Novel Microsatellite Markers Reveal Evidence of Sexual Reproduction in <i>Dematophora necatrix</i> Populations From South African Avocado Orchards

ABSTRACT Dematophora necatrix is a destructive soil‐borne fungal pathogen that causes white root rot (WRR), affecting ornamental plants and fruit trees, such as avocado, particularly in tropical and subtropical regions. The pathogen invades the crown and roots of the host plant, collapsing the conducting vessels. Typical symptoms of WRR include progressive root necrosis, foliar chlorosis, severe wilting and eventual plant death, which occurs shortly after infection. Despite its destructive nature and economic impact, little is known about its population biology and evolution. Previous studies on its genetic diversity relied on outdated molecular tools, limiting comparability. In this study, we developed and validated nine informative polymorphic simple‐sequence repeat (SSR, microsatellite) markers to assess the genetic diversity of D . necatrix populations in South Africa. Significant genetic differentiation was observed between the Western Cape population and those from Limpopo, Mpumalanga and KwaZulu‐Natal. Furthermore, evidence of mixed reproduction was also found in these three regions, while the Western Cape population was predominantly clonal. These novel markers provide critical insight into the pathogen's population structure, reproduction and possible dispersal pathway. By revealing region‐specific differences in genetic structure and reproductive strategies, these markers establish a foundation for tracing pathogen dissemination routes and for designing more effective, locally adapted WRR management interventions in South Africa.