Browsing by Author "Ranjith, M T"

Now showing 1 - 4 of 4

Characterization of resistance in tomato (Solanum lycopersicum L.) genotypes against whitefly (Bemisia tabaci genn.)
(Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2023-02-23) Kattumulla Tejaswee.; Ranjith, M T
: Tomato, Solanum lycopersicum (Mill.), is one of the most popular vegetables cultivated in tropical and subtropical regions of the world. In India, it has been cultivated across an area of 841 thousand ha, with a production of 20.38 metric tonnes (Statista, 2022). However, tomato production is hindered by various abiotic and biotic factors and among the biotic factors, the polyphagous sucking insect pest, whitefly, Bemisia tabaci (Genn.) causes both direct and indirect damage and yield loss to the tune of 25-100 per cent (Mutisya et al., 2016). Both nymphs and adults of B. tabaci feed on phloem sap and devitalizes the tomato plants and also serves as a vector for the causal organism of tomato leaf curl virus disease. To manage the whitefly menace in tomato, farmers rely heavily on chemical insecticides. However, the polyphagous nature of the insect as well as its innate ability to develop resistance to insecticides makes the management of the pest all the more difficult. Exploiting host plant resistance could be an alternative tool to manage whitefly infestation in tomatoes. Thus, the present study entitled “Characterization of resistance in tomato (Solanum lycopersicum L.) genotypes against whitefly (Bemisia tabaci Genn)” was undertaken in the Department of Entomology, College of Agriculture, Vellanikkara, Kerala Agricultural University, Thrissur during 2021-2022. 50 tomato genotypes obtained from different institutes viz., IARI, IIHR, NBPGR, KAU, TNAU and local collections were screened for whitefly resistance under polyhouse conditions. The tomato genotypes showed significant variation with respect to eggs, nymphal and adult populations of whitefly. The mean (pooled) number of eggs per plant varied between 1.63 and 7.28 eggs/cm2 and within the plants, the highest mean number of eggs was recorded on the top leaves (8.20 eggs/cm2), followed by the middle leaves (7.40 eggs/cm2), and the bottom leaves (6.30 eggs/cm2). Whereas, the mean (pooled) number of nymphs per plant varied from 1.45 to 7.41 nymphs/cm2 and within the plant, the highest number of nymphs was observed on the middle canopy (6.53 nymphs/cm2) followed by upper (5.84 nymphs/cm2) and bottom (4.62 nymphs/ cm2) parts of the canopy. However, the mean (pooled) number of adult whiteflies per plant ranged from 1.68 to 7.19 adults/ cm2 and within the plant, the highest number of adults were recorded on the upper canopy (8.20 adults/ cm2), followed by middle (7.20 adults/ cm2) and the bottom (5.90 adults/ cm2). Further, the genotypes were categorized based on scale given by Pradhan (1964). Three genotypes LC Idukki, LC Palakkad and EC 519806 which recorded the mean population of active stages of whitefly <3.67/ cm2 come under the resistant category, whereas eleven genotypes with a mean population ranging from 3.67 to 5.57 were categorised as moderately resistant. Sixteen genotypes were classified under the moderately susceptible category with a mean population ranging from 5.57 to 7.46, whereas 18 genotypes with a mean population >7.46 were considered as the highly susceptible category. The leaf area damage due to the feeding activity of whitefly, which results in the degradation of chlorophyll was measured indirectly in terms of the hue value of scanned photographic images of the leaves represented as integrated densities. The tomato genotypes classified under the resistant category recorded a low hue value ranging from 47 to 53, whereas in the susceptible genotypes, the hue value reached up to 99.5. Morphological characters like the type, length and density of trichome, and leaf lamina thickness were analyzed. Observation of the trichome type revealed that LC Idukki and LC Palakkad possessed three types of trichome i.e., type IV (glandular), type V (nonglandular), and VI (glandular). The length of the non-glandular trichome (Type V) present in the tomato genotypes varied from 513.10 μm to 1475.05 μm. The non-glandular trichome and glandular trichome densities recorded in the tomato genotypes ranged between 30.5 to 74.5 per mm2 and 5.50 to 98.00 per mm2, respectively. Leaf lamina thickness was measured and it ranged from 233.20 μm to 440.5 μm. There was a significant positive correlation between the whitefly population and the parameters such as nonglandular trichome density, leaf lamina thickness and length of trichome. However, a significant negative correlation exists between and glandular trichome density and whitefly population and it is presumed that the trichome type IV and VI present in the genotypes confers resistance to whitefly infestation. The biochemical parameters such as relative leaf water content (91.16 %), and total amino acid content (3.58 mg g-1) were found to be low, whereas, the total phenol (4.56 mg/ g), total flavonoid (1.82 𝜇𝑔 gˉ¹), and total alkaloid content (0.59 mg g-1) were significantly higher in resistant genotype LC Idukki. It was found that there was a significant positive correlation between the whitefly population and parameters such as relative water content and total amino acid content, whereas a significant negative correlation was observed between the whitefly population and parameters such as total phenol, flavonoid and alkaloid contents. Based on the present investigation, LC Idukki, LC Palakkad and EC 519806 may be rated as resistant to whitefly. The studies also show that resistance could be mediated by the type, density and length of leaf trichomes, along with leaf lamina thickness. It also indicated that the resistance in tomato to whitefly could be related to biochemical constituents of the plant, which, however, need to be confirmed. Sustained efforts could lead to the development of whitefly resistant tomato genotypes, providing the muchneeded edge to whitefly management in tomatoes.
Detection and biochemical characterization of insecticide resistance in Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae)
(Department of Agricultural Entomology, College of Agriculture,Vellanikkara, 2024-03-15) Harsha Thomas.; Ranjith, M T
Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), popularly known as tomato fruit borer or cotton bollworm, or gram caterpillar is a highly polyphagous insect pest causing severe damage to economically important agricultural crops worldwide. It has been reported to cause yield loss to the tune of 50 to 90 per cent in various crops (Ahmed et al., 1986; Lingappa and Yelshetty, 1994) and the extent of damage caused by this pest in various crops under different agro- national importan to reduce H. armigera menace in various crop ecosystems. However, the indiscriminate use of chemical insecticides has accelerated the field-evolved resistance in H. armigera to the major group of insecticides, thus making the management all the more difficult. H. armigera is a major threat to tomato and chilli, which are widely grown in Palakkad district in Kerala. Although farmers apply new generation insecticides on a large scale to manage this pest, it has often been claimed that control is not possible when these insecticides are applied in recommended doses. Hence, screening of resistance in H. armigera to commonly used insecticides and elucidating the biochemical mechanisms of resistance is necessary to develop better alternatives that could be feasible and effective for sustainable pest management. With these objectives, the and biochemical analysis of insecticide resistance in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) was undertaken at the Department of Agricultural Entomology, College of Agriculture, Vellanikkara, Kerala Agricultural University, Thrissur during the period from 2022 to 2024. Two field populations of H. armigera were collected from the tomato-growing belts of Palakkad, Kerala, and Kolar, Karnataka, and were screened for field-evolved resistance against various insecticides viz., chlorpyriphos, quinalphos, lambda-cyhalothrin, flubendiamide, chlorantraniliprole, emamectin benzoate, and spinosad. A susceptible population (ISS) was collected from IARI, New Delhi and maintained at AINPVPM laboratory. The biochemical mechanism conferring insecticide resistance was analyzed for the three major detoxifying enzymes, carboxylesterase, cytochrome P450, and glutathione S-transferase. Subsequently, as a confirmatory test, synergistic bioassay at 1:2, 1:4, and 1:6 ratios was conducted to confirm the involvement of enzymes in resistance. The major synergists used for the study were piperonylbutoxide (PBO) inhibiting cytochrome P450, triphenyl phosphate (TPP) which inhibits carboxyl esterase, and diethyl maleate (DEM) which inhibits glutathione S-transferase. In H. armigera field population collected from Kerala (PKT1), a high level of resistance was marked for the insecticides, chlorpyriphos ( ), quinalphos ( ), and lambda-cyhalothrin ( ), however a low level of resistance was recorded in PKT1 against chlorantraniliprole ( ) and emamectin benzoate (21- ) whereas, flubendiamide ( ) and spinosad ( ) marked a negligible resistance ratio. The H. armigera field population collected from Karnataka (KAT2), on the other hand, exhibited a high level of resistance towards chlorpyriphos ( ), quinalphos ( ) lambda-cyhalothrin ( ), and chlorantraniliprole ( ), whereas a low level of resistance was noted against the insecticide, spinosad ( ). The insecticides emamectin benzoate ( - ) and flubendiamide ( ) displayed a minimal resistance ratio. The biochemical analysis revealed that Kerala population (PKT1) showed a high carboxylesterase activity (16.545 µmol/min/mg) followed by glutathione S-transferase (0.569 µmol/min/mg). Whereas, the level of cytochrome P450 enzyme (0.592 pmol/min/mg) in the PKT1 remained lower than the susceptible population (0.773 pmol/min/mg). The field population collected from Karnataka (KAT2) exhibited significantly high levels of carboxylesterase (26.83 µmol/min/mg) and cytochrome P450 (1.293 pmol/min/mg) when compared to the susceptible population [with low carboxyl esterase (10.622 µmol/min/mg) and cytochrome P450 (0.494 pmol/min/mg)] indicating their involvement in conferring resistance to pyrethroids (lambda-cyhalothrin), organophosphates (quinalphos), and diamides. Conversely, the levels of GST remained low (0.133 µmol/min/mg) in KAT2. To elucidate the resistance mechanism mediated by metabolic detoxifying enzymes, a synergistic bioassay was conducted only for PBO and TPP as the activity of GST remained significantly low. Synergistic bioassay gave a better result at a 1:4 (insecticide: synergist) ratio. Kerala population did not show a significant synergism for chlorpyriphos and quinalphos in combination with PBO and TPP. However, lambda-cyhalothrin was synergized with a significant synergistic ratio (SR) of 96.39 by PBO and 53.596 by TPP. This indicates that resistance conferred to lambda-cyhalothrin was primarily due to enzymes particularly carboxylesterase, whereas resistance to organophosphate was not attributed to any detoxifying enzymes rather, other mechanisms might have involved. The organophosphate and pyrethroid insecticides on the other hand were synergised effectively by PBO and TPP in Karnataka population. The synergistic ratios obtained for chlorpyriphos with PBO at 1:6 ratio was125.428, while the synergism by TPP did not drop the LC50 to the fiducial limit in case of susceptible population.For quinalphos, a significant synergism was obtained at a 1:4 ratio by both PBO and TPP with SR valued at 122.524 and 134.576. The most effective and significant synergism was observed for lambda- cyhalothrin with PBO (SR=386.909) and TPP (148.375) at 1:4 ratio. This indicates the involvement of detoxifying enzymes especially cytochrome P450 and carboxylesterase in conferring resistance towards organophosphate and pyrethroids. The lack of significant synergism of Chlorantraniliprole by PBO, and TPP suggests that other mechanisms might have involved, particularly mutations in the ryanodine receptor (RyR) gene (Jouraku et al., 2019). It can be concluded from the present study that H. armigera infesting tomato in both Kerala and Karnataka is showing a varying level of resistance towards both conventional and new generation insecticides. The biochemical analysis reveals that different mechanisms are involved in both the geographical populations towards conferring resistance to these insecticides. Hence, it is important to keep a track on the status of resistance development in H. armigera consistently for the effective pest management and modification of management tools. This helps to minimize economic losses to the farmers and reduces the environmental impact.
Identification of larval morphotypes of helicoverpa armigera (Hiibner) (Lepidoptera: noctuidae) and their characterization using molecular markers
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 2015) Ranjith, M T; Mani Chellappan
Mechanisms of host plant resistance in Tomato (Solanum lycopersicum L.) genotypes to cotton whitefly (Bemisia tabaci Genn.)
(Department of Agricultural Entomology, College of Agriculture, Vellanikkara, 2024) Naveena Unnikrishnan.; Ranjith, M T
Tomato (Solanum lycopersicum) is one of the most widely cultivated crops worldwide, with India ranked second in global production (Ministry of Agriculture and Farmers Welfare, MOAFW, 2023). The cotton whitefly (Bemisia tabaci) is a major pest of tomato, inflicting direct damage by feeding on phloem sap and serving as a vector for the tomato leaf curl virus (ToLCV). The extensive use of synthetic insecticides has led to resistance in whitefly populations, alongside concerns about environmental and health risks. As a result, developing host plant resistance has emerged as a sustainable alternative for pest management. Building on a previous study at the Department of Agricultural Entomology, College of Agriculture, Vellanikkara, which evaluated fifty tomato genotypes for whitefly resistance under polyhouse conditions (Tejaswee, 2023), the current study, titled "Mechanisms of host plant resistance in tomato genotypes to cotton whitefly," was conducted during 2023-2024. The primary objectives were to evaluate the resistance of different tomato genotypes to cotton whitefly under field conditions and to investigate the mechanisms behind host plant resistance. Twenty tomato genotypes selected from the previous research (Tejaswee, 2023) were evaluated for their resistance to whitefly under field conditions. The genotypes exhibited significant variation in the density of all life stages of Bemisia tabaci. The number of whitefly eggs ranged from 1.33 ± 0.30 (LC Palakkad) to 11.80 ± 0.22 (EC 617060) on the top leaves, 0.90 ± 0.40 (LC Palakkad) to 11.03 ± 0.29 (EC 617060) on the middle leaves, and 0.73 ± 0.24 (LC Palakkad) to 7.63 ± 0.39 (EC 617060) on the bottom leaves. Nymph populations varied from 1.27 ± 0.21(LC Palakkad) to 11.23 ± 0.37 (EC 617060) on the top leaves, 0.93 ± 0.16 (LC Palakkad) to 8.73 ± 0.37 (EC 617060) on the middle leaves, and 0.70 ± 0.21 (LC Palakkad) to 6.47 ± 0.24 (EC 635520) on the bottom leaves. Adult whitefly populations ranged from 0.73 ± 0.30 (LC Palakkad) to 12.50 ± 0.37 (EC 617060) on the top leaves, 0.50 ± 0.35 (LC Palakkad) to 10.33 ± 0.55 (EC 638522) on the middle leaves, and 0.43 ± 0.15 (LC Palakkad) to 8.03 ± 0.27 (EC 617060) on the bottom leaves. The pooled mean counts for all life stages were highest on the top leaves, followed by the middle and bottom leaves. Three genotypes viz., LC Idukki, LC Palakkad, and EC 519806 had mean whitefly populations under 2.62 per leaf, classifying them as resistant. Six genotypes with a mean population between 2.62 and 5.31 were moderately resistant, while six others were moderately susceptible (5.31–8), and five genotypes with >8 were highly susceptible. Additionally, the screening of genotypes for the incidence of Tomato leaf curl virus (ToLCV) and the coefficient of infection (CI) revealed that LC Palakkad, LC Idukki, and EC 519806 were highly resistant to the leaf curl disease. In the free-choice assays, whitefly settling and oviposition preferences were monitored at regular intervals in the customised experimental arenas. EC 617060 had the highest whitefly count, with 9.33 ± 0.577 per leaf at 24 hours and 7 per leaf at 48 hours. No whiteflies were observed on LC Palakkad and LC Idukki after 48 hours. LC Palakkad and LC Idukki had the lowest oviposition preference, with only 0.67 eggs/cm², while the highest oviposition (7.33 eggs/cm²) was recorded on EC 635520 and EC 638522. The epicuticular wax content of the tomato genotypes varied from 0.032 ± 0.002 mg/cm² (EC 617060) to 0.197 ± 0.002 mg/cm² (LC Palakkad). A significant negative correlation was observed between wax content and both oviposition and settling preferences of B. tabaci. Additionally, settling and oviposition preferences were negatively correlated with glandular trichome density, but positively correlated with non-glandular trichome density and trichome length. In the no-choice experiment, the developmental parameters of B. tabaci were observed in clip-cages. Oviposition rates (OR) on the tomato genotypes ranged from 0.31 ± 0.10 to 4.24 ± 0.58 eggs per day. Pre-adult survival (PS) rates varied from 0.57 ± 0.07 to 0.90 ± 0.01, while adult survival (AS) rates ranged from 0.72 to 0.98 ± 0.02. The developmental period (DP) of B. tabaci ranged from 21.95 ± 0.03 to 31.97 ± 2.77 days. Oviposition, pre-adult survival, and adult survival showed negative correlations with phenol, flavonoid, and alkaloid content, but positive correlations with free amino acid content and relative water content. In contrast, the developmental period was positively correlated with phenol, flavonoid, and alkaloid content, and negatively correlated with free amino acid and relative water content. The present study identified LC Idukki, LC Palakkad, and EC 519806 as highly resistant to whitefly, B. tabaci, exhibiting low level of whitefly population and ToLCV incidence, reduced settling preference, oviposition, survival rates, and longer developmental periods. While glandular trichomes and epicuticular wax contribute to resistance through antixenosis, the study highlights the crucial role of antibiosis, especially through phenolic compounds, in disrupting the development of B. tabaci. These results emphasize antibiosis as the primary resistance mechanism against B. tabaci in the evaluated tomato genotypes. Thus, the present study offers valuable insights for further research into host plant resistance mechanisms, aiding the development of sustainable and economically viable integrated pest management strategies for tomato cultivation.