Sementes recalcitrantes: problemas na pós-colheita

Abstract

RESUMOAtualmente, das 6.721 espécies consideradas de importância econômica 7% possuem sementes que, além de serem sensíveis à dessecação, não toleram armazenamento sob baixas temperaturas, dificultando sua conservação por períodos prolongados. A curta longevidade restringe o prazo de utilização das sementes, sendo necessário realizar a semeadura logo após sua extração dos frutos, ou tentar conservá-las sob condições adequadas de temperatura, embalagem e, principalmente, de teor de água; sementes com teores de água acima de 10% a 13%, a incidência de microorganismos pode comprometer sua viabilidade. Estudos técnico-científicos têm revelado características ecológicas, morfológicas e fisiológicas das sementes recalcitrantes que podem contribuir para o aprimoramento de suas técnicas de propagação. Com base nas informações literárias disponíveis, esta revisão tem por objetivo abordar os principais problemas encontrados após a colheita dessas sementes. Palavras-chave: sementes recalcitrantes, conservação. ABSTRACT RECALCITRANTS SEEDS: POST-HARVEST PROBLEMSAt present, 7% of 6.721 species with some economic importance have seeds that are sensitive to dehydration and do not tolerate storage at low temperatures. The short longevity can reduce the time of seeds utilization, being necessary either to sow then immediately after fruit extraction, or to maintain them under adequate conditions of temperature, storage and water content. Also, seeds with water content above 10%-13% could have the viability reduced by the action of microorganisms. Some studies show ecological, morphological and physiological characteristics of recalcitrant seeds, which can contribute to improve propagation techniques. Therefore based on available literature, this revision was carried out to approach the main problems that can be found after harvesting of recalcitrant seeds.

Biological activities and chemical constituents of Araucaria angustifolia : An effort to recover a species threatened by extinction

“…However, due to the recalcitrant characteristics of the seeds, the viability of their effective use can be compromised by the drying processes such as those used with corn, rice, beans and others (Fonseca and Freire, 2003). In this way, many studies have looked for storage alternatives aiming the pinhão conservation.…”

Sementes recalcitrantes: intolerantes a baixas temperaturas? Embriões recalcitrantes de Inga vera Willd. subsp. affinis (DC.) T. D. Penn. toleram temperatura sub-zero

“…Acima de determinados níveis de hidratação, a água torna-se congelável, tanto nas sementes intolerantes à dessecação quanto nas tolerantes, podendo ocasionar danos devido à formação de cristais de gelo nos tecidos e levando à perda da viabilidade (Fonseca & Freire 2003). A principal conseqüência da formação de cristais de gelo é a ruptura mecânica, tanto da estrutura citoplasmática quanto da membrana celular, pela expansão da água congelada, resultando na desagregação celular (Taiz & Zeiger 2004).…”

Tetrazolium test for viability estimation of Eugenia involucrata DC. and Eugenia pyriformis Cambess. seeds

“…To interpret the tetrazolium test, according to França-Neto et al (1998), the analyst must know the seed structures and have experience and capacity for critical judgment. It is important to mention that the uvaia seeds staining were weak (Figure 2), making it difficult to assess them, differently from the cherry seeds situation (Figure 1), demonstrating that the staining pattern can be different for each species and depends primarily on the concentration used.…”

“…Therefore, studies on seeds storage are necessary, since the feasibility is under direct influence of time and storage conditions (Fonseca and Freire, 2003). Some studies regarding the seeds storage of Eugenia species have been reproduced to verify the ideal time and storage conditions, as reported by Barbosa et al (1990); Andrade and Ferreira (2000); Scalon et al (2004); Delgado and Barbedo (2007); Justo et al (2007); among others.…”

“…Among tests with fast results, there is the tetrazolium test based on the dehydrogenize enzymes activity that reduces salt at 2,3,5-triphenyl tetrazolium chloride in the seeds living tissues, generating a compound called trifenilformazan of red color and not diffusible, indicating that a respiratory activity exists, and cell and tissues viability (França-Neto et al, 1998). This test can be used to speed up the seed's quality evaluation, allowing decisions making related to the seed management (Pinto et al, 2008).…”