Silicon supplementation improves early blight resistance in Lycopersicon esculentum Mill . by modulating the expression of defense-related genes and antioxidant enzymes

Abstract

Early blight is the most devastating disease in tomato which causes huge yield losses across the globe. Hence, development of specific, efficient and ecofriendly tools are required to increase the disease resistance in tomato plants. Here, we systematically investigate the defensive role and priming effect of silicon (Si) in tomato plants under control and infected conditions. Based on the results, Si-treated tomato plants showed improved resistance to Alternaria solani as there was delay in symptoms and reduced disease severity than non-Si-treated plants. To further examine the Si-mediated molecular priming in tomato plants, expression profiling of defense-related genes like PR1, PR2, WRKYII, PR3, LOXD and JERF3 was studied in control, Si-supplemented, A. solani-inoculated and Si + A. solani-inoculated plants. Interestingly, Si significantly increased the expression of jasmonic acid (JA) marker genes (PR3, LOXD and JERF3) than salicylic acid (SA) marker genes (PR1, PR2 and WRKYII). However, Si + A. solani-inoculated plants showed higher expression levels of defence genes except WRKYII than A. solani-inoculated or Si-treated plants. Furthermore, pre-supplementation of Si to A. solani-infected tomato plants showed increased activity of antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and peroxidase (POD) than control, Si-treated and A. solani-inoculated plants. Altogether, present study highlights the defensive role of Si in tomato plants in response to A. solani by increasing not only the transcript levels of defense signature genes, but also the activity of antioxidant enzymes.

Keywords: Alternaria solani; Antioxidant enzymes; Early blight; Lycopersicon esculentum; PR genes; Silicon.

Fig. 1

Disease resistance screening of Si-treated tomato plants after A. solani infection. Forty-five-day-old Si-treated and non-Si-treated tomato plants were infected with A. solani. Si-treated plants showed reduction and delay in disease severity than non-Si-treated-inoculated plants. C: control (a: 3 dpi, b: 6 dpi, c: 9 dpi, d: 12 dpi, e: 15 dpi) and Si: Si treated (f: 3 dpi, g: 6 dpi, h: 9 dpi, i: 12 dpi, j: 15 dpi)

Fig. 2

Disease scoring like lesion diameter of Si-treated and non-Si-treated plants after A. solani infection at different dpi. Three biological replicates were used. Values are mean ± SD of each condition. Statistically significant difference is shown by different asterisks on bars (^*p < 0.05; ^**p < 0.01) between Si-treated and control-inoculated plants

Fig. 3

Early blight disease severity was monitored in-Si + infected and + Si + infected plants based on total leaf area infected. Values are (mean ± SD) of three replicates. Bars with different asterisks depicting statistically significant difference (^*p < 0.05; ^**p < 0.01)

Fig. 4

Relative expression levels of PR1, PR2, PR3, LOXD, WRKYII and JERF3 genes in L. esculentum in response to Si treatment and inoculation with A. solani determined by qRT-PCR. Expression levels were compared with an internal control alpha tubulin. Data represent mean ± S.D of three technical replicates. Asterisks indicating statistically significant differences between Si-treated, A. solani-inoculated and Si + A. solani-inoculated plants (^*p < 0.05; ^**p < 0.01)

Fig. 5

Activity of antioxidant enzymes in control, Si-treated, Si + A. solani- and A. solani-inoculated L. esculentum plants a SOD, b CAT, c APX, d GR, e POD. Data presented are the mean ± SD of three replicates. Different letters on bars indicate significant differences between means at P ≤ 0.05