Cronartium flaccidum sporulates on new Euphrasia species in natural habitats in Finland

Abstract

Summary Natural sporulation of a pine stem rust, Cronartium flaccidum, was investigated in forested habitats in northern Finland. First, a diffuse sample (100) of seven species of hemiparasitic plants was collected in their natural habitats close to one another. C. flaccidum was found to sporulate on six species. The rust was most common on Melampyrum sylvaticum with 21% of the plants and 2% of the leaves carrying telia. Telia occurred occasionally also on Euphrasia frigida, E. nemorosa, E. stricta, Pedicularis palustris ssp. palustris and Melampyrum pratense (less than 5% of the plants and 0.3% of the leaves). The rust was absent on Rhinanthus minor. Second, a diffuse sample of each of M. sylvaticum, M. pratense, Euphrasia sp. and Rhinanthus sp. was collected from 10 sample plots surrounding the city area. C. flaccidum occurred on 0.29% of the leaves of M. sylvaticum, and 0.02%–0.03% of M. pratense and Euphrasia, but it was lacking from Rhinanthus. The results indicated that C. flaccidum was most common and widespread on M. sylvaticum, but sporulated sporadically also on Euphrasia sp., P. palustris and M. pratense. This is the first report of sporulation of C. flaccidum on Euphrasia frigida and E. nemorosa in their natural habitats. In contrast, a second rust observed in this survey, Coleosporium sp. needle rust, was much more common than C. flaccidum on the investigated plants. In the first site, 43%–54% of plants and 8%–17% of leaves of Melampyrum spp. and 0%–13% of plants and 0%–2% of leaves of Euphrasia spp., Rhinanthus minor and Pedicularis palustris carried uredinia or telia. In the second site, 9%–15% of leaves of Melampyrum spp. and 1%–2% of Euphrasia sp. and Rhinanthus sp. carried rust uredinia and/or telia. The results indicate frequent spore dispersal of both Cronartium and Coleosporium in the area, and versatile rust sporulation on hemiparasitic plant species.

New alternate hosts for Cronartium spp.: Odontites, Euphrasia, Rhinanthus and Papaver

“…Different varieties of E. stricta occur throughout Finland in road sides, backyards of houses and water sides (Hämet‐Ahti et al., ), thus being potential species to spread C. flaccidum efficiently in practice. Recently, C. flaccidum was also found to sporulate in natural habitats of E. stricta in several locations in northern Finland (Kaitera, Kalleinen, Mikkilä, & Hantula, ; Kaitera, Hiltunen, Kauppila et al., ). In this study, C. flaccidum was found also commonly on wild Euphrasia in a severely damaged pine stand in northern Finland.…”

“…In this study, C. flaccidum was found also commonly on wild Euphrasia in a severely damaged pine stand in northern Finland. Besides E. stricta, C. flaccidum has also been found to sporulate on E. frigida and E. nemorosum in natural habitats (Kaitera, Kalleinen et al, 2017). Therefore, Euphrasia are highly susceptible species that are also severely infected in natural forests, thus being able to spread the rust efficiently.…”

“…Therefore, these plants evidently spread the rust under natural conditions. Among these species, M. sylvaticum is a known wild alternate host (Kaitera & Hantula, 1998), and recently, C. flaccidum was also found to sporulate on natural plants of E. stricta (Kaitera, Hiltunen, Kauppila et al, 2017;Kaitera, Kalleinen et al, 2017) in Finland and in Germany (Kummer & Klenke, 2015). The present finding of the rust is, therefore, the most northern one and confirms that also Euphrasia can play an important role along with M. sylvaticum as an alternate host of C. flaccidum.…”

Diversity and abundance of culturable fungal endophytes in leaves of susceptible and resistant alternate hosts of Cronartium pini and C. ribicola

“…It can spread via over 50 alternate hosts (Kaitera et al, 2015). The main susceptible plant genera for C. pini are Melampyrum, Pedicularis, Euphrasia, Veronica and Impatiens (Kaitera, 1999;Kaitera et al, 1999Kaitera et al, , 2012Kaitera et al, , 2015Kaitera et al, , 2017Kaitera et al, , 2018. Cronartium ribicola Fisch.…”

Diversity and abundance of culturable endophytes in leaves of susceptible and resistant alternate hosts of Cronartium pini and C. ribicola

“…The main susceptible plant genera for C. pini are Melampyrum, Pedicularis, Euphrasia, Veronica and Impatiens (Kaitera, 1999;Kaitera et al, 1999Kaitera et al, , 2012Kaitera et al, , 2015Kaitera et al, , 2017Kaitera et al, , 2018. Cronartium ribicola Fisch.…”