Ex situ conservation and desiccation tolerance in Lecythis pisonis Cambess seeds
Name: CAROLINE PALACIO DE ARAUJO
Publication date: 23/02/2024
Examining board:
Name |
Role |
|---|---|
| RODRIGO SOBREIRA ALEXANDRE | Advisor |
Summary: The species Lecythis pisonis Cambess. is a chestnut tree belonging to the Lecythidaceae family, commonly found in the Atlantic Forest and Amazon biomes. Studies related to its propagation and ex situ conservation are important, contributing to the protection of its genetic resources over time. This research answers important questions related to the propagation of the seminiferous species L. pisonis, whose objectives were a) Chapter I – to study fixed temperatures and thermal shocks at different exposure times on the physiology of seeds and initial growth of L. pisonis seedlings; b) chapter II – analyze the influence of seed size and shading on seedling emergence and the phenotypic and photosynthetic plasticity of L. pisonis seedlings; c) chapter III – analyze tolerance to desiccation and maintenance of seed viability of the chestnut tree L. pisonis; and d) chapter IV – analyze the physiological quality of L. pisonis seeds during ex situ storage under different temperature conditions and time variations. Chapter I was divided into experiment 1 (fixed temperatures 30; 35; 40; 45 and 50 °C and thermal shocks at temperatures 30-35; 30-40; 30-45; 30-50; 35-40; 35-45; 35-50; 40-45; 40-50 and 45-50 °C at exposure times of 20 h/4 h and 21 h/3 h) and experiment 2 (fixed temperatures 30 and 45 °C and thermal shock 30-45 °C at exposure times 23.5 h/0.5 h; 23 h/1 h; 22 h/2 h; 21 h/3 h; 19 h/5 h; 18 h/6 h and 17 h/7 h ). Both were conducted in a completely randomized design, with four replications of 25 seeds each, totaling 100 seeds/treatment. In Chapter II, the treatments were arranged in a randomized block design and split-plot system, analyzing seed mass (small: 4 to 5.9 g; medium: 6 to 7.9 g and large: 8 to 9.9 g) x reduction in light capacity (0; 30; 50; 70 and 80%), using four repetitions of 25 seeds each, totaling 100 seeds/treatment. In Chapter III, the treatments were arranged in a randomized block design, consisting of treatments with different water contents in the seeds (30%, 15%, 10%, and 4%). Then, part of the seeds with a water content of 4% was stored in aluminum containers for three months at freezer (-20) and ultrafreezer (-86 °C) temperatures. Each treatment consisted of 100 seeds, organized in four replications of 25 seeds each. Chapter IV was divided into two storage experiments, with L. pisonis seeds placed in Kraft Nat® paper bags (jute bags) measuring 23.5 x 10 x 31.5 cm and stored in germination chambers of the Biochemical Oxygen Demand (BOD) type, at temperature and relative humidity of 25 °C (RH = 63%); 6 °C (RH = 49%); 2 °C (RH = 31%) and -6 °C (RH = 10%), with the emergence of experiment 1 conducted in BOD and that of experiment 2 in a greenhouse. In Chapter, I, experiment 1 presented efficient results when exposing L. pisonis seeds to thermal shock 30-45 °C (20 h/4 h) and in experiment 2, when subjecting the seeds to thermal shock 30-45 °C (21h/3h). In both cases, there was high seedling emergence, high vigor, and an efficient antioxidant system, with increased activity of the enzymes SOD, CAT, and APX. In Chapter II, it was observed that large seeds showed the highest seedling emergence (83.9%) when exposed to shading of 49.32% (~50%). In Chapter III, seedling emergence decreased depending on the water content in the seeds (30>15>10>4%), varying between 88 and 64% emergence, respectively, which were classified as intermediate seeds. In Chapter IV, experiment 1 obtained greater germination (95%) and seedling emergence (65%) in seeds stored at 2 °C for 11 months. For experiment 2, seeds stored at a temperature of 6 °C achieved seedling emergence rates greater than 70% for most months of storage. It is concluded in Chapter I that the thermal shock of 30-45 °C at exposure times of 20 h/4 h and 21 h/3 h are optimal for the emergence of L. pisonis seedlings. In Chapter II, the use of large seeds (8 to 9.9 g) and 50% shading is recommended for the emergence of L. pisonis seedlings. In Chapter III, it is concluded that L. pisonis seeds have intermediate characteristics. In Chapter IV, it is concluded that it is possible to preserve L. pisonis seeds for one year in storage at a temperature of 6 °C, which are classified as intermediate seeds.
Keywords: seeds, germination, oilseed plants, seed storage, seed physiology.
