Maturação, secagem e armazenamento de sementes de cártamo: estudos morfofisiológicos

Abstract

Safflower is a multi-purpose plant; however, it has received special attention due to the quality of the oil extracted from its grains, which is rich in linoleic and oleic acids. With great potential for expansion in Brazil, as a winter alternative in rotation systems, the success in establishing safflower culture in the country depends on, among other factors, the definition of an adequate seed production program. In this sense, in this work carried out at the Federal University of Grande Dourados, Dourados - MS, three researches were conducted covering different stages of the safflower seed production chain. In the first study, divided into two parts, it was initially sought to determine the changes that occur in the moisture content, size and dry matter of the seeds between 5 and 37 days after anthesis (DAA), in addition to verifying the dynamics of acquisition germination and expression of physiological dormancy during maturation. Also, identify possible morphological indicators, in chapters and seeds, linked to the physiological maturity of the seeds. In the second part, the objective was to verify differences between the physiological quality of seeds harvested immediately after the complete senescence of the chapters and vegetative structures of the mother plant and of seeds from a single harvest in a total area, at the end of the crop cycle, when 97 to 99% of the mother plants were completely senescent. The development of safflower seeds is characterized by rapid external growth and gradual accumulation of dry matter, which, under the conditions of this work, was stabilized at 29 DAA (physiological maturity), with a moisture content corresponding to 26.1%. The seeds gradually acquire the ability to germinate from the final third of the dry matter accumulation, with a maximum reached a few days before physiological maturity, this germination being partially inhibited by the presence of primary physiological dormancy. It was also concluded that the triggering of the senescence of the chapters, along with the color transition from greyish to whitish seeds, due to natural dehydration, can be used as physiological maturity indicators for the seeds of this species. Finally, it can be said that the single harvest in total area, taking into account the disparity in the maturation process between plants and the occurrence of adverse climatic conditions, impairs the germination and vigor of the safflower seeds. In the second research of this work, safflower seeds, harvested with a moisture content of 25.8%, were subjected to drying in an experimental dryer with air temperatures between 40 and 70 °C, until reaching 6.6% moisture. Subsequently, these were evaluated for physiological quality, immediately after drying and every 60 days, until 240 days of storage under uncontrolled conditions. The increase in the temperature of the drying air allows for a more abrupt removal of the water molecules contained within the seeds, causing immediate and latent damage to the physiological quality of the seeds, especially from 60 °C. Thus, it is suggested that the drying temperature of safflower seeds does not exceed 40 °C, especially when they present moisture contents close to or above 25.8% at the time of drying. In the third study, the effect of seed moisture content and ambient temperature on the after-ripening dynamics and deterioration of safflower seeds during storage was verified. For that, seed lots with different initial moisture contents (7.4; 6.1 and 4.7%), obtained after artificial drying, were packed in permeable and non-permeable packages (called conventional and airtight systems, respectively) and subsequently stored for 200 days in an environment without temperature and relative humidity control (26.2±2.3 °C and 46.4±8.6%). Concomitantly, a batch of seeds with an initial moisture content of 7.4%, packed in semipermeable packaging, was kept in a cold chamber (16.4±0.8 °C and 79.7±9.3%). At the beginning of storage and every 50 days, the seeds were evaluated for moisture content and physiological characteristics linked to dormancy, viability and vigor. The dynamics of after-ripening of safflower seeds are influenced by the seed moisture content and the prevailing ambient temperature, in which low storage temperatures slow down the process, but do not prevent it, and, at average ambient temperature, close to 25 °C, after-ripening is favored by the maintenance of moisture contents between 5.0 and 6.0%, decelerating, within the range of 4.7 to 8.5%, as the moisture content increases. Considering the adoption of initial moisture contents between 4.7 and 7.4%, the use of packaging that does not allow sudden variations in the moisture content makes it possible to maintain the viability and vigor of safflower seeds for periods of up to 150-200 days under environmental conditions similar to this research, with efficiency similar to that provided by the low temperature of a cold chamber. On the other hand, the significant increase in the moisture content of the seeds, allowed by the use of permeable packaging in storage in an uncontrolled environment, accelerates the deterioration process, even though the moisture content does not exceed 8.5%.