formation within the extracellular matrix of multicellular tissues ( Taylor et al., 2015 ). Therefore, new protocols have been developed involving the use of cryoprotectants to allow cooling of plant cell contents into a vitrification state without the
Alexandre Bosco de Oliveira, Wagner A. Vendrame, and Luciana Cardoso Nogueira Londe
Michela Centinari, Maria S. Smith, and Jason P. Londo
systemic cryoprotectant products. Surface cryoprotectants are thought to cover green tissues with a physical barrier, which may prevent the formation of ice crystals inside the plant ( Fuller et al., 2003 ). Systemic cryoprotectants are used to mimic
David G. Himelrick, Robert M. Pool, and Philip J. McInnis
Several cryoprotectant chemicals were tested for their ability to increase the freeze resistance of grapevine (Vitis labruscana Bailey) leaf and dormant bud tissue. DuPont Surfactant WK, ethylene glycol, and BRIJ 35 were effective in lowering the low-temperature exotherm (LTE) in `Concord' grape buds below controls by 5.4, 5.1, and 3.9C, respectively, in March. Measurements taken in April showed BRIJ 35 and Surfactant WK to be notably superior to the other products, giving LTEs 14.1 and 12.2C below controls, respectively. Ethylene glycol, Frostguard, and Frost Free were less effective. LTEs were also significantly decreased in grape leaf disks 4.1C by BRIJ 35, 2.1C by Frostguard, and 0.4C by Frost Free treatments. Chemical name used: trimethylnonylpolyethoxyethanol (DuPont Surfactant WK).
Michele R. Warmund and James T. English
Cryoprotectants were applied at labeled rates to primary flowers of `Honeoye' strawberry (Fragaria × ananassa Duch.) plants at full bloom to determine their effects on the floral organs. Frostgard at 50 ml/liter or KDL at 22 ml/liter injured pistils and resulted in misshapened fruit. Floral buds that were closed when cryoprotectants were applied were uninjured. In other experiments, efficacies of cryoprotectants were determined after floral tissues of `Honeoye' strawberry plants were inoculated or not inoculated with the ice-nucleation-active (INA) bacteria, Pseudomonas syringae van Hall and subjected to sub-freezing temperatures. None of the products protected primary or secondary flowers against freezing injury regardless of the occurrence of INA bacteria. INA bacteria were not recovered from primary flowers of treated plants that were killed by low temperature exposure, indicating that non-bacterial nuclei may incite freezing in these tissues.
K.B. Perry, A.R. Bonanno, and D.W. Monks
The ability of two cryoprotectants to protect tomato and pepper transplants during frost and freeze conditions was evaluated in Clayton, NC. A commercially available cryoprotectant (50% propylene block copolymer of polyoxyethylene, 50% propylene glycol, tradename FrostFree) was evaluated during 4 spring and 3 fall seasons. An antitranspirant (96% di-1-p-Menthene, i.e. Pinolene, a terpenic polymer, 4% inert, tradename VaporGard) was evaluated for 2 spring and 1 fall season. Protection from these products was not observed under the field conditions experience? Yield differences were not observed between the treated and untreated plants. With several days of cool weather preconditioning, transplants survived air temperatures of -2.0 to -1.0 C with no damage. However, with no preconditioning, damage occurred at -1.0 C without the formation of frost. At -3.5 C all plants, both treated and untreated, died. Both crops were stunted and delayed by periods of cold temperatures even when no freezing temperatures were experienced.
Katharine B. Perry, A. Richard Bonanno, and David W. Monks
A commercially available cryoprotectant (50% propylene block copolymer of polyoxyethylene, 50% propylene glycol; trade name FrostFree) and an antitranspirant (96% di-1-p-menthene, i.e., pinolene, a terpenic polymer, 4% inert; trade name Vapor Gard) were evaluated for their ability to protect `Pik Red' tomato (Lycopersicon esculentum Mill.) and `Keystone Resistant Giant #3' pepper (Capsicum annuum L.) plants during frost and freeze occurrences in the field. Tests were conducted during four spring and two fall seasons. Protection from these products was not observed under field conditions when minimum air temperature reached -3.5C and -l.0C on separate occasions. Yields for treated and untreated plants were similar. Neither cryoprotectant injured the foliage in the absence of cold events.
Kurt D. Nolte, Andrew D. Hanson, and Douglas A. Gage
Proline and various betaines can function as osmoprotectants and cryoprotectants when accumulated in the cytoplasm of cells. Genetic engineering can raise levels of these compounds and thereby improve stress resistance; Citrus species are potential candidates for this. Before attempting such engineering, it is necessary to characterize the natural osmoprotectants of Citrus and related genera. We therefore surveyed 55 cultivated and wild species of the Aurantioideae, analyzing proline and betaines in leaves of mature trees. Some citrus relatives accumulated proline alone; others accumulated proline and proline betaine, as did all Citrus species studied. The levels of these two compounds ranged from about 20 to 100 μmol·g-1 dry mass, and were significantly inversely correlated. Proline betaine is known to be synthesized from proline and to be a better osmoprotectant. Because Citrus species all have more proline than proline betaine, there is scope for engineering more of the latter. Many species had small amounts of hydroxyproline betaine; other betaines were essentially absent. The lack of other betaines means that it would also be rational to engineer the accumulation of glycine betaine or similar compounds.
M.F. Aoun, K.B. Perry, W.H. Swallow, D.J. Werner, and M.L. Parker
Gregory L. Reighard, William C. Newall Jr., and Charles J. Graham
Late spring freezes often result in significant flower bud kill in deciduous fruit trees. Some products have been marketed as frost protectant compounds which purportedly protect flower stigmas and ovaries from freezing injury and death. Two of these compounds, Frost Free and Frostgard, were tested at two locations in South Carolina over three years. Varieties `Junegold', `Loring', `Redhaven', and `Jefferson' were treated with Frost Free (FF) in years 1988-1990 and with Frostgard (FG) in 1990. Significant differences in fruit yield and vegetative growth occurred during this period, but no consistent trends were evident. In 1989, FF-treated `Redhaven' and `Jefferson' trees averaged 10.5 and 21.8 kg more fruit/tree than the controls. However, no lethal cold temperatures occurred during the bloom period. In 1990, FG-treated `Redhaven' trees averaged 8.0 kg more fruit/tree than the control trees. The fruit from FF-treated trees were lower in Brix, had less red color, and vegetative shoot growth was slightly greater than that of the FG and check trees. These data suggest that Frost Free may have plant growth regulator properties.
Hilary A. Sandler
The benefit of applying an antitranspirant for protection of cranberry (Vaccinium macrocarpon Ait.) vines exposed to desiccating conditions was evaluated at four different sites, two sites per year, for a period of 1 year each. Overall, plots receiving one fall application of an antitranspirant produced more berries and greater total fruit mass the following year than did nontreated plots. Overall dry leaf mass was not significantly affected. At one site, treated plots had more flowering uprights and more flowers per upright per unit of ground area than the nontreated plots. For cranberry growers who cannot maintain a winter flood, one fall application of pinolene (Vapor Gard) may offer some protection against winter injury. Further research is needed to document long-term yield effects as well as to clarify the role of the antitranspirant in protecting exposed vines and floral buds against adverse winter conditions. Chemical name used: di-1-p-menthene (pinolene).