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Limited water availability is a major constraint to canola (Brassica napus L.) yield in the Mediterranean-type climate region. Selecting and breeding for genotypes with conservative water use characteristics is a promising strategy to improve yield in this environment. Three experiments were conducted to investigate transpiration responses (TR) to vapour pressure deficit (VPD) and progressive soil drying with 8-20 canola genotypes. We used the linear-plateau model to describe TR to elevated VPD and decreased fraction of transpirable soil water (FTSW) and identified the VPD and FTSW thresholds for plant to limit its transpiration. Canola genotypes showed significant variations in both VPD and FTSW thresholds. The genotypes with conservative water use reduced TR at a lower VPD threshold and decreased TR at a higher FTSW threshold than the profligate ones. We found that the conservative genotypes had low VPD and high FTSW thresholds while the profligate ones had high VPD and low FTSW thresholds. This conservative and profligate water use characteristics were consistent during both vegetative and reproductive stages. Furthermore, the relative yield of genotypes under drought conditions was positively related to the FTSW thresholds during the reproductive stage, indicating the better relative yield performance of conservative genotypes in water-limited farming system. We conclude that canola genotypes with lower VPD and higher FTSW thresholds could conserve water and defer water use for reproductive growth while the profligate genotypes can be deployed to take advantage of high rainfall in the high rainfall zone of southern Australia.

Nitrogen is an essential element for plant growth, and the relationship between leaf N content and photosynthesis has been widely studied in different species under steady-state light. However, under natural conditions, the light intensity at the leaf level is always changing, inherently heterogeneous in time and space. Therefore, the effect of leaf N content on photosynthesis under dynamic light conditions needs further study. At present, the effects of leaf N content on leaf non-steady-state photosynthesis have not been reported in canola (Brassica napus L.). To clarify the relationship between leaf N content and the speed of the response leaf gas exchange to variations in light intensity, eight genotypes of canola varying in leaf N content were used to study the temporal response of gas exchange to a step increase in irradiance. We found there were significant differences in non-steady-state photosynthesis, physiological characteristics, and anatomical traits across genotypes (the maximum amplitude was about fivefold), despite the lack of contrast under normal, steady-state photosynthesis. In addition, initial stomatal conductance to water vapor in the darkness and leaf N content per leaf area were negatively correlated with the time required to achieve 50% and 100% of the maximum photosynthetic rate. Contrarily, the time required to reach 50% of the maximum stomatal conductance was positively correlated with the time required to achieve 90% of the maximum photosynthetic rate across genotypes. It is concluded that the genotypes of canola with higher N content per leaf area show a faster induction of photosynthesis to fluctuating light conditions., (© 2021 Scandinavian Plant Physiology Society.)

Background: Drought stress is a major abiotic factor that affects rapeseed (Brassica napus L.) productivity. Though previous studies indicated that long non-coding RNAs (lncRNAs) play a key role in response to drought stress, a scheme for genome-wide identification and characterization of lncRNAs' response to drought stress is still lacking, especially in the case of B. napus. In order to further understand the molecular mechanism of the response of B. napus to drought stress, we compared changes in the transcriptome between Q2 (a drought-tolerant genotype) and Qinyou8 (a drought-sensitive genotype) responding drought stress and rehydration treatment at the seedling stage., Results: A total of 5546 down-regulated and 6997 up-regulated mRNAs were detected in Q2 compared with 7824 and 10,251 in Qinyou8, respectively; 369 down-regulated and 108 up- regulated lncRNAs were detected in Q2 compared with 449 and 257 in Qinyou8, respectively. LncRNA-mRNA interaction network analysis indicated that the co-expression network of Q2 was composed of 145 network nodes and 5175 connections, while the co-expression network of Qinyou8 was composed of 305 network nodes and 22,327 connections. We further identified 34 transcription factors (TFs) corresponding to 126 differentially expressed lncRNAs in Q2, and 45 TFs corresponding to 359 differentially expressed lncRNAs in Qinyou8. Differential expression analysis of lncRNAs indicated that up- and down-regulated mRNAs co-expressed with lncRNAs participated in different metabolic pathways and were involved in different regulatory mechanisms in the two genotypes. Notably, some lncRNAs were co-expressed with BnaC07g44670D, which are associated with plant hormone signal transduction. Additionally, some mRNAs co-located with XLOC_052298, XLOC_094954 and XLOC_012868 were mainly categorized as signal transport and defense/stress response., Conclusions: The results of this study increased our understanding of expression characterization of rapeseed lncRNAs in response to drought stress and re-watering, which would be useful to provide a reference for the further study of the function and action mechanisms of lncRNAs under drought stress and re-watering.

Slow germination speed caused by low temperature stress intensifies the risk posed by adverse environmental factors, contributing to low germination rate and reduced production of rapeseed. The purpose of this study was to understand the transcriptional regulation mechanism for rapid germination of rapeseed. The results showed that seed components and size do not determine the seed germination speed. Different temporal transcriptomic profiles were generated under normal and low temperature conditions in genotypes with fast and slow germination speeds. Using weight gene co-expression network analysis, 37 823 genes were clustered into 15 modules with different expression patterns. There were 10 233 and 9111 differentially expressed genes found to follow persistent tendency of up- and down-regulation, respectively, which provided the conditions necessary for germination. Hub genes in the continuous up-regulation module were associated with phytohormone regulation, signal transduction, the pentose phosphate pathway, and lipolytic metabolism. Hub genes in the continuous down-regulation module were involved in ubiquitin-mediated proteolysis. Through pairwise comparisons, 1551 specific upregulated DEGs were identified for the fast germination speed genotype under low temperature stress. These DEGs were mainly enriched in RNA synthesis and degradation metabolisms, signal transduction, and defense systems. Transcription factors, including WRKY, bZIP, EFR, MYB, B3, DREB, NAC, and ERF, are associated with low temperature stress in the fast germination genotype. The aquaporin NIP5 and late embryogenesis abundant (LEA) protein genes contributed to the water uptake and transport under low temperature stress during seed germination. The ethylene/H 2 O 2 -mediated signal pathway plays an important role in cell wall loosening and embryo extension during germination. The ROS-scavenging system, including catalase, aldehyde dehydrogenase, and glutathione S-transferase, was also upregulated to alleviate ROS toxicity in the fast germinating genotype under low temperature stress. These findings should be useful for molecular assisted screening and breeding of fast germination speed genotypes for rapeseed.

To understand the influence of temperature on floral initiation and to reveal the relationship between floral bud development and yield potential of rapeseed (Brassica napus L.), early- ("1358"), intermediate- ("Zhongshuang No.11") and late- ("Zheshuang No.8") maturity genotypes were sown on different sowing dates under field conditions during four crop seasons. A multiplicative model was introduced to distinguish and quantify the effects of photoperiod and temperature on pre-floral initiation phase. Parameters in this model showed that early-maturity genotype was more sensitive to photoperiod; while late-maturity genotype was more sensitive to vernalization. The relationships between cumulative temperature and mean temperature of pre-floral initiation phase could be well descried by exponential equation. The developmental rate of pre-floral initiation phase against mean daily temperature displayed an asymmetrical distribution, and it decreased rapidly when the mean temperature exceeded the optimum. Leaf primordia differentiated from the shoot apical meristem showed significant linear relationship with the thermal time at pre-floral initiation phase; dynamic change of floral bud differentiated from the shoot apical meristem robustly fitted to a sigmoidal logistic curve. According to the fitted logistic equation, the maximum differentiation rate varied from 1.7 to 4.1 per 10 °Cd due to different sowing dates and genotypes. Averaged across growing seasons, sowing dates and genotypes, bud degeneration rate was 33% on the main raceme, and varied from 58% to 99% on the seven primary branches. The yield showed a significant correlation with floral bud number although the latter showed serious degeneration. In conclusion, the floral bud quantity largely determines rapeseed yield, and thus the genotypes with strong vernalization requirement should be planted early to extend the vegetative stage to achieve more fertile floral buds while the genotypes with weak vernalization requirement should be planted late to avoid flowering in chilling environment., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Low temperature seriously affects the growth of crops and poses a huge threat to food production. The application of wood vinegar can be used as a cost-effective and environmentally friendly strategy to promote crop growth and enhance stress resistance, and the physiological resistance to low-temperature stress of rapeseed still needs further research. The present study investigated the effects of spraying wood vinegar on the growth, photosynthesis, osmotic adjustment, and antioxidant enzymes of rapeseed seedlings under low-temperature stress. The results showed that spraying wood vinegar at normal temperature reduced the stomatal conductance but increased the leaf area and total biomass of rapeseed and enhanced stomatal density and water use efficiency. The leaf area and total biomass of rapeseed sprayed with wood vinegar at low temperature improved by 22% and 31%, respectively, and stomatal density and water use efficiency increased by 14% and 83%, respectively, and intercellular CO2 concentration and stomatal conductance were reduced by 9% and 41%, compared to the low-temperature, respectively. Besides, the application of wood vinegar liquid improved the proline, soluble protein, and soluble sugar content of leaves by 208%, 38%, and 115%, respectively, and the activity of superoxide dismutase increased by 27%, the content of malondialdehyde decreased by 46%, compared to the low-temperature. Spraying wood vinegar could alleviate low-temperature stress by improving the anti-oxidant enzyme content and osmoprotectants, reducing the stomatal conductance, and enhancing water use efficiency. These results provide new insights for wood vinegar to relieve the low-temperature stress of rapeseed, and this strategy can be used for low-temperature rapeseed cultivation and management, and benefit farmers' plant profit. [ABSTRACT FROM AUTHOR]

Wood vinegar is formed by the condensation of smoke produced during the production of biochar. It mainly contains acetic acid, butyric acid, catechol, and phenol. Wood vinegar has a compound effect of promoting crop growth similar to plant growth regulators and is environmentally friendly. Moreover, it can enhance the biological and abiotic resistance of crops. In this study, foliar spraying was carried out systematically in the field with the hybrid variety of Huayouza 9 for two years to study the effects of wood vinegar and its compounds on the growth of rapeseed (Brassica napus L.). We applied four treatments with tap water as a control (CK), namely wood vinegar diluted 400-fold (M), M mixed with gibberellin (T1), M mixed with sodium D-gluconate (T2), and M mixed with melatonin (T3). They were sprayed in the seedling stage and overwintering stage, respectively. The results showed that the seed yield, the leaf area index, and the number of pods per plant of rapeseed treated with M increased by an average of 9.58%, 23.45%, and 23.80% in two years as compared to the CK, respectively. Compared with M, the seed yield of rapeseed treated with T1, T2, and T3 increased by an average of 7.88%, 6.90%, and 1.32% in two years, respectively. The treatments also improved the quality of rapeseed. In particular, the glucosinolate content of rapeseed treated with T2 and T3 decreased by an average of 12.83% and 6.72% in two years compared to the CK, respectively. The four treatments selected in the current study improved the resistance of rapeseed at the low temperature of 2–6 °C by increasing the activity of superoxide dismutase and proline and soluble protein contents, as compared to the CK. Besides, all treatments containing M reduced the incidence of Sclerotinia sclerotiorum and Peronospora parasitica (downy mildew) in rapeseed. More specifically, the T3 treatment significantly decreased the infection rate of these two diseases mentioned above by an average of 17.33% and 12.14% in two years compared to the CK, respectively. Therefore, the study and application of wood vinegar due to its compound effects on crop growth and yield is of great importance to sustainable agriculture, crop ecology, and environmental protection. [ABSTRACT FROM AUTHOR]