Melatonin is a naturally occurring compound in plants.  Here, we tested the effect of exogenous melatonin on rapeseed (Brassica napus L.) grown under salt stress.  Application of 30 μmol L^–1 melatonin alleviated salt-induced growth inhibition, and the shoot fresh weight, the shoot dry weight, the root fresh weight, and the root dry weight of seedlings treated with exogenous melatonin increased by 128.2, 142.9, 122.2, and 124.2%, respectively, compared to those under salt stress.  In addition, several physiological parameters were evaluated.  The activities of antioxidant enzymes including peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were enhanced by 16.5, 19.3, and 14.2% compared to their activities in plants without exogenous melatonin application under salt stress, while the H₂O₂ content was decreased by 11.2% by exogenous melatonin.  Furthermore, melatonin treatment promoted solute accumulation by increasing the contents of proline (26.8%), soluble sugars (15.1%) and proteins (58.8%).  The results also suggested that higher concentrations (>50 μmol L^–1) of melatonin could attenuate or even prevent the beneficial effects on seedling development.  In conclusion, application of a low concentration of exogenous melatonin to rapeseed plants under salt stress can improve the H₂O₂-scavenging capacity by enhancing the activities of antioxidant enzymes such as POD, CAT and APX, and can also alleviate osmotic stress by promoting the accumulation of osmoregulatory substances such as soluble proteins, proline, and water soluble glucan.  Ultimately, exogenous melatonin facilitates root development and improves the biomass of rapeseed seedlings grown under salt stress, thereby effectively alleviating the damage of salt stress in rapeseed seedlings.

RNA sequencing of the sensitive GH01 variety of Brassica napus L. seedling roots under 12 h of waterlogging was compared with previously published data of the ZS9 tolerant variety to unravel genetic mechanisms of waterlogging tolerance beyond natural variation. A total of 2 977 genes with similar expression patterns and 17 genes with opposite expression patterns were identified in the transcription profiles of ZS9 and GH01. An additional 1 438 genes in ZS9 and 1 861 genes in GH01 showed strain specific regulation. Analysis of the overlapped genes between ZS9 and GH01 revealed that waterlogging tolerance is determined by ability to regulate genes with similar expression patterns. Moreover, differences in both gene expression profiles and abscisic acid (ABA) contents between the two varieties suggest that ABA may play some role in waterlogging tolerance. This study identifies a subset of candidate genes for further functional analysis.

Combined with remote sensing data and meteorological data, cold damage risk was assessed for planting area of double cropping rice (DCR) in Hunan Province, China. A new methodology of cold damage risk assessment was built that apply to grid and have clear hazard-affected body. Each station cold damage annual frequency and average annual intensity of cold damage was calculated by using 1951-2010 station daily mean temperature and simple cold damage identification index. On this basis, average annual cold damage risk index was obtained by their product. The spatial analysis models of cold damage risk index about double-season early rice (DSER) and double-season later rice (DSLR) were established respectively by the relation of average annual cold damage risk index and its geographic factors. Critical threshold of level of average annual cold damage risk index for DSER and DSLR were respectively divided by the correlative equation of cold damage annual frequency and average annual intensity of cold damage. 2001-2010 planting area of DCR, acquired by time series analysis of MOD09A1 8-d composite land surface reflectance product, was as target of assessment. The results show average annual intensity of cold damage is exponential function of cold damage annual frequency, average annual cold damage risk index is directly proportional to cold damage cumulant and cold damage annual frequency, and is inversely proportional to happen times of cold damage and the square of statistical time sequence length. Cold damage risk of DSER is higher than DSLR in Hunan Province. In the 10-yr stacking map, DCR planting in low risk area accounted for 11.92% of total extraction area, in moderate risk area accounted for 69.62%, in high risk area accounted for 18.46%. According to the cold damage risk assessment result, DCR production can be guided to reduce cold damage losses.

The objective of this study was to determine the relationship between seed yield and other important agronomic traits ofearly-maturing rapeseed as a rotation crop in a double-cropping rice area using Pearson’s correlation coefficient as well asto estimate direct and indirect effects of specific yield component traits on seed yield via path analysis. Nineteen rapeseedgenotypes were grown at ten environments in South China during 2008-2009 and 12 characters were evaluated. Analysisof variance showed that environment had a significant impact on all characters. For most characters the genotype byenvironment interaction was weak and not statistically significant. Simple correlation analysis indicated that the numberof primary branches (PB), number of pods on the main raceme (PR), and number of seeds per pod made significantcontributions to seed yield per plant (SYP), while 1 000-seed weight was negatively correlated with SYP (r=-0.485, P<0.05).Furthermore, number of pods per plant (PP), PB, and PR had the greatest direct effects on SYP. In addition, PP and PB werethe best indicators to predict seed yield in stepwise regression analysis. Finally, yield component differences betweenearly- and medium-maturity varieties were compared; this showed that to improve the seed yield of early varieties, moreemphasis should be given to increase PP, PB, and PR, and reduce plant height and shortening of growth duration inbreeding practice.