BackgroundPhotosynthesis can be roughly separated into biochemical and photochemical processes. Both are affected by drought and can be assessed by non-invasive standard methods. Gas exchange, which mainly assesses the first process, has well-defined protocols. It is considered a standard method for evaluation of plant responses to drought. Under such stress, assessment of photochemical apparatus by chlorophyll fluorescence needs improvement to become faster and reproducible, especially in growing plants under field conditions. For this, we developed a protocol based on chlorophyll fluorescence imaging, using a rapid light curve approach.ResultsAlmost all parameters obtained by rapid light curves have shown statistical differences between control and drought stressed maize plants. However, most of them were affected by induction processes, relaxation rate, and/or differences in chlorophyll content; while they all were influenced by actinic light intensity on each light step of light curve. Only the normalized parameters related to photochemical and non-photochemical quenching were strongly correlated with data obtained by gas exchange, but only from the light step in which the linear electron flow reached saturation.ConclusionsThe procedure developed in this study for discrimination of plant responses to water deficit stress proved to be as fast, efficient and reliable as the standard technique of gas exchange in order to discriminate the responses of maize genotypes to drought. However, unlike that, there is no need to perform daily and time consuming calibration routines. Moreover, plant acclimation to the dark is not required. The protocol can be applied to plants growing in both controlled conditions and full sunlight in the field. In addition, it generates parameters in a fast and accurate measurement process, which enables evaluating several plants in a short period of time.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-017-0209-z) contains supplementary material, which is available to authorized users.

Sugarcane (Saccharum spp.) is a monocotyledonous semi‐perennial C4 grass of the Poaceae family. Its capacity to accumulate high content of sucrose and biomass makes it one of the most important crops for sugar and biofuel production. Conventional methods of sugarcane breeding have shown several limitations due to its complex polyploid and aneuploid genome. However, improvement by biotechnological engineering is currently the most promising alternative to introduce economically important traits. In this work, we present an improved protocol for Agrobacterium tumefaciens‐mediated transformation of commercial sugarcane hybrids using immature top stalk‐derived embryogenic callus cultures. The callus cultures are transformed with preconditioned A. tumefaciens carrying a binary vector that encodes expression cassettes for a gene of interest and the bialaphos resistance gene (bar confers resistance to glufosinate‐ammonium herbicide). This protocol has been used to successfully transform a commercial sugarcane cultivar, SP80‐3280, highlighting: (i) reduced recalcitrance and oxidation; (ii) high yield of embryogenic callus; (iii) improved selection; and (iv) shoot regeneration and rooting of the transformed plants. Altogether, these improvements generated a transformation efficiency of 2.2%. This protocol provides a reliable tool for a routine procedure for sugarcane improvement by genetic engineering. © 2017 by John Wiley & Sons, Inc.

The objective of this work was to assess the morphophysiological characteristics and the ionic imbalance in the substrate, roots, and leaves of young oil palm (Elaeis guineensis) plants under different levels of saline stress, following a substrate salinization protocol in which the level of salt was known. Bifid oil palm plants were subjected to different NaCl rates (0.0, 0.5, 1.0, 1.5, and 2.0 g NaCl per 100 g substrate on a dry basis), and their morphophysiological responses were evaluated for a period of 12-14 days. This protocol generated different levels of stress due to the gradients of electrical conductivity and water potential in the saturation extract of the substrate, according to the added NaCl. Based on the rates of real evapotranspiration and leaf gas exchange, the osmotic effect of the salt reflected negatively on leaf temperature, on the chlorophyll content index, and on the chlorophyll fluorescence variables. The increase in Na and Cl levels in the saturation extract culminated with the increasing availability of Ca, K, and Mg in the solution and their accumulation in the leaves. However, the plants poorly absorbed Na and Cl. The obtained results are indicative that, for a better characterization of the osmotic and ionic phases of salinity stress, it is necessary to reduce the applied level of salinity stress and to increase the evaluation period.

The recent and continuous development of unmanned aerial vehicles (UAV) and small cameras with different spectral resolutions and imaging systems promotes new remote sensing platforms that can supply ultra-high spatial and temporal resolution, filling the gap between ground-based surveys and orbital sensors. This work aimed to monitor siltation in two large rural and urban reservoirs by recording water color variations within a savanna biome in the central region of Brazil using a low cost and very light unmanned platform. Airborne surveys were conducted using a Parrot Sequoia camera (~0.15 kg) onboard a DJI Phantom 4 UAV (~1.4 kg) during dry and rainy seasons over inlet areas of both reservoirs. Field measurements of total suspended solids (TSS) and water clarity were made jointly with the airborne survey campaigns. Field hyperspectral radiometry data were also collected during two field surveys. Bio-optical models for TSS were tested for all spectral bands of the Sequoia camera. The near-infrared single band was found to perform the best (R2: 0.94; RMSE: 7.8 mg L−1) for a 0–180 mg L−1 TSS range and was used to produce time series of TSS concentration maps of the study areas. This flexible platform enabled monitoring of the increase of TSS concentration at a ~13 cm spatial resolution in urban and rural drainages in the rainy season. Aerial surveys allowed us to map TSS load fluctuations in a 1 week period during which no satellite images were available due to continuous cloud coverage in the rainy season. This work demonstrates that a low-cost configuration allows dense TSS monitoring at the inlet areas of reservoirs and thus enables mapping of the sources of sediment inputs, supporting the definition of mitigation plans to limit the siltation process.

Quinoa stands out as an excellent crop in the Cerrado region for cultivation in the off-season or irrigated winter season. Here, we tested the effects of different water regimes on the agronomic characteristics, physiology, and grain quality of different elite quinoa genotypes under field conditions. The experiment was conducted under field conditions at Embrapa Cerrados (Planaltina, DF, Brazil). The experimental design was in randomized blocks, in a split-plot scheme, with four replications. The plots were composed of 18 quinoa genotypes and modified BRS Piabiru (the currently used genotype), and the split-plots were divided into 4 different water regimes. The following variables were evaluated: productivity and productivity per unit of applied water (PUAA), plant height, flavonoids, anthocyanins, gas exchange, chlorophyll, leaf proline, and relative water content. Our results showed that water regimes between 309 and 389 mm can be recommended for quinoa in the Cerrado region. CPAC6 and CPAC13 presented the highest yield and PUAA under high and intermediate WRs, and hence were the most suitable for winter growth under irrigation. CPAC17 is most suitable for off-season growth under rainfed conditions, as it presented the highest PUAA under the low WRs (247 and 150). CPAC9 stood out in terms of accumulation of flavonoids and anthocyanins in all WRs. Physiological analyses revealed different responses of the genotypes to water restriction, together with symptoms of stress under lower water regimes. Our study reinforces the importance of detailed analyses of the relationship between productivity, physiology, and water use when choosing genotypes for planting and harvest in different seasons.