* To whom all correspondence should be addressed. E-mail: weerasak@kku.ac.th JOURNAL OF PURE AND APPLIED MICROBIOLOGY, June 2016. Vol. 10(2), p. 853-863 Application of Microorganisms for Induced Resistance in Jerusalem Artichoke (Helianthus tuberosus L.) against Stem Rot Caused by Sclerotium rolfsii Sacc. Punyisa Charirak 1 , Weerasak Saksirirat 1,2 *, Sanun Jogloy 3 and Suwita Saepaisan 1,2 1 Section of Plant Pathology, Department of Plant Science and Agricultural Resources, Faculty of Agriculture, Khon Kaen University, Khon Kaen - 40002, Thailand. 2 Agricultural Biotechnology Research Center for Sustainable Economy, Khon Kaen University, Khon Kaen - 40002, Thailand. 3 Plant Breeding Research Center for Sustainable Agriculture, Khon Kaen University, Khon Kaen - 40002, Thailand. (Received: 13 February 2016; accepted: 09 March 2016) Jerusalem artichoke (Helianthus tuberosus L. ) is a multipurpose crop grown for bio-fuel, feed additive and functional food products. Stem rot disease caused by Sclerotium rolfsii Sacc. is an important threat for Jerusalem artichoke production in the tropics, and disease control using induced resistance strategy is worth exploring. The objective of this study were to investigate the induction of chitinase and β-1,3-glucanase activities in leaves of H. tuberosus after treated with microorganisms, Bacillus firmus BSR 032, Trichoderma harzianum T9 and mycorrhizal fungus, Glomus clarum and to evaluate their efficacy on controlling the disease under green house condition. Increase in chitinase and β-1,3-glucanase activity and reduction in disease incidence were observed for the plants treated with these antagonistic microorganisms. The highest and most consistent increase in chitinase and β-1,3-glucanase was observed in the plants treated with T. harzianum T9 followed by T. harzianum T9+G. clarum, and β-1,3-glucanase was found at higher activity than chitinase. The T. harzianum T9 could reduced the disease incidence of 44.4%, followed by T. harzianum T9+G. clarum (22.8%), B. firmus BSR 032+G. clarum (15%), B. firmus BSR032 (8.6%) and G. clarum (4.2%), respectively. This T. harzianum T9 is a promising antagonistic microorganism for controlling stem rot disease. Keywords: Antagonistic microorganisms, chitinase, disease control, disease incidence, 1,3-glucanase. Jerusalem artichoke ( Helianthus tuberosus L.) is native plant of North America and known as a source of inulin, a dietary fiber that is beneficial to health 1 . Consuming Jerusalem artichoke tubers helps reduce human lipid levels in blood and risks of diabetes and heart disease 2,3 . As a source of carbohydrate, the plant can be also used in production of acetone, butanol and ethanol 4,5 . Jerusalem artichoke is used as a food for human consumption and also feed for animals 6,7,8 . Sugar yield of Jerusalem artichoke under Mediterranean conditions could be as high as 7.48 to 10.82 tons ha -1 depending on years 9 . Yield in the tropical regions is rather low because shorter crop cycle, and the crop can be produced all year with irrigation. Stem rot disease caused by Sclerotium rolfsii is a devastating threat to Jerusalem artichoke production in the tropics and can cause severe