Alfalfa (Medicago sativa) is a highly valuable perennial forage legume that suffers from autotoxicity, which decreases plant resistance, reduces soil fertility, causes serious soil-borne diseases, and promotes ecological imbalance. We evaluated the effects of autotoxicity on the seed germination of 22 alfalfa varieties, and then elucidated the oxidative damage and lipid peroxidation in two alfalfa varieties with contrasting autotoxicity tolerances. The technique for order of preference by similarity to ideal solution (TOPSIS) method was used to rank the germination of the 22 alfalfa varieties when exposed to six autotoxic concentrations (0, 0.025, 0.075, 0.125, 0.175, and 0.225 g∙mL−1). We found WL656HQ and 3105C to be autotoxicity-tolerant and autotoxicity-sensitive varieties, respectively. The germination index mainly affects the comprehensive allelopathic index of WL656HQ and 3105C, which were the simple vigor index and radicle length according to the random forest model, respectively. 3105C eliminates reactive oxygen species (ROS) via antioxidant enzymes and antioxidants under T1 (0.025 g∙mL−1), but the oxidative stress system and the oxidative scavenging system cannot maintain the balance under T2 (0.125 g∙mL−1), causing oxidative bursts. In comparison, WL656HQ used its oxidative scavenging system (peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR)) to maintain its redox dynamic balance by removing excess ROS at all concentrations. In conclusion, the positive and negative indicators of autotoxicity for the two varieties were ascorbate (ASA) and hydroxyl free radicals (OH•), and proline (Pro) and dehydroascrobate (DHA), respectively. The most sensitive autotoxic concentrations of 3105C and WL656HQ were T2 (0.125 g∙mL−1) and T1 (0.025 g∙mL−1), respectively.
Background Medicago sativa L. ‘Qingshui’ is a valuable rhizomatous forage germplasm resource. We previously crossed Qingshui with the high-yielding Medicago sativa L. ‘WL168’ and obtained novel rhizomatous hybrid strains (RSA-01, RSA-02, and RSA-03). Telomere dynamics are more accurate predictors of survival and mortality than chronological age. Based on telomere analyses, we aimed to identify alfalfa varieties with increased stamina and longevity for the establishment of artificial grazing grasslands. Methods In this study, we performed longitudinal analysis of telomerase activity and relative telomere length in five alfalfa varieties (Qingshui, WL168, RSA-01, RSA-02, and RSA-03) at the age of 1 year and 5 years to examine the relationship among telomerase activity, rate of change in relative telomere length, and longevity. We further aimed to evaluate the longevity of the examined varieties. Telomerase activity and relative telomere length were measured using enzyme-linked immunosorbent assay and real-time polymerase chain reaction, respectively. Results We observed significant differences in telomerase activity between plants aged 1 year and those aged 5 years in all varieties except WL168, and the rate of change in telomerase activity does not differ reliably with age. As telomerase activity and relative telomere length are complex phenomena, further studies examining the molecular mechanisms of telomere-related proteins are needed. Relative telomere lengths of Qingshui, WL168, RSA-01, RSA-02, and RSA-03 in plants aged 5 years were higher than those aged 1 year by 11.41, 11.24, 9.21, 10.23, and 11.41, respectively. Relative telomere length of alfalfa tended to increase with age. Accordingly, alfalfa varieties can be classified according to rate of change in relative telomere length as long-lived (Qingshui, WL168, and RSA-03), medium-lived (RSA-02) and short-lived (RSA-01). The differences in relative telomere length distances of Qingshui, WL168, RSA-01, RSA-02, and RSA-03 between plants aged 1 and 5 years were 10.40, 13.02, 12.22, 11.22, and 13.25, respectively. The largest difference in relative telomere length was found between Qingshui and RSA-02 at 2.20. Our findings demonstrated that relative telomere length in alfalfa is influenced by genetic variation and age, with age exerting a greater effect.
Cultivating new alfalfa (Medicago sativa L.) varieties with high yield and quality is of great significance for improving alfalfa yield and promoting the development of the grass and livestock industry. Plant height is an important indicator of alfalfa yield and is closely related to photosynthetic capacity, harvest index and yield. However, the underlying cause of the variation in height among alfalfa plants is not clear. In this paper, we measured the phenotypic traits, photosynthetic physiology and endogenous hormone content of tall- and short-stalked alfalfa materials and analyzed the important external and internal factors that caused the difference in plant height of alfalfa. We found that the phenotypic traits of tall- and short-stalked alfalfa materials showed significant differences, and dwarf alfalfa showed significant shortening of the main stem internode length. There were also some differences in light and physiological indicators and endogenous hormone contents between tall- and short-stalked alfalfa materials. Through correlation analysis, we found that the phenotypic traits and physiological indicators significantly correlated with alfalfa plant height were the number of internodes, stem diameter, average internode length, leaf–stem ratio, leaf area, Pn (net photosynthetic rate), Tr (transpiration rate), upper leaf SP (soluble protein), Suc (sucrose) content, middle stem Sta (starch) content, middle stem ZT (zeatin) and IAA (indole-3-acetic acid). Further analysis showed that Tr, IAA and LA played a direct role in plant height, with Tr contributing the most to plant height, followed by IAA. Finally, we found that the starch content of the middle stem had a significant impact on plant height through principal component analysis. These results provide new insights into the formation and genetic improvement of plant height traits in leguminous forages such as alfalfa.
Rhizome-rooted alfalfa (Medicago sativa L.) is an excellent forage for establishing grazing and ecological grasslands, requiring a high and stable yield. Studying the genetic and physiological basis of stable expression of biomass traits is essential for improving production performance in rhizome-rooted alfalfa. We analyzed forage mass and photosynthetic physiological indices of the improved progenies (RSA−01, RSA−02, and RSA−03), parental “Qingshui” (CK1), and “WL168” (CK2) at ages one and five years and their relationships, then revealed heterotic stability. Moreover, we explored the effects of interannual dynamics and genetic differences on tested indices. The results revealed compared with the forage mass of CK1, RSA−03 at ages one and five years increased by 22.17% and 19.72%, respectively, while RSA−01 and RSA−02 varied from 1.40% to 8.65%, indicating obvious heterosis in forage mass of RSA−03. At one year of age, Gs value, Car content and SS content of RSA−03 were higher than those of CK1; SS content of RSA−03 were higher than those of CK2 and RSA−02; Ci, Gs and Tr values of RSA−03 were higher than those of RSA−01. At five years of age, Pn, Gs, and WUE values, and Sta content of RSA−03 were higher than those of CK1; Ci value and Suc content of RSA−03 were higher than those of CK2; Car content and Gs value of RSA−03 were higher than those of other progenies. The forage mass; Chl(a/b) ratio; Pn, Gs, and WUE values; Suc content of RSA−03 at age five years were higher than those at age one year by 9.99%–44.24%. Through path analysis, Gs and NSC were direct factors affecting forage mass at age one year, and both Pn and SP affected forage mass indirectly through Gs; Gs and Chl(a+b) were direct factors affecting forage mass at age five years, and SS affected forage mass indirectly through Gs. Interestingly, Chlb, Chl(a/b), Pn, Tr, Gs, Ci, Suc, SP, and SS were more influenced by age than genetics, while the opposite was true for Car and Sta. Accordingly, RSA−03 showed obvious and stable heterosis in forage mass and photosynthetic physiology, recommending the establishment of grazing pastures and ecological vegetation.
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