Cold Hardiness Level Research Articles

Apoplastic Antioxidant Enzymes in the Leaves of Two Strawberry Cultivars and Their Relationship to Cold-Hardiness

In this study, apoplastic antioxidant enzymes in the leaves of two strawberry cultivars (‘Aromas’ and ‘Diamante’) and their relationshipto cold-hardiness were investigated. Fully expanded, uniformly sized leaves from 1-year-old field plants of the cultivars were collected atthe hardening (late autumn, in November and winter, in January) and de-hardening (summer, in July) stages. Leaf samples were exposedto low temperatures of 5, -5, -10, -20 and -30ºC for 12 h to determine their cold-hardiness (LT50; lethal temperature, where 50% of theplants were killed). Cold-acclimation produced a remarkable increase in cold-hardiness. It was found that ‘Diamante’ had higher coldhardinessthan ‘Aromas’. Moreover, malondialdehyde and total carotenoid content increased during the hardening stage and decreasedduring the de-hardening stage. The activities of catalase, peroxidase and ascorbate peroxidase in the leaf apoplast and nicotinamideadenine dinucleotide phosphate oxidase activity in the leaf tissue were correlated with changes in cold-hardiness. The activities of theseenzymes were higher in the hardening stage than in the de-hardening stage. The activities of apoplastic catalase, peroxidase and ascorbateperoxidase varied significantly depending on the cold-acclimation stage and the cold-hardiness level of the cultivars. This study indicatesthat elevated apoplastic antioxidative enzymes may be determinants of cold-hardiness in the strawberry plant. The lower malondialdehydecontent and higher total carotenoid and apoplastic enzyme activities in ‘Diamante’ indicated an enhanced cold-hardiness capacity of thiscultivar, serving to protect the plant from oxidative damage.

A semi-physiological model of cold hardening and dehardening in walnut stem

It has been hypothesized that the increase in temperature in this century could lead to an increase in frost damage to plant tissues. Several models have been proposed to describe the development of cold hardiness, but never taking into account extreme climatic and/or physiological events. Our results on walnut tree (Juglans regia L.) show that cold hardiness was best correlated with average daily temperatures minimal temperatures over the last 15 days before sampling (T(min 15 days)), indicating that the freezing tolerance depended on the tree's climatic history. Moreover, this study also shows that the accumulation of sucrose and the water content (WC) decrease are an essential step towards cold hardiness. Thus, a simple linear model based on climatic (T(min 15 days)) and physiological (soluble sugars, WC) explanatory variables was developed to predict the cold hardiness level in walnut stem at any time during the leafless period. Each of the three input variables can be assigned a specific role contributing to the simulated function, cold hardiness. The extent and robustness of this relation was assessed on extreme physiological events on walnut trees bearing three main branches. On each tree, one branch was defoliated to limit the local carbohydrate and transpiration, one was girdled to increase local carbohydrate and prevent carbohydrate export and the third one was kept untreated as control. As expected, these treatments impacted both local carbon reserves and WC in the stems born by each main branch in comparison with the control on the same tree. The impact of these treatments on stem's freezing tolerance, as evaluated by an electrolyte leakage method (LT₅₀), confirmed the direct impact of soluble sugar and WC on cold hardiness over a wide range of carbohydrate and WC. This is discussed in relation to the branch autonomy theory for carbon but also for water during summer growth and winter periods. The present study demonstrates the importance of physiological parameters in the prediction of cold hardiness and proposes a way to model cold hardiness with extreme climatic and/or physiological events.

Annual changes in MODIS vegetation indices of Swedish coniferous forests in relation to snow dynamics and tree phenology

Remote sensing provides spatially and temporally continuous measures of forest reflectance, and vegetation indices calculated from satellite data can be useful for monitoring climate change impacts on forest tree phenology. Monitoring of evergreen coniferous forest is more difficult than monitoring of deciduous forest, as the new buds only account for a small proportion of the green biomass, and the shoot elongation process is relatively slow. In this study, we have analyzed data from 186 coniferous monitoring sites in Sweden covering boreal, southern-boreal, and boreo-nemoral conditions. Our objective was to examine the possibility to track seasonal changes in coniferous forests by time-series of MODIS eight-day vegetation indices, testing the coherence between satellite monitored vegetation indices (VI) and temperature dependent phenology. The relationships between two vegetation indices (NDVI and WDRVI) and four phenological indicators (length of snow season, modeled onset of vegetation period, tree cold hardiness level and timing of budburst) were analyzed. The annual curves produced by two curve fitting methods for smoothening of seasonal changes in NDVI and WDRVI were to a large extent characterized by the occurrence of snow, producing stable seasonal oscillations in the northern part and irregular curves with less pronounced annual amplitude in the southern part of the country. Measures based on threshold values of the VI-curves, commonly used for determining the timing of different phenological phases, were not applicable for Swedish coniferous forests. Evergreen vegetation does not have a sharp increase in greenness during spring, and the melting of snow can influence the vegetation indices at the timing of budburst in boreal forests. However, the interannual variation in VI-values for specific eight-day periods was correlated with the phenological indicators. This relation can be used for satellite monitoring of potential climate change impacts on northern coniferous spring phenology.

Cold-hardiness of olive (Olea europaeaL.) cultivars in cold-acclimated and non-acclimated stages: seasonal alteration of antioxidative enzymes and dehydrin-like proteins

SUMMARYSeasonal patterns of antioxidative enzymes and proteins and their relations to cold-hardiness of nine olive (Olea europaeaL.) cultivars (Ascolona, Domat, Gemlik, Hojoblanca, Lecquest, Manzanilla, Meski, Samanli and Uslu) are documented in the current study. Fully expanded, uniformly sized leaves from 2-year-old shoots of the cultivars were collected from 20-year-old trees in cold-acclimated (CA, in January) and non-acclimated (NA, in July) stages. Leaf samples were exposed to low temperature at 4, −5, −10 and −20°C for 12 h to determine their cold-hardiness (LT50; assessed by electrolyte leakage). Cold-acclimation produced an increase in freezing tolerance of all cultivars (by lowering LT50). Domat and Lecquest were found to have the highest cold-hardiness among the nine cultivars investigated. Ascolona, Gemlik, Hojoblanca had moderate cold-hardiness, while Samanli, Meski, Uslu and Manzanilla were more sensitive. Activities of catalase (CAT: EC 1·11·1·6), ascorbate peroxidase (APX: EC 1·11·1·11) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase significantly varied depending on the cold-acclimation stage and the cold-hardiness level of the cultivars. Activities of the three antioxidative enzymes and total soluble proteins (TSP) were higher in the CA stage than in the NA stage. Although no accumulation of major polypeptides, except a 23 kDa protein, was detected either in CA samples or NA samples by SDS-PAGE, anti-dehydrin immunoblots revealed that the 43 and 23 kDa polypeptides were detectable during cold-acclimation of olive cultivars. Accumulation of both 43 and 23 kDa dehydrin was significantly higher in the CA stage than in the NA stage in all cultivars. Accumulation of 43 kDa dehydrin was correlated with cold-hardiness of the cultivars, while 23 kDa dehydrin was considered as cultivar-dependent since its accumulation was not parallel to LT50values of the cultivars. Indeed, the tissues of cvs Domat, Lecquest, Ascolona, Hojoblanca and Gemlik were found to enhance the structural stability of cellular membranes in the CA stage by increasing both the activity of such enzymes as CAT, APX and NADPH oxidase to activate the antioxidative systems and the expression of 43 kDa dehydrins.

A Temperature Index Model to Estimate Long-term Freeze-risk of Satsuma Mandarins Grown on the Northern Coast of the Gulf of Mexico

Estimates of long-term freeze-risk aid decisions regarding crop, cultivar, and rootstock selection, cultural management practices that promote cold hardiness, and methods of freeze protection. Citrus cold hardiness is mostly a function of air temperature, but historical weather records typically contain only daily maximum (Tmax) and minimum (Tmin) air temperatures. A mathematical model was developed that used Tmax and Tmin to estimate air temperature every hour during the diurnal cycle; a cold-hardiness index (CHI500) was calculated by summing the hours ≤10°C for the 500 h before each day; and the CHI500 was regressed against critical temperatures (Tc) that cause injury. The CHI500 was calculated from a weather station located within 0.1 km of an experimental grove and in the middle of the satsuma mandarin (Citrus unshiu Marc.) industry in southern Alabama. Calculation of CHI500 was verified by regressing a predicted CHI500 using Tmax and Tmin, to a measured CHI500 calculated using air temperatures measured every hour for 4 winter seasons (1999-2003). Predicted CHI500 was linearly related to measured CHI500 (r2 = 0.982). However, the slope was a little low such that trees with a CHI500 = 400, near the maximum cold-hardiness level achieved in this study, had predicted Tc that was 0.5 °C lower than measured Tc. Predicted and measured Tc were similar for nonhardened trees (CHI500 = 0). The ability of predicted Tc to estimate freeze injury was determined in 18 winter seasons where freeze injury was recorded. During injurious freeze events, predicted Tc was higher than Tmin except for a freeze on 8 Mar. 1996. In some freezes where the difference in Tc and Tmin was <0.5 °C there were no visible injury symptoms. Injury by the freeze on 8 Mar. 1996 was due, in part, to abnormally rapid deacclimation because of defoliation by an earlier freeze on 4-6 Feb. the same year. A freeze rating scale was developed that related the difference in Tc and Tmin to the extent of injury. Severe freezes were characterized by tree death (Tc - Tmin > 3.0 °C), moderate freezes by foliage kill and some stem dieback (1.0 °C ≤ Tc - Tmin ≤ 3.0 °C), and slight freezes by slight to no visible leaf injury (Tc - Tmin < 1.0 °C). The model was applied to Tmax and Tmin recorded daily from 1948 through 2004 to estimate long-term freeze-risk for economically damaging freezes (severe and moderate freeze ratings). Economically damaging freezes occurred 1 out of 4 years in the 56-year study, although 8 of the 14 freeze years occurred in two clusters, the first 5 years in the 1960s and 1980s. Potential modification of freeze-risk using within-tree microsprinkler irrigation and more cold-hardy cultivars was discussed.

WALNUT CULTIVAR PERFORMANCE OF COLD RESISTANCE IN SOUTH CENTRAL FRANCE

In south-central France, walnut exhibited freezing tolerance by acclimation in the fall and deacclimation in the spring. The cold hardiness level varied with the different cultivars and dates. Cold tolerance performances of 7 walnut fruit cultivars (Chandler, Franquette, Fernor, Fernette, Lara, Pedro, Serr) and of the hybrid Juglans regia × Juglans nigra NG38 were compared in the same location, at the INRA Center of Clermont-Ferrand. For these comparisons, an electrolyte leakage conductivity method (LT50) was used and adapted for walnut. In all cases NG38 (Juglans regia × Juglans nigra) appeared particularly cold resistant.

Effects of Ice Cover on Annual Bluegrass and Creeping Bentgrass Putting Greens

Damage as a result of ice cover on putting greens affects golf courses in cold climates. The objectives of this study were to assess cold-hardiness levels and injury of annual bluegrass [Poa annua f. reptans (Hausskn.) T. Koyama] and creeping bentgrass (Agrostis stolonifera L. cv. Penncross) under ice cover maintained for various periods of time under laboratory and field conditions. In the lab, cold-hardened plants of both species were subjected to either snow-covered, ice-covered, or ice-encased treatments and tested for cold-hardiness levels at various periods of time. Ice-encased annual bluegrass plants stored for 90 d were dead, while ice-covered and snow-covered plants had cold-hardiness levels of −4°C and −18°C, respectively. In contrast, at 150 days after treatment (DAT), creeping bentgrass that was ice encased had a cold-hardiness level of −18°C, while snow-covered plants had a cold-hardiness level of −27°C. In the field, annual bluegrass and creeping bentgrass plants were subjected to the following treatments: snow cover, ice cover, and snow or ice removed 45 DAT and then were sampled at various times to determine cold-hardiness levels. As in the lab, ice cover had less impact on bentgrass than annual bluegrass. At 90 DAT, ice-covered creeping bentgrass had cold-hardiness levels of −29°C while annual bluegrass plants were dead at 75 DAT. Snow-covered annual bluegrass plants still had cold-hardiness levels of −16°C at 75 DAT. Removing the snow or ice after 45 DAT had little or no effect.

Climate change and the effect of temperature backlashes causing frost damage in Picea abies

In boreal and nemoboreal forests, tree frost hardiness is modified in reaction to cues from day length and temperature. The dehardening processes in Norway spruce, Picea abies, could be estimated to start when the daily mean temperature is above 5 °C for 5 days. Bud burst will occur approximately after 120–170 degree-days above 5 °C, dependent on genetic differences among provenances. A reduced cold hardiness level during autumn and spring and an advanced onset of bud burst are expected impacts of projected future global warming. The aim of this study was to test if this will increase the risk for frost damage caused by temperature backlashes. This was tested for Sweden by comparing output from the Hadley Centre regional climate model, HadRM3H, for the period 1961–1990 with future IPCC scenario SRES A2 and B2 for 2070–2099. Different indices for calculating the susceptibility to frost damage were used to assess changes in frost damage risk. The indices were based on: (1) the start of dehardening; (2) the severity of the temperature backlash; (3) the timing of bud burst; and (4) the cold hardiness level. The start of dehardening and bud burst were calculated to occur earlier all over the country, which is in line with the overall warming in both climate change scenarios. The frequency of temperature backlashes that may cause frost damage was calculated to increase in the southern part, an effect that became gradually less pronounced towards the north. The different timing of the onset of dehardening mainly caused this systematic latitudinal pattern. In the south, it occurs early in the year when the seasonal temperature progression is slow and large temperature variations occur. In the north, dehardening will occur closer to the spring equinox when the temperature progression is faster.

Inheritance of Cold Hardiness and Dehydrin Genes in Diploid Mapping Populations of Blueberry

Summary Studies of herbaceous plants suggest that cold hardiness is a complex, quantitatively inherited trait. Although development of cold hardiness is an integral part of the life cycle of woody perennial plants, studies on the genetic control of cold hardiness in woody perennials are scarce. A better understanding of the genetic control of cold hardiness would be valuable for developing more effective strategies to increase cold hardiness and, hence, climatic adaptation of woody perennial crops. In blueberry, three major dehydrins of 65, 60, and 14 kDa have been found to increase with cold acclimation and decrease with deac-climation. A comparison of these dehydrin levels among various blueberry cultivars and selections has revealed their level of accumulation to be closely associated with cold hardiness level. Efforts are underway to isolate and map the dehydrin genes of blueberry utilizing blueberry populations that segregate for cold hardiness in order to determine if the dehydrin genes map to or co-segregate with QTLs controlling cold hardiness. Progress has been made toward this goal. Cold hardiness levels were determined for a portion of the blueberry mapping populations (derived from testcrosses of Vaccinium darrowi Camp X V. caesariense Mackenz. F1s to another V. darrowi and another V. caesariense) using a laboratory controlled freeze-thaw regime, followed by visual assessment of injury to floral buds. As expected, the V. darrowi and V. caesariense parents were found to differ significantly in terms of cold hardiness levels (LT50s of -13°C and -20°C, respectively). Mean cold hardiness level of F1s (LT50 of -14.7°C) was skewed toward the V. darrowi parents suggesting that cold hardiness is a partially recessive trait. The sequence of a 2.0 kb cDNA clone, which encodes the 60 kDa blueberry dehydrin, was used to map a dehydrin-related gene to current linkage group 12 of the V. caesariense testcross population. A preliminary comparison of the segregation pattern of the dehydrin-related gene to that of the cold hardiness trait suggests that the marker does not segregate with cold hardiness.

572 Cold Hardiness of Summer and Fall Flowering Evergreen Azalea Hybrids

To date, few summer and fall flowering azaleas exist. Recently, Rhododendron oldhamii, a summer-flowering species, was hybridized with several commercial hybrids. These crosses produced various sizes and colors of flowers that bloom throughout the summer until frost, and again in the spring. However, the cold hardiness level of these azaleas is unknown. Therefore, we evaluated their cold hardiness during several months of the fall and winter. Laboratory cold hardiness tests revealed that there was a range of cold hardiness levels among the new hybrids. `Fashion' and hybrids 02003 and 4003 tended to acclimate earlier than the others, maintain a good level of midwinter cold hardiness, and retain their hardiness into the early spring. Hybrid 15001 acclimated early and had good midwinter cold hardiness, but lost its cold hardiness in the late winter, while 04003 and 09004 acclimated late in the fall and did not attain a high level of cold hardiness in the winter. `Lee's Select' and hybrid 08002 seemed to fall between the groups previously mentioned showing intermediate cold hardiness throughout the winter season. The laboratory cold hardiness results were similar with field observations.

Leaf and Stem Cold Hardiness Estimates of Six Selections of Chinese Evergreen Oak over Two Winter Seasons

Abstract Two of six selections of Chinese evergreen oak (Quercus myrsinifolia Blume) were identified through laboratory cold hardiness estimations to possess more spring cold hardiness potential than the other selections tested. The leaves and stems of all selections had similar cold hardiness levels in the fall and midwinter. Data collected over two winter seasons revealed that leaves reached a cold hardiness level of − 15 to − 18°C (5 to 0°F) during the midwinter. The stems were slightly less cold hardy than the leaves and attained a cold hardiness level of − 12 to − 15°C (10 to 5°F). In the spring, however, the cold hardiness levels of the leaves of two of the selections were 5 to 9°C (9 to 16°F) more cold hardy than the other selections. while their stems were 6 to 9°C (11 to 16°F) more cold hardy than those of the other selections. The data indicated that these two selections of Chinese evergreen oak may be able to avoid injury when exposed to late spring frosts better than other selections included in the study.

Cold hardiness expression in interspecific hybrids and amphiploids of the Triticeae

Gene expression for cold hardiness was investigated in a number of interspecific or intergeneric hybrids and amphiploids of wheat (Triticum aestivum L. em. Thell. or T. turgidum L.) and other members of the tribe Triticeae to assess the potential of alien species as donors of cold-hardiness genes for the improvement of wheat. Thinopyrum ponticum (Agropyron elongatum) hybrids with nonhardy T. aestivum had cold-hardiness levels similar to that of the more hardy Thinopyrum parent. Hybrids of Triticum cylindricum and both hardy and nonhardy T. aestivum were intermediate in cold hardiness with a tendency toward greater hardiness than the parental mean. Cold hardiness of hybrids between T. aestivum and Thinopyrum intermedium (Agropyron intermedium) was also close to the parental midpoint. Cold hardiness of T. aestivum – Secale cereale hybrids was greater than the less hardy parent. In contrast, cold-hardiness genes were not expressed beyond the level of the wheat parent in amphiploids combining wheat and the very hardy diploid species Agropyron cristatum and Secale cereale. The cold-hardiness level was also poor in an amphiploid produced from two relatively hardy tetraploid species (T. turgidum and T. cylindricum). These observations indicate that changes in ploidy level, relative to the parents, may influence the cold-hardiness potential of an interspecific combination by affecting gene dosage and possibly cell size. Poor expression of cold-hardiness genes from very hardy diploid genomes also indicated some degree of suppression, or homoeoallelic dominance of wheat cold-hardiness genes in amphiploids. Therefore, the performance of an interspecific hybrid or amphiploid of wheat may not give an accurate indication of the potential of alien species as gene donors for the improvement of wheat cold hardiness.Key words: gene expression, Triticum sp., triticale, Thinopyrum sp., Agropyron sp., Secale cereale.

CHANGES IN THE COLD HARDINESS OF ALFALFA DURING FIVE CONSECUTIVE WINTERS AT BEAVERLODGE, ALBERTA

Plants of Medicago falcata ’Anik’ were samples to assess their relative cold hardiness during the fall, winter and spring periods from 1974–75 to 1978–79. Precipitation and soil temperature patterns and cold hardiness profiles varied considerably from year to year. Environmental conditions in the fall appeared to exert the greatest influence on the cold hardiness profile and the maximum cold hardiness level in mid-winter. In general, plants started to harden in mid-September, but during one fall hardening period there was a delay associated with the early development of crown buds and the accompanying flush of growth during August and September. During two fall hardening periods, water-saturated soil conditions were associated with a dehardening phase in October. Conditions favoring delayed fall hardening and complete dehardening in the late fall were also associated with a lower level of hardiness in mid-winter. The maximum hardiness level, and the month during which it occurred, fluctuated considerably each year. Plants began dehardening as soil temperatures increased in late winter and early spring during 3 of the 5 yr. In the remaining 2 yr, plants began to deharden prior to an increase in soil temperature.