Previous research has optimized the colchicine dropper technique for chromosome doubling under greenhouse conditions. In recent years, in vitro germination of cut strawberry achenes has greatly increased germination rates. Combining the two techniques would be especially useful when chromosome doubling is desired for interspecific hybridization. Fragaria vesca was chosen for initial study. Treatments included colchicine levels of 0%, 1%, 2%, 3%, 4%, or 5% (w/v); exposure time to colchicine was from 6 to 16 to 26 hours; application was at the cotyledon stage or after the first true leaf formed; presence or absence of 3 g activated charcoal/liter; and presence or absence of DMSO. Media consisted of MS salts and vitamins, 30 g sucrose/liter, and 2.5 g phytogel/liter. Charcoal enhanced upward growth of seedlings, thus allowing better placement of colchicine droplets. Reduced exposure time and application at the first true-leaf stage allowed higher levels of colchicine to be used without greatly reducing the vigor of treated seedlings.
Bob Bors and J. Alan Sullivan
Bob Bors and J. Alan Sullivan
Fragaria vesca has been introgressed into F. ×ananassa in the form of decaploids and synthetic octoploids. As F. vesca is self-incompatible and crosses with most diploid Fragaria species when used as a female parent, it could serve as a bridge for introgression of additional genetic material. A primary goal of this study was to screen selections of F. vesca for interspecific crossability among diploid species. The F. vesca collection included 10 cultivars of the alpine strawberry, F. vesca var. semperflorens, as well as 30 wild runnering types gathered from around the world. The following diploid species were represented by one to three genotypes each: F. viridis, F. nubicola, F. nipponica, F. nilgerens, F. iinumae, F. daltoniana, F. gracilis, as well as two unnamed species from China. Fragaria vesca was used as the female parent and the other species provided the pollen. Crossing took place in the greenhouse, with one pollination occurring during the “popcorn” or “balloon” stage. Germination was performed in vitro using cut achenes shortly after fruit ripening. The alpine strawberry cultivars were easier to cross than wild selections of F. vesca. Their continuous blooming habit combined with higher positioning of flowers allowed for easier and perhaps less-damaging emasculation. Crossability, as measured by seed set and germination, was more variable in wild-type F. vesca and generally lower than alpine strawberry cultivars.
Robert H. Bors and J. Alan Sullivan
Interspecific crosses with Fragaria moschata (6x) have been hampered by ploidy level differences, poor seed set, and extremely poor seed germination. Modification of pollination practices, embryo rescue, and use of several genotypes has allowed over 80 synthetic tetraploids to be created from 14 cross combinations. Germplasm for the experiment consisted of eight selections of F. moschata (6x), two of F. nubicola (2x), and two of F. viridis (2x). Both 2x × 6x and 6x × 2x crosses were performed. Initially, negligible seed set occurred on F. nubicola and F. viridis when multiple flowers per truss were pollinated. When only one cross was performed per truss, with other flowers removed, seed set was greatly enhanced. F. moschata was much more tolerant of multiple crosses per truss. The crossing combination of F. moschata × F. nubicola gave the worst seed production. Other species combinations were capable of producing good seed set with noticeable differences between individual selections. When achenes were halved, only 1% appeared normal, 2% were underdeveloped or shrunken, the remainder were empty. Many of the malformed and most of the normal embryos germinated using the cut achene method. Achenes were surface-sterilized, cut in half, and placed on MS media with activated charcoal (3g·L–1), sucrose (30g·L–1), and no hormones. Germination occurred only from achenes from fully ripened fruit. Viable hybrids were obtained from 2x × 6x as well as 6x × 2x crosses. Fragaria viridis–F. moschata hybrids closely resembled F. moschata while F. nubicola–F. moschata hybrids were more intermediate in leaf morphology.
Robert H. Bors and J. Alan Sullivan
Fragaria species from the center of diversity have not been integrated into octoploid commercial strawberry cultivars because of ploidy level differences. Even though traits such as disease resistance, enhanced flavor, cold hardiness, and vigor are known to exist in the diploid, tetraploid, and hexaploid species, they cannot be easily used for breeding. The synthetic octoploid method circumvented introgression difficulties by combining lower ploidy species and doubling to the octoploid level. Although easily crossed to cultivars, the use of synthetic octoploids has been minimal as it has been extremely difficult to create them. By working to improve bottlenecks of the original system, improved methodology has been developed and 170 synthetic octoploids have been produced. This represents more than a 100-fold increase in efficiency. The following factors played a major role in improving the system: wide germplasm base; use of F. vesca as a common genome; embryo rescue; 5% colchicine applied in vitro by dropper method for 24 hours followed by a quick rinse and continuous light in a 18C growth chamber. F. vesca, F. nilgerrensis, F. nubicola, F. viridis, F. orientalis, and F. moschata have been incorporated into synthetic octoploids in this study.
Fadi H. Karam and J. Alan Sullivan
Distinct differences in freezing tolerance among a cold-hardy wild rose species Rosa fedtschenkoana Regel., a garden rose, `Jack Frost', and their hybrid could be detected under laboratory conditions using 2-cm-long shoot segments with buds. The garden rose did not survive - SC, but the cold-hardy species survived freezing to -10C and the hybrid to –5C. One week of acclimation at 4C was adequate for R. fedtschenkoana; longer periods did not improve the rate of survival. Immersing tissue in 5%, 10%, or 20% sucrose during acclimation improved the rate of survival of R. fedtschenkoana but not of `Jack Frost'. Applications to rose breeding are discussed.
Jean-Pierre Privé and J. Alan Sullivan
Growth rates for two types of tissue-cultured plant stock for `Heritage', `Ruby', and `Redwing' red raspberry (Rubus idaeus L.) were examined. Actively growing plantlets from the greenhouse (G) were compared to cold-treated (CT) plantlets from cold storage. The greatest differences between these two occurred during the first 6 weeks after planting. At 4 weeks, CT plants for all cultivars had longer canes and internodes, sometimes twice that of G plants. Although `Heritage' had greater total plant dry weights following chilling, `Ruby' and `Redwing' had less. Chilling had no effect on `Heritage' root growth but did reduce root dry weight for `Redwing' and `Ruby'. Relative growth rate (RGR) and leaf area ratio (L-AR) were more effective variables for analyzing growth as they considered differences in initial biomass and cane number and provided a better representation of the data during the initial 6 weeks of growth. All cultivars showed a greater total plant RGR and LAR for the CT plants at 6 weeks. During the first 4 weeks, the G plants were more efficient producers of root dry matter while the CT plants were more efficient producers of cane dry matter. By 6 weeks, the G plants had partitioned a greater percentage of their assimilates into cane growth while the leaves, canes, and roots of the CT plants contributed equally to total RGR. No difference in total or individual component RGR was observed after 6 weeks.
Robert H. Bors and J. Alan Sullivan
Several interesting attributes have been observed while working with European and Asian species of Fragaria. F. nilgerrensis has shown immunity to aphids and leaf diseases. F. iinumae produces runners that frequently have unusual tap roots. F. moschata demonstrated excellent winter hardiness in a water-logged field during an unusually long cold winter (1995–96) in southern Ontario, excellent leaf disease resistance, and high susceptibility to Botrytis. When grown in the greenhouse, F. moschata fruit taste like a concord grape. F. pentaphylla (Guelph P-1 and P-2) displayed unusually bright red-colored fruit that were uniformly wedged, firm, but lacking flavor. F. pentaphylla P-1 is extremely vigorous and immune to leaf diseases. F. nubicola and F. daltoniana are the smallest and least-vigorous plants in the Univ. of Guelph's collection, yet they appear to confer hybrid vigor to their progeny when crossed to other species. F. daltoniana's leaf has a waxy cuticle and dark green color similar to F. chiloensis. F. viridis has a spicy, cinnamon-like flavor. When F. viridis is crossed to most other diploids, powdery mildew and leaf diseases are prevalent. F. orientalis crosses easily to synthetic tetraploids, has a flavor similar to F. viridis and F. nubicola, but is extremely susceptible to viruses. Aroma is quite variable in F. vesca with the most desirable originating from Russian accessions.
Justine Vanden Heuvel, J. Alan Sullivan, and John T.A. Proctor
The effect of three trellising systems (Hedgerow, V-Trellis, and Single-Sided Shift-trellis) and four cane densities were studied on Rubus ideaus L. cv. Titan red raspberries. Yield, cane growth, canopy microclimate, disease load, canopy light penetration, and fruit quality were examined. The treatments significantly affected yield and yield components. The V-trellis had a higher yield (+19%) and a larger fruiting framework than the hedgerow, while the shift-trellis had a lower yield than the hedgerow (-36%) and the V-trellis (-50%) due to a small fruiting framework. Path analysis indicated that interrelationships among yield components were significantly affected by trellising system. The shift-trellis was found to have lower quality berries than the other systems. These differences were related to light penetration into the different canopies. An optimum cane density was not found for any system. Yield potential per cane decreased as cane density increased; however yield per square meter increased as cane number increased. Berry quality decreased as cane density increased. Differing cane density did not affect canopy microclimate or disease load.
David C. Percival, John T.A. Proctor, and J. Alan Sullivan
Field experiments consisting of trickle irrigation (TI), IRT-76 plastic film (PF), and straw mulch were initiated to determine the influence of soil temperature and water status on carbon partitioning during the establishment of Rubus idaeus L. `Heritage' (1993, 1994), `Autumn Bliss' (1994), and `Summit' (1994) micropropagated raspberries. Environmental, vegetative, reproductive, and nutrition data were collected. Photosynthesis (Pn) measurements were recorded under field conditions using a Li-Cor LI-6200 portable photosynthesis system. Neither node number nor shoot: root ratio was influenced by TI, PF, or straw mulch. PF, however, increased root and shoot weight, total flowers produced, total berries harvested, and foliar N and P. Although differences existed among cultivars, field Pn measurements indicated that, regardless of groundcover treatment or cultivar examined, the maximum Pn rate occurred at a root-zone temperature of 25C. Hence, results from this study indicate that conditions in both the air and root zone physical environment regulate carbon assimilation and partitioning.
David C. Percival, John T. A. Proctor, and J. Alan Sullivan
A study examining the influence of trickle irrigation (TI), IRT-76 plastic film (PF) and straw mulch (SM) on the establishment of Rubus idaeus L. cv. `Heritage' micro-propagated raspberries was initiated at Cambridge, Ontario in 1993. Environmental, nutritional, vegetative and reproductive data were collected. Soil temperature and soil water status were greatly affected by TI, PF and SM. TI lowered soil NO3-N and increased soil NH4-N and Mg. PF increased soil NO3-N and NH4-N. Foliar N decreased by 10% with TI and increased by 8% with PF. Foliar P and Ca increased by 45 and 6% respectively, with TI. Node number was not influenced by TI, PF or SM. PF however, increased cane height, cane diameter, dry weight and leaf area by 14, 17, 77 and 11% respectively, and TI increased cane diameter by 13%. Although TI increased the number of fruiting laterals by 63%, there was no effect of TI, PF or SM on harvested berry number or weight.