Chilling Temperature Research Articles

A Conceptual Framework for Winter Dormancy in Deciduous Trees

The perennial life strategy of temperate trees relies on establishing a dormant stage during winter to survive unfavorable conditions. To overcome this dormant stage, trees require cool (i.e., chilling) temperatures as an environmental cue. Numerous approaches have tried to decipher the physiology of dormancy, but these efforts have usually remained relatively narrowly focused on particular regulatory or metabolic processes, recently integrated and linked by transcriptomic studies. This work aimed to synthesize existing knowledge on dormancy into a general conceptual framework to enhance dormancy comprehension. The proposed conceptual framework covers four physiological processes involved in dormancy progression: (i) transport at both whole-plant and cellular level, (ii) phytohormone dynamics, (iii) genetic and epigenetic regulation, and (iv) dynamics of nonstructural carbohydrates. We merged the regulatory levels into a seasonal framework integrating the environmental signals (i.e., temperature and photoperiod) that trigger each dormancy phase.

SMRT sequencing of a full-length transcriptome reveals transcript variants involved in C18 unsaturated fatty acid biosynthesis and metabolism pathways at chilling temperature in Pennisetum giganteum

BackgroundPennisetum giganteum, an abundant, fast-growing perennial C4 grass that belongs to the genus Pennisetum, family Poaceae, has been developed as a source of biomass for mushroom cultivation and production, as a source of forage for cattle and sheep, and as a tool to remedy soil erosion. However, having a chilling-sensitive nature, P. giganteum seedlings need to be protected while overwintering in most temperate climate regions.ResultsTo elucidate the cold stress responses of P. giganteum, we carried out comprehensive full-length transcriptomes from leaf and root tissues under room temperature (RT) and chilling temperature (CT) using PacBio Iso-Seq long reads. We identified 196,124 and 140,766 full-length consensus transcripts in the RT and CT samples, respectively. We then systematically performed functional annotation, transcription factor identification, long non-coding RNAs (lncRNAs) prediction, and simple sequence repeat (SSR) analysis of those full-length transcriptomes. Isoform analysis revealed that alternative splicing events may be induced by cold stress in P. giganteum, and transcript variants may be involved in C18 unsaturated fatty acid biosynthesis and metabolism pathways at chilling temperature in P. giganteum. Furthermore, the fatty acid composition determination and gene expression level analysis supported that C18 unsaturated fatty acid biosynthesis and metabolism pathways may play roles during cold stress in P. giganteum.ConclusionsWe provide the first comprehensive full-length transcriptomic resource for the abundant and fast-growing perennial grass Pennisetum giganteum. Our results provide a useful transcriptomic resource for exploring the biological pathways involved in the cold stress responses of P. giganteum.

Elucidating the regulatory roles of microRNAs in maize (Zea mays L.) leaf growth response to chilling stress.

MAIN CONCLUSION: miRNAs control leaf size of maize crop during chilling stress tolerance by regulating developmentally important transcriptional factors and sustaining redox homeostasis of cells. Chilling temperature (0-15°C) is a major constraint for the cultivation of maize (Zea mays) which inhibits the early growth of maize leading to reduction in leaf size. Growth and development take place in meristem, elongation, and mature zones that are linearly located along the leaf base to tip. To prevent shortening of leaf caused by chilling, this study aims to elucidate the regulatory roles of microRNA (miRNA) genes in the controlling process switching between growth and developmental stages. In this respect, hybrid maize ADA313 seedlings were treated to the chilling temperature which caused 26% and 29% reduction in the final leaf length and a decline in cell production of the fourth leaf. The flow cytometry data integrated with the expression analysis of cell cycle genes indicated that the reason for the decline was a failure proceeding from G2/M rather than G1/S. Through an miRNome analysis of 321 known maize miRNAs, 24, 6, and 20 miRNAs were assigned to putative meristem, elongation, and mature zones, respectively according to their chilling response. To gain deeper insight into decreased cell production, in silico, target prediction analysis was performed for meristem specific miRNAs. Among the miRNAs, miR160, miR319, miR395, miR396, miR408, miR528, and miR1432 were selected for confirming the potential of negative regulation with their predicted targets by qRT-PCR. These findings indicated evidence for improvement of growth and yield under chilling stress of the maize.

Quality of vacuum packaged beef as affected by aqueous ozone and sodium citrate treatment

ABSTRACT This study was targeted to investigate the effect of the combination of aqueous ozone (AO) and sodium citrate (SC) pretreatment on quality of vacuum packaged beef stored at chilling temperature. The steers were randomly divided into five treatment groups, containing the group C (steers without any treatment), DW (steers pretreated with distilled water), AO, SC and AO+SC. During processing, the parameters included total Viable Count (TVC), total Volatile Basic Nitrogen (TVB-N), pH, meat color, metmyoglobin (Met-Mb), thiobarbituric acid reactive substances (TBArs), Warner–Bratzler shear force (WBSF), and purge loss were measured and compared. Firstly, the TVC in beef steaks of group AO+SC was significantly lower than group AO and SC during the whole storage (P < .05). In addition, the TVB-N values in AO+ SC group were significantly decreased than AO group at the end of storage time. Furthermore, compared with the group only treated by AO, the group AO+SC displayed higher L* (lightness) value, lower a* (redness) value and lower Met-Mb. The values of WBSF and purge loss of group AO+SC was lower than group AO, as well as TBArs. The treatment methods and storage time had significant interactive effects on TVC, TVB-N, pH, L*, Met-Mb, and TBArs (P < .05). The combination treatment of AO and SC showed better effect on inhibiting the microbial growth and decreased the deteriorated effect of AO on beef quality including TBArs, WBSF, and purge loss.

Crystallization Kinetics of Composite Materials Based on Polyethylene Mixture with High and Low Density

The influence of the ratio of high-density polyethylene and low-density polyethylene on the regular changes in breaking stress, tensile yield stress, elongation, and chilling temperature of composite materials are considered. In accordance with the Avrami equation, the formation and development of crystallization centers in a zone of the first-order phase transition are investigated.

Shelf Life of Tilapia (Oreochromis niloticus) Dumplings with addition of Bagasse Liquid Smoke during Storage at Chilling Temperature (±5°C)

Tilapia (Oreochromis niloticus) can be used to process fish dumplings. Tilapia dumplings are susceptible to microbiological quality deterioration so that the shelf life is low. The liquid smoke of bagasse contains phenol, acid, and carbonyl that can be used as natural preservatives to extend the shelf life of fish dumplings. The aim of this study was to determine the effect of adding bagasse liquid smoke to the quality and shelf life of tilapia dumplings by treating the concentration of liquid smoke stored in chilling temperatures (±5°C). The material used tilapia and bagasse liquid smoke. The experimental method used split-plot in time 2 factors, differences concentration of liquid smoke (0% and 2.5%) and storage time (0, 5, 10, 15, 20 days) with 3 repetitions. The testing parameters of fish dumplings are a sensory test, total phenol, TPC, TVBN, and pH. Non-parametric data were analyzed using Kruskal-Wallis and Mann-Whitney for further test. Parametric data were analyzed using ANOVA and BNJ for further test. The result shows that tilapia dumplings without the addition of liquid smoke rejected on the 10th day with a sensory value 5.63±0.47; total phenol 102.04±0.00; TPC 5.2×104±0.01CFU/g; and pH 7.42±0.08 while according TVBN value rejected on the 5th day with 15.13±0.64 mg/100g. Tilapia dumplings with addition of 2,5% liquid smoke rejected on the 15th day with an sensory value 5.87±0.45; total phenol 116.85±0.01; TPC 5.4×104±0.01CFU/g; TVBN 18.82±0.84 mg/100g and pH 7.33±0.10. Bagasse liquid smoke can increase the shelf life of tilapia dumplings up to 10 days during chilling storage.

Quality changes of little tuna fillet (Euthynnus affinis) during chilling temperature storage

Deterioration of fish quality affects the accumulation of metabolites, flavor changes, the formation of volatile components, as well as an increase in the number of bacteria. Chilling temperature storage is the way to maintain the quality of fish. This research was aimed to determine quality changes of little tuna (Euthynnus affinis) through organoleptic test, chemical properties and protein analysis during chilling temperature storage. Observations were conducted every 48 hours for 14 days. The parameters observed were proximate, organoleptic, pH, water-soluble protein, metmyoglobin level, and its molecular weight. Little tuna was still in fresh criteria on the 4th day with organoleptic value of 7 and was spoiled on the 10th day. The chemical composition of the fish changed during storage, increased in moisture content, decreased protein levels, and increased ash content. The values of water-soluble protein decreased during the storage while the metmyoglobin level increased during storage. In conclusion, little tuna suffered a setback in quality during 14 days of chilling temperature storage. The storage time influenced the level of water-soluble protein and the level of metmyoglobin produced.

Performance test & analysis on fan coil unit and improved induction air unit system

Induction air unit was improved by decreasing the induction ratio and adding the rectifier. Performance test on fan coil unit and improved induction air unit system was carried in the model houses. Test results showed: (1) Induction air unit system could meet the temperature requirement of room. It had a strong dehumidifying ability and much uniformity air velocity in the range of comfortable. (2) Induction air unit system had little temperature gradient and difference. (3) The unit was energy efficient combined with the extensive air handling unit and medium temperature chiller. Improved induction air unit would be used in the high quality air conditioning spaces.

Seed Priming with Melatonin Improves the Seed Germination of Waxy Maize under Chilling Stress via Promoting the Antioxidant System and Starch Metabolism

Chilling stress is one of the major abiotic stresses affecting waxy maize plant growth. Melatonin (MT) is able to improve tolerance to abiotic stress in plants. To investigate the effects of seed priming with MT on tolerance to chilling stress in waxy maize, the seed germination characteristics and physiological parameters were tested with varied MT concentrations (0, 50, 100 µM) and treatment times (12, 24 h) at ambient (25 °C) and chilling (13 °C) temperature. MT primed seeds significantly enhanced the germination potential (by 20.29% and 50.71%, respectively), germination rate (by 20.88% and 33.72%), and increased the radicle length (by 90.73% and 217.14%), hypocotyl length (by 60.28% and 136.14%), root length (by 74.59% and 108.70%), and seed vigor index (46.13%, 63.81%), compared with the non-priming seeds under chilling stress. No significant difference was found in priming time between primed and non-primed seeds. In addition, lower H2O2 and malondialdehyde concentrations, increased antioxidant enzyme activities (superoxide dismutase, peroxidase, catalase and ascorbateperoxidase), and promoted starch metabolism were found in primed seeds compared to non-primed ones. It was suggested that seed priming with MT improved waxy maize seed germination under chilling stress through improving antioxidant system and starch metabolism, which protected from oxidative damage.

Comparative Study on Farm Materials and Quality Parameters of Pangus (Pangasianodon hypophthalamus) of Different Farms in Trishal Area

The present study was conducted to carry out a comparative study on farm materials (water, soil, feed) and the quality parameters of pangus (Pangasianodon hypophthalamus) of five different farms in Trishal area under Mymensingh district. The study was carried out during May-June, 2016. Most of the pangus farmers used homemade or farm made supplementary feeds for pangus culture The percent moisture, protein, lipid and ash content in fresh fish ranged from 77.05 to 78.79, 14.21 to14.84, 3.55 to 4.49 and 2.03 to 2.67 whereas after 24 hrs of death of fishes, these percent values changed as 77.05 to 78.79, 14.21 to14.84, 3.55 to 4.49 and 2.03 to 2.67. Slight changes observed in different quality parameters in the fish samples 24 hrs after death as dead fishes were preserved at chilling temperature in a homestead refrigerator till analysis. Therefore, the study could be concluded that- though the values for different parameters of farm materials (water, soil, feed) and quality parameters of fish samples differed but was mostly not significant. The differences observed in the parameters might be due to the variations in management techniques of each farm.&#x0D; J. Environ. Sci. &amp; Natural Resources, 11(1-2): 109-119 2018

Regulation of carbon metabolism in two maize sister lines contrasted for chilling tolerance.

Maize can grow in cool temperate climates but is often exposed to spring chilling temperatures that can affect early seedling growth. Here, we used two sister double-haploid lines displaying a contrasted tolerance to chilling to identify major determinants of long-term chilling tolerance. The chilling-sensitive (CS) and the chilling-tolerant (CT) lines were grown at 14 °C day/10 °C night for 60 d. CS plants displayed a strong reduction in growth and aerial biomass compared with CT plants. Photosynthetic efficiency was affected with an increase in energy dissipation in both lines. Chilling tolerance in CT plants was associated with higher chlorophyll content, glucose-6-phosphate dehydrogenase activity, and higher sucrose to starch ratio. Few changes in cell wall composition were observed in both genotypes. There was no obvious correlation between nucleotide sugar content and cell wall polysaccharide composition. Our findings suggest that the central starch-sucrose metabolism is one major determinant of the response to low temperature, and its modulation accounts for the ability of CT plants to cope with low temperature. This modulation seemed to be linked to a strong alteration in the biosynthesis of nucleotide sugars that, at a high level, could reflect the remobilization of carbon in response to chilling.

Early detection of eggplant fruit stored at chilling temperature using different non-destructive optical techniques and supervised classification algorithms

Eggplant fruit is a chilling injury sensitive vegetable and should not be stored at lower than 12 °C postharvest, although fruit are often placed in temperatures as low as 0–5 °C. For this reason, a rapid early detection of eggplants previously stored at chilling temperatures would allow early removal of those fruit from the market. Eggplant fruit (cv. Fantasy) were stored either at 2 °C (chilling injurious temperature) or at 12 °C (safe storage temperature) for 10 days. Every 2 days, fruit from each group were sampled and left at room temperature, for one additional day. Color measurements in the CIE L*a*b* mode and reflectance data in the wavelength range 360–740 nm, Fourier Transform (FT)-NIR spectra (800–2777 nm) and hyperspectral images at the visible (400–1000 nm) and near infrared (900–1700 nm) part of the electromagnetic spectrum were also acquired on each fruit. Three supervised algorithms; partial least square (PLS), supervised vector machine (SVM) and k-nearest neighbor (kNN) were applied to classify fruit according to the storage temperature. Chilling injury (CI) was subjectively evaluated, according to the presence of black seeds or of brown discolored flesh area. According to the results, although chilling injury symptoms started being evident only after the 4th day of storage at 2 °C, it was possible to discriminate fruit earlier, since day 2, by processing the FT-NIR spectral data with the SVM classifier (100 and 92% non-error-rate (NER)) in calibration and cross validation, respectively) in the whole period data set. Color or FT-NIR spectral data classified with PLSDA permitted relatively good classification of fruit (>83% accuracy) since the 4th day of storage, while L, C, H° color measurements or Vis-NIR hyperspectral imaging data combined with PLSDA generate trustworthy models only after the 6th day of storage. On the other hand, NIR hyperspectral imaging technique and kNN classification algorithm were incapable to separate the fruit either accurately or consistently. These results indicate a good potential of adapting selected protocols, in terms of technique, processing of the raw data and supervised classification algorithm, in order to minimize postharvest losses induced by the improper temperature management of chilling sensitive fruit, such as the eggplants.

Sensitivity analysis of tree phenology models reveals increasing sensitivity of their predictions to winter chilling temperature and photoperiod with warming climate

The phenology of plants is a major driver of agro-ecosystem processes and biosphere feedbacks to the climate system. Phenology models are classically used in ecology and agronomy to project future phenological changes. With our increasing understanding of the environmental cues affecting bud development, phenology models also increase in complexity. But, we expect these cues, and the underlying physiological processes, to have varying influence on bud break date predictions depending on the specific weather patterns in winter and spring. Here, we evaluated the parameter sensitivity of state-of-the-art process-based phenology models that have been widely used to predict forest tree species phenology. We used sensitivity analysis to compare the behavior of models with increasing complexity under specific climatic conditions. We thus assessed whether the influence of the parameters and modeled processes on predictions varies with winter and spring temperatures. We found that the prediction of the bud break date was mainly affected by the response to forcing temperature under current climatic conditions. However, the impact of the parameters driving the response to chilling temperatures and to photoperiod on the prediction of the models increased with warmer winter and spring temperatures. Interaction effects between parameters played an important role on the prediction of models, especially for the most complex models, but did not affect the relative influence of parameters on bud break dates. Our results highlighted that a stronger focus should be given to the characterization of the reaction norms to both forcing and chilling temperature to predict accurately bud break dates in a larger range of climatic conditions and evaluate the evolutionary potential of phenological traits with climate change.

Study of an integrated radiant heating/cooling system with fresh air supply for household utilization

With the increasing demand for indoor thermal comfort in recent years, radiant heating & cooling systems have been very popular in China. However, for the household air-conditioning in hot-summer and cold-winter regions, an effective solution of heating and cooling source supply for radiant air-conditioning system remains to be developed. In this paper, an energy-efficient radiant heating/cooling system with fresh air supply is proposed and investigated for household utilization numerically. Under summer conditions, dehumidified fresh air supply is a tough problem in radiant cooling since the chilling water temperature for radiant cooling is much higher than traditional air-conditioning systems. In the proposed system, the fresh air handling unit is composed of both pre-cooling dehumidification coil and liquid desiccant dehumidifier, where high-temperature chilling water is used for cooling source and small part of condensing heat is used for liquid desiccant regeneration. The results indicated that the fresh air can be steadily supplied and sufficiently dehumidified for indoor air quality and humidity control. The chilling water flow rate in pre-cooling coil (mw,coil) and the solution flow rate from regenerator to dehumidifier (ms,SS) can be recognized as control parameters to reliably regulate the indoor air humidity. The load ratio of sensible heat to latent heat had no significant impact on COPsys, which means the system can operate with a steady energy efficiency despite of the indoor heat load. Satisfactory energy-saving potential was revealed in the proposed system with a COP improvement of 25.8%–30.1% compared to the conventional system under typical summer conditions in Nanjing.

Investigating the impact of chilling temperature on male Aedes aegypti and Aedes albopictus survival

In genetic control programmes, including the sterile insect technique (SIT), it is crucial to release insects of the highest quality with maximum survival. It is likely that male mosquitoes will follow the trend of other insects in SIT programmes and be stored, transported and eventually released under chilled conditions. The aim of our study was to investigate the impact of different chilling temperatures on male Aedes aegypti and Ae. albopictus survival by exposing them to a range of temperatures for different durations. Ae. aegypti were found to be less sensitive to the impact of chilling, with only 6°C causing a marginal decrease in survival in comparison to non-chilled controls. Conversely, Ae. albopictus displayed a significantly reduced survival at all chilling temperatures even when exposed for a short time. In both species, longer exposure to low temperatures reduced survival. Our results uncovered that Ae. albopictus are more sensitive to chilling, regardless of the temperature, when compared to Ae. aegypti. Such results indicate differences in thermal tolerances between species and the necessity of conducting experiments on a species by species basis when determining temperature limits for any insect destined for release as part of a genetic control programme.

Comparative Transcriptome Analyses Revealed Conserved and Novel Responses to Cold and Freezing Stress in Brassica napus L.

Oil rapeseed (Brassica napus L.) is a typical winter biennial plant, with high cold tolerance during vegetative stage. In recent years, more and more early-maturing rapeseed varieties were planted across China. Unfortunately, the early-maturing rapeseed varieties with low cold tolerance have higher risk of freeze injury in cold winter and spring. Little is known about the molecular mechanisms for coping with different low-temperature stress conditions in rapeseed. In this study, we investigated 47,328 differentially expressed genes (DEGs) of two early-maturing rapeseed varieties with different cold tolerance treated with cold shock at chilling (4°) and freezing (−4°) temperatures, as well as chilling and freezing stress following cold acclimation or control conditions. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that two conserved (the primary metabolism and plant hormone signal transduction) and two novel (plant-pathogen interaction pathway and circadian rhythms pathway) signaling pathways were significantly enriched with differentially-expressed transcripts. Our results provided a foundation for understanding the low-temperature stress response mechanisms of rapeseed. We also propose new ideas and candidate genes for genetic improvement of rapeseed tolerance to cold stresses.

Enzymatic activities of curry leaves (Murraya koenigii L.) during storage in chilling temperature

Curry leaves are highly susceptible to chilling injury (CI) under prolonged storage at 4-8°C. CI in plants is a complicated process interconnected through several biochemical reactions especially enzymatic activities. Present study monitored the activities of polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL), lipoxygenase (LOX), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) in curry leaves stored at 4°C under perforated LDPE packaging (100 g package‑1). Leaves without packaging served as control. Surface colour (L*, a*, and b*), electrolytic leakage, chlorophyll content, total phenolic content (TPC) and total antioxidant activity (TAA) were measured in leaf samples. Samples were analysed every 3 days for 15 days. Prolonged chilling temperature induced CI in curry leaves. Leaf surface colour such as (L* and b*) gradually decreased while leaf redness (a*) gradually increased, reflecting browning enzymatic activities and chlorophyll degradation. Electrolytic leakage was severe in control leaves. TPC influenced the TAA activities in curry leaves, and the values tended to decrease with time (P<0.05). During the initial storage period (0-8 days), enzymatic activities remained constant but increased markedly during 9-15 days at 4°C. LOX increased in control leaves throughout storage, and as a consequence, PPO, POD and PAL activities were also higher in control. Similarly, SOD, CAT, and GPX were also found higher in control, indicating that prolonged chilling increased reactive oxygen species in control samples. The LDPE package that acted as a barrier between the package and samples and slightly reduced the CI in curry leaves.

Heat treatment effects on chilling injury and disease incidence in sweet orange fruits stored at chilling and non-chilling temperatures

Citrus chilling injury causes 25% postharvest losses by shortening its storage life and lowers its market value in developed countries. In citrus fruits, chilling injury is characterized by increased moisture loss and disease susceptibility. The present study was conducted with the objective to evaluate the effects of pre-storage heat treatments (HTS: control, 5, 10, 15 and 20 min), heat treatment methods (HTM: wet heat treatment [WHT], vapor heat treatment [VHT]), and exposure temperatures (ET: chilled [2.5 °C], non-chilled [10 °C]) on citrus fruits (cv. Blood Red having sour orange rootstock) during 2015–2016 at the University of Agriculture, Peshawar, Pakistan. Sweet orange fruits and fruit discs of 10 mm diameter were simultaneously treated with WHT and VHT. The heat treated fruits and fruit discs were separated into two lots. One lot was held at non-chilling temperature (10 ± 1 °C), while the other lot was exposed to chilling temperature (2.5 ± 1 °C) for 75 days and packed in fiber board packages. The fruits and fruit discs after 75 days storage at both storage temperatures (10 ± 1 °C and 2.5 ± 1 °C) were incubated at ambient temperature for 7 days (simulated marketing time) and analyzed for different chilling injury parameters. Heat treatment periods (HTS), exposure temperature (ET) and their interactions (HTS × ET) showed significant (p ≤ 0.05) differences for the majority of the traits. The interaction of HTS × HTM was significant (p ≤ 0.05) for weight loss and surface pitting. However, heat treatment methods (HTM) and interaction of ET × HTM × HTS was significant for surface pitting and weight loss, respectively. The non-chilled (10 ± 1 °C) fruits revealed lower weight loss (6.80%), surface pitting (4.40%), disease incidence (7.07%), disease expansion (3.97 mm), ion leakage (15.77%) while the ascorbic acid increased (32.38 mg 100 g−1). However, chilling (2.5 °C) triggered the increase in weight loss (8.32%), surface pitting (16.13%), disease incidence (14.59%), lesion diameter (10.37 mm) and ion leakage (27.96%) in sweet orange. Heat treatments with WHT and VHT for 5–10 min resulted in reduced weight loss (6.07%), surface pitting (3.33%), disease incidence (2.00%), disease expansion (5.00 mm) and ion leakage (20.23%) in sweet oranges. Heat treatments with WHT and VHT for 15–20 min, accelerated the fruit senescence by increasing the weight loss (8.98%), surface pitting (15.67%), disease incidence (15.33%), disease expansion (8.33 mm) and ion leakage (23.62%). In comparison to heat treatment methods, highest weight loss (7.57%), surface pitting (11.53%), ion leakage (21.94%) and disease incidence (10.86%) were recorded in VHT, whereas WHT treatments had lowest weight loss (7.55%), surface pitting (9.00%), ions leakage (21.80%) and disease incidence (10.79%). Therefore, modest WHT pre-storage heat treatment (5–10 min) is recommended for storage of sweet orange.

Chilling accumulation in fruit trees in Spain under climate change

Abstract. Growing trees are quite vulnerable to cold temperatures. To minimise the effect of these cold temperatures, they stop their growth over the coldest months of the year, a state called dormancy. In particular, endodormancy requires accumulating chilling temperatures to finish this sort of dormancy. The accumulation of cool temperatures according to specific rules is called chilling accumulation, and each tree species and variety has specific chilling requirements for correct plant development. Under global warming, it is expected that the fulfilment of the chilling requirements to break dormancy in fruit trees could be compromised. In this study, the impact of climate change on the chilling accumulation over peninsular Spain and the Balearic Islands was assessed. For this purpose, bias-adjusted results of 10 regional climate models (RCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5 were used as inputs of four different models for calculating chilling accumulation, and the results for each model were individually compared for the 2021–2050 and 2071–2100 future periods under both RCPs. These results project a generalised reduction in chilling accumulation regardless of the RCP, future period or chilling calculation model used, with higher reductions for the 2071–2100 period and the RCP8.5 scenario. The projected winter chill decrease may threaten the viability of some tree crops and varieties in some areas where the crop is currently grown, but also shows scope for varieties with lower chilling requirements. The results are relevant for planning future tree plantations under climate change, supporting adaptation of spatial distribution of tree crops and varieties in Spain.

Cool temperature caused by late planting affects seed vigor via altering kernel biomass and antioxidant metabolism in cotton (Gossypium hirsutum L.)

Cotton in double cropping systems (rapeseed-cotton or wheat-cotton) is often late-planted and experiences a much longer period of cool temperature at the late growth stage, which impairs seed quality. A two-year field experiment with two planting dates (normal and late planting date) was conducted to investigate the effects of late planting on cottonseed vigor and its relationship with seed biomass accumulation and kernel antioxidant metabolism during seed development. With the delay of planting date and the increasing height of fruiting branches, the mean daily temperature during boll period decreased from 25.9 °C to 20.7°C. Meanwhile, the seed, kernel and vigor index decreased by 2.6–12.1%, 4.7–15.0% and 2.5–16.0% respectively. The direct path coefficient of growing degree days (GDD) and the indirect path coefficients via GDD for seed, kernel and vigor index were positive and high. Seed vigor was more sensitive to the change of kernel index than seed index and the cool temperature limited the accumulation of kernel biomass mainly via reducing the maximum velocity of kernel biomass accumulation (Vmax), which led to a significant decline in seed vigor especially in the late planting date. Under cool temperature caused by late planting, the time of the maximum activity for each H2O2-scavenging enzyme was postponed with their maximum activities being decreased, which caused slow reduction in the content of malondialdehyde and H2O2 content during the late stage of seed development. In addition, peroxidase (POD) had the closest correlation with cottonseed vigor compared with catalase, ascorbate peroxidase and glutathione reductase. Altogether, low seed vigor occurred in late planting could be attributed to the decreased kernel biomass and prolonged duration of oxidative damage on membranes caused by cool temperature. The GDD of boll period is valuable for estimating cottonseed harvesting time especially under late planting conditions and seeds with high POD activity are more tolerant to cool temperature.