Senna cana (Nees & Mart.) H. S. Irwin & Barneby : morfologia de frutos, sementes, plântulas, plantas jovens e ecofisiologia da germinação

Abstract

The objective of this study was determine the weight of one thousand seeds and number of seeds per fruit; to describe the morphological aspects of fruits, seeds, seedlings, germination stages, seedlings and the normal and abnormal seedlings of Senna cana; recommend effective pre-germinative treatment (s) in overcoming seed dormancy; indicate the best substrate (s), temperature (s); to study the effect of light to be used in tests of germination and vigor and to evaluate the effect of saline and water stress on germination and vigor. For the morphological study, descriptions and illustrations of the morphological characteristics of fruits, seeds, germination, seedling and seedling phases were carried out. The water content was determined by the oven method at 105 ± 3ºC, for 24 hours. In order to overcome dormancy of the seeds, in addition to the control (without treatment), scarification with sandpaper nº 100 for mass in the opposite part of the thread, scarification with sandpaper nº 100 for mass, followed by imbibition in water for 24 hours; immersing in water at 80°C until reaching room temperature. For the substrate and temperature effects, the seeds were seeded between the substrates: fine and medium vermiculite, sand, coconut powder, sugarcane bagasse, paper towel (organized in rolls) and blotting paper and constant temperatures of 10, 15, 20, 25, 30, 35 and 40°C, and alternating temperature of 20-30°C distributed in transparent plastic boxes (11 x 11 x 3.5 cm), all under continuous light. In order to evaluate the light quality, the seeds were submitted to four regimes of luminosity: white, red, red-extreme and absence of light, all by photoperiod of 24 h. The substrate was moistened with aqueous solutions in amounts equivalent to 2.5 times the dry paper weight, equivalent to osmotic potentials of 0.90; -0.68; -0.46; -0.34; -0.24; -0.13 and 0 MPa for NaCl and -0.50; -0.38; -0.25; -0.19; -0.13; -0.06 and 0 MPa for CaCl2. In the evaluation of the water stress, the substrate paper blotter was moistened with solutions of polyethylene glycol (PEG 6000), using the following levels of osmotic potential: 0; -0.05; -0.1; -0.2; -0.4; -0.6 and -0.8 MPa. The evaluated parameters were: germination and vigor (first count, IVG, TMG, CPA, CR, MSPA and MSR). To overcome the dormancy of the seeds of the S. cana, mechanical scarification is recommended, using sandpaper for mass nº 100. To perform germination and vigor tests of the species studied, it is recommended to alternate temperature of 20-30°C in combination with the substrate blotter paper. The seeds germinated in all light conditions offered, but it can be considered as preferential positive photoblastic. The increase of the NaCl and CaCl2 concentration in the solution caused a reduction in the water potential of the soil, inducing a lower water absorption capacity in the seeds, which resulted in a lower seed germination potential when compared to the control treatment. It is considered a low salt tolerance glycoprotein with a maximum NaCl tolerance of -0.13 and -0.68 MPa and for CaCl2 at -0.06 and -0.50 MPa. The PEG 600 did not favor the germination of S.cana seeds. It is a species tolerant to water stress with maximum germinability limit of -0,2 MPa.