Comprehending new insights on variability, pathogenesis and pathogenicity factors of Macrophomina phaseolina and host plant defence mechanisms

Abstract

Macrophomina phaseolina infects mainly roots and stems of several crops as well as leaves, pods and seeds of some crops. Microsclerotia produced by it play an important role in its survival and pathogenesis. It enters root epidermis, crosses cortical tissue, and reaches xylem, where it forms mycelia and sclerotia, resulting in the blockage of water and nutrient movement, which leads to yellowing, withering and death of the plant. Despite the fact that Macrophomina was previously considered a monotypic genus with M. phaseolina as the only species, recent studies have identified a number of other species, such as M. pseudophaseolina, M. euphorbiicola, M. vaccinii and M. tecta, indicating that Macrophomina is a polytypic genus. Sclerotial viability is affected by high soil moisture and low soil temperature. As the disease is favored by hot and dry weather conditions, climate change, which leads to water stress, and global warming, which leads to rising temperatures, are exacerbating the disease and spreading it worldwide, including temperate countries. Water stress during the flowering period of crops is typically the most favourable condition for disease outbreaks. Although it is referred to as a hemibiotroph in some literature, it is called a necrotroph because it enters a living cell first, but kills the surrounding cells and continues to grow, reproduce and multiply within the dead cell. As its genome contains a higher number of different pathogenicity genes, especially an array of genes/gene clusters encoding cell wall-degrading enzymes, effector proteins, peptidases, phytotoxins, transporters, etc., it is more virulent and pathogenic than other necrotrophic fungi. Among the phytohormones, jasmonic acid (JA) and ethylene (ET), but not salicylic acid (SA), are mainly involved in activating various host defense mechanisms against the colonization of M. phaseolina in the root system. Screening genotypes for resistance to M. phaseolina would be an effective approach for its management.