Winter-hardy Cultivars Research Articles

Adaptive Potential of Seed Crops on the Example of Apple Tree Varieties and Quince Seedlings

Apple is the main fruit crop in the European part of Russia. Quince is a promising crop as a valuable low-growing rootstock for pears. The most favorable conditions for growing pome crops (apple and common quince) are in the Central and Central Black Earth regions (Voronezh, Tula, Lipetsk, Kursk, Belgorod, Oryol, Ryazan and Tambov regions). Currently, there is a wide variety of varieties and rootstocks (of various selections) for apple and pear trees, but choosing more adaptive ones for each ecological-geographical zone in intensive gardening is considered relevant. The studies were carried out on the basis of VNIISPK in 2018–2023. Apple cultivars of VNIISPK breeding and foreign cultivars grafted on rootstock 54-118 as well as common quince of VNIISPK breeding selected according to a complex of valuable economically useful characteristics were used as objects of study. The research of the presented work was carried out on the basis of the methodological recommendations “Programs and methods for the variety study of fruit, berry and nut crops” and “Methods for the accelerated assessment of winter hardiness of fruit and berry plants”. Severe frosts occur in the Central region of Russia (Orel region) in winter (January-February). Over the past five years, the lowest air temperature was recorded in the winter of 2020/2021, when in February it dropped to minus 30°C. In the field, the studied apple cultivars on the clone rootstock 54-118 showed sufficient winter hardiness. As a result of freezing of annual branches in laboratory conditions, it was revealed that Ligol (the Polish cultivar) and the VNIISPK cultivars Orlovsky Partizan, Vyatich, Orlovskoe Polesie and Pamyat Semakinu had bud and wood damage according to all I, II, III components of winter hardiness. The most winter-hardy cultivar Rozhdestvenskoe of VNIISPK breeding stood out. In VNIISPK, seedlings of common quince with high winter hardiness of the aboveground and root systems adapted to the climatic conditions of the central part of Russia and possessing restrained growth have been identified. Studies have shown that these quince seedlings being in deep dormancy can withstand frosts up to -36°C and are able to tolerate a decrease in temperature in the zone of the root layer up to -10°C without significant damage.

Lentil Cultivar Evaluation in Diverse Organic Mediterranean Environments

Lentil (Lens culinaris Medik.) production faces challenges due to shifting environmental conditions, potentially leading to a transition towards cooler or highland Mediterranean environments. This study assessed the responses of five lentil genotypes across five diverse locations (L1–L5) managed under organic cropping systems over two seasons, focusing on key parameters including seed yield (SY), crude protein (CP), cooking time (CT), seed loss percentage (SL), and yield loss per hectare (YL) caused by bruchid (Bruchus sp.). Excessive seasonal rainfall (500 mm), low winter temperatures (−17.9 °C), bruchid SL, and spring sowing were identified as crucial, particularly in challenging environments like highlands. Genotype selection was highlighted as essential for balancing yield and stability, with the small-seeded cultivar ‘Dimitra’ demonstrating lower YL due to bruchid. Additionally, increased CP was noted in response to heightened bruchid infestations. Specific recommendations were proposed for different environments: In productive lowland areas with low bruchid pressure and high CTs (L1), prioritizing cultivars like ‘Samos’, ‘Dimitra’, and ‘Thessalia’ enhances quality. Locations with high bruchid populations (L4) were not favored organic production but can serve as genetic resistance screening sites. High-elevation environments (L3, L5) proved significantly less productive, underscoring the requirement for earlier and winter-hardy cultivars. These insights guide lentil cultivation, emphasizing the need for tailored breeding strategies adaptable to changing environments.

Cover crop cultivars and species differ in root traits potentially impacting their selection for ecosystem services

Background and aimsCover crops have the potential to aid in adapting agricultural systems to climate change impacts through their ecosystem services, such as preventing soil erosion, remediating soil structure, and storing carbon belowground. Though roots are integral to these processes, there is a lack of cover crop root trait data. This study aims to characterize rooting behavior of several commercially available cover crops and assess how differences in root system architecture potentially impact their selection for ecosystem services.MethodsTwenty-two cover crop cultivars across the grass, legume, and brassica families were grown in O’Fallon, Missouri, USA. Canopy cover was monitored throughout the growing season. Shoot and root biomass samples were collected and analyzed.ResultsCereal rye and winter triticale were the most winter hardy cultivars and provided the highest percent canopy cover. Cereal rye and winter triticale also generated the highest amount of shoot and root biomass among treatments but diverged in their root system architectures. Winter triticale forms coarser roots and exhibited deeper rooting, which may be better suited for carbon sequestration. Rapeseed and Siberian kale have favorable C:N ratios for nutrient recycling, but rapeseed may invest more into lateral root formation and have a higher potential to “catch” excess nutrients.ConclusionSelection of cover crops for ecosystem services should account for root system architecture and their suitability for these ecosystem services. Differences in root traits among cultivars within the same family highlight the potential to breed cover crop root system architecture to further enhance ecosystem service efficacy.

Frost hardiness of 10 olive cultivars after natural and controlled freezing

Selecting winter-hardy cultivars is an effective way to avoid freezing damage in olive trees. In this study, we evaluated the cold hardiness of 10 olive cultivars in the field after a natural freezing event (-12°C in December 2016, Sorkhe, Semnan, Iran) and treatment with controlled freezing temperatures ranging from 0°C to -21°C. The 50% lethal temperature (LT50) based on electrolyte leakage (LT50-EL) and tetrazolium tests (LT50-TZ) before, during, and after dormancy were determined in each cultivar's shoots. The proline and soluble carbohydrate content of leaves and shoots also were measured during dormancy. The LT50-EL had a mean of -9.5°C and ranged from -16.5°C to -4.8°C. The LT50-TZ had a mean of -10.2°C and ranged from -16.3°C to -6.4°C. We classified the olive cultivars into five groups based on their lab-freezing evaluations using cluster analysis. 'Manzanilla', 'Mission', and 'Rashid' were very sensitive to freezing, while 'Roughani' and 'Zrad' were the hardiest cultivars. In Field evaluation, the recovery ability and yield of each cultivar were evaluated six years after freezing damage. Visual scoring indicated that 'Roghani' and 'Zard' had the least amount of trunk damage. However, 'Zard' showed low regrowth power in the field after freezing damage despite its high freezing tolerance in lab and field experiments. 'Roughani' had the maximum fruit yield among the 10 olive cultivars six years after freezing damage (P < 0.01). Our finding indicates that laboratory techniques be combined with field assessments to more accurately evaluate the cold hardiness of olive trees.

Особенности органогене за труднокул ьтивируемых ни зкорослых сортов вишни обыкновенной (Prunus ceras us L.) в кул ьтуре in vitro

The article presents the results of research on clonal micropropagation of sour cherry (Prunus cerasus L.) which is difficult to reproduce at the proliferation stage by traditional methods. A number of modern winter-hardy domestic cultivars of P. cerasus are promising for plantation cultivation of this crop in the Nonchernozem zone of the European part of Russia. The method of clonal micropropagation is advisable to obtain a large amount of healthy and genetically homogeneous rootstocks of fruit crops. Regenerated plants of P. cerasus of low-growing, mid-season and winter-hardy cultivars Assol’ and Shokoladnitsa were used as research objects. The growth and developmental features of P. cerasus regenerated plants were studied during in vitro cultivation on a QL nutrient medium supplemented with growth regulators of the cytokinin group (6-BAP, thidiazuron, zeatin) in different concentrations. The highest indicators for the length of microshoots (average 13.4 mm) and the number of leaves (average 6.0 pcs.) of P. cerasus plants in in vitro culture are recorded for the Shokoladnitsa cultivar. The maximum length of microshoots of P. cerasus Assol’ cultivar is observed on the 60th day of cultivation on a QL nutrient medium with the addition of zeatin at a concentration of 0.3 mg/l (10.5 mm) and thidiazuron at a concentration of 0.3 mg/l (9.8 mm), while the maximum number of leaves (7.8 pieces) is observed with addition of 0.3 mg/l zeatin. The maximum length of microshoots of P. cerasus of the Shokoladnitsa cultivar is observed when grown for 60 days on a QL nutrient medium with the addition of 6-BAP at concentrations of 0.5 mg/l (17.7 mm) and 1.0 mg/l (14.2 mm), while the maximum number of leaves (7.2 pieces) is observed with addition of 0.3 mg/l zeatin.

Inheritance of ornamental traits in bird cherry families with the cultivar ‘Nezhnost’ in their pedigree

Background. Bird cherry plants are highly ornamental; they are diverse in shape, size and color of leaves and flowers, flowering and fruiting schedules. At present, they are widely used for landscaping parks and public gardens. In Russia there is a need to release new highly ornamental and winter-hardy cultivars using the genetic potential of both known and newly developed genotypes.Materials and methods. In our experiment we used a pink-flowered sample found by R. A. Mastinskaya in the vicinity of Novosibirsk and transferred to Krymsk Experiment Breeding Station of VIR, where it was studied and released as a cultivar named ‘Nezhnost’. One of its seedlings from free pollination became known as No. 11-5-37. Crosses included cvs. ‘Colorata’ (source of the spring red leaf trait), ‘Purpurnaya Svecha’ (summer/autumn red leaf), ‘Pamyati Salamatova’ (number of flowers, and brush length), accessions Nos. 1-1-8 and 11-1-8 from the Central Siberian Botanical Garden’s collection (diameter of flowers and inflorescences), and selected forms “Tereshkovoy 38” and “Tereshkovoy 48/2” planted in Akademgorodok (brush length, number of flowers, and flower diameter).Results. Unlike European genotypes, these cultivars and hybrids are adapted to the conditions of Siberia. Over a long observation period, freezing was not observed on plants even in the most severe winters. Our data indicate a manifold composition of the gene complexes controlling the manifestation of both the pink flower trait and spring red leaves.Conclusion. A possibility of obtaining pink-flowered seedlings in a number of cross combinations and peculiarities of the inheritance of traits in them are shown. Five hybrids were identified for combining valuable traits; they are promising for ornamental and breeding uses. Some of them have already been developed into new ornamental cultivars.

Agronomical evaluation of low dormancy alfalfa populations selected by an indoor screening method

AbstractFall dormancy is a vital component of alfalfa (Medicago sativa L.) yield in northern climates, but selection for the trait is often done at the expense of winter survival. We performed one cycle of selection to reduce fall dormancy in two winter hardy cultivars (Yellowhead and Peace) using a new indoor screening method. We compared the reduced dormancy populations with their respective initial cultivars for fall dormancy, yield, and winter survival at four sites across Canada. During the establishment and the first production years, plants of the reduced dormancy populations were generally taller in the fall than their respective cultivar, which resulted in a one unit increase of their fall dormancy class. Under field conditions, plants of the reduced dormancy populations had a similar winter survival than those of the initial cultivars. Under simulated winter conditions, freezing tolerance was not affected by selection for reduced dormancy in Peace, whereas a decrease from −24.0 to −21.5 °C was observed in Yellowhead. However, in this cultivar, we noted a 37% yield increase under field conditions and a 40% more vigorous regrowth under simulated winter conditions in the reduced dormancy population. These results showed that the indoor selection method effectively reduced fall dormancy and that indirect responses for yield and winter survival were dependent on the genetic background used as selection material. This selection method could therefore be promising to develop alfalfa cultivars adapted to northern latitudes with high winter hardiness and improved late season yield.

Effects of decreasing photoperiod on cold acclimation of asparagus seedlings

Cold acclimation is a vital process for surviving subzero temperatures in asparagus ( Asparagus officinalis L.). A winter hardy cultivar, “Guelph Millennium” (GM), cold acclimates, senesces, and develops freezing tolerance earlier in the fall compared to “UC157” (UC), a cultivar adapted to warm climates. Decreasing photoperiod can induce timely senescence and freezing tolerance in both woody and herbaceous perennials, although its effects on asparagus are unclear. The objectives of this research were to study the effects of daylength and cold, and their interaction, on the induction of freezing tolerance in asparagus. Seedlings of GM and UC were subjected to four treatments: constant (15.5 h) or decreasing (15.5–14 h) photoperiods with either high (23 °C) or low (11 °C) temperatures. Decreasing daylengths did not impact the acquisition of freezing tolerance at either temperature. For UC, low temperature accompanied by decreasing photoperiod diminished root:shoot ratio and increased crown water percentage, which are both indicators of reduced dormancy. A decreasing photoperiod and high temperature increased crown fructan (total and high-molecular weight) and decreased glucose and proline concentrations in GM compared to UC. These results suggest that decreasing daylengths, similar to those occurring in late summer in Southern Ontario, may be a signal for crown metabolite partitioning. This effect may be a contributing factor to the timely senescence and cold acclimation seen in GM compared to UC.

Evaluation of strawberry cultivars as sources of high winter hardiness and productivity

Background. The realization of high productivity potential in strawberry plants significantly depends on their adaptability to soil and climate conditions of their cultivation. Winter hardiness is the most important trait in the central part of Russia. With this in view, the purpose of this study was to identify sources of high winter hardiness combined with high productivity and yield potential among the studied cultivars.Materials and methods. The research was carried out at the primary variety testing site of the All-Russian Research Institute of Fruit Crop Breeding (VNIISPK), Orel Province, in accordance with the published program and methodology of fruit, berry and nut variety studies. The testing covered 23 domestic and foreign strawberry cultivars. An Espec PSL-2KPH climate chamber (Japan) and a Polair refrigerator cabinet (Russia) were used for artificial freezing.Results. Winter hardiness of strawberry cultivars was assessed under artificial freezing conditions. Cvs. ‘Korona’, ‘Tsaritsa’, ‘Solovushka’ and ‘Sara’ were the most winter-hardy cultivars. The study of the cultivars in the field made it possible to identify the most productive and large-fruited ones: ‘Alba’, ‘Azia’, ‘Bereginya’ and ‘Tsaritsa’. Cv. ‘Tsaritsa’ combines high winter hardiness and high yield productivity and yield potential, being a valuable source of these traits in breeding practice. According to a set of indicators ‘Tsaritsa’ is promising for large-scale cultivation in the Central Black Earth Region of Russia.

Breeding of subtropical (Diospyros kaki L., Feijoa sellowiana Berg) and citrus crops (Citrus reticulata Blan. var. unchiu Tan.) in FRC SSC of RAS

This paper presents the results of the breeding work carried out by the Subtropical Scientific Centre of the Russian Academy of Sciences. The purpose of the research is to improve the assortment of subtropical and citrus crops. The objects of research were 230 hybrid forms, of which citrus - 138 hybrids, persimmons - 56, feijoa - 36. Currently, the breeders of the FRC SSC of RAS are working hard to develop new winter-hardy, high yielding, and high-quality cultivars resistant to growing conditions. The sources of priority traits have been identified, which are included in hybridization for the development of new cultivars with improved economic and biological traits. Over the past 5 years, the State Register of Breeding Achievements of the Russian Federation has included 3 cultivars of feijoa and 1 cultivar of kaki persimmon created in the Centre. On the test are 3 promising forms of tangerine, 2 feijoa and 1 form of kaki persimmon.

Mapping freezing tolerance QTL in alfalfa: based on indoor phenotyping

BackgroundWinter freezing temperature impacts alfalfa (Medicago sativa L.) persistence and seasonal yield and can lead to the death of the plant. Understanding the genetic mechanisms of alfalfa freezing tolerance (FT) using high-throughput phenotyping and genotyping is crucial to select suitable germplasm and develop winter-hardy cultivars. Several clones of an alfalfa F1 mapping population (3010 x CW 1010) were tested for FT using a cold chamber. The population was genotyped with SNP markers identified using genotyping-by-sequencing (GBS) and the quantitative trait loci (QTL) associated with FT were mapped on the parent-specific linkage maps. The ultimate goal is to develop non-dormant and winter-hardy alfalfa cultivars that can produce extended growth in the areas where winters are often mild.ResultsAlfalfa FT screening method optimized in this experiment comprises three major steps: clone preparation, acclimation, and freezing test. Twenty clones of each genotype were tested, where 10 samples were treated with freezing temperature, and 10 were used as controls. A moderate positive correlation (r ~ 0.36, P < 0.01) was observed between indoor FT and field-based winter hardiness (WH), suggesting that the indoor FT test is a useful indirect selection method for winter hardiness of alfalfa germplasm. We detected a total of 20 QTL associated with four traits; nine for visual rating-based FT, five for percentage survival (PS), four for treated to control regrowth ratio (RR), and two for treated to control biomass ratio (BR). Some QTL positions overlapped with WH QTL reported previously, suggesting a genetic relationship between FT and WH. Some favorable QTL from the winter-hardy parent (3010) were from the potential genic region for a cold tolerance gene CBF. The BLAST alignment of a CBF sequence of M. truncatula, a close relative of alfalfa, against the alfalfa reference showed that the gene’s ortholog resides around 75 Mb on chromosome 6.ConclusionsThe indoor freezing tolerance selection method reported is useful for alfalfa breeders to accelerate breeding cycles through indirect selection. The QTL and associated markers add to the genomic resources for the research community and can be used in marker-assisted selection (MAS) for alfalfa cold tolerance improvement.

Porfiry Afanasyevich Dibrova: at the origins of scientific pomiculture in the Urals

Porfiry Afanasyevich Dibrova was one of the first scientists and breeders standing at the origins of scientific pomiculture in the Urals. He was the author of 23 cultivars of apple, six of pear, one of sour cherry, and one of black currant. In the 1940s, he was the leader of collecting missions exploring the local assortment of fruit and berry crops in 50 districts of Sverdlovsk and Molotov (Perm) Provinces, and the Udmurt Republic. P.A. Dibrova was one of the authors of the first standard set of fruit and berry cultivars for the abovementioned areas. He studied regularities in the inheritance of valuable agronomic and biological traits of fruit crops and identified promising sources for apple and pear breeding. He launched the main plant breeding trends in the Middle Urals, now followed by contemporary breeders: the development of highly winter-hardy cultivars of apple and pear with fruiting precocity, stable yields, excellent fruit quality, and improved biochemical composition in fruits.

Biomorphological and useful agronomic traits of the hexaploid winter triticale cultivar ‘Bilinda’ approved for cultivation in the Northwestern Region of the Russian Federation

A priority of agricultural production for the Northwest of Russia is to develop and introduce winter-hardy and productive cultivars of small grain forage crops, such as winter triticale, capable of producing high yields of grain and green biomass.‘Bilinda’, a new promising tetraploid winter triticale cultivar grown for grain forage, was studied from 2004 through 2019 at Leningrad Research Institute for Agriculture “Belogorka”. The data of the State Variety Trials (2017–2019) were also taken into account. Conventional techniques were used in the experiments, phenological observations, field and laboratory evaluation tests, and statistical data processing. Electrophoresis of gliadin in the grain of cv. ‘Bilinda’ and its registration as a “protein formula” were performed using the technique developed and approbated by the Molecular Biology Dept. of VIR. The hexaploid winter triticale cultivar ‘Kornet’ (k-3636) served as the reference. Cv. ‘Bilinda’ was developed using individual and mass selection of genotypes with recessive control of the ear’s morphological characters, which resulted in producing a homogeneous population with high yield potential and large plump grains. On average across the testing period, cv. ‘Bilinda’ significantly exceeded the reference ‘Kornet’ in grain yield (+1.04 t/ha), number of grains per ear (+32.3 pcs), and 1000 grain weight (+7.7 g), and in addition demonstrated higher winter hardiness than the reference (up to 98%). Under epiphytotic incidence of Septoria leaf blotch, the tested cultivar manifested a high level of resistance (scoring 7–9 points). ‘Bilinda’ is among high-yielding cultivars resistant to most leaf diseases. In 2020, this cultivar was approved for cultivation in the Northwestern Region (2) of Russia. Applying the method of variety identification based on the electrophoretic spectra of gliadin, a storage protein in grain, a protein “passport” was produced to ensure monitoring of the cultivar’s integrity and authenticity.

Use of apple tree gene pool to create adaptive cultivars with high quality fruits

The apple tree gene pool was evaluated by resistance to adverse winter conditions based on the analysis of weather data for 50 years. 70% of winter-hardy and highly winter-hardy cultivars were revealed in the group of traditional local cultivars. Many local Central Russian cultivars are widely used in the breeding of new winter-hardy cultivars in central Russia, the Volga region, the Urals, Siberia, the Altai, the Far East and the south of the country. Positive results were obtained by using cultivars obtained from stepped crossbreeding, combining a complex of valuable qualities (winter resistance, immunity to scab, high qualities of fruits) in selection. On the basis of damaging factors' modeling, resistance to -38° C temperature and resistance to frost after thaw were confirmed in most VNIISPK breeding cultivars; winter-hardy cultivars with a resistance threshold -40°C: Vyatich, Orlovskiy partizan, Orlovskoye polesie, Zdorovye, Ministr Kiselev, Pamyat' Semakinu, Rozhdestvenskoye. Cultivars Idared, Golden Delicious, Granny Smith, Gala, Jonagold, Pink Lady, Fuji, Honeycrisp are recommended for use in breeding in combination with winter-resistant cultivars to create new high-quality apple tree cultivars with long keeping quality.

Correlations Between Yield and Several Traits in a Set of Winter Peas Cultivars

Pea (Pisum sativum L.) has long been an important component of the human diet, providing an excellent source of protein. Twenty four winter peas cultivars of different origins were tested, along with one spring cultivar, under conditions of South-eastern part of Romania, during 2017-2019 period. The objective of the study was to analyze correlations between yield and several plant traits, and to assess possibilities of combining high yield with suitable winter hardiness, earliness, protein content and thousand grains weight (TGW) in lines selected in the National Agricultural Research and Development Institute (NARDI) Fundulea breeding program from crosses between winter and spring cultivars. Statistical analysis showed that environment (years) was the most important driving factor for the studied agronomic traits. Nevertheless, differences among cultivars were significant when tested against the GxE interaction, for all traits, except winter hardiness, the latest maturing cultivars (originated from USA) yielded less under studied conditions, but the correlation between vegetation period and yield was positive for European cultivars and Fundulea lines. Our results suggested that the most winter hardy cultivars had smaller grains. Yield and TGW had a highly significant negative correlation with protein content when the two American cultivars were included, but the correlation was not significant in the European cultivars and Fundulea lines. Some winter peas lines, derived from winter x spring crosses, combined high yield with good levels of winter hardiness, earliness TGW and protein content.

Assessing alfalfa production under historical and future climate in eastern Canada: DNDC model development and application

The DeNitrification-DeComposition (DNDC) model was developed to better simulate alfalfa (Medicago sativa L.) production with winterkill effects in eastern Canada. The pre-development DNDC produced “fair” simulations of alfalfa yield and biomass (index of agreement (d) > 0.7, Nash-Sutcliffe efficiency (NSE) > 0) but normalized root mean square error (nRMSE) was > 30% whereas the improved model indicated “good” to “excellent” performance (nRMSE = 3.9–29%; d = 0.93–0.99; NSE = 0.76–0.99). Under future RCP4.5 and 8.5 scenarios, average annual yields increased by 60.3% and 81.8% respectively due to earlier planting/spring regrowth with additional cuttings, increased C assimilation and reduced water stress under higher CO2 concentrations. For locations at Ottawa and Quebec City there could be an increased incidence of winterkill under future climate due to reduced snow cover which leads to colder soil/crown temperatures as well as reduced fall hardening. This study indicated that the use of winter hardy cultivars could mitigate winterkill effects and increase production.

Plum Research and Growing in Latvia

Abstract Plums have been commercially grown in Latvia since the 19th century. Plantations expanded especially in the 1920s–1930s. At that time, many cultivars were introduced, mostly from Western Europe. After the severe winters of 1939/40, 1941/42, 1955/56, and 1978/79, the plum orchard area significantly decreased because of a lack of winter-hardy cultivars. For this reason, cultivars from Russia, Belarus, and Estonia were introduced. Among the old landraces, highly winter-hardy ‘Latvijas Dzeltenā Olplūme’ is still important. Previously it used to be productive and had good fruit quality. Unfortunately, nurseries often propagated the hardiest clones, which lacked productivity. As Latvian consumers love yellow plums, at present breeding and propagation of productive clones from old orchards is ongoing. In the mid-20th century, active plum breeding started in Latvia, crossing hardy genotypes with high quality donors. From this period ‘Lāse’ and ‘Minjona’ are still grown. Since the 1980s, plum breeding has been undedrtaken at the Institute of Horticulture. The crossing work in plums concentrated on the hexaploid group, aiming to combine large fruit size with good flavour, different time of ripening (in particular, early to medium late) and and good winter-hardiness. New cultivars include ‘Sonora’, ‘Ance’, and ‘Adelyn’, which have good quality, and productivity 20–30 kg per tree, and in some years up to 70 kg per tree. The most widely used rootstocks are seedlings of Prunus cerasifera Ehrh. ssp. divaricata C.K. Schneid., which is more hardy that the common myrobalan plum. These rootstocks have good compatibility with most cultivars except gages, and are adapted to different soil types and are disease tolerant. Their drawback is a long growth season which reduces winter-hardiness of grafted cultivars. Also, they tend to form suckers around the stem. A hardy seedling PU-20651 (P. salicina ssp. ussuriensis × P. cerasifera) was bred at the Institute, which was shown to slightly reduce tree vigour. Testing of several Western European and Russian rootstocks did not result in their introduction into production. Trials are presently being carried out with size-reducing root-stocks originated from cultivar Wangenheim VVA-1, Weiwa, S766, and M633. Commercial production of plums in Latvia is relatively small, as the area of orchards is the smallest among fruit trees. Plums are grown mostly for fresh consumption, with a small part for jams, yoghurt, and ice-cream additives. Fruits are sold mostly in small shops, markets and at farms. The main reason is the climate, which allows growing of a limited range of cultivars that tolerate the –30 °C winter temperatures in some years (about every five years). About 20 cultivars are grown commercially; the share of the six most popular plum cultivars is 69% of the total plum production. In recent years, plantations of new cultivars developed at our Institute have expanded, especially regarding the early ripening cultivar ‘Ance’.

The effect of cold acclimation on the low molecular weight carbohydrate composition of safflower.

Understanding cold acclimation and identifying the low molecular weight carbohydrates that support the development of freezing tolerant safflower seedlings will aid in breeding winter-hardy cultivars for temperate cropping systems. Three field selected lines of winter safflower (WSRC01: PI 651878; WSRC02: PI 651879; WSRC03: PI 651880) were cold acclimated for four weeks at 4 °C and compared to seedlings grown for two weeks at 20 °C. The commercial spring-type cultivar, Olé, served as a non-hardy check. Leaf, stem, and root fructose, glucose, sucrose, raffinose, and stachyose concentrations all increased to variable extents across the PI accessions after cold acclimation. In comparison with Olé, winter safflower accessions tended to be more responsive to cold acclimation by increasing metabolite concentration. Verbascose was only recovered within leaf tissue and PI 651880 was the only entry to show a substantial alteration in verbascose concentration due to cold acclimation. Based on these data, no specific low molecular carbohydrate was responsive or responsible for the accumulation of freezing tolerance, but a concert of metabolites and their responsiveness may help explain the observed differences in development, freezing tolerance, and ultimately winterhardiness among safflower germplasm.

Introduction and Breeding of Rhododendrons in Latvia

Abstract Rhododendrons are relatively new beautiful ornamental plants in Latvia forming an essential part of public and private gardens, although they were introduced in Latvian territory already during the first half of 19th century. Rhododendrons deserve their immense popularity due to the diversity of their habitat, size and type of blossoms and leaves and their flowering season. There are about 1000 rhododendron species in the wild up to now whereas breeders in various countries have created more than 30 000 cultivars. Intensive rhododendrons introduction and acclimatization in Latvia started in 1957 when Rihards Kondratovičs, at the time director of the Botanical Garden, University of Latvia, started his research on the introduction and acclimatization of rhododendrons. Winterhardiness of about 400 wild species in Latvia was tested and 76 species were found to be suitable. Following the development of an extensive collection of wild rhododendron species and cultivars, the Rhododendron Breeding and Experimental Nursery “Babīte”, University of Latvia, was established at 1980 and the active breeding of new winterhardy cultivars was started. In 2017, the collection of outdoor rhododendrons of the University of Latvia consists of 76 species and 265 cultivars, including 109 cultivars bred in Latvia by Professor Rihards Kondratovičs.

Use of Electrical Conductivity to Assess Irrigation Impacts on Grapevine Winter Hardiness

A simple method involving measurement of electrical conductivity of grapevine cane tissue was evaluated. ‘Sovereign Coronation’ vines on two sites were subjected to five irrigation treatments based upon reference evapotranspiration (ET0) and various crop coefficients (Kc): non-irrigated control; 100% ET0 × Kc = 0.75; 150% ET0 × Kc = 0.75 (ET0 × 1.12); 100% ET0 × Kc = 0.2 to 0.8; 150% ET0 × Kc = 0.2 to 0.8. ‘Chardonnay’ vines were likewise subjected to several irrigation treatments: non-irrigated control, early season deficit (irrigation until berry set), midseason deficit (irrigation until lag phase of berry growth), late season deficit (irrigation until veraison), and full season irrigation (irrigation until harvest). Cane samples were collected from December to March inclusive, and cane segments were subjected to multiple temperature treatments (−24, −26, −28, −30, −32°C) in addition to a non-treated control. Treated cane segments were thinly sliced and incubated in distilled water (t1) at room temperature and at 100°C (t2), after which the electrical conductivity (EC) was read. Two indices calculated from both EC values (ItA, ItB) were responsive to irrigation. However, there was little relationship between either ItA and ItB versus irrigation in ‘Sovereign Coronation’, likely because it is a very winter-hardy cultivar. Nonetheless, there was a relationship between both ItA and ItB versus irrigation in ‘Chardonnay’, whereby treatments to which high irrigation volumes were applied also had high ItA and ItB values, suggesting higher potential winter damage. In summary, the technique described herein is relatively inexpensive and not time-consuming and, therefore, may constitute a rapid method for assessment of grapevine winter injury.