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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.

The application of high-quality seeds ensures successful crop establishment, healthy growth, and improved production in both quantity and quality. Recently, biochar-based seed coating has been recognized as a new, effective, and environmentally friendly method to enhance seed quality, seedling uniformity, and nutrient availability. To study the impact of biochar coating on the surface mechanical properties of coated seeds, rice emergence and growth, and related physical and physiological metabolic events, laboratory experiments were performed on two water-saving and drought-resistance rice (WDR) varieties (Huhan1512 and Hanyou73) using biochar formulations with varying contents (20%–60%). The results showed that the appropriate concentration of biochar significantly improved emergence traits and seedling performance of the two rice varieties, compared to the uncoated treatment, and that the optimal percentage of biochar coating was 30% (BC30). On average, across both varieties, BC30 enhanced emergence rate (9.5%), emergence index (42.9%), shoot length (19.5%), root length (23.7%), shoot dry weight (25.1%), and root dry weight (49.8%). The improved germination characteristics and vigorous seedling growth induced by biochar coating were strongly associated with higher water uptake by seeds, increased α-amylase activity and respiration rate, and enhanced accumulation of soluble sugar and soluble protein. Moreover, the evaluation results of mechanical properties related to seed coating quality found that increasing the proportion of biochar in the coating blend decreased the integrity and compressive strength of the coated seeds and reduced the time required for coating disintegration. In conclusion, biochar coating is a cost-effective strategy for enhancing crop seed quality and seedling establishment. [ABSTRACT FROM AUTHOR]

Although gibberellic acid (GA3) improves seed germination and seedling growth in stressful conditions, the mechanisms underlying GA3-priming improved drought tolerance have not been defined. To investigate the effects of GA3-priming on physiology and antioxidant enzymes, we primed rapeseed seeds with polyethylene glycol (PEG-6000)-induced stress and quantified the changes in reactive oxygen species (ROS) homeostasis, root morphology, osmotic adjustment, stomatal morphology, and cell ultrastructure analysis. Drought stress reduced the germination rate and the subsequent growth. GA3-priming improved rapeseed germination rate and seedling growth under PEG-6000-simulated drought stress. Our results indicate that the lower germination rate and the inhibition of seedling growth in non-primed seeds under drought conditions were associated with higher production of ROS. However, GA3-primed seedlings accumulated higher activities of superoxide dismutase, peroxidase, catalase, ascorbic acid, and glutathione. They thus developed a stronger antioxidant defense system for scavenging the over-accumulated ROS under drought. GA3-priming also contributed to osmotic adjustments by promoting the accumulation of proline, soluble sugars, and soluble proteins. Ultimately, GA3-priming protected the cell wall from degradation and preserved chloroplast from autophagy. These ameliorative effects of GA3-priming under drought stress were further confirmed by significantly improving the rapeseed root morphology in hydroponic experiments. We conclude that GA3-priming improves seed germination and promotes productivity by regulating physiological and biochemical responses to drought stress. [ABSTRACT FROM AUTHOR]

Seed germination and stand establishment are the first steps of crop growth and development. However, low seed vigor, improper seedbed preparation, unfavorable climate, and the occurrence of pests and diseases reduces the germination rate and seedling quality, resulting in insufficient crop populations and undesirable plant growth. Seed coating is an effective method that is being developed and applied in modern agriculture. It has many functions, such as improving seed vigor, promoting seedling growth, and reducing the occurrence of pests and diseases. Yet, during seed coating procedures, several factors, such as difficulty in biodegradation of coating materials and hindrance in the application of chemical ingredients to seeds, force us to explore reliable and efficient coating formulations. Biochar, as a novel material, may be expected to enhance seed germination and seedling establishment, simultaneously ensuring agricultural sustainability, environment, and food safety. Recently, biochar-based seed coating has gained much interest due to biochar possessing high porosity and water holding capacity, as well as wealthy nutrients, and has been proven to be a beneficial agent in seed coating formulations. This review presents an extensive overview on the history, methods, and coating agents of seed coating. Additionally, biochar, as a promising seed coating agent, is also synthesized on its physico-chemical properties. Combining seed coating with biochar, we discussed in detail the agricultural applications of biochar-based seed coating, such as the promotion of seed germination and stand establishment, the improvement of plant growth and nutrition, suitable carriers for microbial inoculants, and increase in herbicide selectivity. Therefore, this paper could be a good source of information on the current advance and future perspectives of biochar-based seed coating for modern agriculture. [ABSTRACT FROM AUTHOR]

Low temperature is a main adverse factor affecting successful seedling establishment in the Yangtze River basin, and thus low‐temperature stress tolerance at the germination and seedling emergence stages is an important attribute for rapeseed (Brassica napus L.) production. The present study was conducted to evaluate the low‐temperature stress tolerance indices (STIs) of a large conventional rapeseed genotype population at the germination and seedling emergence stages. Twelve seed germination‐ and seedling emergence‐related indices were investigated under normal and low‐temperature conditions, and the broad‐sense heritability of these indices ranged from 25.4 to 57.6%. Therefore, the selection of genotypes with strong low temperature tolerance is a feasible way to guarantee seedling establishment. Using principal component analysis, the STIs during the seed germination and seedling emergence stages have been divided into three main categories: dry matter weight, germination speed and final germination percentage, and root length with a seedling vigor index. The top three genotypes ranked by comprehensive STI score were Huayou No. 2, SWU44, and 2012‐K8053; the bottom three genotypes ranked by comprehensive STI score were Chuanyou18, wx1025, and 97096. The results of the present study could provide valuable information for breeders to utilize the rapeseed germplasm resources in the Yangtze River basin to achieve the goal of low‐temperature resistance breeding. [ABSTRACT FROM AUTHOR]

Chitin hydrogels were successfully prepared from chitin solution dissolved in NaOH/urea aqueous solution at low temperature by crosslinking with epichlorohydrin. The experimental results indicated that the chitin hydrogels were hydrophilic, had a microporous structure, and had a large surface area, leading to excellent water uptake ability and water-retention properties. Moreover, they exhibited good mechanical properties and a high equilibrium swelling ratio. The growth indexes of rapeseed, including the germination rate, root length, shoot length, fresh weight and dry weight, for chitin hydrogel (CG2) were not significantly different from those of soil and significantly higher than agar. Chitin hydrogel as a plant growth regulator could promote seed germination and growth when applied to Brassica napus rapeseed sowing. Moreover, chitin was safe and biodegradable so it would be suitable to use as soilless culture media for plant growth. This work provided a new pathway for the application of chitin hydrogels in the agriculture field. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Melatonin-priming improved seed germination under the drought stress. • Melatonin-priming detoxified the ROS activities through enhancement of antioxidants. • Melatonin-priming potentially regulated stomatal traits coping with drought stress. • Seed priming with melatonin prevented chloroplasts autopepsia and cell wall degradation. Water stress encumbers the rapeseed growth and development primarily by oxidative alteration to biological membranes and interrupted tissue water status. Seedling tolerance to water stress is vital for better crop development through the entire period under drought stress condition. The enhancement of plant stress tolerance due to melatonin application is already known; however, the specific underlying mechanisms are still not fully understood. The current study was done to investigate the effect of melatonin-priming on rapeseed germination and subsequent seedling growth under PEG-6000 simulated drought stress. Drought stress significantly inhibited germination and seedling growth, led to oxidative stress from excessive H 2 O 2 generation, and reduced the chlorophyll content. Melatonin-priming alleviated the oxidative damage and the amount of chlorophyll reduction in rapeseed seedlings under the drought stress. The stomatal traits such as number, stomatal length and width were greatly improved in melatonin-primed treatment. Melatonin-priming also preserved the chloroplast structure, maintained cells expansion and strengthened the cell wall in response to drought stress. The results revealed that the ameliorative effects of melatonin-priming may be ascribed to enhancement of antioxidant enzymes activities, increase in the content of non-enzymatic antioxidants, and increase in the amounts of osmo-protectants. The present data suggest that priming seeds with melatonin can be a prime strategy regarding the development of crop drought resistant in crop production. [ABSTRACT FROM AUTHOR]