In general, several authors, such as INMAN-BAMBER (2004), PIMENTEL (2004), COELHO (2012), have mentioned thesugarcane canopy and productivity reduction when thewater supply is limited. However, there is little knowledge on water restriction and its effects on sugarcanegrowth, especially attheinitialphase. This information makes it possible to recommend sugarcane planting ideal periods as a function of rainfall distribution, as well as to recommend a possible “rescue irrigation” during dry spell periods without affecting significantly initial crop growth and, consequently, final production. Based on the hypothesis that sugarcaneinitialgrowth has no significant reduction until a certain level of waterdeficit, this study aimed to quantify such amount for sugarcane plants grown at different available soil water depths.
Due to the low water availability in the substrate, a positive correlation between Ψw, stomatal conductance and photosynthesis in both genotypes was observed (Table 1). Similar effects were demonstrated in different sugarcane genotypes cultivated underwaterdeficit conditions in the field (Smit and Singels 2006; Endres et al. 2010). It could be inferred that the TCP02-4587 genotype provided better drought adaptations underthe present experimental conditions. This could be explained by a possible osmotic adjustment that occurred during waterdeficit (Jamaux et al. 1997). During thewaterdeficit period, the HoCP93-776 genotype had a low relative leaf water level value at 77.8%, whereas the TCP02-4587 genotype reached 83.8% (Fig. 4B). The maintenance of the RWC in the TCP02-4587 plants may be the result from protoplasts being hydrated for a longer time period during water shortage conditions. This may also be an indicator of the degree to which the tissues and cells are hydrated, which is a crucial factor for optimal physiological functioning (Begg and Turner 1976). Silva et al. (2011) determined average RWC values from 73% to 79% for sensitive sugarcane genotypes and RWC values from 85 to 87% for tolerant genotypes underwaterdeficit conditions in the field. This confirmed that tolerant plants possessed higher capacity to save water during the drought period. Silva et al. (2007); Rodrigues et al. (2009) and Graça et al. (2010) also observed a small RWC reduction in the tolerant genotypes, with an average RWC above 80%. According to Graça et al. (2010), the decreased relative water content stimulates an adjustment of the photosynthetic capacity to tolerate the changes in water availability. This study illustrated that the TCP02-4587 genotype maintained relatively high RWC values during water restriction, thereby indicating drought tolerance in this genotype.
Waterdeficit is one of the major factors limiting the production of sugarcane, especially in areas where there is a prolonged period of water deficiency, such as the West Central Brazilian region. One way to overcome this problem is to cultivate resistant or tolerant varieties. An experiment was set up atthe Jalles Machado Sugar Mill, located near Goianésia, Goiás State, Brazil, to evaluate agronomic performance of several sugarcane families. A comparative analysis was carried out among the families under two irrigation regimes, one under regular environmental conditions and another under monthly irrigations during the period of water deficiency. Evaluated families consisted of 25 progenies planted in a factorial design with three replications with 20 plants each. The first ratoon crop was evaluated for four yield components, stalk height, stalk diameter, stalk number and Brix. By analysis of variance, stalk number and stalk height were influenced by water stress conditions during theinitialgrowthphase, and for stalk diameter and Brix, water regime had no effect on the average expression of the characters during thegrowthphase. The method of classification in four categories proved to be adequate. Some families had high values for stalk diameter, stalk number and stalk height underwater stress conditions. This study showed that it is possible to select sugarcane families underwaterdeficit conditions associated with higher stalk diameter, stalk number and stalk height.
randomized experimental design, with four replicates. Salinity was obtained by the addition of NaCl into the local water supply, being these waters used to prepare the nutrient solution and to replace the evapotranspirated water volume. We noticed a reduction in leaf area, fresh and dry mass of shoot, K content in plant and water consumption of the crop and, increased contents of P, Na, Cl in the plants, with increasing salinity of the solution. The use of brackish water for watercress cultivation in hydroponics is possible as an alternative for producers who have availability of brackish water and restricted possibility of fresh water. A reduction in dry mass of plants was observed with increasing electrical conductivity.
∆S was obtained by the difference between initial and final values of soil water storage in the 14-day interval, monitored through access tubes installed in each experimental subplot, 0.10 m away from the forage cactus and sorghum crops, using a capacitive probe (Diviner@2000, Sentek Pty Ltda. Australia), previously calibrated for the experimental area, as described by Araújo Primo et al. (2015). Readings were taken in relative frequency and automatically converted to water depth at every 0.10 m, until the 0.70 m depth, one layer below the lower limit depth of the control volume (0.60 m). Readings were taken at 3 day intervals, from June 2012 to June 2013.
ABSTRACT: Plants in natural environments are subjected to a multitude of environmental cues. However, studies addressing physiological analyzes are usually focused on the isolation of a stress factor, making it difficult to understand plants behavior in their extremely complex natural environments. Herein, we analyzed how environmental variability (noise) may influence physiological processes of Glycine max underwaterdeficit conditions. The plants were kept in a greenhouse (semi-controlled environment – E SC ) and in a growth chamber (controlled environment – E C ) under two water regime conditions (100 and 30% of replacement of thewater lost by evapotranspiration) for 30 days. The environmental variability was daily monitored with automatic sensors to record temperature, humidity, and irradiance. The physiological responses were analyzed by leaf gas exchanges, chlorophyll fluorescence, biomembrane integrity, and growth parameters. The results showed that water deficiency caused significant reductions in the physiological parameters evaluated. However, the environment with high variability (E SC ) caused more extensive damages to biomembranes, regardless thewater regime likely compromising physiological efficiency. The lower variability of E C promoted higher
ABSTRACT - Tropical kudzu (Pueraria phaseoloides (Roxb.) Benth., Leguminosae: Faboideae) is native to the humid Southeastern Asia. Tropical kudzu has potential as a cover crop in regions subjected to dryness. The objective of this paper was to evaluate the effect of soil water depletion on leaflet relative water content (RWC), stomatal conductance (g) and temperature (T L ) in tropical kudzu. RWC of water-stressed plants dropped from 96 to 78%, following a reduction in SWC from 0.25 to 0.17 g (H 2 O).g (dry soil) -1 . Stomatal conductance of stressed plants decreased from
Figure 2 shows the stress-strain curves of Nafion membrane as received, the membrane soaked in water for 24 h and membrane soaked in boiling water for 1 h. The increase of water content decreases theinitial slope of the curve, and increasing the degree of elongation the modulus reduces, particularly for the membrane soaked in waterat its boiling temperature. The high water content swells the membrane and works as a plasticizer reducing the intermolecular for- ces, mainly the ionic interaction in ionomer increasing the degree of elongation. The stress-strain curve of Nafion membrane shows no yield point, and in the experimental conditions used, it is not observed the break point and also the elongation at break, so Nafion-acid membrane present a reasonably high tenacity and toughness (area underthe stress-strain curve). No necking was observed in the experimental range of applied tension mode (small strain).
actual importance of diffusional and metabolic limitations to photosynthesis imposed by drought. Generally, theinitial decrease of photosynthesis is due to stomatal closure, which protects the plant against excessive water loss, but simultaneously limits CO 2 availability to the leaf mesophyll (Chaves 1991; Flexas et al. 2002; Flexas & Medrano 2002). Besides stomatal limitations, metabolic limitations to photosynthesis, related to reduced RuBP regeneration (Gimenez et al. 1992; Gunasekera & Berkowitz 1993), Rubisco activity (Medrano et al. 1997), ATP production (Tezara et al. 1999; Lawlor & Cornic 2002), photosystem II (PSII) activity and electron transport rate (Long et al. 1994) have also been proposed. The extension of stomatal and metabolic limitations imposed by water stress on photosynthesis will affect diurnal patterns of gas exchange. An efﬁ cient regulation of photosynthesis throughout the day refl ects plant capacity to maintain an internal balance among several processes as it responds to varying environmental conditions (Geiger & Servaites 1994). The general objective of this study is to better understand the mechanisms used by castor bean to tolerate drought. More speciﬁ cally this paper aims to study the effects of soil water-deﬁ cits on plant growth and biomass allocation and on the daily
The different osmotic potentials were obtained through the values proposed by Villela et al. (1991), using polyethylene glycol (PEG 6000). Then, the germination test was installed, in which the seeds were placed on two sheets of paper towel, covered with a third sheet and arranged in the form of a roll, moistened with distilled water (control) or solution of PEG 6000 at different potentials (-0.1; -0.2; -0.3; -0.4; -0.5; -0.6 MPa), in the amount equivalent to 2.5 times the dry weight of the substrate.
Soil water content monitoring was performed using the TDR100 time-domain reflectometer (Campbell Scientific Brasil, São Paulo, SP, Brazil), consisting of 40 probes with 0.3 m of length, interconnected by 50Ω coaxial cables, seven SDMX50 multiplexers, and one CR10X datalogger. The probes were installed in the 0.0–0.3 and 0.3–0.6-m layers, about 0.2 m from the central row of the plants of each plot. For the installation of the deepest probe, it was necessary to excavate the soil to a depth of 0.3 m, which allowed maintaining the original structure and density of the layer. Soil moisture was recorded every 30 min. The values of humidity, at a daily scale, were obtained by the average of the 48 records for each day.
Pimentel (2004) and Martins (2008) consider waterdeficit and salinity as the main sources of abiotic stress affecting plant production and development. According to Zambolim and Junqueira (2004), there are several sources of abiotic stress that predispose mango tree to diseases, being climate and the use of susceptible rootstock, some of them. For Waller (2013), unfavorable climatic factors can favor the primary attack of pests and pathogens and reduce resistance, making them more vulnerable to secondary attack, such as fungal diseases. Some authors have demonstrated this correlation in several cultures (SCHOENEWEISS, 1981; RISTAINO; DUNIWAY, 1989; VIDA et al., 2004; DESPREZ- LOUSTAU et al., 2006). In contrast, other authors have demonstrated the opposite (JACOBI; RIFFLE, 1989; SWART et al., 1992; MAUCH-MANI; MAUCH, 2005); therefore the environmental effect on the incidence of fungal diseases varies according to disease and climate.
from which they are developed remains problematic (Chang et al., 2010), possibly in part because derived empirical formulations do not include the potential for polar or- ganic gases to partition to polar solvents such as water and react in that medium. Parikh et al., find that when an Odum 2-product or volatility basis set (VBS) SOA model is ap- plied to independent smog chamber studies where relative humidity (RH) and particle
Guinn and Mauney (1984) stated that the severe waterdeficit applied to cotton limited the yield as a function of the decrease in the number of bolls per area, which occurs due to the reduction in flowering and young boll shedding. Other authors, such as Wen et al. (2013), also affirmed that waterdeficit in cotton causes boll shedding and thus lower productivity. Loka and Oosterhuis (2012) showed that the reproductive stage is the most sensitive stage to waterdeficit in cotton, while De Kock, De Bruyn and Human (1993) stated that the peak bloom phase is most sensitive to waterdeficit, confirming the results found here.
was applied to two soybean cultivars (MG/BR46-Conquista – conventional, and BRS-Valiosa-RR – transgenic) at two phenological stages (V2 – first fully expanded trifoliate leaves, and V4 – third fully expanded trifoliate leaves), using three soil water potentials (-0.03 MPa, -0.07 MPa, and -0.5 MPa). Phytotoxicity, and plant height were evaluated at 3, 7, 14, and 21 days after the herbicide application. The shoot dry weight, root dry weight, and root system nodulation were evaluated. The soybean plants had lower phytotoxicity when subjected to application of chlorimuron-ethyl underwaterdeficit conditions. The use of chlorimuron-ethyl reduced thegrowth and biomass of soybean plants and affected the plants' root system nodulation. The transgenic cultivar (BRS-Valiosa-RR) presented better performance when subjected to a moderate waterdeficit (-0.07 MPa), which contributes to biological nitrogen fixation.
The problem of the lack of adequate water resources for agriculture has intensified in recent years, making it necessary to use waters with relatively high concentration of salts for the irrigation of crops all over the world. The objective of this study was to evaluate the influence of potassium (K) fertilization as a salt stress attenuator on gas exchanges and photochemical efficiency of West Indian cherry. The crop was cultivated under greenhouse conditions in the municipality of Campina Grande, PB, in lysimeters filled with 250 kg of sandy loam soil. Treatments were distributed in randomized blocks, in a 2 x 4 factorial scheme, with two levels of electrical conductivity of irrigation water - ECw (0.8 and 3.8 dS m -1 ) and four K doses (50,
The higher the stress, the more damages to the cell membranes, leading to an increase in electrolyte leakage. The plant’s ability to maintain plasma membrane integrity is lower, which may indicate stress sensitivity. The maintenance of membrane integrity after waterdeficit is an important indicator of stress tolerance (Bajji et al. 2002). Wheat cultivars with lower electrolyte leakage were classified as stress tolerant because they demonstrated the ability to maintain membrane integrity. The same was observed in safflower (Zebarjadi et al. 2010) and in peanut cultivars (Clavel et al. 2005). In the present study, line IMA 16 showed the lowest electrolyte leakage under stress and good ability to maintain membrane stability, indicating drought tolerance.
Genotypes Pingo-de-ouro-1-2, Pingo-de-ouro-2, BRS Xiquexique, Tracuateua-192, Canapuzinho-2 and Canapuzinho showed the highest in the HMG underwater stress conditions, but this fact did not result in higher yields; conversely, the genotype Tracuateua-192, despite having increased the HMG with the imposition of thedeficit, presented the lowest productivity among all genotypes studied. Lima (2008) found no significant reductions in the value of this variable for cowpea when water stress was imposed during the reproductive period. According to Nascimento et al. (2004), this component of production reflects the relationship between source and drain. When the HMG is reduced, this indicates that production was limited atthe source. This may occur due to the large number of pods, as in case of the properly irrigated treatments, or by the effect of water stress on photosynthesis or translocation of photoassimilates. The highest mass of grains may reflect a compensation for size drain limitations. These authors found results in cowpea that disagree with the data obtained in this experiment, once the one hundred grains mass in response to waterdeficit during the fructification was significantly reduced.
In thegrowth cycle of the second leaf (first ratoon) the varieties showed the same growth profile with RB867515 and RB72454 growing faster than the other and the RB92579 being the least to the first ten-day period of November 2007 when it reached 397 cm tall and was second only to RB867515 which reached 424 cm. In this crop, water deficiency began early (in the first 10-day period of September) and undermined thegrowth of varieties, especially thegrowth of RB92579 which is characterized for keeping thegrowth rate in the final phase of growing above the other cultivars used in this experiment. WIEDENFELD & ENCISO (2008) evaluating thegrowth of sugarcane in four cycles of cultivation (sugarcane until the third ratoon, irrigated by drip) observed an average height of stem of 208 cm, with an average growth rate of 1.50 cm day -1 . SILVA et al. (2009) studying the variety SP-791011 in the State of Paraiba (Brazilian northeast) observed that in 12 months of cultivation of second ratoon, produced stem with 231 cm in length, in irrigated planting and 185 cm in non-irrigated dry land crop.