Levels Of Cold Tolerance Research Articles

Identification of Candidate Genes for Cold Tolerance at Seedling Stage by GWAS in Rice (Oryza sativa L.).

Due to global climate change, cold temperatures have significantly impacted rice production, resulting in reduced yield and quality. In this study, we investigated two traits related to the cold tolerance (CT) of 1992 diverse rice accessions at the seedling stage. Geng accessions exhibited higher levels of CT compared to xian accessions, with the GJ-tmp subgroup displaying the strongest CT. However, extreme CT accessions were also identified within the xian subspecies. Through GWAS analysis based on the survival rate (SR) and leaf score of cold tolerance (SCT), a total of 29 QTLs associated with CT at the seedling stage were identified, among which four QTLs (qSR3.1a, qSR4.1a, qSR11.1x, and qSR12.1a) were found to be important. Furthermore, five candidate genes (LOC_Os03g44760, LOC_Os04g06900, LOC_Os04g07260, LOC_Os11g40610, and LOC_Os12g10710) along with their favorable haplotypes were identified through gene function annotation and haplotype analysis. Pyramiding multiple favorable haplotypes resulted in a significant improvement in CT performance. Subsequently, three selected accessions (CX534, B236, and IRIS_313-8565), carrying different superior alleles for CT, were selected and recommended for molecular breeding for CT using marker-assisted selection (MAS). The findings from this study provide valuable resources for enhancing rice's ability for CT while laying a foundation for the future cloning of novel genes involved in conferring CT.

The supercooling point depression is the leading cold tolerance strategy for the variegated ladybug, [Hippodamia variegata (Goezel)

The variegated ladybug, Hippodamia variegata is one of the most effective predators of various pests that hibernate as adult beetles. During the overwintering period from April 2021 to March 2022, we examined the supercooling point (SCP), cold tolerance, and physiological adaptations of beetles in Kerman, Iran. The beetles exhibited their greatest cold tolerance (63.4% after 24h at -5°C) when their SCP was lowest (-23.2°C). Conversely, from April to October 2021, the SCP reached its peak (approximately -13.0°C), while cold tolerance was at its lowest level (6.7% after 24h at -5°C). Cryoprotectant content (trehalose, glycerol, and glucose) was at its highest level in September (11.15, 10.82, and 6.31mg/g, respectively). The critical thermal minimum (CTmin) reached its lowest point of -2.2°C in January and February. The lowest point of the lower lethal temperature (LLT) coincided with the lowest level of the SCP and the highest level of cold tolerance (in February, LT50 = -5.3°C, SCP = -23.2°C, and survival = 77.78% at -4°C/24h). Chill-coma recovery time (CCRT) was examined at five different temperatures and two different exposure durations. The CCRT increased with a decrease in exposure temperature and time (68.0s at -2°C after 2h and 102.0s at -2°C after 4h). As the majority of the overwintering beetle's mortality occurred at temperatures significantly higher than SCP, the adults of H. variegata are chill-susceptible insects that primarily rely on a depressed supercooling point to cope with unfavorable conditions during the overwintering period.

Effects of species, sex, and diet on thermal tolerance of Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae).

Thermal tolerance greatly influences the geographic distribution, seasonality, and feeding habits of mosquitoes; this study aimed to examine the impacts of species, sex, and diet on thermal tolerance in mosquitoes. We found that Culex quinquefasciatus was inherently significantly more cold tolerant than Aedes aegypti, while Ae. aegypti had improved heat tolerance compared to Cx. quinquefasciatus. There were no differences in thermal tolerance between sexes within either species. We observed similar levels of cold tolerance between all diets tested, but observed decreased heat tolerance in mannitol-fed mosquitoes. Our results suggest that although dietary factors such as sugar alcohols and sugars may play a role in thermal tolerance in mosquitoes, there are likely physiological and genetic factors that can have a greater influence on the limits of thermal tolerance within a species.

Tropical super flies: Integrating Cas9 into Drosophila ananassae and its phenotypic effects

Ectotherms such as insects are animals whose body temperature largely depends on ambient temperature and temperature variations provide a selection pressure affecting the geographical distribution of these species. However, over the course of evolution, some insect species managed to colonize environments characterized by various temperature ranges. Therefore, insects provide an excellent study system to investigate the basis of adaptation to temperature changes and extremes. We are generally using the vinegar fly Drosophila ananassae as a model system to investigate the genetic basis of cold tolerance. This species has expanded from its tropical ancestral range to more temperate regions resulting in a cosmopolitan, domestic distribution. Previously, we identified candidate genes significantly associated with cold tolerance in this species. We now established molecular genetic tools to assess the function of these genes. Using CRISPR/Cas9 methodology for genome editing and the PiggyBac system, the Cas9 enzyme was successfully integrated into the genome of three fly strains with different levels of cold tolerance. We further report on preliminary findings that the Cas9 integration itself did not have a consistent effect on tolerance to cold. In conclusion, we offer with our study the molecular tools that allow studying stress-related candidate genes in D. ananassae in the future. In addition, we point out and provide guidance on the challenges that come with genome editing in a non-model species.

The BrAFP1 promoter drives gene-specific expression in leaves and stems of winter rapeseed (Brassica rapa L.) under cold induction

BrAFP1(antifreeze protein in winter turnip rape) effectively limits recrystallization and growth of ice crystals. The BrAFP1 expression level determines whether the freezing-induced damage to winter turnip rape plants is avoided. This study analyzed the activity of the BrAFP1 promoters of several varieties at various cold tolerance levels. We cloned the BrAFP1 promoters from five winter rapeseed cultivars. The multiple sequence alignment revealed the presence of one inDel and eight single-nucleotide mutations (SNMs) in the promoters. One of these SNMs (base mutation from C to T) at the –836 site away from the transcription start site (TSS) enhanced the transcriptional activity of the promoter at low temperature. The promoter activity was specific in cotyledons and hypocotyls during the seedling stage and was referential in stems, leaves, and flowers but not the calyx. This consequently drove the downstream gene to be specifically expressed in leaves and stems, but not in roots at low temperature. The truncated fragment GUS staining assays revealed that the core region of the BrAFP1 promoter was included in the 98 bp fragment from the –933 to –836 site away from the TSS, which was necessary for transcriptional activity. The LTR element of the promoter significantly enhanced expression at low temperatures and suppressed expression at moderate temperatures. Moreover, the BrAFP1 5′-UTR intron bound the scarecrow-like transcription factor and enhanced expression at low temperature.

Screening of rice germplasms (Oryza sativa L.) for seedling stage cold tolerance utilizing morphological and molecular markers

Cold temperature is a devastating abiotic stress for rice production, especially in the areas where low temperature prevails throughout the crop duration or in particular growth stages. Boro cultivation season in eastern India is such a replica of rice cultivation under occasional colder climate. Therefore, it is imperative to study a large collection of germplasms for potential cold tolerant stocks. In this study, 106 germplasms from eastern India were cultivated during Boro season in field as well as under 10 °C and 28 °C temperature conditions inside plant growth chamber. Six seedling growth parameters were used as phenotypic markers and 56 cold tolerance quantitative trait loci linked simple sequence repeats (SSRs) were utilized as molecular markers. Leaf yellowing and germination index were also incorporated within the framework of cold tolerance screening to enrich the multidimensional approach. Based on the k-means clustering for each morphological parameter in each condition, the genotypes were ranked and the resulting total ranks for each genotype eventually grouped them into four clusters, i.e. highly susceptible, susceptible, moderately tolerant and tolerant as different level of cold tolerance. Among the screened SSRs, only 33 were polymorphic and most informative were RM336, RM566 and RM1349 due to higher marker efficiency threshold. Combining both morphology and molecular analysis, highly tolerant landraces such as Neera, Barnamali, Khaiya Boro and genotypes such as Purbachi, CB1, Gotra, UPR 103-80 were identified which may be of greater use in development of high yielding cold tolerant genotypes.

Full-length transcriptome analysis of maize root tips reveals the molecular mechanism of cold stress during the seedling stage

BackgroundAs maize originated in tropical or subtropical zones, most maize germplasm is extremely sensitive to low temperatures during the seedling stage. Clarifying the molecular mechanism of cold acclimation would facilitate the breeding of cold tolerant maize varieties, which is one of the major sustainability factors for crop production. To meet this goal, we investigated two maize inbred lines with contrasting levels of cold tolerance at the seedling stage (IL85, a cold tolerant line; B73, a cold sensitive line), and performed full-length transcriptome sequencing on the root tips of seedlings before and after 24 h of cold treatment.ResultsWe identified 152,263 transcripts, including 20,993 novel transcripts, and determined per-transcript expression levels. A total of 1,475 transcripts were specifically up-regulated in the cold tolerant line IL85 under cold stress. GO enrichment analysis revealed that 25 transcripts were involved in reactive oxygen species (ROS) metabolic processes and 15 transcripts were related to the response to heat. Eight genes showed specific differential alternative splicing (DAS) in IL85 under cold stress, and were mainly involved in amine metabolism. A total of 1,111 lncRNAs were further identified, 62 of which were up-regulated in IL85 or B73 under cold stress, and their corresponding target genes were enriched in protein phosphorylation.ConclusionsThese results provide new insights into the molecular mechanism of cold acclimation during the seedling stage in maize, and will facilitate the development of cultivars with improved cold stress tolerance.

Photosynthesis Mediated by RBOH-Dependent Signaling Is Essential for Cold Stress Memory.

Cold tolerance is improved by cold stress acclimation (CS-ACC), and the cold tolerance level is ‘remembered’ by plants. However, the underlying signaling mechanisms remain largely unknown. Here, the CS memory mechanism was studied by bioinformation, plant physiological and photosynthetic parameters, and gene expression. We found that CS-ACC induced the acquisition of CS memory and enhanced the maintenance of acquired cold tolerance (MACT) in cucumber seedlings. The H2O2 content and NADPH oxidase activity encoded by CsRBOH was maintained at higher levels during recovery after CS-ACC and inhibition of RBOH-dependent signaling after CS-ACC resulted in a decrease in the H2O2 content, NADPH oxidase activity, and MACT. CsRBOH2, 3, 4, and 5 showed high expression during recovery after CS-ACC. Many BZR-binding sites were identified in memory-responsive CsRBOHs promoters, and CsBZR1 and 3 showed high expression during recovery after CS-ACC. Inhibition of RBOH-dependent signaling or brassinosteroids affected the maintenance of the expression of these memory-responsive CsRBOHs and CsBZRs. The photosynthetic efficiency (PE) decreased but then increased with the prolonged recovery after CS-ACC, and was higher than the control at 48 h of recovery; however, inhibition of RBOH-dependent signaling resulted in a lower PE. Further etiolated seedlings experiments showed that a photosynthetic capacity was necessary for CS memory. Therefore, photosynthesis mediated by RBOH-dependent signaling is essential for CS memory.

Phenotypic and Molecular Characterization of Rice Genotypes’ Tolerance to Cold Stress at the Seedling Stage

Rice plants are affected by low-temperature stress during germination, vegetative growth, and reproductive stages. Thirty-nine rice genotypes including 36 near-isogenic lines (NILs) of BRRI dhan29 were evaluated to investigate the level of cold tolerance under artificially induced low temperature at the seedling stage. Three cold-related traits, leaf discolouration (LD), survivability, and recovery rate, were measured to determine the level of cold tolerance. Highly significant variation among the genotypes was observed for LD, survivability, and recovery rate. Three NILs, IR90688-74-1-1-1-1-1, IR90688-81-1-1-1-1-1, and IR90688-103-1-1-1-1-1, showed tolerance in all three traits, while IR90688-118-1-1-1-1-1 showed cold tolerance with LD and recovery rate. IR90688-92-1-1-1-1-1, IR90688-125-1-1-1-1-1, IR90688-104-1-1-1-1-1, IR90688-124-1-1-1-1-P2, IR90688-15-1-1-1-1-1, and IR90688-27-1-1-1-1-1 showed significantly higher yield coupled with short growth duration and good grain quality. Genetic analysis with SSRs markers revealed that the high-yielding NILs were genetically 67% similar to BRRI dhan28 and possessed cold tolerance at the seedling stage. These cold-tolerant NILs could be used as potential resources to broaden the genetic base of the breeding germplasm to develop high-yielding cold-tolerant rice varieties.

Transcriptome and Physiological Analysis of Rootstock Types and Silicon Affecting Cold Tolerance of Cucumber Seedlings.

Cucumbers grafted on rootstocks with different de-blooming capacity show varying levels of cold tolerance. The content of fruit bloom correlates with its silicon-metabolizing capacity, and rootstock grafting can alter not only the cold tolerance but also the silicon-metabolizing capacity of the scion. The molecular mechanisms responsible for resistance due to rootstocks and silicon and the pathway that affects cold tolerance, however, remain poorly understood. Therefore, we performed physiological and transcriptome analysis to clarify how rootstock types and silicon affect cold tolerance in cucumber seedlings. Then, we randomly selected eight differentially expressed genes (DEGs) for quantitative real time PCR (qRT-PCR) analysis to proof the reliability of the transcriptome data. The results showed that silicon can enhance the cold tolerance of cucumbers by boosting the phenylpropanoid metabolism, and rootstock grafting can boost the active oxygen scavenging ability and synthesis level of hormones in cucumbers and maintain the stability of the membrane structure to enhance cold tolerance. The difference in cold tolerance between the two rootstocks is because the cold-tolerant one has stronger metabolic and sharp signal transduction ability and can maintain the stability of photosynthesis, thereby contributing to the stability of the cellular system and enhancing tolerance to cold.

Contrasting root and shoot cold tolerance of a conifer with indeterminate growth

Yellow-cedar (Callitropsis nootkatensis (D. Don) D.P. Little), a conifer in the Cupressaceae with indeterminate growth, is undergoing severe decline and mortality in southeast Alaska and the coast of northern and central British Columbia. This decline is attributed to cold damage to roots associated with climate warming and reduced snowpack. The cold tolerance of indeterminate conifer species is little studied, and less is known about root cold tolerance, as most studies focus on shoots. We compared the seasonal cycle of cold hardiness in roots and shoots of yellow-cedar seedlings from high- and low-elevation populations over 1 year. Freezing tolerance of shoots followed a typical seasonal cycle, with low levels of cold tolerance observed from April to October and moderate levels of cold tolerance observed in mid-winter. Differences in shoot cold tolerance among populations were consistent with the latitude and elevation of origin. In contrast, at the same freezing temperatures, roots of all seedlings had consistent, high levels of cold damage throughout the year.

Expanded Supercooling Capacity With No Cryoprotectant Accumulation Underlies Cold Tolerance of the European Grapevine Moth

The European grapevine moth, Lobesia botrana (Denis et Schiffermuller), is a serious invasive pest that causes significant losses to the flowers and fruits of grapes in most of the world. This multivoltine pest passes the winter as the third-generation diapausing pupa. The current study was designed to compare nondiapausing (first and second generations) and diapausing pupae (third generation) and to investigate the relationship among cold tolerance, the supercooling point (SCP), and diapause development of the third-generation diapausing pupae. The lethal temperatures (LTs) for the three generations were determined using 24-h exposure at subzero temperatures. The mean SCP of the pupae was estimated at approx. -22.6°C, the lowest level of which (-23.7°C) was recorded in the well-developed diapausing pupae in February. The highest level of cold tolerance was also recorded in February. There were no significant differences among the temperatures required to kill 30, 50, and 90% of the pupae. The temperatures significantly decreased from October onward and reached the lowest levels in February during which the lowest SCP and the highest cold tolerance were observed in the diapausing pupae. No significant differences were found in the cryoprotectant levels, among the diapausing and nondiapausing pupae, and the diapause development. The highest activity of cAMP-dependent protein kinase (AMPK) was recorded in the late diapause in February. The findings suggested a relationship among SCP depression, cold tolerance enhancement, and diapause development. A bimodal cold-tolerance strategy (freeze-intolerant and freeze-tolerant) was found to be a feature of the pupae.

Balance between oxidative stress and the antioxidant system is associated with the level of cold tolerance in sweet potato roots

Abstract The balance between oxidative stress and antioxidant defense system was investigated in roots of the cold-sensitive (cvs. BRS Rubissol and BRS Cuia) and cold-tolerant (cv. Beauregard) sweet potato stored at 6 or 13 °C for 60 d. We hypothesized that the absence of chilling injury symptoms on cv. Beauregard stored at 6 °C depends on the induction capacity of enzymatic and non-enzymatic antioxidant systems. The manifestation of chilling injury symptoms on cvs. BRS Rubissol and BRS Cuia were associated with the loss of membrane integrity, increased lipid peroxidation, accumulation of hydrogen peroxide (H2O2), and low catalase (CAT) and ascorbate peroxidase (APX) activities. In these cold-sensitive cultivars, proline and total phenolics increased with the progression of chilling injury, acting as markers for cold sensitivity, and parallel increased activity of phenylalanine ammonia-lyase. In contrast, constitutive levels of enzymatic and non-enzymatic antioxidants, as well as stress-induced increased CAT and APX activity played an important role in the detoxification of H2O2 in the tolerant cv. Beauregard. Our results suggest that the balance between oxidative stress and antioxidant system is involved in the tolerance of cv. Beauregard to chilling injury.

Physiological response of Xinjiang wild walnut germplasm to low temperature stress

We examined the physiological response of 1-year-old branches of 37 Xinjiang wild walnut germplasm resources in Gongliu wild walnut forest under cold temperatures (-20 ℃ and 4 ℃) for 12 hours, compared the responses with that of Juglans mandshurica. The relative conductivity (REC), free proline (PRO), soluble sugar (SS), malondialdehyde (MDA) content and peroxidase (POD) activity were measured in an artificial climate chamber by simulating spring low temperature. Subordinate function and principal component analysis were used to evaluate the physiological response of walnut germplasm to low temperature. The results showed that the REC, PRO, SS, MDA content and POD activity of Xinjiang wild walnut were increased. By evaluating the relationship between low temperature resistance and habitat, we found that cold tolerance level was middle valley > east valley > west valley > general valley. Xinjiang wild walnut showed stronger cold tolerance than J. mandshurica. Seven germplasm with cold resistance were selected from the total 37 wild walnut germplasm in Xinjiang, which provided a reference for improving walnut varieties and their responses to sudden weather change in late spring and other growing stages.

A method for evaluating cold tolerance in rice during reproductive growth stages under natural low-temperature conditions in tropical highlands in Kenya

ABSTRACT Cold tolerance of New Rice for Africa (NERICA) and their parent varieties was evaluated under natural air temperature conditions of Kenyan tropical highlands using the multiple-sown field evaluation method. Rice varieties were cultivated 10 times to expose them to a shift in temperature during 20-day periods before heading (critical period), measuring the average daily mean temperature during the critical period (Tmean) for each variety and filled grain ratio, which was used as an indicator of cold tolerance. Tmean of each variety was low in 6 out of 10 experiments. In the remaining four high-temperature experiments, there were no significant varietal differences in filled grain ratio. In the six low-temperature experiments, all varieties experienced 20.1−21.5°C Tmean. After comparison under virtually the same cold stress, NERICA 1, 3, 4, 7−10, 12, 17, 18, and WAB 56–104 were judged as cold-tolerant; NERICA 2, 5, 11, 13, and 14, and WAB 56–50 and 181–18 were moderately tolerant, and NERICA 6, 15, and 16 were cold-susceptible varieties. These evaluations generally corresponded with previous experimental results under temperature-controlled environments, showing the practicality of multiple-sown field cold tolerance evaluation in Kenya. It also indicated that NERICA varieties, which recorded different levels of cold tolerance and whose average number of days to heading in all experiments were 66−78, are suitable as a set of standard check varieties in this region to evaluate cold tolerance of rice varieties with this range of days to heading.

ITRAQ-based quantitative proteomics analysis of cantaloupe (Cucumis melo var. saccharinus) after cold storage

BackgroundCantaloupe is susceptible to cold stress when it is stored at low temperatures, resulting in the loss of edible and commercial quality. To ascertain the molecular mechanisms of low temperatures resistance in cantaloupe, a cold-sensitive cultivar, Golden Empress-308 (GE) and a cold-tolerant cultivar, Jia Shi-310 (JS), were selected in parallel for iTRAQ quantitative proteomic analysis.ResultsThe two kinds of commercial cultivars were exposed to a temperature of 0.5 °C for 0, 12 and 24 days. We found that the cold-sensitive cultivar (GE) suffered more severe damage as the length of the cold treatment increased. Proteomic analysis of both cultivars indicated that the number of differentially expressed proteins (DEPs) changed remarkably during the chilly treatment. JS expressed cold-responsive proteins more rapidly and mobilized more groups of proteins than GE. Furthermore, metabolic analysis revealed that more amino acids were up-regulated in JS during the early phases of low temperatures stress. The DEPs we found were mainly related to carbohydrate and energy metabolism, structural proteins, reactive oxygen species scavenging, amino acids metabolism and signal transduction. The consequences of phenotype assays, metabolic analysis and q-PCR validation confirm the findings of the iTRAQ analysis.ConclusionWe found that the prompt response and mobilization of proteins in JS allowed it to maintain a higher level of cold tolerance than GE, and that the slower cold responses in GE may be a vital reason for the severe chilling injury commonly found in this cultivar. The candidate proteins we identified will form the basis of future studies and may improve our understanding of the mechanisms of cold tolerance in cantaloupe.

Is rapid cold-hardening an aerobic process? Characterization of changes in metabolic activity during its induction and effects of anoxia in flesh fly

Rapid cold-hardening (RCH) is a type of phenotypic plasticity that promotes a swift improvement of cold tolerance in insects. A brief exposure to mild cold dramatically increases insect survival to a subsequent cold exposure that would be lethal otherwise. In adult male flesh fly, Sarcophaga bullata, as little as 15 min at 5 °C significantly improved organismal survival at −7°C from 0 to 66.7 ± 11.1%. In this study, we investigated whether this RCH response is an aerobic process in S. bullata by characterizing changes in metabolic activity during its induction. At the level of whole organism, CO2 production continued at a level above our detection limit, and a relatively greater rate was observed during the early phase before it stabilized after ~1 h of the RCH induction. Similarly, in isolated flight muscle tissues, those maintained at 5 °C for 10 min exhibited significantly greater rates of oxygen consumption, compared to those maintained at 5 °C for 1 h (2.82 ± 0.29 vs. 1.36 ± 0.22 μl O2 mg−1 DM h−1). When these tissues were exposed to LaCl3, a treatment that should inhibit RCH ex vivo, oxygen consumption rates of the muscles were reduced significantly to a level similar to those that had been maintained at 5 °C for 1 h. Interestingly, however, the RCH response was still evident among individuals exposed to chilling under anoxia. Compared to those exposed to anoxia for 30 min only at 25 °C, flies exposed to 5 °C for 2 h under anoxia following the initial exposure exhibited a significantly greater level of cold tolerance at −7.5 °C (41.7 ± 7.1 vs. 91.8 ± 3.9%). Our results suggest that while relatively greater rates of metabolic activity are associated with the early phase of the RCH induction, it can proceed under the anoxic condition, thereby suggesting its independence to aerobic respiration.

Vacuolar sucrose cleavage prevents limitation of cytosolic carbohydrate metabolism and stabilizes photosynthesis under abiotic stress.

Stabilization of central carbohydrate metabolism plays a key role in plant stress response. Carbohydrates are substrate for numerous metabolic and stress-responsive reactions and have been shown to be involved in diverse signalling processes on a whole-plant level. Regulation of enzymatic sucrose synthesis and degradation is well-known to be central to many stress-related processes as it significantly impacts stress tolerance. Leaf sucrose metabolism involves sucrose cleavage by invertases and ATP-consuming resynthesis catalysed by hexokinase and sucrose phosphate synthase. These reactions establish a metabolic cycle. To study the physiological role of sucrose cycling, a kinetic model was developed to simulate dynamics of subcellular sugar concentrations in Arabidopsis thaliana under combined cold and high-light stress. Model simulation revealed that subcellular reprogramming of invertase-driven sucrose cleavage varies substantially between natural accessions of Arabidopsis which differ in their cold tolerance levels. A stress-induced shift of sucrose cleavage from the cytosol into the vacuole could only be observed for the tolerant accession while the susceptible accession increased the cytosolic proportion of sucrose cleavage. Under stress, reduction in vacuolar invertase activity significantly affected maximum quantum yield of photosystem II and CO2 assimilation rates. While wild-type plants circumvented a limitation of sucrose cleavage by increasing vacuolar invertase activity, mutant plants were not able to compensate their deficiency of vacuolar by cytosolic activity. Consequently, the capacity for cytosolic hexose generation was lower than for enzymatic hexose phosphorylation suggesting a role of vacuolar invertase activity in preventing a limitation in cytosolic hexose metabolism under stress. ENZYMES: Invertase, EC 3.2.1.26; Hexokinase, EC 2.7.1.1.

Trait collection of rice by cold tolerance

Goal. To assess rice cultivars for cold tolerance; to select the most valuable in terms of economic characteristics sources for their further use in breeding; to create a trait collection on their basis.Result and Discussion. The article presents the results of studying a rice collection. The collection material is represented by 51 accessions of different eco-geographical origin (European, Eastern, Mid-Asian, Latin American). The accessions belong to two subspecies: japonica and indica. Most of the accessions (22) are from Ukraine and account for 43.1%. Temperature is one of the most important environmental factors affecting the crop establishment and development. In Ukraine, rice is cultivated in the most northern zone of rice growing and, therefore, it is liable to negative effects of cold weather during the seed germination, sprouting, anthesis and grain ripening. Consequently, it is essential for breeders to create cultivars that will be tolerant to low temperatures during the sprouting period, with high field germinability and increased germinative power. Seed germination is particularly affected by temperature. Fifty one rice cultivars were investigated for the seedling development, seed germination rate and seedling growth intensity at 14°C; possible states of embryonic roots were estimated; lengths of these stages were determined. Selection of material with a set of parameters allowed forming a trait collection with increased levels of resistance to abiotic environmental factors. In breeding, it is very important to identify sources of valuable traits and to assess extent of their influence on the plant performance. The research distinguished rice accessions for breeding by levels of cold tolerance, performance and its components. We selected six donors of several valuable traits, the use of which will enhance the breeding efficiency (Kuban 3, Vikont, UkrNDS 8839, Ontario, VNIIR 546, Kaz ER – 6). Thus, the comprehensive assessment of the accessions allowed us not only to replenish the rice gene pool, but also, basing on this research, to choose starting material to involve it in further breeding for creating new cold-tolerant varieties. While creating such cultivars, we revealed morphological traits of rice, which are used as test parameters characterizing the stress tolerance of accessions.Conclusions. The study resulted in formation of the trait collection representing the genetic diversity of cultivars and breeding lines. Each trait and gradation has corresponding standards. Cultivars-standards reflect more specific and stable expression of a trait. The collection was created by 4 basic traits and 3 gradations and contains accessions from 9 countries (Ukraine, Russia, Kazakhstan, Uzbekistan, Kyrgyzstan, USA, Bulgaria, China, and Hungary). The standard accessions selected can serve as sources of economically valuable features to create starting material for breeding.

ارزیابی تحمل به سرمای گیاه خاکشیر (L. Descurainia Sophia) تحت شرایط کنترل شده

Introduction Flixweed is an annual dicotyledonous winter herb from Cruciferae (Brassicaceae) family which grows in many countries of the world. In Iran it is seen in many of wheat and canola producing regions. Flixweed is used for healing a variety of diseases such as measles and smallpox, cough, asthma, edema and tumor. It also has diuretic, anticancer, antipyretic, antioxidant, anthelmintic, analgesic and tonic activities [2]. In temperate and cold regions of Iran, winter cold is one of the most important environmental stresses which affect growth, development and yield of plants. So determination and improvement of freeze tolerance of winter plants such as Flixweed might promote their cultivation and utilization in cold regions. At present measuring the survival after a recovery period which is followed by a freezing test in controlled conditions is a common method for determining the level of plants freeze tolerance. Calculation of LT50 point or critical temperature based on survival percentage of plant is considered as a quantitative and simple method for evaluating the cold tolerance [1]. But sometimes this criterion is not enough alone and other indices (for example dry weight and Reduced dry matter temperature 50% of plants (RDMT50)) are used to achieve a more accurate estimation of cold tolerance level [3]. In spite of numerous medicinal and industrial properties of Flixweed, there is not a lot of information about freeze tolerance of this plant, so the objective of this study was evaluating the freeze tolerance of Flixweed by survival % and some of growth traits after recovery period. Materials and methods In order to evaluate freeze tolerance in some of Flixweed, a factorial experiment was conducted based on completely randomized design with three replications in faculty of agriculture, Ferdowsi University of Mashhad in autumn of 2009. Experimental factors include five ecotypes of Flixweed (Eghlid, Sabzewar, Hamedan, Torbat-e-Jam and Neyshabour) and 10 freezing temperature levels (from zero to -18 with 2 °C intervals). For this aim, Flixweed seeds were cultivated in pot in autumn and they were grown in natural weather until 5-7 leaf stage. Afterward for applying freezing temperatures, plants were transferred to a thermo gradient freezer. The initial temperature of programmable freezer was 5°C; but gradually decreased in a rate of 2°C.h-1 until reached to desired temperatures. When the freezer temperature reached to -2°C, the plants were treated by the Ice Nucleation Active Bacteria (INAB) to help the formation of ice nuclei in them, also to prevent from super-cooling of samples and to ensure that the mechanism of freeze resistance is tolerance not avoidance. After artificial freezing stress applying (which lasted up to two hours for each freezing temperature); Flixweed seedlings were transferred to greenhouse for recovery. Three weeks after freezing stress, survival percentage (SU %), Lethal temperature for 50% of plants according to the survival% (LT50su), number of leaf and reduced number of leaf temperature 50% (RNLT50), number of node and reduced number of node temperature 50% (RNNT50), dry weight and reduced dry matter temperature 50% (RDMT50) were evaluated. Analysis of variance was performed by MSTAT-C software and correlations between data were carried out by MINITAB 16 program. Mean separation was conducted by least significant difference (LSD) test at 1% probability level. Results and Discussion Results showed that Hamedan ecotype had the highest SU% and Neyshabour ecotype had the lowest SU%. In Eghlid and Neyshabour ecotypes, decline of SU% begun from higher temperarures (-8 °C) compared with other ecotypes (-10 °C). This trend was seen for dry weight and number of leaf too. At -12 °C, number of node in Hamedan ecotype decreased 30% approximately than control, while in Eghlid and Neyshabour ecotypes, this reduction was much higher. In this experiment LT50su ranged between -10.2 to -12.1 °C depending on the ecotypes. Ranking of Flixweed ecotypes according to the LT50su, RNLT50, RNNT50 and RDMT50 indices showed that the Neyshabour and Hamedan ecotypes were the most sensitive and tolerant Flixweed ecotypes to freezing stress respectively. In this survey, there was high and positive correlation between survival percentage and dry weight (r=0.69***), in addition there was negative and significant relationship between SU%, LT50su and RNNT50 (r=-0.67*** and r=-0.82*** respectively). Conclusion According to these results, it seems that temperature threshold for winter injury happening in Flixweed is -12 °C. Despite this for better understanding of cold tolerance of Flixweed, further researches are required under controlled and field conditions.