Effect of Extending the Growing Period on Yield Formation of Sugar Beet

Autumn sown sugar beets (winter beets) are expected to yield markedly higher than spring sown beets. This requires a continuous growth during an extended growing period. So far, bolting‐resistant sugar beet varieties are not available to test winter beets under field conditions in Central Europe. The objective of this study was therefore to analyse yield formation and sugar storage of sugar beet plants during an extended growing period to estimate whether sugar beet has the potential to generate the theoretically expected yield increase. From 2008 to 2012, pot experiments were carried out in the glasshouse with 11 sowing dates spread over the years with sequential harvests. The oldest plants were grown for 859 days (14 242 °Cd). Root fresh matter yield continuously increased till the latest harvest. In contrast, the sugar concentration reached an optimum value between 3400 and 5000 °Cd and then decreased with time. Despite longer growing periods, the number of cambium rings, which are regarded as essential for sugar storage, did not change. This points to an early and genetically fixed determination of the formation of cambium rings. Additionally, the rate of photosynthesis decreased concomitantly with the sugar concentration. In conclusion, there is some evidence that the sugar concentration of the storage root is limited by the sink capacity, which in turn controls the source activity by a feedback regulation of photosynthesis and leaf formation. The dry matter composition of the storage root changed towards lower sugar concentration and concurrent higher concentration of cell wall compounds (marc). The sugar yield still increased beyond a thermal time at which winter beets will probably be harvested in practice. Hence, the theoretical yield increase in autumn sown sugar beets can be realized, provided that the plants show sufficient winter hardiness and bolting resistance.     

Growth analysis of autumn and spring sown sugar beet

Slow leaf formation in spring is regarded as the main factor limiting sugar beet yield. It is therefore expected that yield can be enhanced when plants develop leaves earlier resulting in an extended growing period. The aim of this study was to analyse leaf and storage root growth of sugar beet plants sown in autumn or very early in spring with regard to possible yield increases. In 2005/06 and 2006/07, field trials were conducted at 4 sites with 6 sowing dates: August, beginning and mid of September, and in February, March and April. Sequential harvests were conducted to follow yield formation.Field emergence of autumn sown sugar beets was fast and reached 90% whereas in early spring it was severely restricted due to low temperature. Leaf and root yield formation of autumn and spring sown sugar beets could well be described with thermal time confirming that sugar beet growth is temperature driven and day length insensitive. Despite longer growing periods autumn sown beets did not form more cambium rings in the storage root than spring sown beets. That might be partly due to the bolting process after winter. However, early spring sown beets as well did not achieve more cambium rings than plants sown in April pointing to a presumably limited ability to adapt cambium ring formation. Because of the shift to reproductive growth, autumn sown beets formed high amounts of shoot dry matter, but not much root dry matter. Furthermore, the root dry matter consisted of a lower sugar and a higher marc content and would therefore not be suitable for sugar recovery. Earlier sowing in spring did not result in a significant yield increase because the benefit from early sowing diminished throughout the season as also obvious from the distance between the cambium rings.For bolting resistant sugar beet varieties, which are expected to be available in near future, the presented data form a basis to predict yield with models. However, it has to be investigated to what extent sugar beet growth and yield formation benefits from early sowing and extended growing periods.     

Genetic variation for shoot elongation before winter and its correlation with vernalization requirement in winter oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Changing climatic conditions in north-western Europe are accompanied by occasional extreme weather conditions. This requires breeding of winter oilseed rape cultivars which are resilient to diverse abiotic stress factors, e.g. frost, drought and heat. The degree of vernalization requirement of winter oilseed rape has been found to be related to frost tolerance and winter hardiness. Shoot elongation before winter in particular has been identified as one decisive factor for frost tolerance in winter oilseed rape. However, the relationship between vernalization requirement and shoot elongation before winter is not known. In the present study the genetic variation for shoot elongation before winter and vernalization requirement of 19 genetic diverse breeding lines and cultivars were analyzed. Autumn and spring sown field experiments in multiple environments were performed to determine shoot elongation before winter and vernalization requirement, respectively. In spring sown field experiments, genotypes with a low vernalization requirement were characterized by the occurrence of long bolting plants with flower buds. Large and significant genotypic variation was found for shoot length in the autumn sown and spring sown environment. Broad sense heritability was quite high for shoot length in the spring sown environment (h²?=?97%), whereas it was only of medium size for shoot length before winter (h²?=?62%). Although the correlation between shoot length before winter and shoot length in the spring sown environment was positive (Spearman’s rank r_S?=?0.48*), a number of genotypes with reduced shoot elongation before winter and low vernalization requirement were identified. Results indicate that genotypes with a reduced shoot elongation before winter independent of their vernalization requirement can be selected in breeding programs.     

Impact of different environments in Europe on yield and quality of sugar beet genotypes

Sugar beet (Beta vulgaris L.) yield and quality are determined by genotype and environment. This study aimed at analysing the relative importance of the environment for yield and quality of sugar beet genotypes and at assessing parameters which could give essential improvement for beet quality if included as additional selection criteria. For that purpose, root yield and quality (sugar, K, Na, amino N, total soluble N, betaine, glutamine, invert sugar, raffinose) of 9 sugar beet genotypes were investigated in 52 environments (25 sites in 2003 and 27 sites in 2004) in randomised field trials across Europe.The environment accounted for about 80% of the total variance for all parameters. Effects of the tested genotypes were larger for the content of betaine (8.5%) and sugar (7.6%) than for other parameters (1–5%). With the exception of invert sugar and amino N, the genotype by environment interaction was about 3% and thereby lower than the main effect of genotypes. Interactions resulted in an increase of the differences between genotypes which can be used to select genotypes in the most discriminating environments. The response of genotypes in sugar content was contrasting to other parameters and points to a physiological limit for sugar storage at about 20%. As no crossover interaction occurred for root yield or any quality parameter, there seemed to be no specific suitability of the tested genotypes to certain environmental stress conditions. This is probably due to the fact that the harvested beetroot is a vegetative storage organ and has no growth stages susceptible to unfavourable environmental conditions such as flowering and grain filling which are important for final yield in cereals. Invert sugar showed the largest relative differences between genotypes which were strongly enhanced in southern and some south-eastern European environments. Because of its importance during processing, considering invert sugar in breeding could improve technical quality for processing considerably for those extreme environments.     

Evaluation of a semi‐controlled test as a selection tool for frost tolerance in durum wheat (Triticum durum)

Most durum wheat (Triticum durum) varieties possess only low winter hardiness due to their frost susceptibility. In North America and Central Europe, durum wheat is therefore typically sown in spring to circumvent the local winter conditions. However, the yield potential of durum in these regions could be much better exploited if durum varieties with increased frost tolerance were available, which could be sown in autumn. A factor limiting breeding for increased frost tolerance is the variation in the occurrence of frost stress across years. The ‘Weihenstephaner Auswinterungsanlage’ is a semi‐controlled test that exposes the plants to all weather conditions. Snow coverage of the plants, serving as frost protection, is prevented by the movable glass lid of the semi‐controlled test. In this study, different scorings for frost tolerance based on this semi‐controlled test were evaluated and compared with frost tolerance data in the field. Our results illustrate the potential of the ‘Weihenstephaner Auswinterungsanlage’ as an indirect selection tool for frost tolerance in durum breeding programmes, especially when regular frost tolerance data from the field are not available.     

Winter Hardiness, Frost Resistance and Vernalization Requirement of European Winter Oilseed Rape (Brassica napus var. oleifera) Cultivars within the Last 20 Years

Cultivars of European winter oilseed rape cultivated in the second half of the 1970s and in the mid-1990s were screened for their winter hardiness, frost resistance and vernalization requirement. A strong correlation between winter hardiness and frost resistance in both groups of rape has been noticed. Among oilseed rapes cultivated in the late 1970s, low erucic acid and particularly double zero cultivars were less winter hard than high erucic acid cultivars. Double zero cultivars were characterized by lower frost resistance and lower vernalization requirement. A significant correlation between vernalization requirement and both frost resistance and field survival has also been shown. Frost resistance of the 1990s (double zero) cultivars was higher than that of double low cultivars from the late 1970s. Their vernalization requirement was still small and did not correlate with either frost resistance or winter hardiness. It was concluded that reduction in the content of glucosinolates in the 1970s involved decrease in winter hardiness and vernalization requirement of cultivars. During the following 20 years winter hardiness of double low cultivars has been improved, but vernalization requirements have not changed. As a result no correlation between winter hardiness and vernalization requirement in contemporary canola cultivars has been observed.     

Estimating winter survival of winter wheat by simulations of plant frost tolerance

Based on soil temperature, snow depth and the grown cultivar's maximum attainable level of frost tolerance (LT_50c), the FROSTOL model simulates development of frost tolerance (LT₅₀) and winter damage, thereby enabling risk calculations for winter wheat survival. To explore the accuracy of this model, four winter wheat cultivars were sown in a field experiment in Uppsala, Sweden in 2013 and 2014. The LT₅₀ was determined by tests of frost tolerance in November, and the cultivars’ LT_50c was estimated. Further, recorded winter survival from 20 winter wheat field variety trials in Sweden and Norway was collected from two winter seasons with substantial winter damages. FROSTOL simulations were run for selected cultivars at each location. According to percentage of winter damage, the cultivar survival was classified as “survived,” “intermediate” or “killed.” Mean correspondence between recorded and simulated class of winter survival was 75% and 37% for the locations in Sweden and Norway, respectively. Stress factors that were not accounted for in FROSTOL might explain the poorer accuracy at the Norwegian locations. The accuracy was poorest for cultivars with intermediate LT_50c levels. When low temperature was the main cause of damage, as at the Swedish locations, the model accuracy was satisfying.     

Relationship between cold resistance,heading traits and ear primordia development of wheat cultivars

Summary For breeding early heading wheat cultivars with resistance to frost damage which are well adapted to dry areas of West Asia and North Africa, the relationships between winter hardiness, ear primordia development and heading traits, i.e. veernalization requirement, photoperiodic response and narrow-sense earliness, were assessed using a total of 30 genotypes of wheat (Triticum aestivum L.) grown in an experiment in Syria. The results of artificial freezing tests indicated that cultivars with good winter hardiness were to be found only in the winter wheat cultivars which required 50 or more days of vernalization treatment. These winter wheat cultivars did not initiate internode elongation without vernalization even at 95 days after planting. Thus their ear primordia were still underground and were protected from frost injury at this stage. Photoperiodic response and narrow-sense earliness were not associated with winter hardiness and earliness of internode elongation, but were related to the number of days to heading after planting. This indicated the possibility for breeding early heading cultivars with winter hardiness and tiller frost avoidance by combining high vernalization requirement, short narrow-sense earliness and neutral response to photoperiod.     

Effects of Temperature and Frost on Genotypes of Medicago truncatuh L. and Medicago aculeata L. from Contrasting Climatic Origins

The growth of M. truncatula and M. aculeata genotypes collected from sites of contrasting altitudes and winter temperatures was compared under different temperature regimes. Genotypes collected from mild winter environments produced more shoot dry matter, had higher leaf area and lower specific leaf weight than those from cold environments; however these effects were largely related to seed size for M. aculeata. Only genotypes from mild environments were responsive to temperature.
Frost tolerance of the genotypes was tested using a laboratory freezing test based on seedling survival. There was a relationship between frost tolerance and winter temperature at site of collection for M. aculeata , with the most frost tolerant genotypes coming from high altitudes. All genotypes of M. truncatula demonstrated low survival rates following frost damage. Genotypes from high altitudes represent a promising source for breeding for first tolerance with greater variation m M. aculeata than M. truncatula.     

Winter hardiness in trench celery

A total of 51 red and white commercial varieties of trench celery were grown and examined for winter hardiness at the National Vegetable Research Station. Although some plants of most varieties survived the winter, none showed a commercially useful degree of winter hardiness, in that none were marketable after moderate frost. The red varieties had a significantly better survival than the white varieties. In the first season, single plant selections were made from the varieties having both the highest percentage of winter survival and the best agronomic characters. Although some of the progenies derived from these selected plants by self-pollination showed a small increase in winter survival as compared with their parent varieties when both were grown in the second season, no plants of these progenies were sufficiently hardy to remain marketable after moderate frost. It was concluded that none of the varieties tested showed any promise as a source of winter hardiness to be used in a breeding programme, and that selection for one generation from within these varieties did not improve winter hardiness to a useful extent.     

Winter hardiness in Turkish populations of cocksfoot,Dactylis glomerata L.

Summary Over a six-year period, Turkish populations of cocksfoot were investigated in the field at Sapporo, Japan, as to winter hardiness. After the first winter, only populations from the mild Marmara, Aegean and Mediterranean regions were badly damaged. As the differential plant survival among geographical groups widened with the elapsing of years, we were able to rank the groups in descending order of relative hardiness from Eastern Anatolia, through the Black Sea, Central Plateau, Marmara and Aegean regions, to the Mediterranean region. This order was maintained throughout the experimental period.Winter temperatures prevailing in the locality of origin was the most important determinant of winter survival of the populations. The growth pattern in autumn and whether plants continued to grow through the winter or were enforced to winter dormancy, were related to differential survival between maritime and mountainous populations. On the other hand, this simple relationship is complicated by introgression. The subspecies distribution in the coastal region is related to a higher level of survival in the populations from the Black Sea region, where the continental type of cocksfoot occurs, than in the populations from the other maritime regions, where introgression has occurred from Daetylis glomerata subsp. hispanica with poor winter hardiness.Present address: Tropical Agriculture Research Center, Okinawa Branch, Ishigaki 907-01, Japan.     

Improved frost tolerance and winter survival in winter barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) by <Emphasis Type="Italic">in vitro</Emphasis> selection of proline overaccumulating lines

Embryogenic calli derived from anther cultures of the two-rowed winter barley cultivar Igri were plated on solid L3 medium containing the proline analogue hydroxyproline (Hyp), 10–20 mmol l^–1. Exposure to Hyp caused severe degeneration of most of the calli. Hyp resistant calli, distinguishable by their lighter colour and higher growth rate, and control calli not exposed to Hyp were plated on L3 regeneration medium. From 22,500 anthers exposed to Hyp 46 Hyp resistant regenerates were obtained, which were transferred to soil. After cultivation for 5–10 weeks at normal growth conditions they were cold hardened at 2 C under short day conditions together with control regenerates. Frost tolerance assays with segments of fully grown leaves of unhardened and cold hardened plants revealed that Hyp resistant regenerants were significantly more frost tolerant than the control regenerants. Improved frost tolerance was found also in the progenies R₁ to R₉, and genotypic segregation in the R₁ generation in a 1:2:1 ratio was indicated. Increased proline content was observed in the R₂ generation and in subsequent generations and was significantly (P 0.001) correlated with increased frost tolerance in the Hyp lines. Comparative studies of R₉ progenies from homozygous R₂ plants with the wild type Igri under field conditions in winter at three locations in Europe as well as crossing experiments confirmed the heritable improvement of frost tolerance and winter survival, respectively, in the Hyp lines. The results support the hypothesis that proline accumulation in cold acclimated winter barley plants is causally related to the acquisition of frost tolerance. Moreover, the described biotechnological procedure may be applicable in breeding programs for improved winter hardiness and possibly also for other stress tolerances.     

Relationship Between Cold Severity and Yield Loss in Chickpea (Cicer arietinum L.)*

Seed yield in chickpea (Cicer arietinum L.) is substantially increased by advancing sowing date from the traditional spring to early winter at low to medium elevation areas around the Mediterranean Sea. This shift, however, increases the probability of the exposure to subzero temperatures as low as -10 °C for up to 60 days in a year. These low temperatures often reduce seed yield of cold-susceptible cultivars. Yield losses from cold were estimated in two experiments conducted at Tel Hadya, Syria. In experiment 1, of 96 genotypes sown on nine dates ranging from autumn to spring during the 1981–82 season, those lacking tolerance to cold were killed and produced no yield in autumn sowing, whereas lines with cold tolerance produced nearly 4 t/ha which corresponds to a four-fold increase over spring sowing. Moderately cold-tolerant genotypes sown during early winter produced substantially more seed yield than the normal spring-sown crop. Seedlings were more cold tolerant than the plants in early or late vegetative stages. In experiment 2, in which yield loss due to cold in the field was estimated in 12 yield trials comprising 288 newly bred lines in the 1989–90 season, the regression of cold susceptibility on seed yield in each of the trials was highly significant and negative. On average, winter-sown trials produced 67 % more seed yield than spring-sown trials, but 125 out of 288 genotypes produced yield more than double in winter sowing. Early maturing lines suffered severe cold damage and many lines produced no seed.     

冬小麦品种抗霜冻力的影响因素分析

应用移动式人工霜箱,研究了冬小麦幼穗抗霜冻力随发育期的变化规律。结果表明,随发育期进程,幼穗抗霜冻力呈下降趋势,从药隔前期开始进入低温敏感期。利用室内人工霜箱,在药隔前期对21个品种进行了抗霜冻力鉴定,进而分析了不同品种、冬春性、越冬抗冻力以及叶片可溶性糖含量等对冬小麦抗霜冻力的影响。结果表明,除少数品种有一定抗霜冻力外,多数品种抗霜冻力无显著差异。品种抗霜冻力与其冬春性和越冬抗冻力均无显著相关性,与叶片可溶性糖含量之间亦无显著相关性。     

Changes in N Composition of Sugar Beet Varieties in Response to Increasing N Supply

The soluble nitrogen (N) components in sugar beet seriously impair sugar recovery. The only N component determined routinely in the sugar factory is amino N (the sum of amino acids in the beet), which is assumed to reflect all the other N components. Amino N is affected by N supply and variety, but only little is known about the other N components such as total soluble N, betaine and nitrate. This study aimed at investigating the effect of N supply on the N composition of sugar beet varieties with special emphasis on N supply by variety interactions. In 2001 and 2002, field trials with four varieties and four N treatments were carried out at six sites in Germany. Storage root yield and the concentrations of sucrose, sodium, amino N, betaine, nitrate and total soluble N in the beet were determined. With increasing N supply, the concentration of amino N increased considerably and that of nitrate slightly, whereas that of betaine remained rather constant. Thus, the N composition of sugar beet changed with increasing N supply and the percentage of amino N of total soluble N increased. Although amino N has the closest correlation with total soluble N, for quality assessment it may overestimate the effect of N supply on other N components. Varieties clearly differed in root yield and quality as well as in all N components. The variety with the lowest amino N had the highest betaine concentration. However, as related to the concentration of total soluble N in the beet, for all varieties amino N as well as betaine showed the same response pattern. This indicates that the N composition of sugar beet is determined by the level of total soluble N, irrespective of variety or N supply. All varieties required the same N supply for obtaining maximum yield or quality. N supply did not affect the ranking of the varieties for all parameters studied, consequently it need not be considered for variety choice.     

Yield of bolting winter beet (Beta vulgaris L.) as affected by plant density,genotype and environment

Winter beet roots and shoots might be a favorable substrate for biogas production in Central Europe. However, detailed information about the attainable yield of this crop is lacking. Thus, the impact of plant density, genotype and environmental conditions on total dry matter yield of winter beet crops that bolt after winter was investigated. A significant increase of the dry matter yield (esp. shoot) was expected by harvesting the 1st shoot after flowering in June followed by a final harvest of the whole plant in July. In 2009/10, 2010/11 and 2011/12, three series of field trials with (i) 3 target plant densities (148, 246, 370 thousand plants ha⁻¹) and (ii) 3 different sugar beet genotypes were conducted at Göttingen (Lower Saxony, GER) and Kiel (Schleswig-Holstein, GER); (iii), additional field trials with 5 different sugar beet genotypes cultivated at 2 target plant densities (148, 246 thousand plants ha⁻¹) were conducted in 2011/12, to investigate the relation between maximum taproot diameter and the shoot and taproot yield of bolting winter beet. The total dry matter yield considerably varied between 4 and 23 t ha⁻¹. It was predominantly affected by the environment and to a substantially lower extent by plant density. Increasing plant densities increased the total dry matter yield, resulting in a significantly higher total dry matter yield at plant densities ≥300,000 plants ha⁻¹ compared with lower plant densities. Genotypic differences in total dry matter yield were negligibly small. Pruning in June substantially increased the total dry matter yield in July by ca. 8 t ha⁻¹ only in one out of three environments.Final yield in June (without pruning) and July (pruning in June) was positively related with cumulated temperature and global radiation, but also with taproot dry matter yield before winter. The taproot, shoot (1st, 2nd) and total plant yield were positively correlated with maximum taproot diameter.In conclusion, high dry matter yields close to yields of established energy crops grown over winter were obtained with winter beet roots and shoots only under very favorable conditions (climate, single plant size). High yields can be achieved after good pre-winter development. However, for sufficient frost tolerance the taproot size of plants must be rather small. Hence, the cultivation of bolting winter beet under Central European climate conditions has to face a severe conflict of goals concerning winter survival and yield formation.     

Overwintering of genetically modified sugar beet, Beta vulgaris L. subsp. vulgaris, as a source for dispersal of transgenic pollen

The potential impact of transgenic crops on community ecology will depend on the distribution and establishment of the new transgenic traits, on the sexual transfer of their new genes to the environment (Bartsch &; Pohl-Orf, 1996) and on the potential ecological impact of the transgenic trait. Flowering and pollen dispersal is important for outcrossing of the genetically engineered trait. For a biennial plant, like the cultivars of Beta vulgaris L., overwintering is normally necessary to become generative and to produce pollen and seeds (Abe et al., 1997), which usually does not happen with sugar beet as a field crop harvested in autumn (Longden 1989). The starting point for the project was a transgenic sugar beet, Beta vulgaris L. subsp. vulgaris (Lange et al., 1998), with rhizomania and herbicide ( Basta®, Liberty®) resistance. Cold tolerance is one of the most important factors for survival of sugar beet in Central- and North-Europe. Among other ways, spreading of transgenic traits into weed beet (Boudry et al., 1993) or wild beet can occur if genetically engineered – biennial – plants survive the winter, flower in spring and spread their pollen. Field experiments were performed with transgenic breeding lines and their hybrids, transgenic and non-transgenic hybrids with Swiss chard and three conventional beet cultivars to evaluate winter survival rates at seven different field sites. We could show that survival of sugar beet – transgenic as well as conventional ones – in Germany and at the Dutch border is possible. Survival rates were well correlated with temperature data and were unexpectedly high. Differences between sugar beet hybrids and breeding lines could be detected but not within different breeding lines or hybrids. There were no differences detectable between transgenic and non-transgenic plants. The data are crucial for the risk assessment of the release of transgenic sugar beet and are the basis for further experiments towards outcrossing and establishment.     

Prediction of Various Effects of Harvest Date in Sugar Beet Growing

One crucial decision in sugar beet growing is determining harvest date. This paper focuses on some aspects associated with harvest date which have to be included in a decision support system for sugar beet growing.
Firstly, a module was created for dirt and crown tare, mainly based on lutum (or clay) and soil moisture contents. An independent test of the module showed poor results, because fine tuning of harvest machinery has an overriding effect. Secondly, the variation in weather conditions during autumn in Wageningen over a period of 38 years was analysed. The ranges of future root and sugar production appeared to be so wide that early predictions of the day on which the sugar quota are exceeded will not be very reliable. Thirdly, risks of severe frost or heavy rainfall in autumn were assessed, based on the same 38 year data set. The risk of frost damage to unharvested beets proved to be negligible when the crop was harvested before November 10, as advised by the sugar industry.
The work described in this study makes the model PIEteR (a field specific bio-economic production model for sugar beet, developed for decision support at field and farm level) more applicable by using its potential to analyse the effects of different years and quota options.     

Breeding winter hardy grasses

Summary Perennial grasses are vital for Norwegian agricultural production. The nature and extent of winter damage on grasslands is highly dependent on climatic conditions, and determines both persistency and yield. Physical stresses such as frost and ice encasement predominate in coastal regions with an unstable winter climate, while biotic stresses such as low temperature fungi are more common in the inland regions. Development of hardening depends on plant adaptation and climatic conditions during autumn and winter. New winter-hardy cultivars should be bred for wide adaptation to winter stresses. The genetic background for the most important character, freezing tolerance, seems to be of polygenic nature with mainly additive gene action. Selection for increased freezing tolerance has been effective over generations in grasses, and in most grass species ample variation still exists to be exploited by breeding. However, in some species like perennial ryegrass, modern biotechnological methods should be used to improve freezing tolerance and winter hardiness.     

Relationship between Prehardening, Photosynthetic Activity at Cold Acclimation Temperatures and Frost Tolerance in Winter Rape (Brassica napus var. oleifera). The Consequences for the Reliability of Frost Resistance Estimation under Controlled Conditions

The effect of prehardening (early stage of growth at moderate low temperatures (+12°C) during the day) on the reliability of frost resistance estimation in a controlled environment has been studied on three winter oilseed rape cultivars differing markedly in their field survival rate (Leo, Górczański and Idol). It has been also examined the relationship between the photosynthetic activity during the first stage of cold acclimation and the level of frost resistance observed in investigated cultivars. Presented results demonstrated that prehardening, which increases to a significant degree the effectiveness of the cold acclimation process, also increases the differences in cold hardiness between cultivars, and limits the magnitude of experimental errors made during frost resistance estimation under controlled conditions. In all studied cultivars, prehardening increases significantly the photosynthetic activity during cold acclimation. On the other hand, both in the prehardened and in the non-prehardened plants, no relation has been found between either gas exchange rates or chlorophyll 'a' fluorescence characteristics at low temperatures and cultivar ability for acclimation. Neither the existing differences in photosynthetic activity, nor the degree of photosynthetic apparatus acclimation to cold, which occurs during prehardening, are the factors responsible for the frost resistance variation observed between studied cultivars.