Fraction Of Transpirable Soil Water Thresholds Research Articles

Inheritance of Early Stomatal Closure Trait in Soybean: Ellis × N09-13890 Population.

Drought conditions exhibit various physiological and morphological changes in crops and thus reduce crop growth and yield. In order to mitigate the negative impacts of drought stress on soybean (Glycine max L. Merr.) production, identification and selection of genotypes that are best adapted to limited water availability in a specific environmental condition can be an effective strategy. This study aimed to assess the inheritance of early stomatal closure traits in soybeans using a population of recombinant inbred lines (RILs) derived from a cross between N09-13890 and Ellis. Thirty soybean lines were subjected to progressive water-deficit stress using a dry-down experiment. The experiment was conducted from June to November 2022 at the West Tennessee Research and Education Center (WTREC), University of Tennessee in Jackson, TN, under controlled environment conditions. This study identified significant differences among soybean lines in their early stomatal closure thresholds. The fraction of transpirable soil water (FTSW) thresholds among 30 tested lines ranged from 0.18 to 0.80, at which the decline in transpiration with soil drying was observed. Almost 65% of the RILs had FTSW threshold values between 0.41 to 0.80. These results, indicating inheritance, are supportive of the expression of early stomatal closure trait in progeny lines at a high level in cultivar development for water-deficit stress conditions. Thus, identifying the differences in genotypes of water use and their response to water-deficit stress conditions can provide a foundation for selecting new cultivars that are best adapted to arid and semi-arid agricultural production systems.

Physiological and biochemical responses of soybean to drought as represented by the fraction of transpirable soil water

The influence of water deficit on plant physiological and biochemical responses as measured by the fraction of transpirable soil water (FTSW) has not been investigated in cultivars developed by the world's largest soybean producer. This information can help obtain plants with improved tolerance to the abiotic stress that most affects soybean production in Brazil, enabling adaptation to edaphoclimatic conditions to enhance the crop's yield potential. We aim to determine the FTSW threshold for transpiration and evaluate changes in the growth, physiological activities, and biochemical and antioxidant responses of soybean cultivars. Three trials were sown on 11/19/2018 (T1), 12/28/2018 (T2), and 9/9/2019 (T3), representing almost the entire soybean sowing window in Brazil. The estimated FTSW threshold values were 0.33, 0.29, and 0.31 in T1; 0.35, 0.41, and 0.43 in T2; and 0.31, 0.49, and 0.45 in T3 for cultivars BMX GARRA IPRO, DM 66I68 RSF IPRO, and NA 5909 RG, respectively. In the three trials, NA 5909 RG showed the greatest height. The POD enzyme was activated in non-irrigated plants in T2 only in cvs. DM 66I68 RSF IPRO and NA 5909 RG. We conclude that cvs. DM 66I68 RSF IPRO and NA 5909 RG showed a more efficient stomatal control, conserving soil water for a longer time, which indicates greater tolerance to water deficit.

Elevated CO2 enhanced water use efficiency of wheat to progressive drought stress but not on maize.

Global rising atmospheric CO2 concentration ([CO2]) and drought stress exert profound influences on crop growth and yield. The objective of the present study was to investigate the responses of leaf gas exchange and plant water use efficiency (WUE) of wheat (C3) and maize (C4) plants to progressive drought stress under ambient (a[CO2], 400 ppm) and elevated (e[CO2], 800 ppm) atmospheric CO2 concentrations. The fraction of transpirable soil water (FTSW) was used to evaluate soil water status in the pots. Under non-drought stress, e[CO2] increased the net photosynthetic rate (An) solely in wheat, and dry matter accumulation (DMA), whereas it decreased stomatal conductance (g s) and water consumption (WC), resulting in enhanced WUE by 27.82% for maize and 49.86% for wheat. After onset of progressive soil drying, maize plants in e[CO2] showed lower FTSW thresholds than wheat, at which e.g. gs (0.31 vs 0.40) and leaf relative water content (0.21 vs 0.43) starts to decrease, indicating e[CO2] conferred a greater drought resistance in maize. Under the combination of e[CO2] and drought stress, enhanced WUE was solely found in wheat, which is mainly associated with increased DMA and unaffected WC. These varied responses of leaf gas exchange and WUE between the two species to combined drought and e[CO2] suggest that specific water management strategies should be developed to optimize crop WUE for different species in a future drier and CO2-enriched environment.

Elevated CO2 effect on the response of stomatal control and water use efficiency in amaranth and maize plants to progressive drought stress

Rising CO2 concentration ([CO2]) in the atmosphere may modulate the response of crop plants to drought stress. This study aimed to investigate the response of leaf gas exchange and plant growth of two C4 species representing both dicot (amaranth) and monocot (maize) to progressive drought under two different [CO2] (ambient (a[CO2], 400 ppm) and elevated (e[CO2], 800 ppm)). The soil water status in the pots was expressed as the fraction of transpirable soil water (FTSW). The results showed that as compared to a[CO2], e[CO2] significantly increased net photosynthetic rate (An) at non-stress condition (An max) for both species, while the increase was more pronounced in maize than in amaranth. Stomatal conductance (gs) at non-stress condition was significantly lower at e[CO2] in both species. The FTSW threshold, at which An starts to decrease, was higher in maize grown at e[CO2] than at a[CO2], whereas it was not affected in amaranth. In both species, gs decreased at higher FTSW threshold when grown at e[CO2] than at a[CO2]. e[CO2] decreased stomatal density (SD) in amaranth but increased it in maize; drought increased SD in amaranth but not in maize. Intrinsic water use efficiency (WUEi) was significantly enhanced by e[CO2] and drought stress at FTSW ranged from 0.0 to 0.6, particularly in maize. e[CO2] increased leaf area of well-watered plants in maize and decreased specific leaf area in amaranth. In amaranth, water consumption of well-watered plants was increased and plant WUE was decreased at e[CO2]. The varied responses of leaf gas exchange and WUE to soil water deficits and e[CO2] among the two C4 species imply their different mechanisms in stomatal control over carbon gain versus water loss in dicot and monocot plants, which is essentially important for selecting crop species and developing strategies to optimize crop WUE in a future drier and CO2-enriched climate. The more physiological and biochemical response from soil, stomatal to plant scale related to various environments would be considered in further investigation.

Genotypic variation of conservative and profligate water use in the vegetative and reproductive stages of canola (

Limited water availability is a major constraint to canola (Brassica napus L.) yield in the Mediterranean-type climate region. Selecting and breeding for genotypes with conservative water use characteristics is a promising strategy to improve yield in this environment. Three experiments were conducted to investigate transpiration responses (TR) to vapour pressure deficit (VPD) and progressive soil drying with 8-20 canola genotypes. We used the linear-plateau model to describe TR to elevated VPD and decreased fraction of transpirable soil water (FTSW) and identified the VPD and FTSW thresholds for plant to limit its transpiration. Canola genotypes showed significant variations in both VPD and FTSW thresholds. The genotypes with conservative water use reduced TR at a lower VPD threshold and decreased TR at a higher FTSW threshold than the profligate ones. We found that the conservative genotypes had low VPD and high FTSW thresholds while the profligate ones had high VPD and low FTSW thresholds. This conservative and profligate water use characteristics were consistent during both vegetative and reproductive stages. Furthermore, the relative yield of genotypes under drought conditions was positively related to the FTSW thresholds during the reproductive stage, indicating the better relative yield performance of conservative genotypes in water-limited farming system. We conclude that canola genotypes with lower VPD and higher FTSW thresholds could conserve water and defer water use for reproductive growth while the profligate genotypes can be deployed to take advantage of high rainfall in the high rainfall zone of southern Australia.

Growth and transpiration of soybean genotypes with HaHB4® transcription factor for drought tolerance.

The expression of HaHB4® transcription factor reduces soybean sensitivity to abiotic stresses, such as water deficit. Studies that quantify the tolerance of HaHB4® soybean to the soil water content in comparison with cultivars currently sown in Brazil are lacking. The objective of this study was to determine the level of drought tolerance of soybean genotypes expressing the HaHB4® transcription factor (TS18-6-610108 and TS18-6-610084) and commercial cultivars (TMG 7063 IPRO and BS IRGA 1642 IPRO) subjected to water deficit during the vegetative phase. We used the fraction of transpirable soil water (FTSW) approach. Parameters related to leaf transpiration, dry matter accumulation, water use efficiency (WUE), and transpiration coefficient (TC) were evaluated in the four soybean genotypes and two treatments (T1-100% replacement of transpired water and T2-without replacement of transpired water). The FTSW threshold for the decline in transpiration was evaluated to identify the onset of water stress in soybean. TS18-6-610108 and BS IRGA 1642 IPRO maintains potential transpiration at low FTSW values. The TS18-6-610108 genotype has 14% higher WUE than the sensitive cultivar under water deficit. Under well-irrigated conditions, the HaHB4® genotypes showed the highest TC values, which indicate well-functioning physiological processes.

Transpiration Rate of White Clover (Trifolium repens L.) Cultivars in Drying Soil.

Determining the performance of white clover cultivars under drought conditions is critical in dry climates. However, comparing the differences in cultivar performance requires equivalent soil water content for all plants, to reduce the water deficit threshold eliciting stomatal closure. In this study, the objective was to compare the rate of stomatal closure in eighty white clover cultivars in response to soil drying. Two glasshouse experiments were conducted, and the daily transpiration rate was measured by weighing each pot. The transpiration rate of the drought-stressed plants were normalized against the control plants to minimize effects from transpiration fluctuations and was recorded as the normalized transpiration rate (NTR). The daily soil water content was expressed as the fraction of transpirable soil water (FTSW). The FTSW threshold (FTSWc) was estimated after which the NTR decreases linearly. The FTSWc marks the critical point where the stomata start to close, and transpiration decreases linearly. The significant difference (p < 0.05) between the 10 cultivars with the highest and lowest FTSWc demonstrates the cultivars would perform better in short- or long-term droughts.

Transpiration response of two bread wheat lines differing in drought resilience and their backcross parent under dry-down conditions.

Improving wheat productivity in drylands largely depends on how plants manage limited water resources. Using fraction of transpirable soil water threshold (FTSWTh) and drought stress response function, we characterized the water conservation traits of two wheat multiple synthetic derivative lines (MSD53 and MSD345) which both contain introgressed segments from Aegilops tauschii but differ in drought resilience. The lines and their backcross parent, ‘Norin 61’, were subjected to dry-down conditions. MSD53 had a higher FTSWTh for transpiration decrease than ‘Norin 61’ and MSD345. In terms of drought stress response function, MSD53 had the lowest threshold suction, suggesting a lower drought resilience capacity compared with MSD345. However, MSD53 exhibited an effective-water-use trait whereas MSD345 exhibited a water-saving trait under dry-down conditions. These results are consistent with the reported higher yield of MSD53 in comparison with MSD345 under drought stress in Sudan, and demonstrate that high FTSWTh supports effective water use for improved agricultural productivity in drylands. The differences in water conservation traits between the two MSD lines may be attributed to variation in introgressed segments, which can be further explored for drought resilience breeding.

Cotton Genotypic Variability for Transpiration Decrease with Progressive Soil Drying

Drought is a major abiotic stress factor limiting cotton yield. It is important to identify the genotypes that can conserve water under drought stress conditions and improve yield. The objective of the current study was to evaluate cotton genotypes for water conservation traits, i.e., high FTSW (Fraction of Transpirable Soil Water) threshold for transpiration. Plants utilize water slowly by declining transpiration at high FTSW and conserving soil water, which can be used by the plant later in the growing season to improve yield. Fifteen cotton varieties were selected based on their differences in transpiration response to elevated vapor pressure deficit (VPD) to study drought responses. Two pot experiments were carried out in the greenhouse to determine the FTSW threshold for the transpiration rate as the soil dried. A significant variation (p &lt; 0.01) in the FTSW threshold values for transpiration decline was observed, ranging from 0.35 to 0.60 among cotton cultivars. Genotypes with high FTSW thresholds also displayed low transpiration under well-watered conditions. Further studies with four selected genotype contrasts in FTSW threshold values for transpiration showed differences (p &lt; 0.05 to 0.001) in gas exchange parameters and water potentials. This study demonstrated that there are alternate traits among the cotton genotypes for enhancing soil water conservation to improve yield under water-limited conditions.

Response of Maize ( Zea mays L.) Hybrids to Diurnal Variation of Vapor Pressure Deficit (VPD) and Progressive Soil Moisture Depletion

This study investigated the transpiration (TR) response to (i) diurnal changes of vapor pressure deficit (VPD) and (ii) soil dry down in four maize hybrids contrasting for yield performance under drought stress in the field. These four hybrids included a popular local variety P3K and a commercial check SC303 that were found to be drought susceptible. The experiment was carried out in pots at early vegetative stage (8-leaf stage). Results showed an increase of TR with increasing VPD but with significant variations between the hybrids tested. The two susceptible hybrids P3K and SC303 had higher TR over nearly the whole range of VPD values than the two other hybrids, with the largest variation recorded at VPD values above 6 kPa. Regarding the TR response to soil moisture depletion, normalized TR (NTR) of all genotypes reduced with soil moisture depletion for all treatments. In addition, NTR showed a significant reduction for plants that were irrigated at 3 days intervals before the experiment as compared to those irrigated daily. There was a trend of higher water extraction, as evaluated with the fraction of transpirable soil water (FTSW) threshold, in the tolerant hybrids relative to the susceptible ones for the two irrigation treatments. In addition, prior exposure to water deficit tends to lower the FTSW threshold which leads to increased water extraction capacity at lower soil moisture level. These results demonstrate that control of TR under high VPD conditions coupled with high water extraction capacity from progressively drying soil can contribute to drought tolerance in maize hybrids.

CO2 elevation modulates the response of leaf gas exchange to progressive soil drying in tomato plants

The objective of this study was to investigate the response of leaf gas exchange of tomato plant to progressive drought stress under ambient (a[CO2], 400 ppm) and elevated (e[CO2], 800 ppm) atmospheric CO2 concentration. The fraction of transpirable soil water (FTSW) was used to evaluate soil water status in the pots. The results showed that stomatal conductance (gs) and transpiration rate (Tr) were significantly lower while the net photosynthetic rate (An) was significantly higher in plants grown under e[CO2] than those under a[CO2] at onset of drought stress. Along with soil drying, the FTSW thresholds at which gs and An started to decrease were significantly lower in plants grown under e[CO2] as compared to plants grown under a[CO2]. The intrinsic water use efficiency and instantaneous water use efficiency of plants grown under e[CO2] was significantly higher than those under a[CO2]. Under e[CO2], the drought-stressed plants had greater leaf area, dry matter and water use efficiency than those grown under a[CO2]. e[CO2] notably enhanced shoot C concentration while decreased shoot N concentration hereby increased the C:N ratio. With the decrease of FTSW, the concentration of abscisic acid in leaf ([ABA]leaf) and xylem sap ([ABA]xylem) increased exponentially. When FTSW > 0.2, under both CO2 environments, gs decreased linearly with increasing [ABA]leaf and [ABA]xylem; and similar slopes but different intercepts were noticed for the regression lines, indicating that the responsiveness of gs to ABA was unaffected by CO2. In conclusion, CO2 elevation retarded the response of leaf gas exchange to progressive soil drying in tomato plants. This result provides novel knowledge for more precise prediction of plant response to drought stress in a future CO2-enriched environment.

VALORES LIMÍTROFES PARA TRANSPIRAÇÃO, DESENVOLVIMENTO E CRESCIMENTO DE Corymbia citriodora (Hook.) K.D. Hill &amp; L.A.S. Johnson EM RESPOSTA À DEFICIÊNCIA HÍDRICA NO SOLO1

RESUMO Quando a disponibilidade de água no solo é reduzida, as plantas respondem diminuindo a taxa de transpiração, o crescimento e o desenvolvimento, na tentativa de aclimatação à deficiência hídrica. Com o objetivo de quantificar essas respostas em mudas de Corymbia citriodora (Hook.) K.D. Hill &amp; L.A.S. Johnson, foi utilizada a metodologia da fração de água transpirável no solo (FATS), em um experimento conduzido em casa de vegetação, sob o delineamento inteiramente casualizado, sendo dois níveis de suplementação hídrica, duas épocas de aplicação da deficiência hídrica e nove repetições. A FATS e os parâmetros de transpiração, crescimento e desenvolvimento foram medidos diariamente durante a aplicação da deficiência hídrica. A FATS crítica, em que a transpiração, o crescimento e desenvolvimento começam a ser reduzidos, foi distinta nas épocas de aplicação da deficiência hídrica devido à diferença das condições meteorológicas. Os valores elevados de FATS indicaram que a espécie possuiu boa aclimatação à deficiência hídrica no solo, quando comparada com as espécies anuais e outras perenes.

Leaf Expansion and Transpiration Responses of Millet Species to Soil Water Deficit

Plant processes, such as leaf expansion, stomatal conductance and transpiration, are affected by soil water, particularly in water–stressed environments. Quantifying the effects of soil water on plant processes, especially leaf expansion and transpiration, could be useful for crop modeling. In order to quantify the leaf expansion and transpiration in response to soil water deficit in three millet species, common (Panicum miliaceum L.), pearl (Pennisetum glaucum L.) and foxtail (Setaria italica L.) millets, a pot experiment was performed at the Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. The soil water status was characterized by the fraction of transpirable soil water (FTSW). Leaf area and transpiration were measured daily. Relative leaf area expansion (RL) and relative transpiration (RT) data were plotted against FTSW. Finally the FTSW thresholds for RL and RT were calculated using linear–plateau and logistic models. The results showed that the thresholds for RL and RT were 0.68 and 0.62, respectively, based on all measured data of the three millet species using the linear–plateau model, indicating that RL and RT were constant when FTSW decreased from 1 to the threshold point. Thereafter, until FTSW = 0, RL and RT declined linearly with a slope of 1.48 and 1.43, respectively. Although millet is cultivated as a resistant crop in arid, semiarid and marginal lands, it showed an early response to soil water deficit at high FTSW thresholds. As leaf expansion and transpiration can be considered morphological and physiological variables, respectively, the results in this study indicate that millet has strong morphological flexibility when faced with soil water deficit.

Limite crítico no solo para transpiração e crescimento foliar em mandioca em dois períodos com deficiência hídrica

A cultura da mandioca geralmente é exposta a mais de um período de deficiência hídrica durante a estação de crescimento. O objetivo deste trabalho foi verificar se há diferença na Fração de Água Transpirável do Solo (FATS) crítica para transpiração e crescimento foliar em plantas de mandioca submetidas a um e dois períodos de deficiência hídrica no solo. Foram conduzidos dois experimentos com a cultura da mandioca, cultivar Fepagro RS 13. Os tratamentos foram quatro regimes hídricos subdivididos em dois períodos, período 1 (P1) e período 2 (P2): regimes hídricos RH1 e RH2 (sem e com deficiência hídrica nos dois períodos, respectivamente) e regimes hídricos RH3 e RH4 (com deficiência hídrica no P1 e P2, respectivamente). Usou-se o método da FATS para indicar os pontos críticos para transpiração e crescimento foliar. A FATS crítica foi 0,35, 0,38 e 0,37 para crescimento foliar e 0,28; 0,26; e 0,28 para transpiração no P1 do RH2 e RH3 e P2 do RH4, respectivamente. No P2 do RH2, a FATS crítica para crescimento foliar e transpiração foi 0,09 e 0,13, respectivamente. Concluiu-se que há diminuição na FATS crítica em mandioca no segundo período comparado ao primeiro período de deficiência hídrica no solo, que pode ser explicada pela menor área foliar, o que permitiu que o período de turgescência das folhas fosse maior e, com isso, demoraram mais a ativar seus mecanismos de controle estomático. A implicação prática desses resultados é que esses podem ser utilizados como parâmetros para irrigação da cultura, e também, na seleção de cultivares mais tolerantes à deficiência hídrica.

Transpiration and leaf growth of potato clones in response to soil water deficit

Potato (Solanum tuberosum ssp. Tuberosum) crop is particularly susceptible to water deficit because of its small and shallow root system. The fraction of transpirable soil water (FTSW) approach has been widely used in the evaluation of plant responses to water deficit in different crops. The FTSW 34 threshold (when stomatal closure starts) is a trait of particular interest because it is an indicator of tolerance to water deficit. The FTSW threshold for decline in transpiration and leaf growth was evaluated in a drying soil to identify potato clones tolerant to water deficit. Two greenhouse experiments were carried out in pots, with three advanced clones and the cultivar Asterix. The FTSW, transpiration and leaf growth were measured on a daily basis, during the period of soil drying. FTSW was an efficient method to separate potato clones with regard to their response to water deficit. The advancedclones SMINIA 02106-11 and SMINIA 00017-6 are more tolerant to soil water deficit than the cultivar Asterix, and the clone SMINIA 793101-3 is more tolerant only under high solar radiation.

Effects of soil water deficits on three genotypes of potted Campanula medium plants during bud formation stage

Abstract: Potted ornamental plants are often exposed to drought stress during shipping and retailing, which decreases the value and postharvest quality. Thus, selection of genotypes which can better withstand soil water deficits is essential for sustainable production. Here, the response of three genotypes of potted Campanula medium (denoted as G100, G102 and G104) to progressive soil drying was investigated and their post-production performance was evaluated for four weeks. The potted plants were grown in a climate controlled greenhouse and were either well-watered (W) or drought-stressed (D) at floral bud formation stage. Soil water status was expressed as the fraction of transpirable soil water (FTSW). In the D pots, FTSW declined fastest in G100, followed by G102, and slowest in G104 after withholding irrigation. In the W plants, stomatal conductance ( g s ) was similar among the three genotypes, whereas transpiration rate ( T ) differed significantly among genotypes and was highest for G100, intermediate for G102, and lowest for G104. Estimated by a linear-plateau model, g s and T of G100 started to decrease at significantly higher FTSW thresholds than did G102 and G104. An earlier closure of stomata and decrease of T in G100 would allow the plant to conserve water in the soil; however, owing to its putative larger leaf area and greater stomatal density on the adaxial leaf surface, G100 quickly depleted soil water and resulted in severe drought stress to the plants as exemplified by the significantly lowered g s , leaf area, and relative water content (RWC). In contrast, a smaller leaf area and a lower stomatal density on the adaxial leaf surface of G104 enabled the plants to slowly deplete soil water and maintain high g s , T , leaf area, and RWC 8 days after withholding irrigation. Coincided with these, the floral bud abortion rate in the D plants was significantly higher for G100 as compared with G102 and G104. It is concluded that in potted ornamentals, a low transpiration rate, hereby a slow rate of soil water depletion, is crucial for maintaining postharvest quality under drought stress.

Maize Hybrid Variability for Transpiration Decrease with Progressive Soil Drying

AbstractDrought is ubiquitous in rainfed cropping systems and often limits maize yields. The sensitivity of transpiration response early in progressive soil drying is a trait with potential to improve crop drought resistance. Simulation studies demonstrated that increased sensitivity to drying soil leading to restricted transpiration rates results in conservation of soil water during vegetative stages for possible use during grain filling. In contrast to other crops, there have been no studies characterizing genotypic variability for this trait in maize. Experiments in controlled environments were conducted to characterize the fraction of transpirable soil water (FTSW) threshold on drying soil for 36 hybrids selected for variation in the field for drought resistance, regions of adaptation and stay green. While FTSW thresholds varied among hybrids from 0.60 to 0.33, these thresholds were not uniformly associated with level of drought resistance in the field. Nevertheless, this study demonstrated a high FTSW threshold corresponded with drought resistance observed in some modern maize germplasm (hybrids #7, 17, 24, 27 and 32). This knowledge can enable breeding work seeking to exploit this adaptive trait to improved drought tolerance in low threshold FTSW germplasm.

Transpiração e crescimento foliar de clones de batata em resposta à fração de água transpirável no solo

A água é vital para as plantas. Uma redução na disponibilidade de água pode afetar a transpiração e o crescimento foliar das culturas. O objetivo deste trabalho foi determinar a resposta da transpiração e do crescimento foliar ao conteúdo de água disponível no solo, representado pela fração de água transpirável no solo (FATS), em dois clones de batata (um antigo e um recente) adaptados ao Sul do Brasil. Foram realizados três experimentos em ambiente protegido por abrigo telado em Santa Maria, RS, dois deles na primavera (cultivo de safra), com plantios em 20/08/2008 (E1) e 20/10/2008 (E2), e um experimento no outono (cultivo de safrinha), com plantio em 25/03/2009 (E3), usando-se dois clones de batata: um antigo ('Macaca') e um recente ('SMINIA793101-3'). A água disponível, representada pela FATS, a transpiração e o crescimento foliar foram medidos diariamente durante o período de imposição da deficiência hídrica. A FATS crítica que começa a alterar a transpiração, indicativo do início do fechamento estomático, foi de 0,39, 0,47 e 0,28 no clone 'Macaca' e de 0,47, 0,49 e 0,33 no clone 'SMINIA793101-3', para os experimentos E1, E2 e E3, respectivamente, enquanto o crescimento foliar começou a ser reduzido, com valor de FATS crítica maior para o clone 'Macaca', indicando que o clone 'SMINIA793101-3' é mais tolerante ao déficit hídrico no solo que o clone 'Macaca'.

Differential sensitivities of transpiration to evaporative demand and soil water deficit among wheat elite cultivars indicate different strategies for drought tolerance

In order to satisfy increasing wheat demands, scaling up wheat production will require boosting yield in suboptimal, drought-prone areas. Under rain-fed environments, one promising option is the identification of traits allowing for soil water conservation until the next rain episode. This can be achieved either by limiting transpiration rate (TR) of the crop to a maximum level when atmospheric drought (or VPD for vapor pressure deficit) is too high or by decreasing stomata conductance earlier in the soil drying cycle. Although promising, those strategies were never explored in wheat. A first objective of this study was to investigate the extent of the genetic variability of TR sensitivity to both VPD and soil water deficit among a group of eight elite wheat lines, which are cultivated under south Australian conditions. Those consisted of seven differentially drought-adapted lines and one check cultivar. TR responses to VPD were highly variable among genotypes, with six lines displaying a breakpoint in their TR response to VPD that ranged from 2.4 to 3.9kPa, while two others had their TR increasing linearly as VPD increased. Transpiration response to a progressively decreasing fraction of transpirable soil water (FTSW) was investigated in those lines. A significant genetic variability in the responses among genotypes was observed. They revealed different FTSW thresholds at which transpiration started to decrease at levels ranging from 0.43 to 0.52, and different slopes for the decrease. A second objective was to investigate the existence of phenotypic correlations between the parameters characterizing transpiration sensitivities to both sources of water deficit (i.e., VPD and FTSW). Significant correlations were observed revealing that genotypes with conservative water use in their response to high VPD were also conservative in response to decreasing FTSW and that the drought tolerance of other lines might stem from an apposite strategy, invoking decreased sensitivity of TR to both sources of drought. Those findings provide new options for breeding drought tolerant lines based on this germplasm.

Broader leaves result in better performance of indica rice under drought stress

Leaf growth is one of the first physiological processes affected by changes in plant water status under drought. A decrease in leaf expansion rate usually precedes any reduction in stomatal conductance or photosynthesis. Changes in leaf size and stomatal opening are potential adaptive mechanisms, which may help avoid drought by reducing transpiration rate, and can be used to improve rice genotypes in water-saving cultivation. The indica rice cultivar IR64 and four of its near-isogenic lines (NILs; BC 3-derived lines) unique for leaf size traits, YTK 124 (long leaves), YTK 127 (broad leaves), YTK 205 (short leaves) and YTK 214 (narrow leaves), were compared in this study for changes in leaf growth and its water status. The plants were subjected to two soil water regimes, well-watered and progressive soil drying measured by the fraction of transpirable soil water (FTSW). Applied drought reduced leaf number, total leaf area, specific leaf area, plant biomass, tiller number, plant height, stomatal conductance, amount of water transpired, leaf relative water content, and leaf water potential more in IR64 and the NILs than in the respective controls; nonetheless, transpiration efficiency (TE) was slightly higher under drought than in the well-watered controls. NILs with broader leaves had higher biomass (and its individual components), less stomatal conductance, and higher TE under drought than NILs with narrow and shorter leaves. Under drought, leaf number was positively correlated with tiller number and plant height; nonetheless, root weight and total biomass, water transpired and TE, and plant height and TE were positively correlated with each other. However, a negative correlation was observed between stomatal conductance and the FTSW threshold at which normalized transpiration started to decline during soil drying. Overall, the IR64-derived lines with broader leaves performed better than NILs with narrow and short leaves under drought.