Neotyphodium endophytes are suggested to be mutualistic symbionts of grasses and regarded as potential biological plant protection agents. We examined the effects of the Neotyphodium endophyte of meadow ryegrass on snow molds in vitro with dual cultures of endophyte and Typhula ishikariensis , and on grass–snow mold interactions in vivo in a greenhouse and in a field experiment. In dual cultures, the endophytes formed an inhibition zone and retarded the growth of T. ishikariensis. In the field experiment, however, the endophyte-infected (E+) meadow ryegrasses were more susceptible to T. ishikariensis than the endophyte-free (E–) grasses. Endophyte infection increased the winter damage of grasses both in greenhouse and in field conditions. After winter, the growth of E+ grasses exceeded the growth of E– plants in the field experiment, indicating the marked tolerance of E+ grasses against winter damage. We detected differences in growth and pathogenesis between the different T. ishikariensis strains and found meadow ryegrass cultivar–endophyte status interaction in the growth of meadow ryegrasses, which highlight the effects of the genetic background of the participants on endophyte–grass–snow mold interactions.

Neotyphodium endophytic fungi are beneficial for certain cultivated grass species by increasing the stress tolerance and herbivore resistance of their host plants. These grass endophytes have been widely studied in temperate regions. Endophyte-infected grasses are also cultivated in sub-artic conditions, but studies on the effects of endophyte infection on grasses under conditions of prolonged snow cover are scarce. A 2-year field experiment was conducted with two originally endophyteinfected meadow fescue (Schedonorus pratensis) cultivars. The growth and reproduction of endophyte-infected (E+) and endophyte-free (E)) plants of two cultivars at two sites, differing in nutrient status and duration of snow cover, were compared at the latitude of the Arctic Circle in Finland. Endophyte infection enhanced plant performance most at the site with the higher nutrient status and the shorter duration of snow cover. The difference in growth between E+ and E) grasses increased during the second growing season and was most pronounced in the reproductive investment of grasses, but the benefits of endophyte infection for reproductive mass were cultivar-dependent. At the site with the lower nutrient status, costs of endophyte infection on the vegetative growth of grasses were found. The results suggest that Neotyphodium infection may benefit meadow fescue in sub-arctic conditions but the extent of the effects is dependent on the cultivar and the environment.

The dry matter yields and forage quality of seven grassland plant species and mixed stands which included three cutting regimes (pasture 4-5 cuts, silage 2-3 cuts, hay and aftermath) were studied at two locations in northern Finland, Ruukki (64°40’N) and Rovaniemi (66° 35’N). Increased cutting frequency lowered the total dry matter yields of all plant species. Production of timothy (Phleum pratense L.) and smooth brome grass (Bromus inermis L.) swards was significantly reduced by taking four or five cuts instead of one or two cuts. Meadow fescue (Festuca pratensis Huds.) and meadow grass (Poa pratensis L.) showed only a minor interaction with harvesting regimes and were less affected by the cutting frequency. The increased cutting frequency raised the crude protein content, this causing the highest protein yields despite the smaller dry matter yields. The inclusion of red clover in seed mixtures had a favourable effect on the crude protein content of grass swards. Stands of sown plants decreased and the proportion of weeds in yields increased with time, reflecting the suitability of plant species to various cutting regimes. Meadow fescue and meadow grass with rapid regrowth had a positive effect on sward density and also caused less invasion of weeds when the cutting frequency was increased.

The development of the yield and nutritive value of timothy (Phleum pratense L.) both in the primary growth and in the regrowth were studied at MTT Plant Production Research, a unit of MTT Agrifood Research Finland, in Rovaniemi (66°35´N) in 1999-2001. The dry matter yield and leaf to stem ratio were measured from the crop samples, and the contents of crude protein and organic matter digestibility of both whole plant samples and leaf and stem fractions were analysed. In primary growth, the most rapid increase of dry matter, 220-240 kg ha -1 per day, was measured around the beginning of the heading stage. There was a very strong positive correlation between the proportion of stems and the amount of dry matter in the primary yield. The daily growth rate of the regrowth was less than half of that of the primary growth. The fastest decrease, 1 percentage unit per day, in crude protein content was measured at the pasture stage (4-5-leaf stage). During the entire sampling period, the average daily decline in crude protein content in the primary growth of timothy was 0.65 percentage units. The main cause for the rapid decline in crude protein content was the high proportion of stems and their low protein content. In the regrowth, during the last four weeks before the harvest, the average daily decline in crude protein content was 0.28 percentage units.The average decline in organic matter digestibility from early pasture stage to late silage stage was 0.9 percentage units per day. The most remarkable change was noticed at the growth stage of timothy when about the half of stems were heading and it was then that the digestibility decreased by more than one percentage unit per day. The rapid decline in organic matter digestibility was due to the low digestibility of stem matter. The daily change in forage digestibility in the regrowth was very small, on average 0.11%.

Four Solanum tuberosum L. cultivars (Nicola, Pito, Puikula, Timo) and somatic hybrids between freezing tolerant S. commersonii and freezing sensitive S. tuberosum were evaluated for their tolerance to freezing and low temperature photoinhibition. Cellular freezing tolerance was studied using ion leakage tests and the sensitivity of the photosynthetic apparatus to freezing and high light intensity stress by measuring changes in chlorophyll fluorescence (FV/FM) and oxygen evolution. Exposure to high light intensities after freezing stress increased frost injury significantly in all genotypes studied. Compared with S. tuberosum cultivars, the hybrids were more tolerant both of freezing and intense light stresses. In field experiments the mechanism of frost injury varied according to the severity of night frosts. During night frosts in 1999, the temperature inside the potato canopy was significantly higher than at ground level, and did not fall below the lethal temperature for potato cultivars (from -2.5 to -3.0°C). As a result, frost injury developed slowly, indicating that damage occurred to the photosynthetic apparatus. However, as the temperature at ground level and inside the canopy fell below -4°C, cellular freezing occurred and the canopy was rapidly destroyed. This suggests that in the field visual frost damage can follow from freezing or non-freezing temperatures accompanied with high light intensity. Therefore, in an attempt to improve low temperature tolerance in potato, it is important to increase tolerance to both freezing and chilling stresses.