Some biochemical defense responses enhanced by soluble silicon in bitter gourd-powdery mildew pathosystem R. M. R. N. K. Ratnayake 1 & W. A. M. Daundasekera 2 & H. M. Ariyarathne 3 & M. Y. U. Ganehenege 4 Received: 24 February 2016 /Accepted: 29 June 2016 /Published online: 9 July 2016 # Australasian Plant Pathology Society Inc. 2016 Abstract Silicon (Si) has been exploited for its beneficial effects in terms of disease control in many plants. Added Si was found to accumulate beneath the cuticle and act as a barrier against pathogen penetration, and also induce biochemical defense re- sponses in plants. This study investigated the effect of soluble silicon (Si) supply on biochemical defense responses against powdery mildew pathogen (Erysiphe sp.) in bitter gourd (Momordica charantia L.), an intermediate Si accumulator. Supplying the sand-based growth medium with 200 ppm potas- sium silicate (Si+) significantly reduced the severity of powdery mildew infections, elevated the activities of enzymes peroxidase, polyphenol oxidase and pathogenesis-related proteins; chitinase and β-1,3-glucanase in bitter gourd leaves after challenged by Erysiphe sp. compared with those grown in control mix (Si - ). After 7 weeks growth in Si-amended medium, leaves accumu- lated nearly seven times as much silicon (3.36 % dry weight) as those grown in control mix (0.44 % dry weight). The total Si content in leaves gradually decreased after the Si amendment was ceased. Si + plants exhibited a stronger antifungal activity against Cladosporium cladosporioides. Three zones with an- tifungal activity were revealed after separation of methanolic leaf extracts on thin-layer chromatography plates, out of which one compound was found to have induced by Si and/ or Erysiphe infection, and another induced only by Si amend- ment. These results suggest that Si would play an active role in strengthening resistance in bitter gourd plants against powdery mildew by stimulating expression of several biochemical de- fense reactions. Keywords Antifungal activity . PR proteins . Momordica charantia . Peroxidase . Polyphenol oxidase . Silicon Introduction Silicon (Si) is not considered as an essential plant nutrient, although many plants accumulate Si from 0.1 to 10 % of its dry matter (Ma and Takahashi 2002). However, it is an agro- nomically important element due to its many beneficial effects on growth and development of many plant species and en- hancing plant resistance to various biotic and abiotic stresses (Datnoff et al. 2009). Many evidence support the fact that Si could control plant disease caused by fungi such as brown spot and blast disease of rice (Volk et al. 1958; Datnoff et al. 1992), rust in bean (Heath 1981), powdery mildew in wheat and barley (Zeyen et al. 2002), anthracnose in cucumber (Kanto 2002) and grape (Bowen et al. 1992, gray mold rot in cucumber (Datnoff et al. 2009) blue mold rot and brown rot in sweet cherry (Qin and Tian 2005) and black sigatoka in banana (Kablan et al. 2012). Although the exact nature of protective effects by Si in plants is a subject of debate, some possible mechanisms have been proposed (Cai et al. 2008). Si can accumulate and deposit beneath the cuticle to form a cuticle-Si double layer and act as a physical barrier to impede Electronic supplementary material The online version of this article (doi:10.1007/s13313-016-0429-0) contains supplementary material, which is available to authorized users. * R. M. R. N. K. Ratnayake ruwankaratnayake@yahoo.com 1 Postgraduate Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka 2 Department of Botany, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka 3 Horticultural Crop Research and Development Institute, Gannoruwa, Sri Lanka 4 Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka Australasian Plant Pathol. (2016) 45:425–433 DOI 10.1007/s13313-016-0429-0