Osmocondicionamento de sementes e seus efeitos na germinação e crescimento de mudas de Sabiá (Mimosa caesalpiniifolia Benth.) sob estresse hídrico.

Abstract

This work aimed to evaluate the effect of priming on the germination and vigor of seeds under osmotic stress (water and saline stress) (Experiment I) and on gas exchange and growth of 8sabiá9 (Mimosa caesalpiniifolia Benth) seedlings under water deficit (Experiment II). Experiment I, related to water stress, was conducted in a completely randomized design (DIC), distributed in a 3×5 factorial scheme, corresponding to treatments without priming; and priming with PEG -1.0 MPa and 100 mM KNO3 and five water potentials (0; -0.5; -1.0; -1.5; and -2.0 MPa) (polyethylene glycol 6000 - PEG). The salt stress experiment consisted of a 3x5 factorial, corresponding to treatments without priming; and priming with PEG -1.0 MPa and 100 mM KNO3 and five doses of NaCl (0; 50; 100; 150; 200 mM), and four replications. Germination percentage, germination speed index (IVG) and average germination time (TMG) were evaluated. In Experiment II, conducted in a pot in a screened environment, the treatments were distributed in DIC, 3x3 factorial scheme, corresponding to three priming treatments (without priming; and priming with PEG -1.0 MPa; KNO3 100 mM) and three levels of water (vase capacity-hp) [80%hp (control), 40%hp (moderate stress) and 20%hp (severe stress)], with four repetitions. The following were evaluated: Relative water content (RWC); transpiration rate (E); stomatal conductance (gs); photosynthesis rate (A); Instantaneous water use efficiency (A/gs); plant height; stem diameter; dry mass of the shoot (DMSH), stem (DMS), roots (DMR), shoot/root dry mass ratio (DMSH/DMR) and total dry mass. 8Sabiá9 seeds were sensitive to water deficit and salinity, however priming increased seed vigor and reduced TMG, regardless of the water potential and salinity imposed. The use of priming with PEG favored gas exchange, MSR and total dry mass of the seedlings. Regardless of the water level imposed on the seedlings, priming with PEG made it possible to obtain seedlings with higher values of height, stem diameter, MSPA and MSPA/MSR. It is recommended to use PEG as a chemical seed priming agent to mitigate the effects of water deficit on 8sabiá9 seedlings.