AGGRESSIVENESS AND PHYSIOLOGICAL SPECIALIZATION OF Septoria tritici Rob. ISOLATES

Pathogenicity tests verifying the behavior of Septoria tritici isolates should be considered as a priority in the selection of resistant wheat materials to this pathogen, since the aggressiveness of each isolate can vary significantly, causing problems in the evaluation and selection of resistant genotypes. The objective of this work was to determine whether physiologic specialization exists among Argentinean and American Septoria tritici isolates, through the analysis of their pathogenicity on cultivars and lines of bread wheat (Triticum aestivum L.). The experiments were carried out in Castelar-Argentina and in Davis-USA. In Castelar, a split plot design (n = 4) was used. The cultivars or lines were randomized in the plots and the isolates in the subplots. Each subplot consisted of three plants belonging to a cultivar or line. In Davis, a strip split plot design (n = 6) was used. A pot containing three plants of each cultivar or line constituted the experimental plots. In both sites, the inoculation was made at the flag leaf phenological stage through foliar aspersion of a conidial suspension adjusted to 10-10 conidia mL. Evaluations were made by recording the leaf area covered with pycnidia (LACP) at the flag leaf stage with the use of rating scales. Differences (P ≤ 0.0001) in LACP were detected among cultivars or lines. Isolate effects and the interaction cultivar × isolate were significant (P ≤ 0.0001). Variations in aggressiveness and virulence were found among the isolates, indicating the presence of horizontal and vertical resistance in the host cultivars.