Bruno França da Trindade Lessa

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.

Efeitos alelopáticos de extratos aquosos de folhas de Amburana cearensis e Plectranthus barbatus na germinação de Amaranthus deflexus

The objective was to verify possible allelopathic effects exerted by aqueous extracts of leaves of Amburana cearensis and Plectranthus barbatus on the seed germination of the weed Amaranthus deflexus. A. deflexus seeds were put to germinate in Petri plates containing aqueous plant extracts obtained from A. cearensis and P. barbatus leaves under two tillage methods – aqueous extract from fresh leaves and aqueous extract by infusion of dried leaves – and two dosages – 50 and 100 g L-1. We used a completely randomized design with 4 replications and a detached witness composing a factorial 2 x 2 x 2 + 1. It was determined the final percentage and germination speed index. Data analysis revealed differences between treatments and the witness, conditioning different allelopathy levels for the extracts used, dramatically affecting the germination of A. deflexus. The A. cearensis fresh leaves extracts has a high level of allelopathy since they prevent almost completely the germination of the weed A. deflexus. The most damaging dosage for germination of A. deflexus was 100 g L-1.

Agronomic Evaluation of Sweet Sorghum in Semiarid Region: Cultivar and Spacing Effects

The objective of this study was to evaluate the agronomic characteristics of two sweet sorghum varieties for row spacing in the semiarid region of the State of Ceara, Brazil. Hence, an experiment was carried out on the Experimental Farm of the Federal University of Ceara, in two agricultural cycles (2015 and 2016), in sandy loam Planosol during the rainy season. Two sweet sorghum varieties (BRS 506 and SF 15), cultivated at 50, 60, 70, and 80 cm row spacing, were evaluated at different times after sowing (30, 45, 60, 75, and 90 days), in a randomized block design repeated four times in the arrangement of subdivided plots (2 × 4 × 5). The BRS 506 variety had higher mean number of leaves and leaf angle +3 in the two cycles evaluated. The highest mean plant height was observed at 90 DAS (328.11 cm). The stalk diameter at 15.59 mm was greatest with 70 cm spacing between rows. The chlorophyll content of the leaves may be influenced by stress factors, such as water and mineral deficiency, primarily nitrogen. The best results for chlorophyll occurred in the first cycle, in which the greatest mean was observed at 75 days, while in the second cycle, a year that presented low precipitation (water stress), the greatest means were observed at 30 days. Taking into consideration our results, BRS 506 variety is recommended for cultivation in semiarid northeastern Brazil, presenting good agronomic characteristics, when sown with 70 cm spacing between the rows.