Differential interaction of Magnaporthe grisea and Fusarium graminearum with ears of wheat cultivars varying in resistance

The inoculation system for M. grisea and F. graminearum in a controlled environment was established. Twenty-seven wheat cultivars were used to optimize the inoculation. The cultivar Milan exhibited the highest resistance to M. grisea but a susceptible reaction towards F. graminearum, whereas cultivar Sumai 3 displayed opposite responses to both pathogens. Upon the point inoculations, M. grisea generally was observed growing in a slower speed than F. graminearum on the ears of both cultivars. Two pathogens showed the downward growth along the rachis, especailly in the susceptible interactions. Staining methods and GFP-labelled strains were employed with confocal laser scanning microscopy (CLSM) to determine the differential spreading of both pathogens in spikelet and rachilla. Spores of M. grisea germinated extensively in the spikelet within 12 hpi, and similar developments of M. grisea in spikelet were found from both cultivars. F. graminearum colonized only the anthers in 12 hpi, mostly in the susceptible cultivar, which also enhanced the development of F. graminearum after 12 hpi. Cultivar resistance had an impact on fungal expansion in the rachilla. Resistance in the plant restricts the pathogen growth. Both pathogens seem to spread through the vascular system and grow systemically downwards in the rachis. The diverse performance of Reactive oxygen speices (ROS) were occurred in the incompatible and compatible interactions. H2O2 was regarded as a clear indication of resistance, in particular in Milan-M. grisea interaction at 48 hpi. O2- tends to serve as a signal of plant reaction and defense response, resulting specific from both plant and pathogen. The transcript accumulations of eight selected genes were tested. Three pathogenesis-related genes (PR2, Chi2, PR5) were considered as defense related genes. The peroxidase (Pox2) and CCR genes were highly induced in Milan interaction with both pathogens, indicating the lignin reaction and signal transdction is the main defense response in Milan. UGT and CYP709C1 genes were more expressed in the resistant cultivar Milan to F. graminearum. And it is assumed that the resistance in Milan to M. grisea is horizontal resistance.