Greenhouse screening of the saprophytic resident microflora for control ofleaf spots of wheat (Triticum aestivum)

Ten microorganisms of the epiphytic microflora of wheat leaves in Buenos Ai res Province, Argentina, were evaluated under greenhouse conditions as pote ntial biocontrol agents of the pathogens Alternaria triticimaculans, Bipola ris sorokiniana, Drechslera tritici-repentis and Septoria tritici in two ap plication sequences (prior to or together with the pathogens). The antagoni sts significantly reduced the expression of the diseases on wheat plants co mpared with control plants not inoculated with the antagonists. Maximum per centage of reduction of the necrotic lesion area (NLA) (40-55%) of S. triti ci resulted when Cryptococcus sp., Rhodotorula rubra and Penicillium lilaci num were sprayed on leaves prior to inoculations with the pathogen. Bacillu s sp., Cryptococcus sp., Fusarium moniliforme var. anthophylium, P. lilacin um and R. rubra reduced significantly (34-52%) the NLA of B. sorokiniana in both of the application sequences. The best antagonistic effect against A. triticimaculans was shown by Aspergillus niger Bacillus sp., Chaetomium gl obosum, F. moniliforme var. anthophylium and Nigrospora sphaerica, with a N LA reduction from 21% to 35% in the co-inoculation or in the sequential app lication. All microorganisms except N. sphaerica performed better than the control against D. tritici-repentis. The area under disease progress curve (AUDPC) of the pathogens appeared to progress similarly, but at lower value s, in treated plants than in untreated controls. The two yeasts and the bac teria decreased AUDPC to 50-55% of S. tritici and B. sorokiniana compared w ith the control in both application sequences, whereas the maximum efficacy against A. triticimaculans was reached by N. sphaerica and A. niger for th e sequential application and by F moniliforme var. anthophylium for the co- inoculation. If the parasitism occurs also in nature, application of antago nists for biological control might provide the opportunity to compete with the pathogens and regulate their colonization in wheat leaves.