10.22376/ijpbs.2019.10.1.p1-12 Volume 1 Issue 4 2010 (October - December) Microbes use Indole 3-acetic acid (IAA) to interact with plants including phytostimulation and circumvention of basal plant defence mechanism. Fungal contamination is the most predominant in lessThan i greaterThan Alternanthera sessilis lessThan /i greaterThan tissue culture than bacteria. lessThan i greaterThan Colletotrichum lessThan /i greaterThan Sp. produced 25 mg/l of IAA in presence of tryptophan (400 mg/l) in Czapex medium. lessThan i greaterThan In vitro lessThan /i greaterThan studies were performed to utilize the IAA for callus induction of lessThan i greaterThan A. sessilis lessThan /i greaterThan , an important medicinal plant used in Siddha system of medicine. In Murashige and Skoog medium supplemented with 9.0 µM 2,4-D + 2.8 µM IAA, callus induction was maximum. Callus induction on 1.8 µM fungal IAA + 1.0 µM IAA (HiMedia) shows the potential application of fungal IAA in plant cell cultures. Karthikeyan Subbarayan,Nithya Varadharajan, Rajagopal Kalyanaraman Indole 3-acetic acid, Alternanthera sessilis, Contamination and Colletotrichum Sp. 257-262