Roberta Cristiane Ribeiro

Um novo clorofilômetro para estimar os teores de clorofila em folhas do capim Tifton 85

The purpose of this research was to evaluate the performance of a new portable chlorophyll meter in the indirect determination of chlorophyll contents in Tifton 85 bermudagrass leaves. In a field trial of short duration, three N doses (0, 75 and 150kg ha-1) were combined with four sampling dates (8, 16, 24 e 28 days after a cut for sward uniformity) in completely randomized blocks, with treatments arranged in a split-plot design. Analyses were performed in the youngest fully expanded leaf blade. Contents of chlorophylls a, b and total were quantified spectrophotometrically, after extraction with acetone 80%, while chlorophyll meter readings, expressed as Falker Chlorophyll Index (FCI) units, provided the same information. Chlorophyll meter readings were sensitive to both N rates and sampling dates. It were obtained significant positive correlations between both methods (chlorophyll a: r=0.646, chlorophyll b: r=0.797 and for total chlorophyll: r=0.721). It was concluded that this new chlorophyll meter constitutes an appropriate tool for the indirect determination of foliar chlorophyll contents in Tifton 85 pastures.

Allelopathic Activity of the Hydrolate and Water Decoction of Brachiaria humidicola (Rendle) Plant Parts on the Germination of Four Tropical Leguminous Species

Knowledge of allelopathic interactions between grasses and legumes can contribute for the successful establishment of mixed tropical pastures in Brazil. The purpose of this work was to evaluate the allelopathic effect of the hydrolate and water decoction of Brachiaria humidicola (Rendle) plant parts (root, shoot, and seeds) on four tropical forage legumes Stylosanthes spp. cv. Campo Grande, Macrotyloma axillare, Calopogonium mucunoides, Desmodium ovalifolium, and on lettuce (Lactuca sativa L.), this last species used as a sensitivity standard in allelopathic bioassays. The results obtained for roots and shoots showed, in the case of hydrolate, the highest inhibitory effect on germination rates of the receiving species, while seed hydrolates had a stimulating effect depending on the legume species. In contrast, water decoction extracts had the highest inhibitory effects on root and seed fraction, and the lowest on the shoot fraction. Regarding the receiving species, germination percentages of M. axillare showed higher tolerance to inhibitory effects of the aqueous extracts of B. humidicola, while D. ovalifolium showed the highest sensitivity.

Phytotoxic effects of phenolic compounds on Calopogonium mucunoides (Fabaceae) roots

Studies on phenols have gained attention owing to their abundance in plants and their effects on plant development. Phenols from forage grasses may exert phytotoxicity on legume crops in intercropping systems. We aimed to identify morpho-anatomical variations in Calopogonium mucunoides Desv. roots treated with phenolic compounds. Seeds of C. mucunoides were treated with (1) distilled water (control), (2) trans-cinnamic acid, (3) a mixture of the flavonoids quercetin, rutin, kaempferol and kaempferol-3-α-rhamnoside, or (4) a combination of the flavonoid mixture and trans-cinnamic acid. After 10 days of treatment, the roots were measured, described and processed according to standard techniques in plant anatomy. In general, non-control individuals showed plant lengths decreased by 40–45%, root-tip necrosis and intense lateral root ramification. Seeds germinated in cinnamic acid presented xylem poles with a greater number of cells and a greater emission of lateral roots. In the seeds treated with flavonoids, cell division was observed in the endodermis and the pericycle, and xylem fibres went through differentiation. The combination of cinnamic acid and flavonoids led to the premature formation of fibres by the phloem. The treatments with flavonoids or cinnamic acid alone were significantly greater in root diameter (868.61 µm and 810.35 µm, respectively) than was the application of both (714.98 µm) or the control (533.76 µm). The results suggest that cinnamic acid and the tested flavonoids negatively affect the development and the root structure of C. mucunoides.