“Secreted in Xylem” Genes (SIX Genes): Relationship to the Aggressiveness of Fusarium oxysporum f. sp. albedinis

Abstract

Fusarium oxysporum f. sp. Albedinis (Foa) is the causal agent of Bayoud disease, responsible for the loss of 75% of date palm trees in Morocco and posing a threat to its cultivation across North Africa. This study examined ten Foa isolated from various Moroccan locations for the presence of the transposable element Fot1 and the distribution of “Secreted in Xylem” (SIX) genes. Pathogenicity assays on date palm seedlings revealed varying levels of aggressiveness among isolates, with a positive correlation between aggressiveness and SIX gene count. Highly aggressive isolates harbored 9–12 SIX genes, while hypo-aggressive and moderately aggressive isolates carried 0–6. SIX2, SIX6, SIX7, SIX11, SIX12, and SIX13 were differently dispersed among aggressive isolates, whereas SIX12 and SIX13 were present in all aggressive isolates, suggesting their potential role in virulence. This study is the first to highlight a correlation between Foa aggressiveness and SIX gene distribution, providing a foundation for future functional analyses to elucidate their role in pathogenicity.