Abstract: Background and Objective: Lettuce seed germination at high temperatures is a problem faced by farmers and seed producers in Brazil. At high temperatures, germination is reduced or null and changes in physiology and the patterns of germination-related enzymes, such as endo-β-mannanase, can occur. The objective of this study was to determine the relationship between endo-β-mannanase activity and tolerance to thermoinhibition in lettuce seeds, as well as to determine the relationship between seeds and antioxidant enzymes. Materials and Methods: Seeds from two lettuce cultivars, Everglades (thermotolerant) and Veronica (thermosensitive), were used. The seeds were assessed for first count, germination and germination speed index at seven temperatures (20, 23, 25, 27, 30, 33 and 35°C). Additionally, the activity of the enzymes endo-β-mannanase, catalase, ascorbate peroxidase and superoxide dismutase and the levels of hydrogen peroxide were quantified in each cultivar at the different temperatures. The experimental design was completely randomized in a 2×7 factorial arrangement, with two cultivars and seven temperatures. Results: At temperatures above 30°C, the Everglades cultivar showed higher values than the Veronica cultivar, including for endo-β-mannanase activity, in all treatments. Additionally, the oxidation levels, as confirmed by the analysis of oxidative pathway enzymes, were higher in the Veronica cultivar, thus confirming that the cultivar is thermosensitive to temperatures above 25°C. Conclusion: It is concluded that high temperature directly affects the germination parameters and consequently the activity of endo-β-mannanase in lettuce seeds, especially in the thermosensitive cultivar Veronica. PubDate: 20 October, 2021
Abstract: Background and Objective: Tridax procumbens is a weed with significant medicinal importance in Brazil. This study evaluated the effects of temperature and KNO3 on Tridax procumbens seed germination and dormancy. Materials and Methods: Two subsamples of 50 achenes were submitted to treatments using a factorial combination of temperature (25 and 30°C) and moistening the substrate with KNO3 solution (0% KNO3, 0.2% KNO3) in a completely randomized experimental design with five replications. Daily germination counts were made using the primary root protrusion and analyzing the accumulated germination percentage, germination speed and accumulated germination curve. Results: Germination percentage increased at the highest temperatures. In contrast, the use of KNO3 at the same temperature slightly decreased germination speed after 21 days of cultivation. The accumulated germination curve adjusted to the logistic model of all treatments showed an asynchrony in seed germination over time. Conclusion: Thus, temperature positively influenced the germination speed index at 21 days, while the presence of 0.2% KNO3 in the substrate influenced it negatively. PubDate: 12 December, 2021
Abstract: Background and Objective: Low germination and high dormancy are common phenomena in many wild herbs of great value, however, the optimum germination temperatures and dormancy breaking methods have not yet been studied. Suaeda salsa, Suaeda crassifolia, Chenopodium glaucum, Descurainia sophia, Amaranthus retroflexus and Alopecurus myosuroides are common wild herbs in China, which are traditionally used in edible, forage, herbal medicine and chemical industry. Therefore, this study was carried out to determine the optimum germination conditions of the above six wild herb seeds. Materials and Methods: Two tests were conducted in this study, the first determining the optimum germination temperature for seeds and the second exploring the dormancy breaking method for dormant species. The effects of four constant temperatures (20, 25, 30 and 35°C), five alternating temperatures (515, 1020, 1525, 2030 and 2535°C) and four dormancy breaking methods of 0.2% potassium nitrate (KNO3), 7-days pre-chilling (PC7), 0.2% KNO3+PC7 and 0.8% sodium hydroxide (NaOH) were studied. Results: The results showed that the seeds of S. salsa, S. crassifolia and A. retroflexus had no dormancy and the optimum germination temperatures were 20, 35 and 35°C, respectively. However, the seeds of C. glaucum, D. sophia and A. myosuroides had different levels of dormancy and the optimum germination conditions were all 0.2% KNO3+PC7 and alternating temperature of 1525°C. In addition, the first and final count time of germination of these six wild seeds was also determined. Conclusion: For non-dormant seeds of S. salsa, S. crassifolia and A. retroflexus, the optimum germination temperatures were 20, 35 and 35°C but for dormant seeds of C. glaucum, D. sophia and A. myosuroides, the combination of 0.2% KNO3+PC7 and 1525°C was the optimum germination condition. PubDate: 12 December, 2021
Abstract: Background and Objective: Sapindus saponaria L. is a plant species of pharmacological importance and also with the potential for the production of biodiesel. Thus, the present study developed a protocol for the cryopreservation of S. saponaria seeds and applied physiological and vigor characters to define the best water content for cryogenic storage, the best defrosting method and assessments on the need for treatment with cryoprotectants. Materials and Methods: The study was developed in two tests, the first defining the best water content for storage and defrosting method. In a second test, seeds were stored with the best water content defined in test 1, under the action or not of cryoprotectants DMSO (10%) and glycerol (10%) and defrosted the seeds applying the best defrosting method also evidenced in test 1. Evaluation of seeds was done at 60, 120 and 180 days of storage in liquid nitrogen. Results: The best germination performance, emergence, emergence speed index (IVE) and germination after accelerated seed aging was observed in seeds stored with 6% water content and thawed quickly in the microwave. Regarding the use of cryoprotectants, this use can be indicated or not, depending on the storage time. Conclusion: Seeds cryoprotected and stored for periods less than or equal to 120 days exhibited inferior performance with regard to emergence, total length and dry seedling mass. PubDate: 09 January, 2021
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