Liofilização com alternativa para superação de dormência em sementes de cinco espécies florestais Amazônicas

Abstract

Dormancy is an ecological characteristic of seeds, which aims to allow germination to occur naturally at the ideal time to increase success of establishment of the new plant. A very common type of dormancy is physical dormancy. Here specialized tissues of the seed coat prevent the absorption of water, which hampers imbibition and consequently germination and the formation of seedlings. Knowing that physical dormancy only occurs in orthodox seeds and that in some species, drying could overcome physical dormancy of the seeds this work evaluated seed lyophilization with the aim to overcome physical dormancy, evaluating the protrusion of the primary root and formation of normal seedlings. Seeds of the following species were used in this study: Dinizia excelsa Ducke, Ochroma pyramidale (Cav. ex Lam.) Urb., Parkia multijuga Benth., Stryphnodendron pulcherrimum (Willd.) Hochr. and Schizolobium parahyba var. amazonicum (Vell.) Blake. A preliminary study revealed that additional freezing before lyophilization is not necessary. Lyophilization was vacuumed for 24 hours at temperatures below -50 ° C at a pressure of 10-1 atm. For the evaluation of the dormancy breaking by lyophilisation, conventional methods were used as proposed earlier for each species. Additionally, was tested the use of 40°C in a dry and humid environment for dormancy breaking of Schizolobium seeds. Lyophilization was successful in overcoming seed dormancy of two species, Stryphnodendron with 60% and Ochroma with 90% germination. Lyophilization did not overcome seed dormancy of Parkia and Dinizia. Lyophilizied seeds of the four species emitted the primary root and developed normal seedlings when treated with conventional methods. Thus, lyophilisation did not reduce germinability. Lyophilization caused mechanical damage in Schizolobium seeds and, in relation to normal seedlings, the formation of abnormal or dead seedlings was high (> 70%). However, exposure to elevated temperature under humid conditions for 120 hours, was more effective than the hot water treatment and resulted in 62% germination. This study showed an alternative method for dormancy breaking of Schizolobium seeds; and revealed for the first time the use of lyophilization as an alternative method to overcome physical dormancy of Stryphnodendron and Ochroma seeds.