Australasian Plant Pathology https://doi.org/10.1007/s13313-019-0615-y ORIGINAL PAPER Evaluation of rust pathogenicity (Phragmidium violaceum) as a biological control agent for the invasive plant Rubus ulmifolius on Robinson Crusoe Island, Chile Rodrigo Vargas-Gaete1,2 & Herman Doussoulin3 & Cecilia Smith-Ramírez4,5,6 & Sebastián Bravo3 & Christian Salas-Eljatib1,7 & Nancy Andrade3 & Bohumil Trávníček8 Received: 7 May 2018 /Accepted: 21 January 2019 # Australasian Plant Pathology Society Inc. 2019 Abstract Rubus ulmifolius is a highly invasive species that negatively affects biodiversity, especially on Robinson Crusoe Island (RCI), one of the two global mini-hotspots of vascular plants. The rust Phragmidium violaceum has been used as a biological control agent for some Rubus species in mainland Chile, New Zealand and Australia. We aim to quantify P.violaceum pathogenicity over R. ulmifolius on RCI, under both field and laboratory conditions, to determine its potential as a biological control. In addition, in order to broaden our knowledge about the pathogenicity of P. violaceum from RCI, it was also tested on a highly susceptible Rubusspecies:R. cf. constrictus. We sampled four forest sites on RCI, measuring abiotic, micro-site, and vegetation variables that could be related with infection. In the laboratory, we inoculated P. violaceum into R. ulmifolius seedlings from RCI and R. cf. constrictus seedlings from mainland Chile. We found a low infection incidence in the field, where only 62 of 182 plots presented infected individuals. Applying a fitted generalized linear model, we predicted ten times more infection of P. violaceum on R. ulmifolius when located in southern aspect slopes and shallow soils (< 30 cm). In the laboratory we determined that rust from RCI infected R. ulmifolius individuals from the island in low density, and did not infect R. cf. constrictus; this low infection rate reinforces our field results. The low infection on R. cf. constrictus may mean that P. violaceum from RCI could originate from very impoverished genetic material. We recommend testing different rust genetic origins, mainly from the Old World, to increase their genetic diversity. Keywords Blackberry . Juan Fernández islands . Restoration . Control invasive species . Rubus constrictus Introduction * Cecilia Smith-Ramírez [email protected] Rubus ulmifolius Schott is a cosmopolitan Rosaceae spe- cies native to Europe and North Africa. This taxa has 1 Laboratorio de Biometría, Departamento de Ciencias Forestales, been reported as invasive in several countries, such as: Universidad de La Frontera, Temuco, Chile Argentina, Australia, New Zealand, United States, Chile, 2 Butamallín - Research Center for Global Change, Universidad de La and some islands of the Azores archipelago (i.e., Terceira, Frontera, Temuco, Chile Graciosa and Pico) (Thorp and Lynch 2000; Mazzolari 3 Facultad de Ciencias Agrarias, Instituto de Producción y Sanidad et al. 2011; Dirnböck et al. 2003; Smith-Ramírez et al. Vegetal, Universidad Austral de Chile, Valdivia, Chile 2017). The damage of invasive plant species on the com- 4 Departamento de Ciencias Biológicas y Biodiversidad, Universidad munities they invade has been well documented, and is de Los Lagos, Av. Fuchslocher, 1305 Osorno, Chile considered a serious threat to biodiversity worldwide 5 Instituto de Ecología y Biodiversidad -Chile (IEB), Santiago, Chile (Knops et al. 1999; Hejda et al. 2009; Vilà et al. 2011). 6 Facultad de Ciencias Forestales y Recursos Naturales, Universidad R. ulmifolius is found in most agricultural and forest land- Austral de Chile, Valdivia, Chile scapes of southern-central Chile (33°-43°S, Matthei et al. 7 Centro de Modelación y Monitoreo de Ecosistemas, Facultad de 1995), probably confused in some areas with R. praecox,re- Ciencias, Universidad Mayor, Santiago, Chile cently described in Chile by Rejmánek (2015). By the first 8 Faculty of Science, Palacký University, Olomouc, Czech Republic half of the 1970s about 5% of the agricultural land area in R. Vargas-Gaete et al. mainland Chile was infested by R. ulmifolius, R. cf. cf. constrictus plants was reduced by 45% in cases of severe constrictus, and probably R. praecox (Oehrens and González infection (Oehrens and González 1977). Moreover, an acces- 1974). In 1927, the botanist Walterio Looser reported sion of R. praecox from Chile, showed to be susceptible to R. ulmifolius on Robinson Crusoe Island (RCI), Chile, for P. violaceum in grenhouse experiments (Bruckart III et al. the first time (Looser 1927). This climbing shrub rapidly be- 2017). It is not known when P. violaceum was released on came highly invasive on the island. Currently, it is estimated RCI, and whether it was intentional or accidental. It was only that about 18% of the island is covered by shrubland com- first detected on the island around 1984–1985 by a Japanese posed of R. ulmifolius, strongly associated with another inva- scientist (Pers com, Ivan Leiva, ex-National Park administra- sive exotic species, Aristotelia chilensis (Diaz 2013; Greimler tor). In this study, we quantified the pathogenicity of et al. 2002). The forest area of RCI, constituted mainly by P. violaceum on R. ulmifolius ca. 32 years after the rust detec- endemic species, is considered one of the two mini global tion on RCI. We included field sampling and exploratory ex- hotspots, after Galápagos (Arroyo 1999), and the top conser- periments in the laboratory. In addition, considering that R. cf. vation priority worldwide by the Durrell Conservation Trust constrictus from the mainland is highly susceptible to (Saunders et al. 2011). Furthermore, it has been reported as P. violaceum,wetestedPviolaceumisolates from the island being the fourth island with most forest displaced by invasive on this species in order to understand their pathogenicity level. species worldwide, after Tahiti, Moorea and Pico Island The aims were to: (a) evaluate the rust pathogenicity over (Smith-Ramírez et al. 2017). R. ulmifolius in different forest sites of RCI; (b) identify envi- On RCI, R. ulmifolius causes severe damage to the forest ronmental conditions related to higher infection of ecosystem (Vargas et al. 2013). Due an effective propagule P. violaceum on RCI; and (c) test the pathogenicity of dispersal strategy through gravity, wind, birds and asexual P. violaceum isolates from RCI on both R. ulmifolius from reproduction (Smith-Ramírez et al. 2013; Mora and Smith- RCI and R. cf. constrictus from the mainland. Ramírez 2016), R. ulmifolius can establish itself almost any- where, even climbing into the canopy of large trees (>10 m), showing unusually high secondary growth in diameter (up to Materials and methods 15 cm). It hinders the main regeneration strategies of the en- demic forest taxa, which can result in local extinction for some Study area plant species (Vargas et al. 2013), also affecting the habitat of endemic land bird species (Hahn et al. 2011). Robinson Crusoe Island (RCI) is located in the South Pacific Phragmidium violaceum (Schulz) Winter is a leaf-rust fun- Ocean (33°38′29^S; 78°50′28^O) 670 km west of San gus indigenous to Europe and Asia (Tykhonenko 2007)that Antonio, in central Chile (Fig. 1). The climate is warm- currently has a global distribution (Morin et al. 2013). This temperate and humid, with short dry summers. Annual aver- rust is an obligate biotrophic pathogen, characterized by high age temperature is 15.3 °C with an average annual rainfall of aggressiveness and strong specificity (Bruzzese and Hasan 1150 mm (Marzol et al. 2001). Average temperature during 1986; Morin et al. 2006, 2011, 2013). Consequently, it has the period comprising one month before the start of the grow- been used as a biological control for some species of the ing season up to the month we sampled (i.e., August to March Rubus genus in Australia, New Zealand and Chile (Oehrens inclusive), over the last 17 years, registered a minimum of and González 1974; Morin et al. 2011). However, the patho- 13.1 °C (2016) and a maximum of 15.9 °C (2009). The year genicity on different species of Rubus has been shown to vary our study was undertaken, the average temperature was (Evans et al. 2005, 2011, Bruckart III et al. 2017). This rust 14.6 °C. Accumulated precipitation over these eight months does not eradicate the host, but decreases its aggressiveness, was more variable, ranging from a minimum of 464.5 mm to which is the effect required on RCI, where invasive species 1126.5 mm (2013 and 2002, respectively). In the latter year, a also have a positive effect in terms of preventing soil erosion strong ENSO climatic fluctuation affected RCI. Throughout (Castillo and Smith-Ramírez 2018). the study year precipitation was 607.5 mm, which is close to In 1973, P. violaceum from Germany was tested and delib- the average in years without the ENSO phenomena (on aver- erately released in mainland Chile near Valdivia (39° 48’S, age 672.8 mm in La Niña years). It is significant that over 71°14’W) to control two Rubus species (Oehrens and 13 years (between 2002 to 2015) no rainfall characteristic of González 1974). After liberation, P. violaceum isolates were El Niño had occurred on the island (Dirección Meteorológica transported and released in several other locations in south- de Chile 1860–2016). central Chile (33°-40° S, Oehrens and González 1974). After RCI formed over a volcanic hotspot about 4.2 million years three years, Oehrens and González (1977) reported that the ago (Stuessy et al. 1984). The soils are developed from collu- effect on R. constrictus (that we call here as R. cf. constrictus) vial sediments and ash, presenting in general, sandy loam was significantly greater than on R. ulmifolius,concludingthat textures and a large, highly erodible skeleton proportion. the former is more susceptible to the rust. Seed viability of R. The upper and lower montane forest covers ca. 1015 ha, Evaluation of rust pathogenicity (Phragmidium violaceum) as a biological control agent for the invasive..