Variation and Transgression of Aggressiveness Among Two Gibberella zeae Crosses Developed from Highly Aggressive Parental Isolates

Gibberella zeae (anamorph: Fusarium graminearum) is the most common cause of Fusarium head blight (FHB) of wheat (Triticum aestivum) worldwide. Aggressiveness is the most important fungal trait affecting disease severity and stability of host resistance. Objectives were to analyze in two field experiments (i) segregation for aggressiveness among 120 progenies from each of two crosses of highly aggressive parents and (ii) stability of FHB resistance of seven moderately to highly resistant winter wheat cultivars against isolates varying for aggressiveness. Aggressiveness was measured as FHB severity per plot, Fusarium exoantigen absorbance, and deoxynivalenol content. In the first experiment, mean FHB ratings were 20 to 49% across environments and progeny. Significant genotypic variation was detected in both crosses (P < 0.01). Isolate environment interaction explained approximately half of the total variance. Two transgressive segregants were found in cross B across environments. Traits were significantly (P < 0.05) intercorrelated. In the second experiment, despite significant (P < 0.05) genotypic variance for cultivar and isolate, no significant (P > 0.05) interaction was observed for any trait. In conclusion, progeny of highly aggressive parents might exhibit increased aggressiveness due to recombination and may, therefore, adapt nonspecifically to increased quantitative host resistance.