Tramesan Elicits Durum Wheat Defense against the Septoria Disease Complex

Abstract

The Septoria Leaf Blotch Complex (SLBC), caused by the two ascomycetes Zymoseptoria tritici and Parastagonospora nodorum, can reduce wheat global yearly yield by up to 50%. In the last decade, SLBC incidence has increased in Italy; notably, durum wheat has proven to be more susceptible than common wheat. Field fungicide treatment can efficiently control these pathogens, but it leads to the emergence of resistant strains and adversely affects human and animal health and the environment. Our previous studies indicated that active compounds produced by Trametes versicolor can restrict the growth of mycotoxigenic fungi and the biosynthesis of their secondary metabolites (e.g., mycotoxins). Specifically, we identified Tramesan: a 23 kDa α-heteropolysaccharide secreted by T. versicolor that acts as a pro-antioxidant molecule in animal cells, fungi, and plants. Foliar-spray of Tramesan (3.3 μM) on SLBC-susceptible durum wheat cultivars, before inoculation of causal agents of Stagonospora Nodorum Blotch (SNB) and Septoria Tritici Blotch (STB), significantly decreased disease incidence both in controlled conditions (SNB: -99%, STB: -75%) and field assays (SNB: -25%, STB: -30%). We conducted these tests were conducted under controlled conditions as well as in field. We showed that Tramesan increased the levels of jasmonic acid (JA), a plant defense-related hormone. Tramesan also increased the early expression (24 hours after inoculation - hai) of plant defense genes such as PR4 for SNB infected plants, and RBOH, PR1, and PR9 for STB infected plants. These results suggest that Tramesan protects wheat by eliciting plant defenses, since it has no direct fungicidal activity. In field experiments, the yield of durum wheat plants treated with Tramesan was similar to that of healthy untreated plots. These results encourage the use of Tramesan to protect durum wheat against SLBC.

Keywords: Septoria disease complex; antioxidant; biostimulant; mushrooms; plant defense; wheat.

Figure 1

P. nodorum ST15465 (upper) and Z. tritici ST18258 (lower) growth assessed by qPCR. At 0, 3, and 9 days after inoculation (dai) in durum wheat (vars. Svevo and Duilio). Mock: without Tramesan, non-inoculated. T: treated with Tramesan; T + Inf: treated with Tramesan, inoculated with the pathogen; Inf: inoculated with the pathogen. Values represent the mean ± SE as described in the methods section. Small capital letters in the chart represent the significantly different groups (p < 0.05; Fisher’s test).

Figure 2

Expression profile of transcripts of genes CERK1, MPK3, NADPHox (RBOH), PAL, PR1, PR4, CHIT2, PR9, and MCA2 in durum wheat var. Svevo at 48 h after treatment with Tramesan (3.3 μM). Expression is relative to values in untreated plants (control) and values represent the mean ± SE as described in the Methods section. Small capital letters in the chart represent the significantly different groups (p < 0.05; Fisher’s test).

Figure 3

Fold induction (reported in log₁₀ scale) of salicylic acid (SA) and jasmonic (JA) acid in durum wheat var. Svevo, after 48 h treatment (T) or untreated (mock) with Tramesan (3.3 μM). Values represent the mean ± SE as described in the methods section. Small capital letters in the chart represent the significantly different groups (*** p < 0.001; t-test).

Figure 4

Expression profile of transcripts at 0 and 24 hours after infection (hai) of genes RBOH, PR1, PR4, and PR9 in durum wheat var. Svevo infected with P. nodorum ST15465 (Inf Pn) or Z. tritici ST18258 (Inf Zt) and infected with pathogens and pre-treated (−48 hai) with Tramesan (Tr + Inf). Expression is relative to values in untreated plants (CT−; without Tramesan, non-inoculated) and values represent the mean ± SE as described in the methods section. Asterisks represent the significantly different values (* p < 0.05; ** p < 0.01; *** p < 0.001; t-test).