Priming, an effective defence mechanism in plants against pests: Study

Agricultural modernisation has led to the widespread use of synthetic chemicals to control pests and pathogens. The pesticides, though very effective, often pollute the environment and can have deleterious effects on animal and human health.

A team of researchers from the Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, and Tata Institute of Fundamental Research, has provided strong molecular evidence for the two-fold advantage of defense ‘priming’ as a sustainable crop protection strategy in the indigenous spice crop ‘Black pepper’ (Piper nigrum).

Priming as a defence mechanism

The deleterious impact of pesticides has led to an urgent need for developing alternative pest and disease-control approaches. One is the development of methods to enhance plants’ own natural defence mechanisms (innate immunity) by ‘priming’. Priming is a mechanism that leads to a physiological state that enables plants to respond more rapidly and/or more robustly after exposure to biotic or abiotic stress.

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Black pepper (Piper nigrum) is an indigenous woody spice crop of global importance. Diseases and pests pose serious production constraints to its sustainable yield. Phytophthora capsici is the major pathogen responsible for the devastating ‘quick wilt’ or ‘foot-rot’ disease affecting black pepper. It infects the leaves, stems, and roots of cuttings in the nursery and pepper plantations.

Current practices of systemic fungicide treatment measures have negative implications and can lead to phytotoxicity and fungicide resistance. “Our study reports, for the first time, the potential of defense priming as an efficient crop protection strategy in Piper nigrum against infection by Phytophthora capsici. Our findings establish a proof-of-concept of the potential of defense priming through stem/vine injection in protecting P. nigrum from infection in nurseries and plantations,” researchers explain.

“Our data open the way for in-depth mechanistic studies for identifying new potential natural agents that can prime the defense of P. nigrum sustainably. This is the first report that provides strong molecular evidence for the two-fold advantage of defense priming in P. nigrum by improving crop protection with a concomitant enhancement in Piperine biosynthesis,” researchers further elucidate.

Effects of Glycol Chitosan treatment

Glycol Chitosan (GC), a water-soluble, non-toxic polymer with several commercial and possible biomedical uses, has been used in this study. It is known to induce plant defense. “It was consistently observed that GC treatment offered protection from the severity of ‘quick wilt’ disease and caused a significant delay in the appearance of symptoms. A noteworthy observation of the study was the significant increase in ‘Piperine’ accumulation in leaves due to priming. Piperine is regarded as largely responsible for the pungent taste of black pepper,” researchers report.

The team conducted studies in rooted cuttings in seedlings, detached leaves of mature plants, and rooted cuttings in the field. They injected GC into the experimental plants’ leaves and subjected them to pathogen infection, post 24 hours of treatment. The development of symptoms and disease spread was observed microscopically and confirmed by molecular pathogen DNA quantification assay. The expression levels of critical genes of the defense signalling pathway were measured along with Lignin and Piperine content quantification.

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“Our study has shown the promising potential of ‘priming’ and has potential implications in crop nurseries and the field. More work is needed to establish the durability of priming and to optimize the method and duration of treatment for a large-scale commercial application,” researchers recommend.

The study team comprised M Indu, B Meera, KC Sivakumar, Chidambareswaren Mahadevan, K Mohammed Shafi, B Nagarathnam, Ramanathan Sowdhamini, and Manjula Sakuntala. The study has been published in Frontiers, an open access journal.

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