Microscopy Research, 2016, 4, 11-19 Published Online April 2016 in SciRes. http://www.scirp.org/journal/mr http://dx.doi.org/10.4236/mr.2016.42002 How to cite this paper: Ajmal, M., Akram, A., Ara, A., Akhund, S., Nayyar, B.G. and Seerat, W. (2016) Stem Histopathology of Sesame Seedlings Infected with Alternaria alternata. Microscopy Research, 4, 11-19. http://dx.doi.org/10.4236/mr.2016.42002 Stem Histopathology of Sesame Seedlings Infected with Alternaria alternata Maryam Ajmal, Abida Akram, Anum Ara, Shaista Akhund, Brian Gagosh Nayyar, Wajiha Seerat Department of Botany, PMAS, Arid Agriculture University, Rawalpindi, Pakistan Received 7 January 2016; accepted 29 March 2016; published 1 April 2016 Copyright © 2016 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract In the present study, histopathology of three varieties of sesame TS 3, TS 5 and SG 27 infected with Alternaria alternata was carried out to understand the mechanism of fungal infection and pene- tration in sesame plant as well as to determine the histological manifestation in sesame cells by light microscopy. Fungus was identified in infected tissues as a dark bluish black with toluidine blue O staining. Light microscopic examination of sesame stem showed that the fungus was present in epidermis, hypodermis and cortical parenchyma tissue as the symptoms became visible by naked eye ten days after inoculation (DAI). As the disease progress, the fungus moved from cortical parenchyma to vascular bundle, xylem and phloem. Later on, it completely overlapped the vascular bundle and entered in pith. When necrotic lesion appeared, fungus was present abun- dantly in epidermis, hypodermis, cortical parenchyma, vascular bundles and in pith. Due to its ex- cessive growth and complete overlapping of cells, disorganization or destruction of cells of sesame took place. It was concluded that the Alternaria alternata was not a tissue limited pathogen in- stead of this it spread in to all tissues of stem from epidermis to pith. Keywords Sesame, Alternaria alternata, Pathogen, Fungus, Light microscopy 1. Introduction Sesame (Sesamum indicum L.) is the most important and oldest oilseed crop, commonly known as till that be- longs to the family Pedaliaceae [1]. Globally sesame production is 4.04 million tons annually with an average productivity which is about 5.1 quintals per hectare [2] in an area of 7.54 million hectares [3]. Pakistan is at 14 th position among the major sesame producing countries in the world having a total production of 31,000 tons in an