Epicuticular waxes for resistance against thrips in onion (Allium cepa L.)
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Date
2023
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Punjab Agricultural University
Abstract
Thrips is an important insect-pest of onion (Allium cepa L.), which is one of the most important commercial bulbous vegetable crops. Present studies were undertaken to determine the extent of genetic variation for thrips resistance and correlation, if any, between epicuticular wax characteristics and thrips infestation in a diverse set of onion genotypes. Thirty genotypes were screened for thrips incidence and accordingly classified into five resistant-susceptibility categories during Rabi 2021-22. Foliage damage was also scored and it exhibited a positive correlation with thrips incidence both during damage study week and season. CIELAB indices were studied 60 DAT and all showed non-significant correlation with foliage damage. L* and Z% exhibited significant negative correlation with thrips incidence. Darker and less bright foliage faced relatively high thrips incidence compared to lighter and brighter foliage. Foliage lightness had a significant positive correlation with thrips
resistance. GC-MS study was undertaken to quantify 16-hentriaconatone wax from leaves wherein QuEChERS-based extraction did not yield acceptable recovery. Total leaf phenol content was estimated before harvesting in selected genotypes and it showed non-significant, positive and negative correlation, respectively, with thrips incidence and resistance. PCRbased molecular study revealed Thrips tabaci Lind. as the prevalent thrips species at research location. FE-SEM revealed varied scattering of spiky, plate-like epicuticular wax crystals (likely ketones) on different leaf surfaces and relative crystal deposition showed an inverse relationship with lightness of foliage colour. Variation in size of stomatal apertures was also observed, however, correlation if any, with thrips incidence and damage could not be determined.
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Sandeep Kaur (2023). Epicuticular waxes for resistance against thrips in onion (Allium cepa L.) (Unpublished M.Sc. thesis). Punjab Agricultural University, Ludhiana, Punjab, India.