Control of Drechslera teres and other barley pathogens by preinoculation with Bipolaris maydis and Septoria nodorum

Preinoculation of barley leaves with either of two nonbarley pathogens, Bipolaris maydis from maize or Septoria nodorum from wheat, 24 h in advance of inoculation with a virulent isolate of Drechslera teres f. maculata resulted in significantly reduced infection by the latter organism. In a range of experiments, the reductions in disease severity measured 39 to 70% and 22 to 65% after preinoculation with B. maydis and S. nodorum, respectively. Furthermore, the disease-reducing capacity exerted by the two inducers is of a general nature since they were effective against D. teres in different barley cultivars and against other barley pathogens such as B. sorokiniana, Erysiphe graminis f. sp. hordei, and Rhynchosporium secalis. Light microscopy of infected leaves revealed that in noninduced control leaves, mycelial growth and sporulation of D. teres was abundant. In contrast, the reduced disease level of D. teres in barley leaves preinoculated with B. maydis or S. nodorum was associated with reduced lesion size, strongly restricted mycelial growth, and little or no sporulation, which are well-known factors of hypersensitive reactions. Hence, our results suggest that host resistance responses are activated and that induced resistance is involved in the suppression of D. teres