A Simplified Method for Agrobacterium-mediated Transformation of Phytophthora palmivora

Phytophthora is an oomycete genus that contains numerous destructive plant pathogens, among which is the broad-host-range species P. palmivora. Functional genomics of Phytophthora has been constrained by the limited availability of robust, easy-to-implement transformation methods. Among the available approaches, Agrobacterium-mediated transformation (AMT) is particularly attractive because it requires minimal specialized equipment and often produces stable transformants with single-copy gene insertions. Most AMT protocols for fungal and oomycete transformation use minimal medium (MM) salts in Agrobacterium induction and co-cultivation media. Preparing these media typically involves making and mixing multiple stock solutions, with some containing numerous components at different concentrations. The process is time-consuming and error-prone, therefore leading to inconsistent transformation success. Here, we present a streamlined, simple, and reproducible AMT protocol for P. palmivora that uses commercially available Murashige and Skoog (MS) basal medium to prepare the Agrobacterium induction and co-cultivation media. This protocol has also been successfully applied to transform P. capsici and may be applied to other Phytophthora spp. as well.