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Douglas V. Shaw and Kirk D. Larson

Performance characteristics for eighteen strawberry cultivars (Fragaria ×ananassa), nine from California and nine from other North American sources, were evaluated in annual hill culture, with and without preplant soil fumigation (2 methyl bromide : 1 chloropicrin, 392 kg·ha-1). Plants grown in nonfumigated soil yielded 57% and 46% of the fruit produced by plants on adjacent fumigated soil for cultivars from California and other North American origins, respectively. Plants in nonfumigated soils also developed fruit with lower berry weight (94% and 95% of fumigated trials) and smaller spring plant diameter (83% and 76%) for California and other sources, respectively. Trait values for exotic cultivars ranged from 39% to 80% of those for California cultivars, and the variance component due to germplasm sources explained 41% to 81% of the phenotypic variance of random effects in the experiment. Conversely, significant germplasm source × fumigation interactions were not detected for any of the growth or performance traits evaluated, and the proportion of variance attributable to these interactions was at most 2% of that due to germplasm source. These results demonstrate that strawberry growth and productivity for California and other North American germplasm sources are increased similarly by fumigation. Despite differing selection history, germplasm developed outside of California contains no obvious genetic diversity useful for developing cultivars specifically adapted to the sublethal effects of organisms in nonfumigated soils.

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Patrick P. Moore, Wendy Hoashi-Erhardt, Chad E. Finn and Chaim Kempler

‘Puget Crimson’ is a new short-day strawberry ( Fragaria × ananassa Duchesne ex Rozier) cultivar jointly released by Washington State University (WSU), Oregon State University, and the U.S. Dept. of Agriculture–Agricultural Research Service (USDA

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Chrislyn Ann Particka and James F. Hancock

Black root rot (BRR) is a widespread disease of strawberry (Fragaria ×ananassa) that causes the death of feeder roots and the degradation of structural roots resulting in an overall decrease in productivity. Black root rot is primarily caused by Rhizoctonia fragariae Husain and W.E. McKeen, Pythium Pringsh., and Pratylenchus penetrans (Cobb) Filipjev and Schuurmans Stekhoven. A previous study identified varying levels of tolerance to BRR in strawberry cultivars with some having high levels of tolerance. In this study, progeny populations were created to determine the amount of genetic variability for BRR tolerance. Genotypes with high, intermediate, and low tolerance to BRR were crossed in a diallel mating scheme, progeny were planted in Vapam (metam sodium)-fumigated and nonfumigated soil, and were analyzed for yield parameters. The results showed significant differences for both treatment and family, but not for the interaction between treatment and family. Pathogen analysis indicated presence of fungal pathogens and nematodes in both fumigated and nonfumigated soil.

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Michelle L. Paynter, Elizabeth Czislowski, Mark E. Herrington and Elizabeth A.B. Aitken

Variation in the virulence of Fusarium oxysporum f. sp. fragariae (Fof) strains is important when evaluating the resistance of plants to this fungus. Twenty-five isolates of F. oxysporum harvested from strawberry (Fragaria ×ananassa) plants growing in Australia were characterized using pathogenicity tests, vegetative compatibility groups (VCGs), and genetic analysis of translation elongation factor 1 alpha (EF-1α). The level of disease varied depending on isolate used, indicating heterogeneous populations of Fof. Two distinct VCGs were identified and corresponded to two of the 10 lineages identified by partial EF-1α. Using a subset of Fof isolates, resistance in eight cultivars ranged from highly resistant to highly susceptible, with some cultivar × isolate interaction. ‘Strawberry Festival’, ‘QHI Sugarbaby’, and ‘DPI Rubygem’ had high levels of resistance across all isolates. Isolates from Western Australia (WA) were genetically distinct from those from Queensland (QLD) and were more virulent to ‘Camarosa’, a major cultivar grown in WA.

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J.M. Mutisya, J.A. Sullivan, S. Couling, J.C. Sutton and J. Zheng

The relationship between severity of leaf scorch epidemics, caused by Diplocarpon earlianum, and components of vegetative growth and fruit yield was examined in `Kent' strawberry (Fragaria ×ananassa Duch.). Plants were treated in July with six densities of initial inoculum of the pathogen, and severity of leaf scorch was assessed at 2-week intervals from late July to late October. After an analysis of vegetative growth in late October, plants were overwintered in the field or grown in a greenhouse, and later assessed for yield components. Relationships between area under the disease progress curve (AUDPC) and plant growth and yield components were examined by regression analysis. Significant negative linear relationships were found between AUDPC values and number of green leaves, leaf area, leaf dry weight, crown number, crown dry mass, and root dry weight. Significant negative relationships were also found between AUDPC values and number of flowers and inflorescences, and total and marketable berries in the subsequent season, in plants maintained in the field or in the greenhouse. Mean berry weight was not significantly affected. Reduction in the number of crowns in plants affected by leaf scorch was a major factor limiting the yield of diseased plants. In an analysis of regrowth at seven weeks after fruit harvest, a significant negative linear relationships was found between AUDPC values and each growth component except crown dry weight. Collectively, the data provide a rationale to optimize timing of treatments, such as chemical fungicides or microbial agents, to control leaf scorch in August, September and October and thereby promote berry yield in the subsequent season.

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Douglas V. Shaw, Thomas R. Gordon and Kirk D. Larson

Strawberry runner plants from the cultivar `Selva' (Fragaria ×ananassa Duch.) were produced using three nursery treatments in each of three years: propagation in soil fumigated with a mixture of 2 methyl bromide: 1 chloropicrin (w/w) at 392 kg·ha-1, propagation in fumigated soil but using planting stock inoculated prior to nursery establishment with a conidial suspension of Verticillium dahliae (106 conidia/mL), and propagation in nonfumigated soil naturally infested with V. dahliae. Runner plants were harvested and stored at 1 °C for 6, 18, or 34 days prior to establishment in fruit production trials. No significant differences were found between runner plants grown in naturally infested soil and runner plants obtained from artificially inoculated mother plants for V. dahliae infection rates detected by petiole isolation immediately prior to transplanting, the percentage of plants visibly stunted due to disease during the following production season, and seasonal yield compared with corresponding noninfected controls. Cold storage of runner plants for 18 or 34 days, produced using either natural or artificial inoculation systems, reduced the initial percentage of infected plants by 42% to 61% and the percentage of stunted plants during the following fruit production season by 43% to 57%, compared with plants from corresponding nursery treatments given only 6 days post-nursery cold storage. Yields for inoculated plants with 6 days cold storage were 16% to 20% less than those for uninoculated controls, whereas yields for inoculated plants with 18 or 34 days of storage were 3% to 9% less than the respective controls. Most of the cold storage effects on initial infection rate, stunting, and yield were realized at the 18 days of storage treatment. A reduction in the fraction of V. dahliae infected plants due to cold storage, suggests either a direct effect of cold storage on the disease organism or stimulation of secondary resistance mechanisms in the plant. Chemical name used: trichloronitromethane (chloropicrin).

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Marvin P. Pritts and Mary Jo Kelly

Various levels of weed competition were implemented in a second-year well-established strawberry (Fragaria ×ananassa `Jewel') planting by cultivating and hand weed removal for defined periods of time over 3 years. The impact of weeds on subsequent productivity was then determined. Sixteen treatments were established where weeds were allowed to grow for defined periods (0, 1, 2, 3, 4, or 5 months) throughout the growing season. Treatments were maintained in the plots for 3 consecutive years. Spring weed biomass in 1997 had no impact on yield that same year. Weed biomass in 1997 was negatively associated with yield in 1998, although the trend was nonsignificant. However, several individual contrasts were significant. For example, the weed-free control treatment had the highest average yield, while season-long weed competition reduced yield by 14%. The inverse relationship between weed biomass and fruit yield became significant in 1999. For every 100 g·m-2 increase in weed biomass in 1998, fruit yield was reduced by 6% in 1999. Season-long uncontrolled weed growth reduced productivity by 51%. However, several plots with a limited amount of weed competition had higher yields than the continuously weeded control. These data indicate that yields from a well-established strawberry planting may not be vulnerable to a limited amount of weed competition for at least 2 years. Furthermore, data suggest that hand weeding and cultivation on a monthly basis for multiple years may be damaging as well. Growers should direct a majority of their efforts and resources toward controlling weeds in the planting year. Once the planting is well-established, growers may limit the number of times they hand weed to two or three per season.

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Sanjun Gu, Wenjing Guan and John E. Beck

High-tunnel strawberry (Fragaria ×ananassa) production for extended seasons has a great economic potential for small farmers. However, information on cultivars that are suitable for high tunnels is rather limited. In this study conducted in the 2014–15 season, strawberry plugs of eight June-bearing cultivars (Florida Radiance, Benicia, Camarosa, Camino Real, Chandler, Strawberry Festival, Sweet Charlie, and Winterstar) and two day-neutral cultivars (San Andreas and Albion) were evaluated for yield performance, fruit quality, and vegetative growth in organically managed high tunnels at two locations in North Carolina. Significant cultivar differences in whole-season yield were observed at Greensboro, NC; but not at Goldsboro, NC. The cultivar Florida Radiance had the highest marketable and total yields, followed by Winterstar and Chandler at Greensboro, whereas Benicia, Winterstar, and Chandler were the top producing cultivars at Goldsboro. Harvest of day-neutral cultivars San Andreas and Albion started in November. For June-bearing cultivars, Florida Radiance began to produce harvestable berries in late December, followed by Winterstar in early January. Peak harvest occurred in April for all cultivars. At the end of the season, ‘Albion’ had smaller canopy size than other cultivars. It also developed the fewest number of branch crowns and least aboveground biomass. Total soluble solid (TSS) content in April was lower than that observed early and late in the season for all cultivars, although Strawberry Festival exhibited a relatively stable TSS throughout the season. ‘Benicia’ produced the largest strawberries in the early season, but its fruit weight was remarkably reduced as the season progressed. Severe frost events occurred on 18 and 20 Feb. that caused an average of 61.5% and 32.2% open blossom damage at Greensboro and Goldsboro, respectively. The recommended cultivars based on this 1-year study are Florida Radiance, Benicia, and Camino Real for June-bearing cultivars, and Albion and San Andreas for day-neutral cultivars.

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Daniel Rowley, Brent L. Black, Dan Drost and Dillon Feuz

Takeda, F. Newell, M. 2006 Effects of runner tip size and plugging date on fall flowering in short-day strawberry ( Fragaria × ananassa Duch.) cultivars Intl. J. Fruit Sci. 6 103 117

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Timothy W. Miller, Carl R. Libbey and Brian G. Maupin

Propane flaming and organic amendments were evaluated for usefulness in matted-row strawberry (Fragaria ×ananassa Duch.). Flaming was used once before transplanting ‘Hood’ strawberry (PRETR), twice before transplanting (PRETR + PRETR), or once before and once after transplanting (PRETR + POSTR) and compared with rototilling before transplanting in 2000–02. Organic amendments tested across flame treatments included corn gluten meal (CGM) at two rates, wheat gluten (WG), and mustard seed meal (MSM) with high or low glucosinolate content, and herbicides included oxyfluorfen, pendimethalin, and a combination of oxyfluorfen + pendimethalin. Amendments/herbicides were applied immediately POSTR in Year 1 and again to established plants in late winter of Year 2. All plots were weeded by hand after weed evaluations were completed and weeding hours recorded. The trial was conducted twice: Iteration 1 and Iteration 2. Effect of flaming on grass and broadleaf weed ratings was brief during Year 1 of both iterations, with only slight differences observed in June and no differences by September. Total weeding time was reduced 12% by flaming PRETR once compared with rototilling in Iteration 1 and was reduced 10% by all flame treatments in Iteration 2. Rototilling reduced total berry yield and average individual fruit weight compared with flaming treatments in Iteration 1; there was no significant effect of flame on strawberry yield or individual fruit weight in Iteration 2. Organic amendments did not reduce weeding time in Iteration 1 compared with the nontreated control, although weeding time was increased 18% by CGM at 487 kg·ha−1 compared with synthetic herbicide treatments. In Iteration 2, total weeding time was reduced 14% for the two pendimethalin treatments and for high-glucosinolate MSM compared with nontreated control plots. First-year strawberry leaf area was reduced by oxyfluorfen + pendimethalin compared with nontreated strawberries (802 and 1086 cm2/plant, respectively) and was generally increased with organic amendments. Strawberry yield in Iteration 1 was increased ≈14% by CGM at 974 kg·ha−1 and WG and low-glucosinolate MSM compared with nontreated strawberry. Oxyfluorfen and oxyfluorfen + pendimethalin reduced strawberry yield by ≈20% and average individual fruit weight by ≈9% (14.8 and 14.5 g/fruit) compared with nontreated strawberry (16.1 g/fruit); high-glucosinolate MSM also reduced average individual fruit weight to 14.8 g/fruit. There were no significant effects of amendments/herbicides on strawberry yield parameters in Iteration 2.