SCREENING FOR BIOLOGICALS TO CONTROL RUMEX LUNARIA L. IN LANZAROTE ISLAND

Abstract

"Rumex lunaria L., a Polygonaceae shrub, has colonized large areas of Lanzarote, Canary Islands, from the 1980s to the present day, revealing an invasive behaviour. Recently, symptoms of disease like leaf spots and lack of turgidity in trunks have been observed. This fact has led to the investigation on fungal communities present in this invasive species in several areas of the National Park and other locations in Lanzarote Island. Our objectives were to detect and select fungal strains with phytopathogenic traits isolated from disease symptomatic plants using different screening techniques. To isolate the potential fungi causing disease symptoms, samples were processed using mycological classical techniques. Identification of fungi was based on morphological and molecular analysis using the accepted DNA barcode for fungi, the rDNA ITS region. Five rapid and cost-effective screening methods were carried out in the laboratory in a sequential order before scaling the study to the nursery plants assay. This sequence of methods allows us to test the potential pathogenic effects of a high number of strains in a relatively short period of time: method 1 -both sides of the midrib of a cut leaf were inoculated with droplets of a spores suspension; method 2 -a branch with leaves maintained in water was inoculated with droplets of a spores suspension; method 3 -the aerial part of seedlings was sprayed with spores suspension; method 4 and 5 -leaves of an adult plant were inoculated with droplets of a spores suspension. Several scales for symptoms were developed according to strains-specific effects on tissue like chlorosis, spots, necrosis. Size of leaves spots were recorded. Of 76 fungal isolated strains, 21 genera were identified, with Alternaria and Penicillium being the most frequent. The screening process led to the selection of Alternaria tenuissima (strain 739) as it showed a constant pathogenic ability along the screening sequence. Thus, it makes it a strong potential biological control agent for the invasive species R. lunaria in Lanzarote Island. This study also contributes to the knowledge on the fungal communities of R. lunaria. "