Abstract

Nnamdi E. K and Onyeka Ckuwendo

Plant produce a host range of organic compounds which are hormones in nature including organic acids and vitamins in complex networks to balance the response to developmental and environmental cues, which could serve as nutrients or signals by microbial populations. Pathogens release phytohormones, small molecules or volatile compounds which act directly or indirectly to activate plant immunity or regulate plant growth. Phytohormones pathways which are linked to each other in a complex network; ABA, ET, gibberellins auxins, cytokinius, pathways are seen as hormone modulators of the SA-JA signaling back bone. Plants employ specific recognition and signaling systems enabling the rapid detection of pathogen invasion and initiation of vigorous defensive responses. Evidence has accumulated showing that classic plant signals such as auxins and cytokinins can be produced by microorganisms to efficiently colonize the root and modulate root system. Plant hormones are able to control some pathogen bacteria through microbial antagonism, which is achieved by competing with the pathogens for nutrients, producing antibiotic, and the production of anti-fungal metabolites. Mutual interactions between stress-specific hormones such as salicyclic acid and jasmonic acid/ethylene SA-JA (ET) are regarded as the central back bone of the immunity in plants. However, growth-promoting hormones (auxins, cytokinins, gibberellic acid, and abscisic acid) either inhibit or potentiate this balance in mediating the protection or susceptibility of the plant against the invading pathogen.