Objectives The purpose of this study was to clarify the seed germination and physiological characteristics of Brassica green manure (GM) seeds with a strong ability to resist drought. We aim to establish reliable methods and suggestions for screening Brassica GM varieties suitable for cultivation in dryland conditions of the Loess Plateau of China.
Methods We collected 30 Brassica green manure (GM) varieties for the indoor germination experiment with the control (water) and drought stress 10% polyethylene glycol (PEG)-6000 solution treatments. The changes in root length, bud length, fresh weight, root: bud length ratio (R: B ratio), germination drought resistance index (GDI), germination index (GI), and relative vigor index (VI) at the seedling stage were analyzed. The tested Brassica GM seeds’ drought resistance ability was comprehensively evaluated by combining the subordinate function, grey correlation analysis, comprehensive drought resistance index (CDI), and systematic cluster analysis method. Three Brassica GM drought-resistant groups (HR-high drought resistant, MR-medium drought resistant, LR-low drought resistant) were obtained by analyzing the differences in drought resistance indexes.
Results Compared with the control treatment, PEG-6000 simulated drought stress (P < 0.05) increased root length and root: bud length ratio at the seedling stage by 52.7% and 96.6%, but decreased the bud length and fresh weight by 21.4% and 36.6%, respectively. Additionally, there was a slight increase in the germination rate of Brassica GM varieties at the seedling stage (P > 0.05) . The correlations between the seedling germination characteristics of Brassica GM varieties and CDI were all above 70%, and the order of closeness was: GDI > VI > root length > bud length > GI> fresh weight > R:B ratio. Cluster analysis was carried out on the weighted drought tolerance index (WDTI) of 30 Brassica GM varieties. At Euclidean distance of 5, 17 Brassica GM varieties were classified as the HR group, 8 as the MR group, and 5 as the LR group. There was no significant difference in bud length among the three drought-resistant groups. The germination rate, root length, fresh weight per plant, and R:B ratio of the HR group were (P < 0.05) higher than MR and LR groups at the seedling stage.
Conclusions GDI, VI, and root length of the 30 Brassica GM seeds were closely related to CDI. However, there were weak relationships between the fresh weight, R:B ratio and CDI. The Brassica GM varieties with strong drought resistance ability can efficiently resist drought stress by increasing the germination rates, R:B ratio, and root length. 17 of the 30 tested Brassica GM varieties are suitable for planting in the dry-land regions of the Loess Plateau, due to strong germination and drought resistance abilities at the seedling stage.
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