Search Results
The molecular mechanisms governing photoperiodic flowering has been well defined in the model systems of Arabidopsis thaliana(a facultative long-day plant) and rice (a short-day plant). Photoperiodic flowering control is of great interest to strawberry (Fragaria×ananassa) breeders and growers, and the genetics of photoperiodic flowering have been well studied, indicating that response to day-length is regulated by a small number of genetic loci. Cultivated strawberry is octoploid, so identification of these loci through forward genetic analyses is not practical. Since the componentry of the flowering response is generally conserved between monocots and dicots, we may assume that similar, if not identical, systems are functioning in strawberry as well. The goal of this work is to understand how cultivars likely containing identical photoperiod-sensing components are differentially sensitive to daylength. The expression patterns of genes relevant to the floraltransition were assessed under specific photoperiod conditions to assess similarities and/or differences to the model systems.
Resistance to fire blight in blackberry (Rubus subgenus Rubus Watson) was studied in both seedling populations and clonally propagated plants. Seedling populations resulted from a partial diallel crossing of seven cultivars (Apache, Arapaho, Chester Thornless, Illini Hardy, Navaho, Triple Crown, and Prime-Jim™). Clonal material evaluated included eleven cultivars (Apache, Arapaho, Chester Thornless, Chickasaw, Kiowa, Illini Hardy, Navaho, Ouachita, Shawnee, Triple Crown, and Prime-Jim) and six breeding selections. Inoculations were made by injection of suspensions of Erwinia amylovora in sterile water. Significant differences in resistance were found among genotypes; `Navaho' was the most susceptible, and `Kiowa' and a breeding selection A-2095, the most resistant. Seedling inoculations showed resistance to be quantitatively inherited and mostly additive, with an overall narrow-sense heritability of h2 = 0.32.
The transition from vegetative growth to reproductive growth is carefully controlled by a number of independent signal transduction systems, one of which interprets photoperiod. Photoperiodic control of flowering time has been well-described in Arabidopsis and rice, revealing the presence of a generally common network of regulatory proteins. Timely and appropriate progression to flowering is critical to profitable production of cultivated strawberry (Fragaria ×ananassa), a species that includes long-day, short-day, and day-neutral cultivars. In an effort to characterize the photoperiodic flowering control mechanism in strawberry, the Fragaria orthologs of the photoperiod pathway genes were cloned and sequenced. Strawberry versions of Constans, Constans-like, Leafy, Flowering Locus T, and Suppressor of Constans Overexpression 1 were identified by screening cDNA libraries and through degenerate PCR approaches. Expression of these transcripts in short-day and day-neutral cultivars was tested under long and short photoperiods. Functional complementation of Arabidopsis mutants was performed where appropriate, alleles were identified, genetic linkage was determined where possible, and relationships between the strawberry genes and homologs from other species were studied. These trials define the mechanistic elements of an agriculturally important pathway in this valuable crop, and lays the foundation for transgenic studies in strawberry to manipulate the floral transition.
Fragaria ×ananassa, the cultivated octoploid strawberry, is an intensively cultivated fruit crop in which relatively small variations in disease susceptibility and flowering habit can have significant economic impacts. In order to facilitate future studies of the molecular mechansisms governing these characters, we have initiated studies to identify and sequence the strawberry homologs of a number of important genes known to be critical to pathogenesis response and photoperiodism in model systems such as arabidopsis, rice, and tomato. Using the primary Florida cultivar Strawberry Festival, we have employed a variety of techniques to identify such genes, including EST sequencing of a salicylate-induced cDNA library, PCR with degenerate primers, and colony hybridization. Possible homologs of the targeted genes and their relationships to similar genes in other species are presented. These results will form the basis of future studies of gene expression and evolutionary relationships among the Rosaceae and other species.
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.