Molecular signature on phloem sap of the enhanced host susceptible phase to Liphaphis erysimi in Brassica species.
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Date
2022-12
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College of Post Graduste Studies in Agricultural Sciences, Central Agricultural University, Imphal
Abstract
The importance of oil and by-products from oilseeds crop in the lives of humans and cattle cannot be underestimate as oilseed crops are lucrative crop with great potential for enhancing human diets, preventing hunger and food insecurity. However, oil seed crops like rapeseed-mustard are extremely susceptible to aphid attack mainly mustard aphid (Liphaphis erysimi) and it serves at the key limiting factor in achieving a surplus productivity with reported losses in yield up to 90%. Mustard aphid is exclusively phloem feeders and they utilized their highly specialized mouthparts to suck and ingest simple sugars, proteins, and amino acids enriched phloem sap from plant sieve elements. The precise access of the host plant's Sieve Element (SE) cell by the aphid stylet is a crucial factor for clonal proliferation. The objective of the present study was to identify optimized factors enhancing host susceptibility toward aphid clonal proliferation and uncover molecular signature of the aphid herbivore phloem sap in comparison to control. Among the 5, 10 and 20 aphid releases on random leaf foliage in B-9, B-54, Pusa Bold, Rohini, RGN-384 and RMM-09-10 revealed that ten aphids enhanced host susceptibility as compared to other aphid doses except in RMM-09-10. It was also recorded that aphid inoculum at 6 AM enhanced host susceptibility in comparison to 6 PM aphid release. Moreover, Relative humidity was a modulating factor in enhancing host susceptibility and 95% RH was the most effective over 70% and 50% RH. Among temperature, 160C and 220C promoted aphid clonal proliferation in comparison to 280C and 340C. The age of the plant was also a factor in modulating host susceptibility. From the present study, an initial aphid inoculum (10), timing of aphid release (6 AM), humidity (95% RH), temperature (220C) and age of plant enhanced host susceptibility towards aphid clonal proliferation. The maximum absorbance of phloem exudate was evidenced from 4 number of leaves, 0.5mM EDTA concentration and 12 hours dark mediated phloem sap isolation without compromising secondary induced stress. The absorbance of aphid herbivore phloem sap at 215 nm is significantly higher in Rohini, RGN-384 and RMM-09-10 but remains same in B-9, B-54 and Pusa Bold. The absorbance of aphid herbivore phloem sap at 260nm is significantly higher in B-9, Rohini and RGN-384 and significantly lower in B-54, Pusa Bold and RMM-09-10. The absorbance of aphid herbivore phloem sap at 280nm is significantly higher in B-9, Rohini and RGN-384 and significantly lower in Pusa Bold and RMM 09-10 but remains same in B-54. The GC-MS analysis of aphid herbivore phloem exudates isolated at the earliest and significant time point identified several reported antimicrobial compounds which shows that aphid herbivore targets on the in-built anti-microbial defense in the phloem sap and upon aphid herbivore, the anti-microbial metabolites concentration was reduced. This finding initiated extended curiosity about the microbiota enrichment from the aphid herbivore phloem exudates. The further study indicated that aphid herbivore enriched phloem microbiota at the earliest and significant host susceptible phase. One of the identified metabolites, dodecanoic acid (DA) showed an anti-biotic effect on aphid herbivore mediated phloem microbiota. The crucial findings from the present study indicated that aphid herbivore reduce the anti-microbial concentration in the phloem sap at the earliest and significant time point which coincided to the enhanced host susceptibility. Therefore, aphid herbivore mediated microbiota inoculum in the phloem sap is a novel phenomenon being reported for the first time in plant-aphid interaction biology.