. This information will be useful for developing groundnut genotypes with resistance to insects for sustainable crop production

Phenotyping for resistance to the sugarcane aphid Melanaphis sacchari (Hemiptera: Aphididae) in Sorghum bicolor (Poaceae)

The sugarcane aphid Melanaphis sacchari (Zehnt.) has become a serious pest of sorghum, particularly during the post-rainy season in India and East and Southern Africa. Therefore, we tested a number of techniques to screen sorghum genotypes for their resistance to M. sacchari. Infesting the plants with aphid-infested leaf cuttings and covering with a nylon net was effective in screening sorghum genotypes for their resistance to M. sacchari. Sprinkling the plants with aphids (filled in an 0.5 ml eppendorf tube) in the greenhouse was also used to confirm whether the resistance of genotypes selected is less susceptible to the aphids under natural infestation. Nine genotypes (Line 61510, ICSV 12001, ICSV 12002, ICSV 12003, ICSV 12004, ICSV 12005, SLR 41, PU 10-1 and DJ 6514) exhibited moderate levels of resistance to M. sacchari. These genotypes also exhibited a lower rate of aphid multiplication in the clip cage and leaf disc assays. The rates of aphid multiplication were lower on the genotypes IS 21807, IS 40615, IS 40616 and IS 40618 than on the susceptible check, Swarna in the clip cage assay under the field conditions. Also, lower rates of aphid increase were also recorded on IS 21807 and IS 40615 in the leaf disc assay under laboratory conditions. Some of the genotypes that exhibited resistance to aphid damage under field conditions showed comparatively higher rates of aphid increase than the susceptible check, Swarna in the clip cage assay, indicating that antixenosis could be one of the components of resistance to M. sacchari in these genotypes. Therefore, the clip cage assay could be used to gain further understanding of the mechanisms of resistance to M. sacchari. There is a need to assess the role of antixenosis and colonization in genotypic reaction against M. sacchari to identify the lines with different mechanisms of resistance to this pest. The results suggested that the nylon net technique could be used to screen sorghum genotypes for resistance to M. sacchari. The genotypes exhibiting resistance to M. sacchari can be used to develop aphid-resistant sorghums for sustainable crop production

Population density and damage by pod borers, helicoverpa armigera and spodoptera exigua in a diverse array of chickpea genotypes under natural infestation in the field

Host plant resistance is one of the important components of resistance to insects, and hence, we evaluated a diverse array of chickpea genotypes for resistance to pod borers, Helicoverpa armigera and Spodoptera exigua under field conditions. Data were recorded on S. exigua egg masses and larvae, H. armigera eggs and larvae, plant damage at the vegetative, flowering and podding stages, and grain yield at crop harvest. During the vegetative stage, significantly lower numbers of H. armigera and S. exigua larvae were recorded on ICC 10393, ICCL 86111, ICC 12475 and RIL 20; while leaf damage was significantly lower on ICC 12475, ICC 10393, ICCV 10, and RIL 25 as compared to that on ICC 3137. During the flowering stage, leaf damage was significantly lower on ICC 12475, RIL 20, RIL 25, ICC 10393, ICCL 86111, KAK 2, and ICCV 10 than on ICC 3137; of which the numbers of H. armigera larvae were significantly lower on ICCL 86111, RIL 20, ICC 10393, RIL 25 and ICC 12475 than on ICC 3137 in one or both sowings/seasons. During the podding stage, the H. armigera and/or S. exigua larval densities were significantly lower on ICC 12475, ICC 10393, RIL 25, ICCV 10, and RIL 20; of which EC 583264, ICC 10393, ICC 12475, ICCL 86111, ICCV 10, RIL 20 and RIL 25 than in ICC 3137. The grain yield of these genotypes was also significantly greater than that of ICC 3137 one or both sowings/seasons, and these genotypes can be used for improving chickpea to pod borer resistance for sustainable crop production

Elevated CO2 influences host plant defense response in chickpea against Helicoverpa armigera

Global atmospheric concentration of CO2 is likely to increase from 350 to 750 ppm over the next 100 years. The present studies were undertaken to understand the effects of elevated CO2 on enzymatic activity and secondary metabolites in chickpea in relation to expression of resistance to pod borer, Helicoverpa armigera. Fifteenday- old chickpea plants [ICCL 86111—resistant and JG 11—commercial cultivar] grown in the greenhouse were transferred to open-top chambers (OTC) and kept under 350, 550 and 750 ppm of CO2. Twenty neonates of H. armigera were released on each plant at 7 days after shifting the pots to the OTCs. Un-infested plants were maintained as controls. After 7 days of infestation, the activities of defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL)] and amounts of total phenols and condensed tannins increased with an increase in CO2 concentration in chickpea. The nitrogen balance index was greater in plants kept at 350 ppm CO2 than in plants kept under ambient conditions. The H. armigera-infested plants had higher H2O2 content; amounts of oxalic and malic acids were greater at 750 ppm CO2 than at 350 ppm CO2. Plant damage was greater at 350 ppm than at 550 and 750 ppm CO2. This information will be useful for understanding effects of increased levels of CO2 on expression of resistance to insect pests to develop strategies to mitigate the effects of climate change

Components of resistance to sorghum shoot fly, Atherigona soccata

Sorghum shoot fly, Atherigona soccata is one of the major constraints in sorghum production, and host plant resistance is one of the components to control sorghum shoot fly. Thirty sorghum genotypes were evaluated for different mechanisms of resistance and morphological and agronomic traits during the rainy and postrainy seasons. The sorghum genotypes, Maulee, Phule Anuradha, M 35-1, CSV 18R, IS 2312, Giddi Maldandi, and RVRT 3 suffered lower shoot fly damage, and also exhibited high grain yield potential during the postrainy season. ICSB 433, ICSV 700, ICSV 25019, ICSV 25022, ICSV 25026, ICSV 25039, PS 35805, Akola Kranti, and IS 18551 exhibited antixenosis for oviposition and antibiosis against sorghum shoot fly, A. soccata. Leaf glossiness, plant vigor, leafsheath pigmentation and trichomes were associated with resistance/susceptibility to shoot fly. Path coefficient analysis indicated that direct effects and correlation coefficients of leaf glossiness, plant vigor, plant height, plant color and trichomes were in the same direction, suggesting that these traits can be used to select sorghum genotypes for resistance to shoot fly. Principal co-ordinate analysis based on shoot fly resistance traits and morphological traits placed the test genotypes into different groups. The genotypes placed in different groups can be used to increase the levels and broaden the genetic base of resistance to shoot fly. The environmental coefficient of variation and phenotypic coefficient of variation for shoot fly resistance and morphological traits were quite high, indicating season specific expression of resistance to sorghum shoot fly. High broadsense heritability, genetic advance and genotypic coefficient of variation suggested the predominance of additive nature of genes controlling shoot fly resistance, suggesting that pedigree breeding can be used to transfer shoot fly resistance into high yielding cultivars. This information will be useful for developing shoot fly-resistant high yielding cultivars for sustainable crop production

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

Pattern of genetic inheritance of morphological and agronomic traits of sorghum associated with resistance to sorghum shoot fly, Atherigona soccata

Sorghum shoot fly, Atherigona soccata is an important pest of sorghum during the seedling stage, which influences both fodder and grain yield. To understand the nature of inheritance of shoot fly resistance in sorghum, we performed generation mean analysis using two crosses IS 18551 × Swarna and M 35-1 × ICSV 700 during the 2013–2014 cropping seasons. The F1, F2, BC1 and BC2 progenies, along with the parental lines were evaluated for agronomic and morphological traits associated with resistance/susceptibility to sorghum shoot fly, A. soccata. The cross IS 18551 × Swarna exhibited significant differences between the parents for shoot fly deadhearts (%) in the postrainy season. The progenies of this cross exhibited lower shoot fly damage, suggesting that at least one of the parents should have genes for resistance to develop shoot fly-resistant hybrids. Leaf glossiness, leafsheath pigmentation and plant vigor score during the seedling stage exhibited non-allelic gene interactions with dominant gene action, whereas 100 seed weight showed both additive and dominant gene interactions. Presence of awns showed recessive nature of the awned gene. Generation mean analysis suggested that both additive and dominance gene effects were important for most of the traits evaluated in this study, but dominance had a more pronounced effect

Quantitative Genetic Analysis of Agronomic and Morphological Traits in Sorghum, Sorghum bicolor

The productivity in sorghum is low, owing to various biotic and abiotic constraints. Combining insect resistance with desirable agronomic and morphological traits is important to increase sorghum productivity. Therefore, it is important to understand the variability for various agronomic traits, their heritabilities and nature of gene action to develop appropriate strategies for crop improvement. Therefore, a full diallel set of 10 parents and their 90 crosses including reciprocals were evaluated in replicated trials during the 2013-14 rainy and postrainy seasons. The crosses between the parents with early- and late-flowering flowered early, indicating dominance of earliness for anthesis in the test material used. Association between the shoot fly resistance, morphological and agronomic traits suggested complex interactions between shoot fly resistance and morphological traits. Significance of the mean sum of squares for GCA (general combining ability) and SCA (specific combining ability) of all the studied traits suggested the importance of both additive and non-additive components in inheritance of these traits. The GCA/SCA, and the predictability ratios indicated predominance of additive gene effects for majority of the traits studied. High broad-sense and narrow-sense heritability estimates were observed for most of the morphological and agronomic traits. The significance of reciprocal combining ability effects for days to 50% flowering, plant height and 100 seed weight, suggested maternal effects for inheritance of these traits. Plant height and grain yield across seasons, days to 50% flowering, inflorescence exsertion and panicle shape in the postrainy season showed greater specific combining ability variance, indicating the predominance of non-additive type of gene action/epistatic interactions in controlling the expression of these traits. Additive gene action in the rainy season, and dominance in the postrainy season for days to 50% flowering and plant height suggested G X E interactions for these traits

Mechanisms and diversity of resistance to sorghum shoot fly, Atherigona soccata

Sorghum shoot fly, Atherigona soccata, is one of the important pests of postrainy season sorghums. Of the 90 sorghum genotypes evaluated for resistance to this pest, RHRB 12, ICSV 713, 25026, 93046 and 25027, IS 33844-5, Giddi Maldandi and RVRT 3 exhibited resistance in postrainy season, while ICSB 463, Phule Anuradha, RHRB 19, Parbhani Moti, ICSV 705, PS 35805, IS 5480, 5622, 17726, 18368 and 34722, RVRT 1, ICSR 93031 and Dagidi Solapur showed resistance in rainy season, suggesting season-specific expression of resistance to A. soccata. ICSB 461, ICSB 463, Phule Yasodha, M 35-1, ICSV 700, 711, 25010, 25019 and 93089, IS 18662, Phule Vasudha, IS 18551 and 33844-5 and Barsizoot had fewer deadhearts than plants with eggs across seasons, suggesting antibiosis as one of the resistance mechanism. Five genotypes exhibited resistance with high grain yield across seasons. Correlation, path and stepwise regression analyses indicated that leaf glossiness, seedling vigour, trichome density, oviposition and leaf sheath pigmentation were associated with the expression of resistance/susceptibility to shoot fly, and these can be used as marker traits to select and develop shoot fly-resistant sorghums