Cronartium rust sporulation on hemiparasitic plants

Abstract

Susceptibility of potential alternate host plants to pine stem rusts belonging to Cronartium spp. was artificially tested in Finland during 2012-2013. Forty-three species representing 11 plant families were inoculated in the laboratory; 34 species (11 families) were inoculated in the greenhouse with aeciospores of Cronartium flaccidum or C. ribicola. Twenty-one selected species (10 families) were also exposed to natural inoculum of C. flaccidum in the field in two severely affected Pinus sylvestris stands. After 5-8 weeks' incubation, C. flaccidum sporulated on 17 species (nine families) in the laboratory, 17 species (eight families) in the greenhouse and seven species (five families) in the field. Cronartium ribicola sporulated on three species (three families) in the laboratory or greenhouse. All of the hemiparasitic plants that belong to Orobanchaceae were infected by C. flaccidum, and several species supported rust sporulation when exposed to natural inoculum. Susceptible species belonged to genera Veronica,

Nasa, Nemesia and Euphrasia: new alternate hosts of Cronartium spp.

“…Both of the tested species of Orobanchaceae, E. stricta and B. alpina , supported uredinia and telia production of C. flaccidum . Both of the tested species (Kaitera & Hiltunen, ; Kaitera et al., ) as well as several other species of Euphrasia , Pedicularis , Rhinanthus and Castilleja have been reported to be susceptible to C. flaccidum (Gäumann, ; Kaitera & Hiltunen, , ; Kaitera et al., , ; Klebahn, ). This indicates the high susceptibility of hemiparasites to C. flaccidum .…”

“…Leaves of 18 species from eight plant families were used in the experiment (Table ). The previously untested species belonged to Plantaginaceae, Loasaceae and Scrophulariaceae completing the species range in families that were already tested in previous studies (Kaitera & Hiltunen, ; Kaitera et al., , ).…”

“…Test plants were inoculated in the greenhouse by dusting spores using an artist's pencil on the lower leaf surface (e.g. Kaitera et al., ). Prior to inoculation, the leaves were moistened using a water sprayer, and after inoculation, the plants were covered with a plastic bag and incubated for 48 hr to achieve maximum spore germination.…”

“…The rust spreads via species of Grossulariaceae ( Ribes ) and Orobanchaceae ( Pedicularis, Castilleja ) in North America and Asia (Kim et al., ; La & Yi, ; McDonald, Richardson, Zambino, Klopfenstein, & Kim, ; Mulvey & Hansen, ; Yokota & Uozumi, ; Yokota, Uozumi, Endo, & Matsuzaki, ; Zambino, ; Zhang et al., ). In Finland, C. ribicola has been shown to infect Asclepias, Bartsia, Castilleja, Loasa, Mentzelia, Pedicularis, Ribes and Tropaeolum after artificial inoculations (Kaitera & Hiltunen, , ; Kaitera, Hiltunen, & Hantula, ; Kaitera, Hiltunen, & Samils, ; Kaitera & Nuorteva, ).…”

“…In northern Fennoscandia, significant damage has been reported on Pinus sylvestris L. (Samils, Ihrmark, Kaitera, Hansson, & Barklund, ; Wulff et al., ). Cronartium flaccidum is able to sporulate on alternate hosts in genera Apocynum, Asclepias, Bartsia, Castilleja, Euphrasia, Gentiana , Grammatocarpus, Hyoscyamus, Impatiens, Loasa (Nasa), Melampyrum , Myrica, Nemesia, Nicotiana, Paeonia , Pedicularis, Rhinanthus, Saxifraga, Schizanthus, Swertia, Tropaeolum,Verbascum, Verbena, Veronica and Vincetoxicum (Gäumann, ; Hylander, Jørstad, & Nannfeldt, ; Kaitera & Hiltunen, , ; Kaitera, Seitamäki, Hantula, Jalkanen, & Kurkela, ; Kaitera et al., , ).…”