Biochemical Changes in Host Plant Invaded by Opportunistic Fungi and Nematodes

In nature, various changes occur in plant system due to biotic and abiotic agents. Changes occurring at physiological, molecular, and biochemical level in plants due to biotic factors mainly phytopathogens such as fungi, bacteria, nematodes, and viruses play an integral role in determining the overall health and functioning of plants. Over the years plants have developed numerous ways to defend themselves against the invading phytopathogens. A number of biochemical reactions take place within plant system leading to the induction of various chemical substances in response to the invading fungi and nematodes such as detoxification of pathogen toxins, pathogenesis-related (PR) proteins (e.g., chitinases and glucanases), toxic phenolics (secondary metabolites secreted by plants as a part of their defence mechanism against stress), protective enzymes (peroxidase, catalase, superoxide dismutase), induction of various signalling pathways (jasmonic acid and salicyclic acid pathways) to activate systemic acquired resistance (SAR), generation of reactive oxygen species (ROS), lipoxygenases, etc. which are either toxic to the invading phytopathogens or may counteract the effect of pathogen toxins. Studies have also revealed an increase in the quantity of total phenolics and soluble sugar in plants, which serve as biochemical markers to assess disease severity, which varies in host cells depending on pathogen attack. Such biochemical assays establish a method for investigating the expression level of biochemical components as a result of a cell response, i.e., a defence mechanism under stress conditions. Proper understanding of such biochemical changes occurring within plants invaded by phytopathogens is of prime importance in improving productivity of plants and for the development of new and improved diseased resistant varieties.