Impact of morphological antixenotic resistance on the establishment of H. armigera on different chickpea germplasms

Introduction

Chickpea (Cicer arietinum L.) is one of the most economically important pulse crop in India (Farooq et al., 2018) [3] and it accounts for 40 per cent of total pulse production followed by pigeon pea (16%), mungbean (13%), lentil (7%) and other legumes (20%) (Mann et al., 2020) [4] . Pod borer, Helicoverpa armigera is one of the most damaging pests of chickpea, Cicer arietinum. To develop insect-resistant cultivars with durable resistance, it is important to understand the contribution of different components of resistance, and therefore, we studied antixenosis mechanisms of resistance to H. armigera in a diverse array. Plant resistance can be classified as antixenosis (non-preference) and antibiosis (how a plant is unsuitable for an herbivore). It has been demonstrated that these mechanism of plant resistance can be inferred from the behavior of H. armigera. These plant-insect pest interaction refer to two different phenomenon, namely the search for the plant and its acceptance (antixenosis). Antixenosis is based on behavioral avoidance of a host due to feature or set of feature that deter the insect from settling and feeding. (Smith, 2005) [8] . The expression of antixenosis in genotype may be consequence of both biochemical and morphological characteristic in plant and mainly effects the visual and olfactory stimuli involved in the host finding behavior. Antixenosis occurs when morphological or chemical factors of plants adversely effect insect behavior leading to delayed acceptance or rejection of a plant as a host (Shoorooei et al., 2018) [7] . Among the cause of antixenosis, morphological and biochemical characteristics of chickpea germplasm can influence female behavior by decreasing the feeding and oviposition and seeking shelter for a host plant (Painter, 1951) [6] . Different chickpea germplasms possess several morphological characteristics that can provide resistance against H. armigera. Among these, pubescence in chickpea crop which refer to the density of trichomes, is considered one of the most important factor for imparting resistance against H. armigera. In chickpea, trichome exudates contains oxalic, malic and citric acid which also imparts resistance against H. armigera (Narayanamma, 2013) [5] . Therefore there is need to explore plant defence mechanism for developing chickpea cultivars with high level of resistance to H. armigera.

Materials and Method: To check the impact of trichome length on feeding of Helicoverpa armigera in chickpea germplasm using Scanning electron microscopy:

To access the antixenosis mechanism of resistance towards H. armigera on the basis of trichome length, growth and development of H. armigera on eleven promising chickpea germplasms. Germplasm RSGD-834, BG4017, DMHC 18-1664, GJG 1803, GJG 1801, NBeG 1635, NBeG 810, RLBGMH-G, JG 2020-60, NBeG 857, RSGD 926 were taken along with checks ICCL3137, ICCL86111, PG3 for the estimation of leaf trichome length using Scanning electron Microscopy (SEM) at the Electron Microscopy Laboratory, College of Veterinary, GBPUA&T, Pantnagar in accordance with the standard protocol established by (Bozzola and Russell, 1999) [1] .

Standard protocol for imaging leaf under scanning electron microscopy for Trichome density and length

Fresh leaves from each genotype were collected, cut into 5mm² sections, and immediately placed in separate vials containing 2.5% glutaraldehyde for primary fixation, followed by overnight storage at 4°C. The samples were then rinsed three times with phosphate buffer solution (pH 7.2-7.4) for 15 minutes each. Dehydration was carried out using a graded ethanol series (30, 50, 70, 90, and 100%) for 15 minutes each, with a final 30-minute dehydration step in absolute ethanol. The specimens were dried at the critical point in CO₂ at 5°C and affixed to aluminum stubs using double-sided carbon tape. Each specimen was mounted with the lower epidermal surface facing upward for examination. The mounted samples were sputter-coated with a thin gold layer using an automated JAFC 1600 sputter coater. Finally, the specimens were analyzed and imaged using a JASM 6610LV Scanning E Plate 1: Counting trichomes on upper leaf surface

Result and Discussion

Impact of morphological antixenotic resistance on the establishment of H. armigera on different chickpea germplasms Antixenotic resistance of promising chickpea germplasm against H. armigera was carried out under laboratory conditions on the basis of morphological features viz., mean trichome density, length of glandular and non-glandular trichomes on upper side, lower side of the leaf and pod.

Trichome density on leaves and pods of promising germplasm of chickpea

In case of pods, the numbers of non-glandular trichomes were few even completely absent in most of the germplasms. On the upper surface of the leaf, the minimum glandular trichome length was recorded on NBeG1635 (225.60 μm), whereas the maximum glandular trichome length was observed on NBeG 810 (300.50 μm). Similarly, the maximum and minimum non-glandular trichome length was recorded in NBeG 810 (245.10 μm) and RLBGMH-4 (180.35 μm), respectively. On the lower surface of leaf maximum trichome length was observed in germplasm NBeG 810 (297.10 trichomes per mm2) whereas the mean glandular trichome length on pod ranged from 241.71μm to 312.05 μm. The highest glandular trichome length on pod was recorded on DHMC 18-1664 (311.05 μm) whereas lowest trichome length was recorded on GJG 1801 (240.71μm) respectively.

Correlation between morphological characteristics of leaves and pods of promising chickpea germplasm and population of H. armigera during 2020-21

The data pertaining to the correlation between morphological characteristics of leaves and pods of promising chickpea germplasms with H. armigera population are presented below. Glandular trichome length on leaves showed non-significant negative correlation with number of eggs, larval population and per cent pod damage (r = -0.166 NS , -0.490 NS , and -0.226 NS , respectively). On the other hand, the length of the non-glandular trichomes on leaf had a non-significant correlation with egg, larval population and pod damage (r = -0.022 NS , -0.419 NS and -0.346 NS , respectively). Whereas in case of pods also, the length of the trichomes (glandular and had non-significant negative correlation with the population of H. armigera, indicating that more the trichome length, lesser would be the number of H. armigera eggs, larval population and pod damage. The above findings are well supported by Brar et al. (2017) [2] who recorded non-significant negative correlation between length of nonglandular and length of glandular trichome on pod with egg, larval population of H. armigera and pod damage.

Conclusion

The study revealed significant variation in trichome density and length among chickpea germplasms, influencing their antixenotic resistance to Helicoverpa armigera. DHMC 18-1664 and NBeG 810 exhibited the highest glandular trichome length on leaves, while DHMC 18-1664 had the maximum glandular trichomes on pods. NBeG 810 showed the longest glandular and non-glandular trichomes. These traits likely contribute to resistance by deterring insect feeding. Overall, DHMC 18-1664 and NBeG 810 emerged as promising resistant germplasms against H. armigera.

References

1. Bozzola JJ, Russell LD. Electron microscopy: principles and techniques for biologists. London: Jones and Bartlett Publishers; 1999. 255 p.
2. Brar HS, Singh R. Role of trichomes on leaves and pods for imparting resistance in chickpea (Cicer arietinum L.) genotypes against Helicoverpa armigera (Hübner). J Appl Nat Sci. 2017;9(4):2193-2198.
3. Farooq M, Ullah A, Lee DJ, Alghamdi SS. Terminal drought-priming improves the drought tolerance in desi and kabuli chickpea. Int J Agric Biol. 2018;30(1):11291136.
4. Mann A, Kumar A, Sanwal SK, Sharma PC. Sustainable production of pulses under saline lands in India. Green Farm. 2020;2(3):253-256.
5. Narayanamma VL, Sharma HC, Vijay PM, Gowda CLL, Sriramulu M. Expression of resistance to the pod borer Helicoverpa armigera (Lepidoptera: Noctuidae) in relation to high-performance liquid chromatography fingerprints of leaf exudates of chickpea. Int J Trop Insect Sci. 2013;33(4):276-282.
6. Painter RH. Insect resistance in crop plants. J Entomol Res. 1951;72(6):481-486.
7. Shoorooei M, Hossein Zadeh A, Maali Amiri R, Allahyari H. Some biochemical responses of common bean (Phaseolus vulgaris L.) to two spotted spider mite (Tetranychus urticae Koch). Iran J Field Crop Sci. 2018;49(3):109-119.
8. Smith TJ, Sharma HC, Pampapathy G, Lanka SK, Ridsdill J. Antibiosis mechanism of resistance to pod borer, Helicoverpa armigera in wild relatives of chickpea. Euphytica. 2005;142(1):107-117.
9. Sree Latha E, Sharma HC. Antixenosis mechanism of resistance to Helicoverpa armigera (Hub) in chickpea (Cicer arietinum Linn.). Int J Curr Microbiol Appl Sci. 2018;7(2):1233-1238.
10. Taggar GK, Singh R. Integrated management of insect pests of rabi pulses. In: Theory and practice of Integrated Pest Management. India; 2012 Feb 14(1):454-472.