Host Preference Associated With Deoxynivalenol and Nivalenol Chemotypes in <i>Fusarium graminearum</i> , <i>F. asiaticum</i> , and <scp> <i>F. meridionale</i> </scp>

Members of Fusarium sambucinum species complex (FSAMSC), major mycotoxigenic phytopathogens, affect cereal crops such as wheat and rice. The predominant members of FSAMSC, F. graminearum, F. asiaticum, and F. meridionale, are distinguished by their trichothecene chemotypes, primarily nivalenol (NIV) and deoxynivalenol (DON) chemotype. While DON has been linked to virulence in certain FSAMSC species, NIV chemotypes exhibit increased aggressive in rice, whereas DON chemotypes preferentially infect wheat. However, the genetic factors driving these chemotype-host associations remain unclear. This study investigated the genetic linkage between DON/NIV chemotype and host preference through molecular and phenotypic analyses. RNA sequencing revealed host-dependent differential expression of trichothecene biosynthetic (TRI) genes during wheat and rice infection by DON and NIV chemotypes. Sequencing confirmed that NIV chemotypes carry a functional TRI13 gene encoding a trichothecene C-4 hydroxylase, whereas DON chemotypes harbour a nonfunctional TRI13 pseudogene (ψTRI13). Genetic manipulation of TRI13 confirmed its role in determining DON/NIV chemotype and host preference. TRI13 deletion in NIV strains converted them into a DON chemotype, while complementation of ψTRI13 in DON strains generated a hybrid chemotype producing both toxins, with the 3-acetyl-DON chemotype showing a more pronounced hybrid profile than the 15-acetyl-DON chemotype. Pathogenicity assays revealed that TRI13 deletion reduced virulence in rice but enhanced colonisation in wheat. Conversely, TRI13 complementation increased rice aggressiveness and decreased wheat infection. This study provides the first genetic evidence for host preference driven by DON/NIV chemotypes in F. graminearum, F. asiaticum, and F. meridionale, offering insights for improved mycotoxin surveillance and disease management strategies.