. The cultivated strawberry, Fragaria × ananassa Duch., is one of the most economically important fruit crops in the world. It first arose from accidental hybridization between two American octoploid species, F . virginiana and F . chiloensis
The founding genetic base of the commercial strawberry, Fragaria × ananassa Duchesne in Lamarck, is limited. It originated ≈250 years ago when a few clones of South American F. chiloensis chiloensis (L.) Miller subsp. chiloensis forma
, such as berries, are even more highly valued when consumers can purchase produce from a local grower or market ( Conner et al., 2009 ). California, Florida, Oregon, and Washington present the largest amount of strawberry ( Fragaria × ananassa
between strawberry ( Fragaria ananassa Duch.) productivity and photosynthesis-related parameters under various growth conditions Fron. Plant Sci. 1607 1 13 Choi, H.G. Moon, B.Y. Kang, N.J. Kwon, J.K. Bekhzod, K. Park, K.S. Lee, S.Y. 2014 Yield loss and
Polyethylene glycol (PEG) was evaluated for its influence on hardening of in vitro-propagated `Fern' strawberries (Fragaria ×ananassa) when applied just before transplanting. Strawberries were micropropagated via shoot tips and grown in vitro until roots were well developed. Plantlets were then transferred onto filter paper bridges in liquid medium with 15% (w/v) of PEG-8000. After treatment in the medium for various periods, the plants were compared to the control (no PEG) for water loss from detached leaves, stomatal aperture, and survival rates after transplanting. Leaf epicuticular wax was also quantified. Overall, the in vitro PEG treatment was not successful in significantly increasing hardiness and survivability of the strawberry plants after transplanting from in vitro conditions to a soil medium. Osmotic stress was created, but apparently not for the time needed to increase survival. Further tests are needed to pinpoint the proper exposure time required to increase hardiness and survivability after transplanting plantlets. To increase survival, the time exposed to PEG should be 15, 18, or possibly 21 days.
Thermotolerance of photosynthesis and productivity in `Chandler' and `Sweet Charlie' strawberry plants (Fragaria ×ananassa Duch.) exposed to three temperature regimes was studied. Net CO2 assimilation rate (A), variable chlorophyll fluorescence (Fv), efficiency of photosystem II (Fv/Fm), relative chlorophyll content, plant growth, and fruit yield and quality were measured. High temperature (40 °C day/35 °C night) was more detrimental to photosynthesis and productivity than the moderate or low temperature (30/25 or 20/15 °C). Net CO2 assimilation rate in both cultivars was markedly reduced by 40/35 °C, although there was slight decline in `Sweet Charlie' at 30/25 °C. `Chandler' maintained significantly higher A rates than `Sweet Charlie' for at least three weeks of heat stress, indicating that `Chandler' might tolerate longer exposure to high temperature. In parallel to the decrease in A rate, intercellular CO2 concentration (Ci) and instantaneous water use efficiency (WUE) were significantly decreased at high temperature. `Chandler' leaves were cooler and transpired more than `Sweet Charlie' leaves, suggesting that each cultivar adopted different heat resistance mechanisms at 40/35 °C. There were changes in Fv and Fv/Fm with increasing temperature, indicating irreversible damage to photosystem II at 40/35 °C might have occurred. The trend of reduction in stomatal conductance (g S) in both cultivars at high temperature did not coincide with the reduction in A rates. Decline in A rates at high temperature was more related to changes in Fv/Fm than to g S activity. The optimal temperature for vegetative growth was 30/25 °C. Reduction in A rate at high temperature resulted in reduction in total leaf area (LA), shoot, root, and leaf biomasses. Strawberry roots were more responsive than shoot growth to temperatures above 20/15 °C. Fruit yield for `Chandler' was higher at 20/15 °C than at 30/25 °C, suggesting that `Chandler' might have a higher source-to-sink relationship at 20/15 °C than at 30/25 °C. Fruit skin color was temperature dependent only for `Chandler'. A quadratic relationship between flower development and duration of exposure to 30/25 °C for both cultivars was observed; more than two weeks of 30/25 °C can be detrimental to flower development. Regardless of the cultivar and duration of exposure, 40/35 °C was the temperature regime most detrimental to fruit set.
water and the required amount of benzoic acid was added to reach 400 μ m . Three liters of the test solution was poured into each plastic container (17 cm × 29 cm × 9.5 cm) and then ED treatment was applied as described previously. Strawberry ( Fragaria
, and leaf water content, ionic composition in salt stressed strawberry (Fragaria × ananassa) Sci. Hort. 130 133 140 Karlidag, H. Yildirim, E. Turan, M. 2009 Salicylic acid ameliorate the adverse effect of salt stress on strawberry Sci. Agr. 66 180 187
, Burlington, Wash., for Fragaria ×ananassa plants. Fragaria virginiana plants were supplied by Kim Hummer (FRA series) and Margaret Stahler (M.S. series). Thanks are due to Jeanette Bergen for technical assistance. The cost of publishing this paper was
Nine commercial strawberry cultivars (Fragaria X ananassa Duch.) and 557 clones of wild F. chiloensis (L.) Duch. from the Pacific coast of the United States were tested in the field for resistance to strawberry aphids (Chaetosiphon spp.). No cultivar was highly resistant but ‘Benton’ consistently supported fewer aphids than the other cultivars. In the first evaluation year, 29 clones of F. chiloensis had fewer aphids than the highly resistant ‘Del Norte’ clone of F. chiloensis on 5 sampling dates, although the differences were not statistically significant but in the second year, only 1 clone, RCP-37, had fewer aphids than ‘Del Norte’.