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Disease-Reducing Effect of Chromolaena odorata Extract on Sheath Blight and Other Rice Diseases

First, fourth, and fifth authors: Department of Plant Biology and Biotechnology, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark; and first, second, and third authors: Department of Plant Protection, College of Agriculture and Applied Biology, Can Tho University, 3/2 Street, Ninh Kieu District, Can Tho City, Vietnam.

Sheath blight caused by Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) is a major cause of crop loss in intensive rice production systems. No economically viable control methods have been developed. We screened aqueous extracts of common herbal plants that could reduce sheath blight lesions and found that foliar spraying and seed soaking application of extracts of either fresh or dried leaves of Chromolaena odorata gave up to 68% reduction in sheath blight lesion lengths under controlled and semi-field conditions. The observed reductions were not dependent on growth conditions of C. odorata and rice cultivar. The effect was observed until 21 days after inoculation and was not dependent on microbial activity. Under semi-field conditions, extracts also reduced severity of other important rice diseases, i.e., blast (Pyricularia oryzae) using foliar spray (up to 45%), brown spot (Bipolaris oryzae) using seed treatment (up to 57%), and bacterial blight (Xanthomonas oryzae pv. oryzae) using both application methods (up to 50%).