Germinação e redução da sensibilidade à dessecação em sementes de Campomanesia adamantium (cambess.) O. Berg (myrtaceae)

Abstract

The conservation of the seeds of native plant species by storing their fruits has been used to maintain seed physiological quality and viability during predetermined periods of time (short, medium, or long term) before sowing. The present study sought to conserve the seeds of Campomanesia adamantium (popularly known as "guavira" or "gabiroba") a native savanna species from southern Mato Grosso State, Brazil. We initially evaluated the effects of fruit size on seed germination and vigor and observed that fruit size hands a direct relationship with the sizes and masses of the seeds and influences their germination and vigor. Small, medium-small, and medium fruits produced large seeds with higher germination percentages and germination speeds, while large fruits produced seedlings showing higher biomass accumulations. The object of the present work was to evaluate C. adamantium seed sensibility to either slow or fast desiccation. To evaluate seed sensitivity to desiccation, their water contents were reduced by 45, 35, 30, 25, 20, 15, 10 and 5% by drying over activated silica gel (fast drying) or at normal room-temperature conditions (slow drying). C. adamantium seeds were found to be sensitive to water content reductions below 21.1% with fast drying and below 17.2% with slow drying due to reductions in their physiological potentials. DNA integrity was not affected by drying by either of the two methods. Activated silica gel (fast) drying to 4.5% water content and laboratory (slow) drying to 5.4% water contents caused losses of RNA integrity of the seeds. To evaluate seed conservation, seeds were submitted to drying under laboratory conditions (slow) to different final water contents and subsequently exposed to various environment conditions: at room-temperature (25 ± 2ºC, 35% RH), in a cold/dry chamber (16 ± 1ºC, 40% RH), under refrigeration (8 ± 1ºC, 35% RH), and under freezing conditions (-18 ± 1ºC, 42% RH) for 0 (recently processed seeds, with only superficial drying for 40 minutes), 30, 60, 90, 120, 150 and 180 days. C. adamantium seeds were found to be recalcitrant and could not support desiccation to levels below 15.3% and subsequent storage under laboratory environment conditions, in a cold/dry chamber, under refrigeration, or in a freezer for 30 days. The desiccation and storage of seeds affected seedling formation, impeding the normal development of root and shoot structures. The deleterious effects associated with dry storage were reflected in the appearance of phenolic compounds and fructans in abnormal C. adamantium seedlings. To evaluate any reductions in sensitivity desiccation in seeds primed with polyethylene glycol and abscisic acid (ABA), seeds were submitted to osmotic treatments with polyethylene glycol (PEG) at concentrations of -1.48 and -2.04 MPa associated, or not, with ABA (100 μM) for 120 hours. Seeds not subjected to these treatments constituted the controls. The seeds were then dehydrated by drying over activated silica gel (fast drying) or under roomtemperature conditions (slow drying), with water content reductions of 20, 15, and 10%. Treatment with polyethylene glycol (-1.48 MPa) without abscisic acid with subsequent drying over silica gel (fast) induced sensitivity of C. adamantium seeds to desiccation at water contents of 15%. This osmopriming, associated or not with abscisic acid, did not induce sensitivity to desiccation in seeds with water contents of 20, 15 and 10% when subjected to slow drying.