Characterization of an alien source of resistance to Fusarium head blight transferred to Chinese Spring wheat

Very few sources of resistance to Fusarium head blight (FHB) of wheat have been identified. Thinopyrum elongatum (Host) D.R. Dewey (2n = 14, EE genome), a wild relative of wheat, carries resistance to FHB on the long arm of its chromosome 7E (7EL). In this report, a strain of Fusarium graminearum Schwabe, the principal causal agent of FHB, transformed to produce green fluorescent protein (GFP), was used to characterize the resistance carried by 7EL when expressed in the susceptible background of 'Chinese Spring' (CS) wheat. Inoculated spikelets of the addition line CS-7EL showed less infection than those of the parental line, CS. This was associated in CS-7EL with upregulation of many genes predicted to be involved in plant defence and downregulation of genes associated with salicylic-acid-induced defence. The difference between CS and CS-7EL in the progression of infection was striking; the fungus spread easily and extensively from the inoculated spikelet into the node and adjacent spikelets in CS, but was effectively blocked from spreading in CS-7EL. Microscopic data showed that fungal growth was inhibited within the inoculated spikelet in CS-7EL, and spread was completely blocked by the node tissue. The blocking of fungal growth through the node into the rachis correlates with the deposition of an unidentified substance in CS-7EL. Additionally, longer internode segments in CS-7EL versus CS may contribute to limiting fungal spread. Our results suggest that the resistance displayed by CS-7EL is multifaceted, involving both physical and chemical factors. Key words: Triticum aestivum, Fusarium graminearum, gene expression, green fluorescent protein, infection spread, wheat rachis. On a identifie jusqu'ici tres peu de sources de resistance a la fusariose de l'epi (FE) chez le ble. Le Thinopyrum elongatum (2n = 14, genome EE), une espece sauvage voisine du ble, porte la resistance a la FE sur le long bras de son chromosome 7E (7EL). Les auteurs ont utilise une souche du F. graminearum, principal agent causal de la FE, transformee pour exprimer une proteine fluorescente verte (PFV) afin de caracteriser la resistance portee par le 7EL lorsqu'exprimee dans la base susceptible du ble Chinese Spring (CS). L'inoculation des epillets de l'addition CS-7EL montre moins d'infection que ceux de la lignee parentale, CS. Ceci s'accompagne chez le CS-7EL d'une regulation a la hausse de plusieurs genes previsibles pour leur implication dans la defense de la plante et une regulation a la baisse de genes associes a la defense induite par l'acide salicylique. La difference de progression de l'infection entre le CS et le CS-7EL est frappante; le champignon s'etend facilement et extensivement a partir de l'epillet inocule dans le noeud et les epillets adjacents chez le CS, mais son etalement se trouve efficacement bloque chez le CS-7EL. Les donnees microscopiques montrent que la croissance fongique est inhibee dans les epis inocules chez le CS-7EL, et le passage a ete completement bloque dans les tissus nodaux. Le blocage de la croissance fongique a travers le noeud vers le rachis correspond a la deposition d'une substance non identifiee chez le CS-7EL. De plus, les segments internodaux, plus longs chez le CS-7EL versus le CS, peuvent contribuer a limiter la croissance du champignon. Les resultats suggerent que la resistance deployee par le CS-7EL comporte plusieurs facettes, impliquant a la fois des facteurs physiques et chimiques. Mots-cles : Triticum aestivum, Fusarium graminearum, expression genetique, proteine fluorescente verte, etalement de l'infection, rachis du ble. [Traduit par la Redaction]
Introduction Fusarium head blight (FHB) is a major disease of wheat, barley, and corn in all temperate regions of the world, which causes significant yield losses as well as reduction [...]