Geneviève Arsenault-Labrecque, Département de Phytologie, Centre de Recherche en Horticulture, Université Laval, Québec, Canada G1V 0A6;
James G. Menzies, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, MB, Canada R3T 2M9; and
Richard R. Bélanger, Département de Phytologie, Centre de Recherche en Horticulture, Université Laval, Québec, Canada G1V 0A6
Silicon (Si) is recognized for its prophylactic role in alleviating diseases when absorbed by plants and has been proposed as a possible solution against soybean rust, caused by Phakopsora pachyrhizi. However, little is known about its potential effects on soybean (Glycine max) because the plant's ability to absorb Si is poorly defined. In this work, our objectives were to evaluate and quantify the absorption of Si in leaves of different soybean cultivars and to determine if such absorption was able to enhance resistance to soybean rust. In a first set of experiments with cv. Williams 82, hydroponic plants were supplied or not with Si and inoculated with urediniospores of P. pachyrhizi. Chemical analyses revealed no significant differences in the plants' Si content regardless of the treatment, which translated into no effect on rust incidence. However, in a second set of experiments with different cultivars, plants of Korean cultivar Hikmok sorip absorbed nearly four times more Si than those of Williams 82. At the same time, plants from this cultivar exhibited a near absence of disease symptoms when supplied with Si. This resistance appeared to be the result of hypersensitive (HR) reactions that were triggered when plants were fed with Si. These results support the concept that a plant's innate ability to absorb Si will dictate the benefits conferred by a treatment with Si and provide evidence that Si can protect soybean plants against soybean rust through mediated resistance.