Abstract
Salvia hispanica seedlings have stood out for their potentialities in nutrients for agri-food industries. Nevertheless, studies related to this species are still scarce, especially with respect to agronomic factors that enable its propagation and development. Hence, this study aimed to evaluate germination, vigor and osmotic adjustment of S. hispanica seeds and seedlings subjected to water and thermal stress. The experimental design was completely randomized, with treatments arranged in factorial scheme, corresponding to five levels of polyethylene glycol (PEG 6000) (0.0; -0.1; -0.2; -0.3 and -0.4 MPa) and five temperatures (20, 25, 30 and 20-30 °C), with four replicates of 50 seeds in each treatment. Germination test was set on blotter paper, moistened with PEG 6000 solutions at the previously mentioned potentials, under 8-h photoperiod. The following variables were analyzed: germination, germination speed index, seedling shoot length, seedling root length, seedling dry matter and contents of chlorophyll, carotenoids, amino acids, proline and sugars. Polyethylene glycol levels of -0.4 MPa at all temperatures and -0.3 MPa at 30 °C and 20-30 °C enable germination and vigor of S. hispanica seedlings. S. hispanica seedlings are able to perform osmotic adjustment under water stress conditions up to the level of -0.3 MPa, when grown from seeds germinated at temperatures of up to 25 ºC.
Highlights
Salvia hispanica L. is native to western and central Mexico and Guatemala and its seeds have stood out for being a potential source of nutrients for agri-food industries and for their beneficial properties for health (MUÑOZ et al, 2012)
For the interaction between osmotic potentials and temperatures, significant effect occurred on germination, germination speed index, shoot length and root length of S. hispanica seedlings at 0.05 probability level (Figure 1)
From -0.1 MPa on, at temperatures of 30 and 20-30 oC, and at -0.2 MPa at temperatures of 20 and 25 oC there were accentuated reductions in the germination speed index of S. hispanica seeds, eventually reaching values lower than 0.5 at the osmotic potential of -0.4 MPa, regardless of the studied temperature. These results indicate that temperature can increase the intensity of water stress on S. hispanica seedlings, as evidenced for the temperatures of 30 oC and 2030 oC, given the accentuated reductions (>30%) with a slight oscillation of the osmotic potential from 0.0 MPa to -0.1 MPa
Summary
Salvia hispanica L. is native to western and central Mexico and Guatemala and its seeds have stood out for being a potential source of nutrients for agri-food industries and for their beneficial properties for health (MUÑOZ et al, 2012). A successful plant establishment at the field depends mostly on seed germination conditions (GORAI; GASMI; NEFFATI, 2011). Studies related to the germination response of seeds to artificial stress conditions are especially important for plant physiology and ecophysiology, and can be used as a tool to identify limits of tolerance, of survival and adaptation of the species to stressful conditions (GUEDES et al, 2013). Seed germination is a process that requires water and heat, and, depending on species, other factors are necessary, such as oxygen and light (MARCOS FILHO, 2015). Water availability directly affects germination, since water absorption triggers a series of physical, physiological and biochemical processes inside the seed, such as activation of enzymes, breakage of chemical bonds and translocation and use of stored substances (BEWLEY et al, 2013). Temperature interferes with water absorption dynamics and with limits and speed of biochemical reactions, besides physiological processes that determine the germination process (CARVALHO; NAKAGAWA, 2012)
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