Photosynthetic and Production of Urochloa ruziziensis Inoculated with Azospirillum brasilense under Drought

Aims: The objective of this study was to evaluate the photosynthetic activity and production of Urochloa ruziziensis when inoculated with Azospirillum brasilense in the presence and absence of drought. Study Design: Randomized block design and factorial 2x2. Methodology: The first factor was the presence or absence of seed inoculation with A. brasilense strains AbV5 + AbV6; the second factor was the presence or absence of drought. The variables evaluated were: relative water content (RWC), soil gravimetric moisture, net assimilation rate of CO2, response in function of active photon flux density, apparent quantum efficiency, light compensation point, absolute integrity of membrane, damage to membranes, dry mass aborted leaves, and total dry mass of aerial part. Results: Results demonstrate that plants maintained in drought presented a reduction in all evaluated variables. Under conditions of drought the use of A. brasilense promoted smaller variations in RWC, net assimilation rate of CO2, apparent quantum efficiency, light compensation point, absolute integrity of membrane, and damage to membranes; no variations were observed for dry mass, aborted leaves or total dry mass of aerial part. Conclusion: The inoculation of U. ruziziensis seeds with A. brasilense mitigates drought damage in plant physiology, but it does not mitigate leaf losses or plant productivity.

Morphophysiogenetic characterization of wild poinsettia biotypes with low resistance to glyphosate

The objective of this work was to compare wild poinsettia (Euphorbia heterophylla) biotypes as to their morphological characteristics, as well as to determine their genetic similarity in the state of Rio Grande do Sul, Brazil, and to confront the light compensation point of susceptible biotypes and of biotypes with low-resistance level to glyphosate. Besides the morphology analysis, the study included the genetic characterization, by AFLP, of susceptible (GR50= 58.65 g ha-1 a.e.) biotypes and of biotypes with low resistance (GR50= 310.36 g ha-1 a.e.) to glyphosate. The competitive ability of the biotypes was inferred according to their light compensation point. The observed morphological characteristics do not allow to differentiate biotypes as to their geographical location, or their resistance level to glyphosate. The genetic analysis identified low genetic diversity among the 15 tested biotypes, with a large amount of subgroups. The biotypes with low resistance formed an isolated group. The susceptible biotypes showed the lowest values of light compensation point and, possibly, they have a greater competitive ability under low-luminosity conditions. The evaluated characteristics do not enable to differentiate genotypes with different levels of glyphosate resistance.

Effects of Light Intensity and Paclobutrazol on Growth and Interior Performance of Pachira aquatica Aubl.

Pachira aquatica Aubl. has recently been introduced as an ornamental foliage plant and is widely used for interiorscaping. Its growth and use under low light conditions, however, have two problems: leaf abscission and accelerated internode elongation. This study was undertaken to determine if production light intensity and foliar application of paclobutrazol [β-(4-chlorophenyl)methyl-α-(1,1-dimethylethyl)-1H- 1,2,4- triazole-1-ethanol] improved plant growth and subsequent interior performance. Two-year-old P. aquatica trunks were planted in 15-cm diameter plastic pots using a peat-based medium and were grown in a shaded greenhouse under three daily maximum photosynthetic photon flux densities (PPFD) of 285, 350, and 550 μmol·m−2·s−1. Plant canopy heights, average widths, and internode lengths were recorded monthly over a 1-year production period. Two months after planting, the plant canopy was sprayed once with paclobutrazol solutions at concentrations of 0, 50, and 150 mg·L−1, ≈15 mL per plant. Before the plants were placed indoors under a PPFD of 18 μmol·m−2·s−1 for 6 months, net photosynthetic rates, quantum yield, and light saturation and compensation points were determined. Results showed that lowering production light levels did not significantly affect canopy height, width, or internode length but affected the photosynthetic light response curve and reduced the light compensation point. Foliar application of paclobutrazol reduced internode length, thereby resulting in plants with reduced canopy height and width and more compact growth form. Paclobutrazol application also reduced the light compensation point of plants grown under 550 μmol·m−2·s−1. Plants with the compact growth form did not grow substantially, dropped fewer leaflets, and thus maintained their aesthetic appearance after placement indoors for 6 months. These results indicated that the ornamental value and interior performance of P. aquatica plants can be significantly improved by producing them under a PPFD range between 285 and 350 μmol·m−2·s−1 and foliar spraying of paclobutrazol once at a concentration between 50 and 150 mg·L−1.

Effects of light on the growth and photosynthesis of Egeria najas planchon

Photosynthesis and growth of Egeria najas (Hydrocharitaceae) from a subtropical reservoir (Itaipu Reservoir, Brazil-Paraguay) were measured in response to low light intensities (0-124 µM m-2 s-1 PAR) in the laboratory. Photosynthesis approached saturation in the range of light intensities used and light compensation point was reached at ca. 6-22 µM m-2 s-1 PAR, indicating that this species had a low light requirement for growth. Light stimulated shoot and root relative growth rates (RGR) but it was not related to ratios between root:shoot RGR. Laboratory observations indicated that (i) both shoot and root growth were simultaneously stimulated by light and (ii) the low light requirements of E. najas may explain its incidence in the Itaipu Reservoir, where biogenic as well as abiogenic turbidity is high.