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Carl H. Shanks Jr. and Patrick P. Moore

More than 170 clones of Fragari ×ananassa Duch., F. chiloensis (L.) Duch., and F. virginiana Duch. were tested for resistance to the twospotted spider mite (Tetranychus urticae Koch). Twenty-seven clones had >75% fewer mites than did F. ×ananassa `Totem', a susceptible clone. About two-thirds of the clones also were tested for resistance to the strawberry aphid [Chaetosiphon fragaefolii (Cockerell)]. Survival and reproduction was significantly lower on two clones each of F. ×ananassa and F. virginiana than on `Totem'.

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C.K. Chandler, D.E. Legard, D.D. Dunigan, T.E. Crocker, and C.A. Sims

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Nathalie Delhomez, Odile Carisse, Michel Lareau, and Shahrokh Khanizadeh

Seventeen strawberry (Fragaria ×ananassa Duchesne) cultivars and six selections were tested under greenhouse conditions for susceptibility to leaf spot induced by Mycosphaerella fragariae (Tul.) Lindau. The level of susceptibility was evaluated based on maximum disease severity and area under the disease progress curve (AUDPC). The 23 genotypes were ranked based on AUDPC and grouped according to their susceptibility. Cluster analysis for AUDPC gave four groups corresponding to low, moderate, high, and very high susceptibility to leaf spot. `Annapolis', `Chambly', `Glooscap', `Redcoat', and `Veestar' consistently showed a low level of susceptibility. The selections SJ89700-1 and SJ8518-11 and `Tribute' showed a very high level of susceptibility, and the remaining cultivars were grouped as either moderately or highly susceptible.

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Shahrokh Khanizadeh, Michel J. Lareau, and Deborah Buszard

An experiment was conducted to evaluate the mechanical harvesting and processing suitability of four standard strawberry [Fragaria ×ananassa (Duch.)] cultivars (`Kent', `Glooscap', `Bounty', and `Midway') and the recent introductions `Chambly' and `Oka'. `Kent', `Glooscap', `Oka', and `Chambly' had the highest yields and heaviest fruit. Similar percentages of berries of all cultivars were destroyed by the harvester. `Oka' and `Midway' were not suitable for this type of mechanical harvesting due to their susceptibility to bruising during harvest. Based on total marketable fruit harvested mechanically, `Chambly' was the most and `Oka' was the least adapted cultivars for this particular harvester. `Chambly' and `Glooscap' were easiest to decap, followed by `Bounty', `Oka', and `Midway'. None of the cultivars tested were suited ideally for machine harvesting, and further breeding is required to produce well-adapted cultivars.

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Shahrokh Khanizadeh, Bertrand Thériault, Odile Carisse, and Deborah Buszard

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Leighan Howard, Philip Stewart, Amit Dhingra, Craig Chandler, and Kevin Folta

Cultivated strawberry (Fragari×ananassa) is a valuable crop, yet has benefitted little from recent advances in biotechnology and genomics. A high-throughput system for transformation and regeneration would hasten elucidation of gene function for strawberry and possibly the Rosaceae in general. In this report, a protocol for high-frequency octoploid strawberry transformation and regeneration is presented. The protocol uses leaf, petiole, and stolon as explants from a newly selected genotype, `Laboratory Festival #9'. This genotype was selected from progeny of a `Strawberry Festival' self-cross exclusively for its rapid regeneration and robust growth in culture. Direct organogenesis has been achieved from the leaf or from prolific callus with multiple shoots being visible in as few as 14 days. Over 100 viable regenerants may be obtained from a single leaf explant of about 3-cm2 size. This laboratory-friendly genotype allows high-throughput, statistically relevant, studies of gene function in the octoploid strawberry genetic background as well as generation of large transgenic populations.

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Douglas V. Shaw and Kirk D. Larson

Yield and fruit size were determined for 49 strawberry (Fragari ×ananassa Duch.) genotypes during a 7 year period, in soils prepared with and without preplant soil fumigation using 2 methyl bromide: 1 chloropicrin (wt/wt). Strawberries were grown in alternate years, with the nonfumigated treatment representing the first, second, third, and fourth strawberry crop cycles initiated without soil fumigation. Highly significant (P < 0.01) effects of soil fumigation treatment were present for yield in a combined analysis over all years; fumigation increased yield by 41% over nonfumigated soils in the first nonfumigated cultivation cycle and by 68% to 74% for subsequent nonfumigated cycles. Fruit size was less affected by soil treatment but increases due to fumigation (2% to 18%) were significant (P < 0.05) in the third or fourth nonfumigated crop cycle. Genotypic variances were highly significant in the combined analysis, whereas geneti × fumigation interaction variances were significant only for fruit size and contributed <8% of the total phenotypic variance for either trait. Genetic correlations were r g = 0.77 and 0.92, respectively, for yield and fruit size treated as independent traits across soil fumigation environments. There was no evidence for genes that confer specific adaptation to nonfumigated soils, or that these genes emerge as important contributors to the phenotypic variation as the soil environment deteriorates with repeated cultivation of strawberry in nonfumigated soil. Chemical names used: trichloronitromethane (chloropicrin).

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Suzanne C. Stapleton, Craig K. Chandler, James F. Price, Daniel E. Legard, and James C. Sumler Jr.

The use of locally grown transplants in Florida strawberry (Fragari×ananassa Duchesne) production has increased since the release of the cultivar Sweet Charlie by the University of Florida in 1992. Previous research has shown that nursery region can influence production patterns of other strawberry cultivars through differences in photoperiod and temperature exposure. Transplants of `Sweet Charlie' strawberry (bareroot and plug plants) from sources representing northern (Canada, Massachusetts, Oregon), southern (Alabama, Florida) and mid latitude (North Carolina) transplant production regions were compared for plant vigor, production, and pest incidence at Dover, Fla. in 1995-96 and 1996-97. Total fruit production was not significantly different forplants among the plant source regions in 1995-96, but total yield from southern source plants in 1996-97 was significantly lower than northern and mid latitude plant sources. Monthly production of marketable fruits varied among the three plant source regions in December, January, and February, during which time market prices fell 46% in 1995-96 and 56% in 1996-97. Plants from northern and mid latitude sources produced significantly greater fruit yield in December than plants from southern sources. Differences among plant sources were detected for early flowering, initial crown size, incidence of foliar disease, arthropod pests, mortality, and fruit weight. Geographic location of strawberry transplant sources influenced fruiting patterns and other components that may affect profitability of `Sweet Charlie' strawberry production in west central Florida.

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Chrislyn A. Particka and James F. Hancock

Black root rot (BRR) is a widespread disease of strawberry (Fragari×ananassa Duchnesne) that causes the death of feeder roots and the degradation of structural roots. The major causal organisms of BRR include Rhizoctonia fragariae Husain and W.E. McKeen, Pythium Pringsh., and Pratylenchus penetrans (Cobb) Filipjev and Schuurmans Stekhoven. The current method of control for black root rot is methyl-bromide fumigation; however, methyl bromide is scheduled to be phased out in 2005, and its effects are short-lived in matted-row systems. The objectives of the study were to measure levels of tolerance to BRR in 20 strawberry genotypes and to determine which pathogens were present in the soil. The genotypes were planted in four blocks each of methyl-bromide fumigated and nonfumigated soil, and were evaluated for crown number, number of flowers per crown, yield, and average berry weight over 2 years. The results showed that all three pathogens were present in the field, and that there was a significant genotype × fumigation interaction for yield and crown number in both years. The cultivars Bounty, Cabot, and Cavendish, all released from the breeding program in Nova Scotia, displayed tolerance to the pathogens that cause BRR.

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Sean B. Fort and Douglas V. Shaw

Seedling offspring of crosses among 10 selected strawberry genotypes (Fragari ×ananassa Duch.) from the University of California strawberry improvement program were established in annual hill culture. Soil treatments consisted of 1) preplant fumigation using a mixture of methyl bromide and chloropicrin or 2) no fumigation. Root systems of individual plants were sampled with a soil probe in January, April, and July 1994 to determine root mass (RM), secondary root mass (SRM), and a subjective root appearance score (RAS). For each trait, genetic analyses of partial diallels were performed to quantify sources of genetic, environmental, and interaction variance. Root trait values differed significantly between soil treatments only for the April sampling date, with all trait values greater in fumigated soils than in nonfumigated soils. For RM and SRM, variance due to general combining ability (GCA) was significant in April and July. Narrow-sense heritabilities (h2 ) for RM increased between January (0.14) and July (0.40); SRM showed a similar trend with a higher h2 on each sampling date. GCA variances were nonsignificant for RAS, however, significant fumigation × GCA interaction variance was detected for RAS in January. Specific combining ability (SCA) variances were nonsignificant for all traits. To further quantify the extent of interactions, correlations (rg ) between genotypic expressions in fumigated soils and nonfumigated soils were calculated for each root trait. These rg values were at or near unity (> 0.85) for RM and SRM on all sampling dates, implying that genetic variability for these traits is conditioned by genes with identical effects within each soil environment. Conversely, rg between soil environments was 0.52, 0.62, and -0.18, for January, April, and July RAS, respectively. These findings suggest that genetic variability exists within this germplasm base for strawberry root mass characteristics. Genetic variation also exists for January root appearance score, but it is not conditioned identically across fumigation treatments.