No abstract

In 1994 to 1996, large yield losses were reported in cultivated arctic bramble (Rubus arcticus) due to berries drying in the middle of the growing season in the entire cultivation area (62° to 66° N) in Finland. Interveinal, angular, purple-red lesions on leaves are associated with the dryberry disease. Cultivations of arctic bramble were inspected in 1995 and 1996, and 69 plant samples and 137 rootstocks were collected and examined for fungi in the laboratory. Perono-spora sparsa was the species most commonly found in all types of samples tested, but Fusarium avenaceum, Cylindrocarpon destructans, and Botrytis cinerea also were detected. P. sparsa was shown to overwinter in the underground parts of arctic bramble. Laboratory tests showed that the two main cultivars of arctic bramble (Pima and Mespi) were susceptible to P. sparsa. Sequences of the internal transcribed spacer (ITS) regions 1 and 2 of the rDNA genes were determined in four and six isolates, respectively, of P. sparsa, and little sequence variability was detected. The corresponding ITS regions of arctic bramble, the above mentioned fungi, a Phoma sp. previously isolated from arctic bramble, and Phytophthora cactorum isolated from strawberry were also determined and compared with the corresponding sequences of P. sparsa. Subsequently, two pairs of primers were designed to the ITS regions that could be used to detect either P. sparsa and Phytophthora cactorum, or only P. sparsa, respectively, by polymerase chain reaction (PCR) using two different types of thermal cyclers (“heated block” Mini Cycler and “hot air flow” Rapid Cycler).

1 SummaryAn outbreak of a dryberry disease caused by Peronospora sparsa (syn. P. rubi) occurred in plantations of arctic bramble (Rubus arcticus subsp. arcticus) in Finland in the middle of 1990s. The disease persists and is most severe in cool and rainy summers. The disease has not been encountered in northern Sweden where cultivars (R. arcticus nothosubsp. stellarcticus) different from those in Finland are used. The occurrence of P. sparsa in wild Rubus spp. is virtually unknown in both areas and it is not known whether they constitute a potential infection source. Therefore, the aim of this study was to investigate the occurrence of P. sparsa on wild Rubus spp. growing in the vicinity of cultivations of arctic bramble. Symptomatic plants were sampled in 1997-1999. P. sparsa was detected using a light microscope, preceded by incubation of the sample in vitru if necessary, and by a polymerase chain reaction (PCR) based method. Plants of cultivated R. arcticus subsp. arcticus were commonly infected by P. sparsa in Finland. P. sparsa was also found on the cultivated R. arcticus nothosubsp. stellarcticus in Finland and Sweden. However, the infected plants of the cultivars of nothosubsp. stellarcticus seemed to be much less damaged than the cultivars of subsp. arcticus. Plants infected with P. sparsa were found in the populations of wild R. arcticus subsp. arcticus in both countries, and in cloudberry (R. chamaemorus) in natural habitats in Finland. In addition, P. sparsa was detected on specimens of R. arcticus subsp. arcticus (collected in 1966-1985) and R. chamaemorus (collected in 1899-1981) in Finnish herbaria. The samples of R. idaeus and R. saxatilis collected from the field in this study or investigated in the herbaria were not infected with P. sparsa. These data show that P. sparsa has not recently invaded Finland but has become an economically significant pathogen during the rapid expansion of cultivation of the apparently sensitive clones of arctic bramble.

No abstract

The pathogenicity and control of seed‐borne fungi of Chinese cabbage (Brassica pekinensis) were studied to evaluate the quality of imported seed lots on the Finnish market and to develop practical methods for seed health testing. Amongst the numerous fungal species in the seed lots, nine were found to be pathogenic on B. pekinensis seedlings, Alternaria raphani and A. brassicicola being the most common and the most pathogenic. A. brassicicola was effectively controlled by dressing seed with thiram or powdered Streptomyces griseoviridis. unlike A. raphani which was mostly located in the inner parts of the seed. Water agar was successfully used as an incubation medium for seed health testing. Surface sterilization of the seeds with sodium hypochlorite was used to determine the internal infection of A. raphani. A linear relationship between the incidence of A. brassicicola and A. raphani was demonstrated. Ten per cent of the seed lots were excluded from seedling production because of high infection with A. raphani.