RESULTS AND DISCUSSION Rheology and breadmaking parameters TOLERANCE TO SEPTORIA LEAF BLOTCH AND ITS ASSOCIATION WITH WHEAT QUALITY CASTRO, Ana Carolina 1-2; SIMÓN, María Rosa 1 1- Cerealicultura. Facultad Cs. Agrarias y Forestales. Universidad Nacional de La Plata. 60 y 119 CP 1900, 2- CONICET, Argentina. ingeniera.anacastro@gmail.com INTRODUCTION Septoria Leaf Blotch (SLB) caused by Mycosphaerella graminicola (Fuckel) J. Schröt in Cohn, anamorph Zymoseptoria tritici ex Desm, is one of the most important foliar diseases of wheat in the world. Tolerance is defined as the ability to maintain grain yield despite the presence of disease symptoms and could be used as a tool to reduce fungicide application. It is known, that there is disease tolerance to SLB in some wheat cultivars, but has not been studied among Argentinean wheat cultivars. In addition, there are contrasting results about the effect of the disease on the wheat quality and how tolerance can influence associations. OBJECTIVE The aim of this study was 1- to determine tolerance to Z. tritici in Argentinean wheat cultivars 2- to analyze the influence of increasing concentrations of inoculum of Z. tritici, on the grain yield (GY), grain protein percentage (GP), test weight (TW), wet gluten (WG), loaf volume (V), alveogram and farinogram parameters among Argentinean wheat cultivars 3- to establish possible relationships between tolerance and wheat quality parameters. MATERIALS AND METHODS The experiments were carried out in the field at the National University of La Plata during 2010 and 2011 with a split-plot design with three replications. The main plot was the inoculum concentration (IC): 1– Non inoculated (NI), 2- Low spores concentration (LC), 3- High spores concentration (HC) and the subplots were ten wheat cultivars: Klein Zorro, Buck 75 Aniversario, Buck Brasil, Buck Guapo, (G1, higher quality group), Klein Escorpion, Klein Flecha , ACA 801 and Relmo Centinela (G2, intermediate quality group), Nidera Baguette 10 (Bag 10) and Klein Chaja (G3, lower quality group). Disease severity at three growth stages, area under disease progress curve (AUDPC), green leaf area duration (GLAD), grain yield, test weight, grain protein, wet gluten, loaf volume, tenacity (P), extensibility (L), P/L ratio, dough strength (W), water absorption (A), development time (B), dough stability (D), degree of softening (E) were determined. Tolerance of wheat varieties to SLB was quantified as the slope of the relationship between GLAD and yield across treatments of contrasting disease pressure within each cultivar and associations with wheat quality variables were established. RESULTS AND DISCUSSION The increase in inoculum concentration caused higher severity and AUDPC values in all cultivars for both years. SLB decreased grain yield (P<0.001) between 18% and 49.6% when the HC was applied, depending on the cultivar. Losses in grain yield could be explained by reductions in GLAD. Differences in the slopes of the regression between GLAD and grain yield suggests the existence of tolerant cultivars. Thus, B. Brasil, Baguette 10, K. Escorpion, B. 75 Aniversario and K. Flecha were the most tolerant cultivars whereas K. Chaja, B. Guapo, ACA 801 and K. Zorro were intolerant in both years. R. Centinela showed higher tolerance in 2011 than in 2010 (Figure 1 and 2). Table 1 shows that GP, WG, L, W, D and V (Figure 3A and 3B) increased significantly (P < 0.001) with HC while P, P/L ratio and E decreased. Test Weight, A and B were not modified by the inoculum concentration. Cultivars showed significant differences. The interaction year × cultivar was also significant for GP, WG, alveogram parameters, A and E. V was negatively associated (r = -0.62) with tolerance to SLB, indicating that those cultivars with lower yield losses (tolerant) had higher increases in V when affected by SLB. K. Zorro K. Chaja ACA 801 K. Flecha R. Centinela B. Brasil B. 75 Aniversario Baguette 10 B. Guapo K. Escorpion Y = 34.3 x + 808.1 Y = 47.09 x - 231.04 Y = 33.8 x + 451.02 Y = 25.8 x + 1209 Y = 51.7 x - 1460 Y= 11.26 x + 2233.6 Y = 20.02 x + 1897.6 Y = 17.64 x + 2038.7 Y = 46,55 x - 621.92 Y = 15.01 x + 2660.2 R2 = 0.9905 R2 = 0.9988 R2 = 0.9615 R2 = 0.9275 R2 = 0.9604 R2 = 0.9992 R2 = 0.3829 R2 = 0.6314 R2 = 0.8736 R2 = 0.9834 Figure 1. Slopes of the lineal regression between green leaf area duration (GLAD) and grain yield for ten wheat cultivars under three inoculation treatments with Zymoseptoria tritici in 2010. Wheat Quality NI LC HC Grain Protein (%) 10.07 a 10.75 b 11.3 c Wet Gluten (%) 20.99 a 21.57 a 22.58 b Rheology and breadmaking parameters   Tenacity (mm) 112.43 c 103.33 b 98.87 a Extensibility (mm) 40.57 a 43.12 ab 47.07 b P/L ratio 2.85 c 2.47 b 2.17 a Dough Strenght (j x 10-4) 192.3 a 198.3 a 218.2 b Dough Stability (min) 10.37 a 12.66 ab 13.73 b Softening Degree (U.B) 98.5 b 74.7 a 73.4 a Loaf Volume (cm3) 305.2 a 306.2 a 335.5 b K. Zorro K. Chaja ACA 801 K. Flecha R. Centinela B. Brasil B. 75 Aniversario Baguette 10 B. Guapo K. Escorpion Y = 33.8 x - 962.29 Y = 47.33 x - 224.59 Y = 36.65 x + 1349.3 Y = 25.91 x + 796.94 Y = 16.53 x + 1637.9 Y = 14.26 x + 1233.3 Y = 21.82 x - 389.22 Y = 15.52 x + 2174.7 Y = 49.61 x - 2559.8 Y = 25.75 x + 1322.5 R2 = 0.9995 R2 = 0.9555 R2 = 0.9733 R2 = 0.9717 R2 = 0.9194 R2 = 0.3653 R2 = 0.9006 R2 = 0.7849 R2 = 0.6126 R2 = 0.9982 Figure 2. Slopes of the lineal regression between green leaf area duration (GLAD) and grain yield for ten wheat cultivars under three inoculation treatments with Zymoseptoria tritici in 2011. 3-B 3-A Table 1. Mean values of quality parameters under three inoculation treatments: NI (Non Inoculated), LC (Low Concentration) and HC (High Concentration) in ten wheat cultivars. Different letters between inoculation treatments within each quality parameter indicate significant differences. Figure 3. Effect of increasing inoculum concentration (left to the right in each figure NI, LC and HC) of Z. tritici in the loaf volume of a tolerant cultivar (Baguette 10) (3A) and intolerant cultivar (B. Guapo) (3B).