DETOXIFICATION OF BENZOXAZOLINONE ALLELOCHEMICALS FROM WHEAT BY GAEUMANNOMYCES-GRAMINIS VAR. TRITICI, G-GRAMINIS VAR. GRAMINIS, G-GRAMINIS VAR. AVENAE, AND FUSARIUM-CULMORUM

The ability of phytopathogenic fungi to overcome the chemical defense barriers of their host plants is of great importance for fungal pathog enicity. We studied the role of cyclic hydroxamic acids and their rela ted benzoxazolinones in plant interactions with pathogenetic fungi. We identified species-dependent differences in the abilities of Gaeumann omyces graminis var, tritici, Gaeumannomyces graminis var. graminis, G aeurnannonzyces graminis var, avenae, and Fusarium culmorum to detoxif y these allelochemicals of gramineous plants. The G. graminis var. gra minis isolate degraded benzoxazolin-2(3H)-one (BOA) and 6-methoxy-benz oxazolin-2 (3H)-one (MBOA) more efficiently than did G. graminis var, tritici and G, graminis var. avenae. F, culmorum degraded BOA but not MBOA. N-(2-Hydroxyphenyl)-malonamic acid and N-(2-hydroxy-4-methoxyphe nyl)-malonamic acid were the primary G, graminis var. graminis and G. graminis var. tritici metabolites of BOA and MBOA, respectively, as we ll as of the related cyclic hydroxamic acids. 2-Amino-3H-phenoxazin-3- one was identified as an additional G. graminis var. tritici metabolit e of BOA. No metabolite accumulation was detected for G. graminis var. avenae and F. culmorum by high-pressure liquid chromatography. The my celial growth of the pathogenic fungi was inhibited more by BOA and MB OA than by their related fungal metabolites. The tolerance of Gaeumann omyces spp. for benzoxazolinone compounds is correlated with their det oxification ability. The ability of Gaeumannomyces isolates to cause r oot rot symptoms in wheat (cultivars Rektor and Astron) parallels thei r potential to degrade wheat allelochemicals to nontoxic compounds.