RAPID METHODS TO SELECT FACULTATIVE PATHOGENS ON INVADER Cenchrus setaceus

Abstract

"Fountain grass, Cenchrus setaceus (Forssk.) Chiov. (syn. Pennisetum setaceum) is an invasive plant with high impact on insular environments such as the Canary Islands. Although there are no mentions on C. setaceus phytopathogens, plant communities with symptoms of withering, yellowing and decay have been found in Canary Islands. Our project aims to find autochthonous potential biological control agents for C. setaceus. Herein, we present a workflow in which we tested fast and cost-effective methods to screen a high number of fungal strains, aiming features like fast colonizers as well as competitive saprophytes and facultative pathogens with ability to cause infection. Affected plants were collected from the islands of Gran Canaria, Tenerife, La Gomera, La Palma and Lanzarote and 243 fungal strains belonging to 38 genera were isolated. First screening was performed on adult plants with pooled multiple species strains – spores suspensions of 10 random strains per pool, each strain representing a genus or a morphotype (n = 83). No symptoms of disease were observed. Most isolated genera in this study were Alternaria and Fusarium, known as cosmopolite phytopathogens. Next screening methods were focused accordingly. Two in vitro single-strain screening methods were employed by using mycelium-inoculated sectioned and entire leaves, to observe the ability of tissue colonization. First screening on sectioned leaves was performed with high amount of inoculum, to increase the chances of colonization and to determine the ability of fungi to use the plant material as substrate. The method was not effective in significantly reducing the number of candidates as most strains had abundant growth. To detect differences in fungal strains acting as facultative pathogens or phytopathogens, the 2nd single-strain screening was performed on physiologically-stressed (pelargonic acid, a desiccant molecule to induce turgor loss) and not pre-treated leaves using less inoculum. Six strains were selected and subsequently evaluated in the last in vivo screening in the presence and absence of the desiccant. Finally, we detected strain 967 Fusarium clavum as able to colonize and reproduce at the crown of the young plants. In view of our experimental process, we propose a workflow for the cost-effective search for potential BCAs in similar situations."