Abstract Downy mildew, inflicted by Peronospora sparsa , causes yield losses in arctic bramble ( Rubus arcticus ssp. arcticus ), boysenberry ( Rubus spp. hybrid) and blackberry ( Rubus fruticosus ), and is a serious threat to the cultivation. Arctic bramble is a high‐value crop but its commercial potential is not realisable partly due to downy mildew. Although P. sparsa has been associated with yield losses in arctic bramble, this has not been experimentally proven, nor have the downy mildew symptoms in arctic bramble fruits been described in a controlled experiment. In this study, downy mildew was found to affect the fruits and reduce the yield of arctic bramble. There was a direct correlation between the number of infected leaves and hard fruits resulting from the infection. Owing to the new pesticide legislation in the European Union, it is important to find alternatives to fungicides in the control of downy mildew. The products ALIETTE (fungicide), PHOSFIK (leaf fertiliser) and BION (pathogen defence elicitor) were effective in downy mildew control, Aliette and Phosfik being more effective than Bion especially in preventing yield losses. No arctic bramble cultivars known to be resistant to downy mildew are available. Evaluation of cultivars Alli, Mesma and Pima in the field showed that Mesma is more resistant to downy mildew than are Alli and Pima. Currently the main cultivar grown in Finland, Pima, was the most susceptible variety. The results of this study suggest that the yields and profitability of arctic bramble production could be improved by selecting more resistant varieties, combined with the application of agrochemicals that can suppress the development of downy mildew.
Preservation of cultivar purity creates a particular challenge for plants that are self-incompatible, require insects for cross-pollination, and have easily germinating seeds and vigorously spreading rhizomes. As the fields must be planted with mixed populations, and a balance must be maintained between the cultivars to achieve effective pollination, methods for field monitoring of the relative density of different cultivars must be practical. Furthermore, a DNA-based method is needed for cultivar verification in the collections and outside of the growing season. The aim of this study was to develop both types of methods for Rubus arcticus (arctic bramble).Morphological parameters were measured from six cultivars grown on three farms. Observations from the flowers and fruits included: petal and sepal number, flower diameter, arrangement of petals, size of calyx in relation to corolla, fruit weight, yield and soluble sugars. Observations from the leaves included: width and height of middle leaflet, shape of the base of terminal leaflet, shape of terminal leaflet, leaf margin serration and fingertip touch. The applicability of simple sequence repeat (SSR) or microsatellite DNA markers developed for red raspberry was tested on eight arctic bramble cultivars.Morphological and molecular identification methods were developed for R. arcticus. The best morphological characteristics were the length-to-width ratio of the middle leaflet and leaf margin serration. A particular characteristic, fingertip touch, was shown by electron microscopy to be related to the density and quality of the leaf hairs. Red raspberry SSR marker no. 126 proved to be applicable for differentiation of the eight arctic bramble cultivars tested. These identification methods are critical to secure the maintenance and management of R. arcticus. However, the challenges faced and approaches taken are equally applicable to other species with similar biology.
The main goal in the cultivation trials is the evaluation of the productivity and downy mildew resistance of a selected arctic bramble clone, which in preliminary trials has shown disease resistance.
The main arctic bramble ( Rubus arcticus) cultivars are susceptible to downy mildew ( Peronospora sparsa), which seriously threatens the cultivation. The efficiency of Aliette, Euparen M, phosphite-containing Phosfik, Phostrol, Farm-Fos-44, and Kaliumfosfiet, as well as Bion was evaluated in the greenhouse. Fewer symptoms and less Peronospora DNA were found in plants treated with Euparen M and Bion, whereas Aliette, Phosfik, and Phostrol gave moderate protection. Three arctic bramble cultivars showed varying susceptibility to P. sparsa. An inexpensive and fast in vitro plate test gave results parallel with those obtained in the greenhouse. Quantitative differences were found in the phenolic profiles of the leaves of different cultivars and in different treatments. Several phenolic compounds were tentatively identified in arctic bramble for the first time, for example, monomeric and oligomeric ellagitannins and galloylglucoses. Negative correlation was found between the amount of P. sparsa DNA and flavonol glycosides and some ellagitannins in the leaves 8 days after inoculation, suggesting a possible role for these phenolics in the defense.
Fluctuations in the yield of wild berries are markedly influenced by weather conditions. However, the cause–effect relationship is often poorly understood. Based on data spanning a 20-year period in Finland, we made an effort to elucidate the influence of different weather conditions on the yield of arctic bramble (Rubus arcticus L.). We analyzed the regression coefficients of various weather conditions in several regression models using the elaboration approach. Temperature accumulated in July had a positive effect on yield. Yield was negatively influenced by temperature accumulated during the previous summer, rainfall in the October of the previous year, and temperature accumulated in May of the same year. It is notable that the same weather conditions had a positive influence on yield of the same year whereas these conditions had a negative effect on the yield potential of the following year. Compared with traditional analysis methods, the elaboration approach provided a better understanding of the relationship between weather parameters and yield. The rarity of a good yield could be explained by the particular vulnerability of arctic bramble to the negative effects of weather conditions. Some of these factors could be controlled in field conditions when cultivating arctic bramble.
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