Lack of association between Fusarium graminearum resistance in spike and crude extract tolerance in seedling of wheat

Fusarium graminearum is a hemibiotrophic plant fungal pathogen that causes head and seedling blight in wheat and other cereals; however little is known about the mechanisms involved in its pathogenicity. To examine the role of pathogen metabolites in pathogenecity, we studied the effects of F. graminearum crude extract on physiological and morphological responses of Falat and Sumai3, as respectively susceptible and resistant wheat cultivars to Fusarium head blight (FHB). Our results showed that seed germination, seedling growth and coleoptile cell development were highly affected by the pathogen crude extract in both cultivars, with Sumai3 growth being more affected than Falat. These results show little correspondence between wheat seedling tolerance to F. graminearumcrude extract and resistance to FHB. Crude extract treatment resulted in significant increase of hydrogen peroxide (H2O2) and malondialdehyde (MDA) content in both cultivars which indicated an oxidative stress. Differential antioxidative responses to crude extract was observed; as activity of polyphenol oxidase (PPO), superoxide dismutase (SOD) and ascorbate peroxidases (APX) increased in Falat and decreased in Sumai3. In addition, a greater phenylalanine ammonia-lyase (PAL) activity was observed in treated seedlings of both cultivars. Quantitative Real- time PCR analysis showed that PAL gene expression in Falat was induced about 4 folds higher than Sumai3 under treatment. Taken together, our data suggest that a better employment of enzymatic and none enzymatic antioxidative systems in Falat could explain its higher degree of tolerance compared with Sumai3.