Fusarium nirenbergiae Causes Fusarium Wilt of Common Bean (Phaseolus vulgaris) in Türkiye

The Fusarium oxysporum species complex (FOSC) comprises cryptic taxa that cannot be reliably distinguished morphologically, necessitating multilocus phylogenetic approaches. During field surveys conducted in June–August 2022 in Central Anatolia (Konya, Nevşehir, and Niğde provinces), wilt symptoms were observed in commercial dry bean fields, with disease incidence ranging from 2% to 14%. Symptomatic plants exhibited chlorosis, stunting, and vascular browning of crown tissues. Fusarium-like isolates were consistently recovered and characterized morphologically. Two representative pathogenic isolates (NKZ and NKK3) that fulfilled Koch's postulates were selected for multilocus sequencing (tef1, cmdA and rpb2), revealing ≥ 99% identity to authenticated Fusarium nirenbergiae reference strains. Concatenated phylogenetic analysis placed the isolates in a well-supported clade with the ex-type strain CBS 840.88ᵀ, clearly separated from F. oxysporum sensu stricto and other FOSC taxa. This study provides the first multilocus phylogenetically confirmed report of Fusarium nirenbergiae causing Fusarium wilt on common bean in Türkiye and underscores the necessity of moving beyond the classical forma specialis concept in regional disease surveillance.