Comparative genomics of two Fusarium graminearum strains of contrasting aggressiveness in bread wheat

By targeting host cellular processes, fungal effectors promote growth and spreading of pathogenic fungi in plant tissues. During the wheat/Fusarium graminearum (Fg) interaction causing the Fusarium head blight (FHB) disease, the nature and the function of these fungal molecular components which control plant susceptibility factors, remain largely unknown. Two Fg strains (Fg1 and Fu10008) contrasting for their aggressiveness in field trials were sequenced using Sequel technology. Fg1 and Fu10008 displayed 11,171 CDS (37,2Mb) and 10,629 CDS (36,1Mb), respectively. The comparative analysis of the predicted proteomes revealed 1,320 specific proteins in Fg1 and 693 in Fu10008, comprising 205 and 81 candidate putative effectors, respectively. A thorough pathotyping of the two Fg strains on three wheat genotypes of different susceptibility to FHB was assessed to test their mycotoxin production and their infection dynamics, including symptoms development and fungal biomass progress in point-inoculated spikelets (PI) and in the uninoculated peripheral ones (Up or Dn). Fg1 strain induced systematically the most severe symptoms in the PI, Up and Dn parts of each wheat genotypes. Whatever the infected genotype, Fg1 initiated symptom development 24 h earlier than Fu10008. Spreading of both strains in Up and Dn spikelets appeared preferentially towards the top of the spike as early as 5 days post-inoculation, displaying symptoms very close to those of the PI parts suggesting that they are related to fungal migration in healthy plant tissues. qRT-PCR and mycotoxin analyzes (DON and ZEA) of the different spike zones are currently performed to refine the early stages of the infection process of both strains. This will allow for connecting these Fg data to recent work investigating the wheat susceptibility factors (Chetouhi et al., 2016) and will contribute to shape an integrated picture of the molecular events piloting FHB