Ten melon germplasm accessions were treated under simulated low-temperature and weak-light conditions in this study to establish an efficient identification system for low-temperature and weak-light tolerance of melon (Cucumis melo L.) germplasm at the seedling stage. The relative changes in 8 growth indicators (including plant height, stem diameter, leaf area, etc.) and 10 physiological indicators (including chlorophyll content, root activity, relative electrical conductivity, etc.) were determined, and the damage indexs were calculated to initially evaluate the low-temperature and weak-light tolerance of each germplasm. Based on the membership function method in fuzzy mathematics, 19 identification indicators were standardized. Dimensionality reduction was performed via principal component analysis (PCA), and 5 principal components with strong correlations to the low-temperature and weak-light tolerance index, peroxidase (POD) activity, root length, root activity, and soluble protein content were extracted (cumulative contribution rate: 87.026%). Cluster analysis was conducted on the 10 melon germplasm accessions, which were classified into three groups. Group Ⅰ including Vedrantais and M18, was classified as strong low-temperature and weak-light tolerant. Group Ⅱ includding IranH, Topmark, M4 and Nantais oblong, was classified as moderate low-temperature and weak-light tolerant. Group Ⅲ including PI124111, MR1, M76 and PMR5, was classified as weak low-temperature and weak-light tolerant. Finally, stepwise linear regression was used to establish a prediction model for low-temperature and weak-light tolerance of melon at the seedling stage, D=-0.058+0.008X15+0.442X9+0.058X1-0.017X19 (R2=0.998, P<0.001), X15 is proline content; X9 is root length; X1 is low temperature and low light tolerance index; X19 is peroxidase activity. To verify the reliability of the above identification results, the expression patterns of CmADF1 and CmCYP195 (key genes responding to low-temperature and weak-light stress) were analyzed in germplasm accessions M4, PI124111 and PMR5 at different time points after low-temperature and weak-light treatment. The results showed that the expression characteristics of CmADF1 and CmCYP195 were consistent with the identified low-temperature and weak-light tolerance types of the germplasm, which further confirmed the reliability of the identification system. The results could serve as identification criteria for evaluating low-temperature and weak-light tolerance of different melon germplasm accessions and provide breeding materials for subsequent improvement of melon varieties with low-temperature and weak-light tolerance.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |