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Abstract
Fruit breeders can easily justify the need to improve cold tolerance. Feature articles describing huge losses from winter cold or spring frosts can be found with regular frequency in grower magazines. In addition millions of dollars are spent annually to protect fruit crops from abnormally cold weather.
Abstract
‘Edelweiss’ and ‘Swenson Red’ grapes were developed from crosses made over 30 years ago with the goal of improving table grape quality in cultivars suitable for northern locations. Both have been grown at the University of Minnesota, Horticultural Research Center since 1968.
Abstract
The problem of observing pollen tube development and mitotic division can often be difficult and the technique can be unreliable. The following method was used with very good success for periodic observation of pollen tube development of several species of Vaccinium.
Abstract
Cold stress resistance of ‘Redcoat’ strawberries (Fragaria x ananassa Duch.) grown under several fall fertilization nutrient regimes was determined by artificial freezing. Stress resistance was determined at the onset of acclimation, October 15, and in midwinter with fully hardened plants. The least tolerant plants during the onset of acclimation were those with nutrient deficiencies, those with high N and low P and K and those with a high imbalance of K, whereas the most tolerant plants resulted from fertilizer applications of balanced NPK and balanced NPK plus high P (1:2:1). Fully hardened plants, artificially frozen to -9°C, -11° and -13° crown temperature showed similar stress responses to fertilization except that plants given high N plus P and K were more tolerant than in the October freeze test. Tissue analyses showed that plants with the highest ratio of P/K in crown and root tissues were also the most resistant to cold stress.
Twelve-week-old Malus seedlings were induced to cold harden by exposure to low temperature and freezing environments. The effectiveness of induced acclimation by exposure to stimuli such as low temperature (3 to 5 °C), frequency of exposure to freezing temperatures (-3 °C), storage time before and after induction and the effects of different screening temperatures (-20, -30, and -40 °C) were investigated with seedlings grown in a greenhouse from open-pollinated `Golden Delicious' apple (Malus pumila (Mill.), `Antonovka' apple (M. baccata (L.) Borkh. × (M. pumila) and `Rescue' apple (M. baccata) × (M. pumila). Differentiation of the seedling populations with respect to cold hardiness was not achieved until after acclimation at cool temperatures (3 to 5 °C) for 6 weeks. Further population differentiation was achieved by exposure to one or more frosts (-3 °C). Once the acclimation response had been initiated the seedlings could be held for up to 11 days, under the same conditions, with no significant decrease in hardiness. Hardiness levels of acclimated and nonacclimated open pollinated seedlings coincided with known inherent hardiness responses for all three maternal cultivars evaluated. A binomial form of regrowth data collection, percent seedling survival, was determined to be the most efficient and most precise measure of evaluation. Induction of cold hardiness in very young seedlings and the use of a controlled freeze testing protocol should facilitate rapid screening of large progenies and improve the rate of progress in breeding for cold hardiness.
Woody plants can be induced to cold-acclimate by exposure to sublethal low temperatures, but only after the onset of vegetative maturity. We monitored seven woody plant taxa, at monthly intervals, to determine the date of vegetative maturity, freeze-killing temperature, cell membrane electrolyte leakage, and the quantity and diversity of endogenous oligosaccharides. The freeze-killing temperature changed from -5 to -7C before vegetative maturity to -15 to -20C after vegetative maturity. There was a 10-fold increase in raffinose and about a 3-fold increase in endogenous stachyose in samples that were cold-acclimated under controlled conditions. In field samples, endogenous raffinose increased from <0.02% in August to 2% to 11% in cortical stem tissues of all cold-acclimated taxa. The tetrasaccharide stachyose increased from <0.02% to 0.25% to 2.5% for similar comparisons. None of the other sugars or polyols showed similar, consistent patterns during the onset of cold acclimation. In response to low temperature, raffinose family oligosaccharides (RFOs) have previously been shown to increase substantially in cabbage, soybean, kidney bean, and Chlorella. RFOs also possess high water-binding characteristics and tend to enhance aqueous glass transitions. Accordingly, we hypothesize that the endogenous production of these oligosaccharides may play an important role in metabolic events associated with cryoprotection of critical cellular functions during low-temperature stress.
Abstract
The technique of differential thermal analysis was used to examine midwinter hardiness of bud and stem tissues of Vitis riparia. Low temperature freezing points (exotherms) were found to occur in both stem and deacclimated bud tissues. Exotherms were not exhibited by fully acclimated buds. The temperature at which the stem tissue exotherm occurred was independent of cooling rate and duration of a thawing pretreatment of 6 to 48 hours. The initiation temperature of the bud exotherms varied with cooling rate and duration of a thawing pretreatment of 6 to 48 hours; an increase in either caused the bud exotherm to occur at a higher temperature than that of the control. It is postulated that deep supercooling of the intracellular water in stem and bud tissues is the characteristic which limits the northern distribution of V. riparia.
Abstract
Freezing injury of highbush blueberry flower buds (Vaccinium corymbosum L. cv. Rancocas and an experimental hybrid) were investigated after natural freezing and by differential thermal analysis (DTA). Terminal buds were less hardy than median and basal buds on the same twig. Apical, less mature florets were also less hardy than median or basal, more mature florets within each bud. DTA analysis of intact flower buds showed that a rate independent free water exotherm was followed by numerous rate dependent floret exotherms. Floret lethality was associated only with the rate dependent low temperature exotherms. Buds were held over water-glycerol solutions in desiccators so that they came into equilibrium with a relative humidity of 100%, 98% or 96% at 4°C. Artificially hydrated buds were hardy to –10° and artificially dehydrated buds were 15°C hardier. A mean survival temperature of the florets (MSTF) from DTA analysis, derived at slow cooling rates related closely to lowest survival temperature (LST66) from artificial freezing hardiness tests. In mid-winter, under environmental conditions of low temperature and low relative humidity, flower buds of a hardy hybrid lost all DTA exotherms and were hardy to at least –40°. Tissue dehydration and accompanying loss of floret low-temperature exotherms was associated with extreme cold tolerance of blueberry flower buds with the hardy experimental hybrid.
No information is available regarding endogenous soluble carbohydrate accumulation in buffalograss [Buchloe dactyloides (Nutt.) Engelm.] during cold acclimation. The objective of this study was to determine composition of soluble carbohydrates and their relationship to freezing tolerance in two buffalograss cultivars, 609 and NE 91-118, with different freezing tolerances. The experiment was conducted under natural cold acclimation conditions in two consecutive years in Fort Collins, Colo. Based upon average LT50 (subfreezing temperature resulting in 50% mortality) from seven sampling intervals in 1998-99 and six sampling intervals in 1999-2000, `NE 91-118' survived 4.5 °C and 4.9 °C colder temperatures than `609', during the 1998-1999 and 1999-2000 winter seasons, respectively. Glucose, fructose, sucrose, and raffinose were found in both cultivars in both years, and were generally higher in acclimated than pre- and post-acclimated stolons. Stachyose was not present in sufficient quantities for quantification. Cultivar NE 91-118 contained 63% to 77% more glucose and 41% to 51% more raffinose than `609' in the 1998-99 and 1999-2000 winter seasons, respectively. In 1999-2000, fructose content in `NE 91-118' was significantly higher than that of `609'. A significant negative correlation was found between LT50 vs. all carbohydrates in 1999-2000, and LT50 vs. sucrose and raffinose in 1998-99. Results suggest that soluble carbohydrates are important in freezing tolerance of buffalograss.
Abstract
The highbush blueberry cultivars, ߢRancocasߣ and ߢEarliblueߣ, failed to acclimate in time to avoid low temp injury to stems exposed above the snow level during the 1st year seasonal change in hardiness was studied. In the 2nd year, however, they hardened to temp as low as -40°C and survived the winter. Acclimation occurred earlier in a native selection of Vaccinium angustifolium Aiton and in ߢRancocasߣ. Selections of V. angustifolium and natural hybrids of V. angustifolium and V. cormybosum L. were found to be hardier than any of the highbush cultivars. A selection of V. constablaei Gray and V. membranaceum Douglas, respectively, were also hardier than the highbush types. A low temp exotherm was found to be present in blueberry stems, but it was associated only with xylem injury which was not as critical for survival as the bark tissues. The bark was injured at temp higher than the xylem and was not associated with any exotherm.