ROLE OF FUNGAL ASCOSPORES IN THE INFECTION OF ORCHARDGRASS DACTYLIS GLOMERATA BY EPICHLOË TYPHINA AGENT OF CHOKE DISEASE
C. Leyronas, G. Raynal
Choke disease due to Epichloë typhina causes economic losses in fields of seed- producing orchardgrass, also known as cocksfoot (Dactylis glomerata). There are currently no means to prevent outbreaks and spread of the disease. In this study, we identified several key events of the biological cycle of the fungus, in particular how it enters plant tissues. Study of seeds of partially choked heads ruled out the vertical transmission of E. typhina in D. glomerata. The fungal mycelium that had colonised the seeds appeared not to be viable: it was not isolated from 360 seeds analysed that had 49% infection rate. Moreover, 280 seedlings and 488 young plants grown from these seeds were free from E. typhina. Ascospores, considered as propagules in horizontal transmission, were previously presumed to infect orchardgrass through cut stems at harvest or through stigmas of florets. E. typhina was not detected (by microscopic or histological analyses) in 332 cut stems that had been inoculated with ascospores. Our research indicates that ascospores (or conidia produced by ascospores) are more likely to infect young vegetative tillers. We assume that after ejection, ascospores fall on seed lemma and palea and enter seedling tissues after germination.