Phytohormones are chemically synthesized molecule which are used different physiological functions of that one of phytohormone is called as Auxin One of the derivatives is considered as IAA (Indole Acetic Acid ) An important factor in a plant's growth and development is phytohormones. The molecular underpinnings of numerous phytohormones, including their production procedures and crucial signalling. components IAA, also known as indole-3-acetic acid, is a hormone or regulator of plant growth. It is a particular auxin. It is a hormone that exists naturally in plants. It influences a variety of physiological processes and controls the expansion and development of plants. It can also be found in some bacteria and fungi, where it regulates gene expression and different physiological reactions. In this investigation we have discuss about the different aspect growth of plants’ IAA also relation to plant pathogen interaction, We also discuss the different impact of IAA level and root development