Plant Defense against Necrotrophic Pathogens

Necrotrophic pathogenic bacteria, fungi and oomycetes\r\nare widely distributed and are responsible for significant crop losses. Host\r\nplants deploy different defense mechanisms and appropriate immune responses to\r\ndefend them against these pathogens. Regardless of the pathogen’s lifestyle,\r\ninfection activates plant immune responses either through Pathogen/Microbe\r\nAssociated Molecular Pattern (P/MAMP) or through Effector Triggered Immunity\r\n(ETI). However, as R-genes are not usually associated with resistance to\r\nnecrotrophs, resistance is largely dependent on the balanced interplay between\r\ncrucial phytohormones in complex signaling pathways involving jasmonic acid\r\n(JA), ethylene, salicylic acid (SA) and abscisic acid (ABA). An increase in\r\nsalicylic acid levels enhances susceptibility to necrotrophic pathogens but\r\npromotes resistance to hemibiotrophs, whereas a deficiency in SA or SA\r\nsignaling has either no significant impact or affects resistance only at the\r\nprimary infection site. The same fashion is observed for JA signaling system\r\nthat appears to elicit resistance against diseases caused by necrotrophic\r\npathogens and can trigger systemic immunity conferring resistance against them.\r\nOn the other hand, ABA can play a positive or negative role in plant defense\r\nresponses to necrotrophs as ABA-mediated defense responses are dependent on\r\nspecific plant-pathogen interactions. Understanding plant immune response\r\nagainst necrotrophic pathogens may lead to the development of resistant or\r\ntolerant crop cultivars.