Plant diseases are major constraints to the world agricultural production. A comprehensive knowledges about plant diseases in tropical and subtropical areas caused by diverse pathogenic microorganisms are introduced. Pathogens modulate host cells to enable their growth and dissemination. Plants require a broad range of defense mechanisms to effectively combat invasion by microbial pathogens. Current knowledges on plant responses to pathogen attack and the mode of attack are introduced for a better understanding of plant-pathogen interactions and an efficient strategies to combat plant pathogens.