Changes in response to drought stress of triticale and maize genotypes differing in drought tolerance

Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D.     

Leaf optical properties during and after drought stress in triticale and maize genotypes differing in drought tolerance

The effect of a short (7 days) and prolonged (14 days) soil drought (D) on leaf optical properties (R reflectance, T transmittance and A absorbance) in PAR and NIR range of irradiation, and on changes in leaf water potential (ψ), leaf injury index (LI), leaf thickness (LT) and chlorophyll (a + b) content (Chl) was studied for maize and triticale genotypes differing in drought tolerance. Under control conditions (C) leaves of maize in comparison to triticale were better hydrated, were thicker and had higher content of chlorophyll (a + b). In non-stressed plants, small differences were observed in measurements of R, T and A. In the range from 500 to 600 nm, the differences between D-resistant and D-sensitive were observed only in transmittance (T) and in range from 700 to 1,100 nm in absorbance (A). In genotypes belonging to the group of D-sensitive T in PAR range and A in NIR range were two times higher than in D-resistant ones. However, in NIR range R for D-sensitive genotypes was lower than for D-resistant ones. The drought stress caused the decrease in ψ, Chl, LT and the increase in leaf injury index (LI). Soil drought applied within 14 days caused larger changes in these physiological characters in comparison to 7 days drought. The observed harmful influence of drought was more visible for maize than triticale. Moreover for genotypes belonging to D-sensitive ones, changes were larger than for D-resistant ones. Similar to changes in ψ, LT and LI drought stress caused changes in leaf optical properties parameters R, A and T. In the PAR range, the highest changes were observed in R, whereas changes in T and A, which were not considerable. Both in maize and triticale, increase in R was higher in plants subjected to 14 days drought than in plants exposed to drought for 7 days. In maize, increase in R was larger for D-sensitive genotype. For both species, changes in T and A of PAR range were small. In NIR range, an increase in R and A, and decrease in T were observed. After 7 days of recovery in plants subjected to shorter period of drought significant differences were still visible in most cases. The same was observed for ψ, LT, LI and Chl parameters. It shows that the period of 7 days rehydration is too short to remove the injuries caused by drought stress. This results indicate that measurements of R, T and A might be useful in practical application for the estimation of the drought tolerance level. Some limitations in the practical application for plant breeding may be caused by relatively high cost of necessary equipment.     

Evaluation of physiological screening tests for breeding drought resistant triticale (x <Emphasis Type="Italic">Triticosecale</Emphasis> wittmack)

Effects of soil drought on crop yield of 4 strains and 7 cultivars of spring triticale was investigated under field condition. The Drought Susceptibility Index (DSI) was evaluated in a two year experiment by the determination of grain loss in conditions of two soil moisture levels (drought-D and irrigated-IR). In the experiment response to drought was evaluated by different screening tests (leaf gaseous exchange, leaf water potential, chlorophyll content and fluorescence, leaf injury by drought and by simulated drought and heat temperature and water loss by excited leaf. The DSI values and the results of screening tests showed the genetic variation in the degree of drought tolerance. The values of DSI enabled the ranking of the tested triticale genotypes with respect to their drought tolerance and allow to divide them into three groups of drought susceptibility. Large differences among studied forms were observed also in changes of leaf water potential, fluorescence and leaf injury. For plants in vegetative stage of growth the tested breeding forms were easily separated into groups of different drought tolerance. Changes of ψ, Fv/Fm and LI as a screening tests were the most suitable techniques for estimation of degree of drought tolerance for triticale. Laboratory screening tests (leaf injury by simulated drought (LI_DS) and high temperature (LI_HT) and water loss (WL) of excited leaf conducted for nonstressed plants in most cases were significantly correlated with DSI. The statistically significant correlation between leaf water potential (ψ) was observed only with leaf fluorescence (Fv/Fm). Changes of Fv/Fm were significantly correlated with ψ, LI and LI_HT for 50 °C. Index of leaf injury (LI) by soil drought were significantly correlated with Fv/Fm, LI_DS (−1.0, −1.5 MPa), LI_HT (45 and 50°C) and water loss (WL). The correlation coefficient between the tests LI_DS and LI_HT were most of the considered cases statistically significant which indicate that the mechanism of membranes injury resulted from simulated drought or high temperature were similar in triticale. Water loss (WL) of excited leaves was the most suitable test for screening drought tolerance in triticale population. Changes of gaseous exchange parameters were not useful as screening test in this research.     

Changes of leaf water potential and gas exchange during and after drought in triticale and maize genotypes differing in drought tolerance

Influence of drought (D) on changes of leaf water potential (Ψ) and parameters of gas exchange in D-resistant and D-sensitive genotypes of triticale and maize was compared. Soil D (from −0.01 to −2.45 MPa) was simulated by mannitol solutions. At −0.013 MPa significant differences in Ψ, net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and internal CO₂ concentration (C _i) of D-resistant and D-sensitive triticale and maize genotypes were not found. Together with the increase in concentration of the mannitol solution the impact of D on E and g _s for D-sensitive genotypes (CHD-12, Ankora) became lower than for the D-resistant ones (CHD-247, Tina). Inversely, impact of D on Ψ was higher in D-sensitive than D-resistant genotypes. From 1 to 3 d of D, a higher decrease in P _N was observed in D-resistant genotypes than in the D-sensitive ones. Under prolonged D (5–14 d) and simultaneous more severe D the decrease in P _N was lower in D-resistant than in D-sensitive genotypes. Changes in Ψ, P _N, E, and g _s caused by D in genotypes differing in the drought susceptibility were similar for triticale and maize. Compared to control plants, increase of C _i was different for triticale and maize genotypes. Hence one of the physiological reasons of different susceptibility to D between sensitive and resistant genotypes is more efficient protection of tissue water status in resistant genotypes reflected in higher decrease in g _s and limiting E compared to the sensitive ones. Other reason, observed in D-resistant genotypes during the recovery from D-stress, was more efficient removal of detrimental effects of D.     

Fluorescence excitation spectra of drought resistant and sensitive genotypes of triticale and maize

An influence of soil drought (7 or 14 d) and 7 d recovery on changes of leaf fluorescence excitation spectra at wavelengths of 450, 520, 690, and 740 nm (F₄₅₀, F₅₂₀, F₆₉₀, F₇₄₀) for drought resistant and sensitive genotypes of triticale and maize was compared. In non-stressed plants the differences between maize and triticale were observed for F₄₅₀ and F₅₂₀, but not for F₆₉₀ and F₇₄₀. Drought caused the increase in F₄₅₀, F₅₂₀, and F₆₉₀ and this increase was more distinct for drought sensitive genotypes. After re-hydration, chlorophyll fluorescence mostly recovered to values of control plants. Drought caused significant increase in F₆₉₀/F₇₄₀ but not in F₄₅₀/F₆₉₀ and F₄₅₀/F₅₂₀. For triticale, highest increase in F₆₉₀/F₇₄₀ was observed in the 4^th and 7^th leaves of resistant genotype and contrarily in maize for the sensitive one. After recovery, the F₄₅₀/F₅₂₀, F₄₅₀/F₆₉₀, and F₆₉₀/F₇₄₀ ratios mostly returned to values of control plants.     

Differences in the physiological state between triticale and maize plants during drought stress and followed rehydration expressed by the leaf gas exchange and spectrofluorimetric methods

The studies were carried out in order to estimate differences in the physiological state between triticale and maize plants subjected to drought stress followed by rehydration. The physiological state of the plants was evaluated by measurements of leaf water potential, net photosynthesis, transpiration and stomatal conductance. Spectrofluorimetric methods for the study of blue, green and red fluorescence were applied. We observed that the soil drought induced a greater water loss in triticale leaves than in maize and consequently caused greater injuries to the photosynthetic apparatus. Moreover, triticale plant recovery was slower than in maize plants during the rehydration phase. The effect was probably connected with the higher functional and structural disorganisation of the photosynthetic apparatus observed during drought stress in triticale. Water stress is responsible for damages to photosystem PS II. The worst light utilisation in photosynthetic light conversion was recorded as an increase in the intensity of red fluorescence. Drought stress induced a strong increase in the intensity of blue and green fluorescence in the studied species and it was still high in maize plants during the first day of rehydration. Increase in the intensity of blue and green fluorescence in maize seems to be the effect of the photoprotection mechanism which prevents damage to PS II through utilisation of excess energy.     

The effect of soil drought on the composition of carbohydrates in yellow lupin seeds and triticale kernels

Carbohydrate analysis was made of yellow lupin seeds (cv. Juno) and triticale kernels (cv. Dagro), produced by plants exposed to drought stress for 21 days after the initial flowering of the first node of lupin and initial earing of triticale. The seeds of all experimental variants were harvest at full maturity, dried and stored in linen bags at 18–20 °C. Soluble carbohydrates were extracted and analysed as described by Horbowicz and Obendorf (1994). Gas chromatographic separation of carbohydrates showed that raffinose family oligosaccharides (RFO) were dominant in lupin seeds. The other carbohydrates present were sucrose (10 %), cyclitols and galactosyl cyclitols (12–13 %). Soil drought resulted in higher levels of verbascose, but decreased the quantities of the other carbohydrates in lupine seeds. In triticale kernels, over 50 % of soluble sugars were composed of sucrose and maltose, while 17.7 % were raffinose and stachyose. In response to drought the content of mono- and oligosaccharides declined. The decrease of soluble carbohydrates content in seeds of lupin and triticale kernels has no effect on the seed germination and vigour. It is assumed that the changes in the concentration of soluble sugars observed under drought may impair the storability of triticale kernels, but improve it for lupine seeds.     

Drought effects on cellular and spatial parameters of leaf growth in tall fescue

The effect of drought and recovery on cellular and spatial parametersof the growth process in tall fescue leaves was studied in twoexperiments. In both experiments plants grown on vermiculiteand maintained in a controlled environment were submitted toa 7 d drought period generated by withholding water. Droughtwas followed by a 3 d recovery period in experiment II. As leafelongation rate (LER) decreased during developing drought boththe growth zone length (initially 40 mm) and the maximum relativeelemental growth rate (initially 0.09 mm mm^–1 h^–1during the dark period of diurnal cycles) within the growthzone declined. But the growth zone still exhibited a lengthof approximately 15 mm when LER approached 0 under severe drought(–2.0 MPa predawn leaf water potential). The growth potentialof the basal 15-mm-long portion of the leaf was conserved duringthe period when drought effected the complete arrest of leafelongation. A (retrospective) analysis of the position-timerelationships of epidermal cells identified on leaf replicas(experiment II) indicated that the cell flux out of the growthzone responded very sensitively to drought. Before drought theflux was maximum at approximately 3.2 cells (cell file h)^–1during the dark period. Flux decreased to 0 when leaf elongationstopped. Flux also varied diurnally both under well-wateredand droughted conditions. In well-watered conditions it wasabout 30% less during the light than the dark period. Cell elongationwas also sensitive to drought. Under well-watered conditionsepidermal cell elongation stopped when cells attained a lengthof approximately 480 µm. During developing drought cellsstopped elongating at progressively shorter lengths. When LERhad decreased to almost nil, cells stopped elongating at a lengthof approximately 250 µn. When drought was relieved followinga 2 d complete arrest of leaf elongation then cells shorterthan 250 µm were able to resume expansion. Following rewateringcell flux out of the growth zone increased rapidly to and abovethe pre-drought level, but there was only a slow increase overtime in the length at which cell elongation stopped. About 2d elapsed until the leaf growth zone produced cells of similarlength as before drought (i.e. approximately 480 µm). Key words: Epidermal cell length, cell flux, (leaf) growth zone, leaf elongation rate, relative elemental growth rate, position-time relationships (path line, growth trajectory), drought, water deficit     

The relations between drought susceptibility index based on grain yield (DSIGY) and key physiological seedling traits in maize and triticale genotypes

The physiological reasons for the differences in sensitivity of C₃ and C₄ plant species to environmental stresses have not been thoroughly explained. In this study the effects of drought stress on the growth and selected physiological traits were examined in the seedlings of 13 single cross maize (C₄ plant) hybrids and 11 spring triticale (C₃ plant) breeding lines and varieties differing in drought sensitivity. For plants in the seedling stage the results demonstrated a genetic variation in dry matter accumulation of shoots and roots (DW_S, DW_R), number (N) and length (L) of particular components (seminal, seminal adventitious, nodal) of the root system, membrane injury by soil drought (LI_D), osmotic and high temperature stress (LI_OS, LI_HT), water potential (ψ), water loss (WL), grain germination in osmotic stress (FG, PI), and seedling survival (SS). Seedlings grown under moderate soil drought showed a decrease in dry matter of the top parts and roots and a decrease in the length of seminal, seminal adventitious and nodal roots in comparison to seedlings grown in control conditions. The observed harmful effects of drought stress were more distinct in drought sensitive genotypes. Used in this paper drought susceptibility indexes (DSI_GY) were calculated in other experiment by determining the changes in grain yield (GY) under two soil moisture levels (irrigated and drought). The variation of DSI_GY for maize ranges from 0.381 to 0.650 and for triticale from 0.354 to 0.578. The correlations between DSI_GY and laboratory tests (LI, FG, SS) confirmed that they are good indicators of drought tolerance in plants. The highest values of genetic variation were observed in LI, DW_S, SS and WL and the lowest in the measurements of ψ FG, PI, L_S, L_SA and L_N. The correlation coefficients between LI_OS and LI_HT tests were, in most of the considered cases, statistically significant, which indicates that in maize and triticale the mechanisms of membrane injury caused by simulated drought or high temperature are physiologically similar. It can be concluded that an approach to the breeding of maize and triticale for drought tolerance using these tests can be implemented on the basis of separate selection for each trait or for all of them simultaneously. In that case, it would be necessary to determine the importance of the trait in relation to growth phase, drought timing and level, as well as its associations with morphological traits contributing to drought tolerance. The obtained values of the correlation coefficient between laboratory tests suggest that the same physiological traits may be applied as selection criteria in drought tolerance of maize and triticale genotypes.     

夏玉米叶片气体交换参数对干旱过程的响应

目前已经开展了大量的干旱对作物叶片气体交换参数影响的研究,但关于作物叶片气体交换参数对干旱过程的响应及其关键阈值的研究仍较少。基于夏玉米七叶期开始的5个初始水分梯度的长时间持续干旱模拟实验资料,分析了不同强度持续干旱过程中夏玉米叶片气体交换参数(净光合速率Pn,气孔导度Gs,蒸腾速率Tr,胞间CO_2浓度Ci和气孔限制值Ls)的变化规律及其关键阈值。结果表明,玉米的净光合速率(Pn),蒸腾速率(Tr)和气孔导度(Gs)在干旱发生初期呈大幅度下降,但随着干旱持续会出现一定的适应性。利用统计容忍限方法确定了夏玉米拔节期Pn,Tr和Gs响应干旱的临界土壤相对湿度(0—30cm)分别为53%,51%和48%,对应的临界叶含水率分别为81.8%,81.3%和81.2%。夏玉米光合作用由气孔限制向非气孔限制转换的0—30cm土壤相对湿度均为44%±2%,对应的叶含水率均为77.6%±0.3%。研究结果可为夏玉米干旱发生发展过程的监测预警提供依据。     

Reflectance and biochemical responses of maize plants to drought and re‐watering cycles

The ability to recover from drought stress after re‐watering is an important feature that will enable plants to cope with the predicted increase in episodic drought. The effects of pre‐drought and re‐watering conditions on leaf spectral properties and their relationships with the biochemical processes that underlie the recovery from pre‐drought conditions should be better understood. The reflectance spectra, 10 spectral reflectance indices (SRIs) and biochemical characteristics of maize (Zea mays) leaves were monitored 7, 14, 21 and 28 days after the initiation of soil drought stress during two successive cycles of drought and re‐watering periods. The leaf reflectance of the two inbred maize lines increased under the drought stress, especially in the visible spectral range. In addition, an obvious recovery of the leaf reflectance was only observed in the first re‐watering period, and its value remained higher than that of the control plants during the second recovery period. A recovery lag in the pigment contents was also observed during the second cycle. The recovery variations in the pattern and magnitude of the SRIs and the total contents of C, N and P that were measured in response to the re‐watering during both cycles were diverse and complex; both full and partial recoveries were observed. The SRIs representing different physiological attributes of plant growth, including the water index, red edge position, photochemical reflectance index and near‐infrared reflectance at 800 nm, showed strong linear relationships (P < 0.01 or 0.05) with the growth and biochemical traits across the successive drought and re‐watering cycles. The results suggest that maize plants can adjust their leaf reflectance properties and employ growth and biochemical strategies to adapt to cyclic drought stress and recover from drought stress after re‐watering.     

Interspecific differences in root architecture among maize and triticale genotypes grown under drought,waterlogging and soil compaction

Environmental stresses (soil compaction, drought, waterlogging) cause changes in plants’ root system structure, also affecting the growth of above-ground parts. The aim of this study was to estimate phenotypic variation among maize and triticale genotypes in root penetration ability through petrolatum-wax-layer (RPA). Also, the effect of shortage or excess of soil water on dry matter of shoots and roots and morphological changes in root system structure in sensitive and resistant maize and triticale genotypes grown in low or high soil compaction level was evaluated. To estimate RPA index, the petrolatum-wax-layer method (PWL) was used. The strength of three petrolatum-wax concentrations 60, 50 and 40 % was 0.52, 1.07 and 1.58 MPa, respectively. High coefficients of variation (CV) were observed in 0.52 and 1.07 MPa and for maize were 19.2 and 21.7 %, and for triticale, 12.5 and 18.3 %, respectively. The data indicate that the use of PWL technique is an effective screening method, and makes it possible to divide the genotypes into resistant and sensitive groups. The second part of this study investigated a multistress effect of soil compaction combined with drought or waterlogging on root and shoot growth and morphological changes in root system structure of maize and triticale genotypes differing in susceptibility to environmental stresses. Seedlings were grown for 4 weeks in root-boxes under conditions of low (LSC 1.1 g cm^?3) or severe (SSC 1.6 g cm^?3) soil compaction. Drought or waterlogging stresses were applied for 2 weeks from 14th to 28th day. In comparison to LSC treatment, in SSC treatment the decrease in dry matter of shoots and roots was greater for sensitive genotypes of maize and triticale (Ancora, CHD-147). Soil drought or waterlogging caused greater decrease of dry matter of shoots and roots in seedlings grown in SSC in comparison to LSC. The root penetration index (RPI) was estimated as a ratio of root dry matter in 15–40 cm root-box layer to total root dry matter. On the basis of RPI it was possible to group the genotypes according to their ability to distribute roots in soil profile. In comparison to LSC, SSC exerted a strong influence on the length of seminal and seminal adventitious roots, as well as the number and length of L- and S-type lateral roots developed on seminal and nodal roots. In both species the restriction effect of soil compaction on number and length of roots was more severe in sensitive (Ankora, CHD-147) than in resistant (Tina, CHD-247) genotypes. The restriction in roots propagation was greater in triticale than in maize. Exposure to drought or waterlogging in the case of genotypes grown in LSC and SSC treatments caused a decrease in number and length of particular components of root system structure. In both species the decrease of root number and length in plants grown under waterlogging was greater than under drought. The observed changes in root system were greater in sensitive (Ankora, CHD147) than in resistant (Tina, CHD-247) genotypes. Statistically significant correlations were found between RPA and RPI and also between these indexes and soil compaction, drought and waterlogging susceptibility indexes. This indicates that genotypes resistant to soil compaction were resistant to drought or waterlogging and also that genotypes resistant to drought were resistant to waterlogging.     

Changes in root system structure,leaf water potential and gas exchange of maize and triticale seedlings affected by soil compaction

The physiological reasons associated with differential sensitivity of C₃ and C₄ plant species to soil compaction stress are not well explained and understood. The responses of growth characteristics, changes in leaf water potential and gas exchange in maize and triticale to a different soil compaction were investigated. In the present study seedlings of triticale and maize, representative of C₃ and C₄ plants were subjected to low (L – 1.10 g cm⁻³), moderate (M – 1.34 g cm⁻³) and severe (S – 1.58 g cm⁻³) soil compaction level. Distinct differences in distribution of roots in the soil profile were observed. Plants of treatments M or S in comparison to treatment L, showed a decrease in leaf number, dry mass of stem, leaves and roots, and an increase in the shoot to root ratio. A drastic decrease in root biomass in M and S treatments in the soil profile on depth from 15 to 40 cm was observed. Any level of soil compaction did not influence the number of seminal and seminal-adventitious roots but decreased their length. The number and total length of nodal roots decreased with compaction. Changes of growth traits in M and S treatments in comparison to the L were greater for maize than for triticale and were accompanied by daily changes in water potential (ψ) and gas exchange parameters (P_N, E, g_s). Differences between M and S treatments in daily changes in ψ for maize were in most cases statistically insignificant, whereas for triticale, they were statistically significant. Differences in the responses of maize and triticale to soil compaction were found in P_N, E and g_s in particular for the measurements taken at 12:00 and 16:00. The highest correlation coefficients were obtained for the relationship between leaf water potential and stomatal conductance, both for maize and triticale, which indicates the close association between stomata behavior and changes in leaf water status.     

夏玉米对土壤水分持续减少的响应及其转折点阈值分析

玉米是世界三大粮食作物之一,玉米生产在中国粮食安全与畜牧业发展中具有举足轻重的作用。干旱是夏玉米生产最主要气象灾害,及时准确地获取干旱信息对夏玉米安全生产至关重要。以夏玉米郑单958品种为材料,设置充分供水和拔节期开始土壤水分持续减少两种水分处理,研究夏玉米对土壤水分持续减少的响应及其转折点阈值,为夏玉米干旱识别与监测提供依据。结果表明,土壤水分持续减少10d后生理指标开始陆续受到胁迫,20d后生物量积累受到抑制,30d左右形态特征开始受到胁迫。夏玉米生理指标中最先受到胁迫的是顶端第1片完全展开叶的含水量和水势,生物量积累指标中为茎生物量,形态指标中为叶数。夏玉米顶端第1片完全展开叶的含水量或水势、茎生物量和叶数开始受到土壤干旱过程胁迫的时间阈值分别为11、21、27d,水分亏缺阈值分别为34、66、86mm,土壤相对湿度阈值分别为64%、56%和52%。表明夏玉米对土壤干旱过程的响应首先表现为生理特征变化、其次为生物量积累变化、最后为形态特征变化。研究结果可为客观辨识夏玉米干旱的发生发展及监测预警提供参考。     

Genotypic variation between maize (Zea mays L.) single cross hybrids in response to drought stress

Effects of soil drought on growth and productivity of 16 single cross maize hybrids were investigated under field and greenhouse experiments. The Drought Susceptibility Index (DSI) was evaluated in a three year field experiment by the determination of grain loss in conditions of two soil moisture levels (drought and irrigated) and in a pot experiment by the effects of periodical soil drought on seedling dry matter. In the greenhouse experiment response to drought in maize genotypes was also evaluated by root to shoot dry mater ratio, transpiration productivity index, indexes of kernel germination and index of leaf injury by drought and heat temperature. The obtained values of DSI enabled the ranking of the tested genotypes with respect to their drought tolerance. The values of DSI obtained in the field experiment allow to divide the examined genotypes into three, and in the greenhouse experiment into two groups of drought susceptibility. The correlation coefficients between the DSI of maize hybrids in the field and the greenhouse experiments was high and statistically significant, being equal to 0.876. The ranking of hybrids drought tolerance, identified on the basis of field experiments was generally in agreement with the ranking established on the basis of the greenhouse experiment. In the greenhouse experiment statistically significant coefficients of correlation with DSI values in hybrids were obtained for the ratio of dry matter of overground parts to dry matter of roots, both for control and drought treatments, whereas in the estimation of the transpiration productivity coefficient and total dry matter the correlation coefficients were not statistically significant. In this study several laboratory tests were carried out for the drought tolerance of plants (kernel germination, leaf injury) on 4 drought resistant and 4 drought sensitive maize hybrids. Statistically significant correlation coefficients between DSI and the examined parameter of grain germination and leaf injury were obtained for the determination of promptness index (PI), seedling survival index (SS) and leaf injuries indexes (IDS, ITS) as a result of exposure to 14 days of soil drought, osmotic drought −0.9 MPa and exposure to high temperature 45 ° or 50 °C. The results of laboratory tests show that in maize the genetic variation in the degree of drought tolerance is better manifested under severe conditions of water deficit in the soil.     

The relationship between seedling growth and grain yield under drought conditions in maize and triticale genotypes

The effects of drought stress on seedlings?? growth and grain yield of 13 single cross maize hybrids and 11 breeding lines and cultivars of spring triticale were studied in greenhouse and field experiments. In the field experiment, the drought susceptibility index (DSI_GY) was calculated by determining the change in grain yield (GY) in conditions with two soil moisture levels (IR, irrigated; D, drought). In the greenhouse experiment the response to soil drought was evaluated using DSI_DW, by determining changes in the dry weight (DW) of vegetative plant parts. Marked variations in GY and DW were observed among the studied genotypes. In control conditions, the GY and DW in drought-sensitive genotypes were higher compared to the drought-resistant ones; but in drought conditions, the decreases in GY and DW in resistant genotypes were smaller than in drought-sensitive ones. DSI_GY and DSI_DW revealed variations in the degree of drought tolerance among the examined maize and triticale genotypes. The values of DSI_GY in the field experiment and DSI_DW in the greenhouse experiment enabled a division of the studied genotypes into drought-resistant or -sensitive groups. A close correlation between DSI_GY and DSI_DW was found. The positive linear correlation and determination coefficients between DSI_GY and DSI_DW were statistically significant (P?=?0.05), being equal to R ²?=?0.614 (maize) and R ²?=?0.535 (triticale). The ranking of the studied genotypes based on DSI_GY was in most cases consistent with the ranking based on DSI_DW, which indicates that genetically conditioned drought tolerance is similar for plants in the seedling and reproductive growth stages or may at least partly have a common genetic background.     

The impact of different soil moisture and soil compaction on the growth of triticale root system

Effects of different soil moisture (soil drought and waterlogging) and soil compaction (1.33 and 1.50 g·cm⁻³) on the growth and morphological traits of the root system were studied in four breeding forms and seven cultivars of triticale. Morphological changes, including the restriction of root extension, expansion and proliferation of laterals roots, occur in plants grown in different soil moisture and in compact soil. The investigations comprised quantitative and qualitative analyses of a developed plant root system through determining the number, length and dry matter of the particular components of the root system. Obtained results have demonstrated a relatively broad variation in the habit of the triticale root system. Plants grown under compact soil and low or high soil water content showed a smaller number and less dry matter of lateral branching than plants grown in control conditions. The harmful effects of compact soil and drought conditions on the growth of roots was greater when compared with that of plants exposed to waterlogging. The observed effects of all treatments were more distinct in a drought sensitive strains. The drought resistant forms were a more characterize with extensive rooting and by smaller alterations in the root morphology under the stress conditions compared with drought sensitive one. Results confirm that the breeding forms (CHD-12 and CHD-173) of a high drought susceptibility was found to be also more sensitive to periodical soil water excess. A more efficient water use and a lower shoot to root (S/R) ratio were found to be major reasons for a higher stress resistance of the breeding forms (CHD-220 and CHD-247). The reasons for a different response of the examined breeding forms and cultivars to the conditions of drought or waterlogging may be a more economical water balance and more favourable relations between the shoot and root dimensions in the drought resistant forms and cultivars. The results suggest that the morphological traits of the triticale root system may be used in practice as direct or indirect selection criteria in maize breeding.     

Leaf water characteristics and drought acclimation in sunflower genotypes

The responses of leaf water parameters to drought were examined using three sunflower (Helianthus annuus L.) genotypes. Osmotic potential at full water saturation (π¹⁰⁰), apoplastic water fraction (AWF) and bulk elastic modulus (BEM) were determined by pressure-volume curve analysis on well watered or on water-stressed plants (−1.0 MPa Ψ₁ < −1.5 MPa) previously drought-pretreated or not. The drought-pretreated plants were subjected to a 7-day drought period (predawn leaf water potential reached −0.9 MPa) followed by 8 days of rewatering. In well watered plants, all genotypes in response to drought acclimation displayed a significantly decreased π¹⁰⁰ associated with a decrease in the leaf water potential at the turgor-loss point (decrease in Ψ_tlp was between 0.15 and 0.21 MPa, depending on the genotype). In two genotypes, drought acclimation affected the partitioning of water between the apoplastic and symplastic fractions without any effect on the total amount of water in the leaves. As a third genotype displayed no modification of AWF and BEM after drought acclimation, the decreased π¹⁰⁰ was only due to the net accumulation of solutes and was consistent with the adjustment of the photochemical efficiency observed previously in this genotype in response to drought acclimation. In water-stressed plants, the osmotic adjustment (OA) can increase further beyond that observed in response to the drought pretreatment. However, the maintenance of photosynthetic rate and stomatal conductance at low leaf water potentials not only depends on the extent of osmotic adjustment, but also on the interaction between OA and AWF or BEM. Adaptative responses of leaf water parameters to drought are thus quite contrasted in sunflower genotypes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Leaf photosynthesis and carbohydrates of CO₂-enriched maize and grain sorghum exposed to a short period of soil water deficit during vegetative development

Among C₄ species, sorghum is known to be more drought tolerant than maize. The objective was to evaluate differences in leaf gas exchanges, carbohydrates, and two enzyme activities of these nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME) C₄ subtype monocots in response to water deficit and CO₂ concentration ([CO₂]). Maize and sorghum were grown in pots in sunlit environmental-controlled chambers. Treatments included well watered (WW) and water stressed (WS) (water withheld at 26 days) and daytime [CO₂] of 360 (ambient) and 720 (elevated) μmol mol⁻¹. Midday gas exchange rates, concentrations of nonstructural carbohydrates, and activities of sucrose-phosphate synthase (SPS) and adenosine 5′-diphosphoglucose pyrophosphorylase (ADGP) were determined for fully expanded leaf sections. There was no difference in leaf CO₂ exchange rates (CER) between ambient and elevated [CO₂] control plants for both maize and sorghum. After withholding water, leaf CER declined to zero after 8 days in maize and 10 days for sorghum. Sorghum had lower stomatal conductance and transpiration rates than maize, which resulted in a longer period of CER under drought. Nonstructural carbohydrates of both control maize and sorghum were hardly affected by elevated [CO₂]. Under drought, however, increases in soluble sugars and decreases in starch were generally observed for maize and sorghum at both [CO₂] levels. For stressed maize and sorghum, decreases in starch occurred earlier and were greater at ambient [CO₂] than at elevated [CO₂]. For maize, drought did not meaningfully affect SPS activity. However, a decline in SPS activity was observed for drought-stressed sorghum under both [CO₂] treatments. There was an increase in ADGP activity in maize under drought for both [CO₂] treatments. Such a response in ADGP to drought, however, did not occur for sorghum. The generally more rapid response of maize than sorghum to drought might be related to the more rapid growth of leaf area of maize.