Charles Lobo Pinheiro

Estresse hídrico e massa de sementes na germinação e crescimento de plântulas de Amburana cearensis (Allemão) A.C. Smith

Amburana cearensis, known locally as Cumaru, is a species found throughout the caatinga biome, being recommended in the reclamation of degraded areas and for use in phytotherapy. The aim of the present work was to determine the levels of tolerance to water stress at germination and on seedling growth in seedlings of the cumaru, as a function of seed weight. The seeds were initially weighed and separated into three classes (light, medium and heavy), then subjected to water stress using solutions of polyethylene glycol 6000 at different potentials (0.0, -0.2, -0.4, -0.6, -0.8 and -1.0 MPa) and left to germinate at 30 °C in germination chambers. The experimental design was a completely randomised 3 x 6 factorial scheme (weight class x water potential). To evaluate germination, first count, final percentage and rate of germination index were determined, while to evaluate seedling growth, the length and dry weight of the epicotyl and of the root axis plus hypocotyl, and the shoot to root ratio were all determined. Data were tested for normality, and if normal, variance analysis, means comparison and regression were carried out. A decrease in water potential impairs the germination and growth of seedlings derived from medium and heavy seeds in relation to light seeds, with potentials of -0.6 MPa or more strictly limiting the formation of normal seedlings of A. cearensis.

A ALELOPATIA AUMENTA O POTENCIAL INVASOR DE Cryptostegia madagascariensis Bojer ex Decne.

Allelopathy is one of the mechanisms related to the invasive potential of exotic species. The objective of this work was to evaluate the allelopatic activity of compounds extracted from the leaves of the invasive species Cryptostegia Madagascariensis in native species of the Brazilian semi arid region. Seeds of the native species Piptadenia stipulacea, Libidibia ferrea and Mimosa caesalpiniifolia were used; Besides the bioindicator species Lactuca sativa. The work was carried out under laboratory conditions. Four species and three extracts (control, fresh leaves and leaves of the litter) were studied, with four replicates each. We evaluated the effects on germination and initial seedling growth. It was observed that L. sativa had its germination and seedling growth reduced by about 50% or inhibited in the presence of the extracts. For the native species, the extracts had a negative effect on seedling growth, reducing the root growth of M. caesalpiinifolia and L. ferrea by 30%.The extract obtained from fresh leaves showed to have greater allelopathic effect when compared to that of litter. Therefore, the production of compounds with allelopathic activity may increase the invasive potential of C. madagascariensis and negatively affect seedling growth of native species of M. caesalpiinifolia and L. ferrea.