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Introduction
Septoria tritici Rob. ex Desm. (teleomorph: Mycosphaerella graminicola (Fuckel) Schroeter) causes Septoria tritici blotch (STB; syn. Septoria leaf blotch) of wheat. STB is currently among the most important disease of wheat worldwide (Brown 2001). The disease attacks wheat in all stages of development and, under favourable conditions, may cause serious yield losses reported to range from 31 to 54% (Eyal et al. 1987; Babadoost and Herbert 1984; Polley and Thomas 1991). In Argentina, yield losses from 21 to 37% (Kraan and Nisi 1993) and from 20 to 50% (Annone et al. 1991) in high-yielding cultivars have been found. STB is controlled as part of an integrated crop management system using resistant cultivars, cultural practices and chemical control. Breeding for resistance is the best and most reliable option. However, wheat cultivars reported to be resistant in one country may sometimes succumb to attack by Septoria populations in another country (Eyal et al. 1981, 1987). Fungicides give effective control of STB and are widely used in Europe.
Although normally not economical, foliar fungicides can be used to control STB outbreaks in Argentina. Applications should be made between tillering and heading, with the objective being to protect the flag leaf. Depending on the weather conditions from tillering to the early dough stage, one or more applications may be needed. A combination of these practices and biological control need to be considered among the strategies for the management of STB (Annone 2005). The use of biocontrol agents in conjunction with plant resistance may provide an equivalent level of control, with less adverse impact upon the environment than the use of chemicals. Previous studies in Argentina indicate that innocuous epiphytic micro-organisms on the wheat leaf surface play important roles in the suppression of STB (Perelló et al. 1998a, b, 2001a, b, 2002).
Trichoderma spp. are fungi that are present in substantial numbers in nearly all agricultural soils and in other environments (Harman 1996). They are not normally regarded as resident organisms on foliar surfaces. Nevertheless, Trichoderma spp. were found on wheat on the phylloplane (Biles and Hill 1983; Mangiarotti et al. 1987) and as an endophyte (Larrán et al. 2002). It was demonstrated that Trichoderma stains can survive in the aerial part of the plants for long periods...