Short Periods Of Water Stress Research Articles

Timing of short period water stress determines potato plant growth, yield and tuber quality

Potato growth in humid climate regions is facing increasing challenges due to short period stresses in water deficit and excess. However, there is a lack of quantitative information on the effects of short period of water stress on potato plant growth and its implications on potato yield and tuber quality. In this study, we conducted a pot experiment to test the effects of short period (2weeks) of water deficit and water excess, respectively, applied at four different potato growth stages (sprouting, vegetative, tuberization and bulking stage) on potato vegetative development and tuber yield and quality. The results show that short period of water deficit overall had negative impacts while short period of water excess had slightly positive impacts on potato vegetative development and tuber yield and quality. For water deficit, the most sensitive periods were the vegetative and tuberization stage whereas for water excess, there were mostly no-significant differences between different potato growth stages. Although the impact of water deficit at the sprouting stage was minor, it was broad and long-lasting. These results confirm the benefits of supplemental irrigation and suggest the low risk of over-irrigation in well drained fields. They further suggest that when the availability of water for irrigation is limited, using water strategically during the period when potato needs water the most can maximize the benefits of supplemental irrigation.

A physiological approach for pre-selection of Eucalyptus clones resistant to drought

Abstract: Water deficit is one of the abiotic stresses that most affects the growth and survival of Eucalyptus. Mechanisms used to tolerate water-limited environments influence the distribution of Eucalyptus species in their natural environment. Here, we take a physiological approach to pre-screen Eucalyptus plants for tolerance to drought. Ten different clones of E. urophylla and E. grandis × E. urophylla that are known to show contrasting responses to water deficit under field conditions, were grown in Clark’s nutrient solution (WW, well-watered) and with polyethylene glycol (-1.0 MPa) to simulate water deficit (WD). Clones responded differently to drought with differentiated photosynthetic limitations in drought-treated clones. Photosynthetic rates, stomatal conductance, transpiration and internal CO2 concentrations were reduced in all genotypes under stress conditions. Clone i144 had a smaller reduction in the evaluated physiological traits, also showing increased root growth in WD-treated plants. Clones 3367 and i224, thought to be moderately tolerant, also followed these patterns. Clones gg157, 1568 and 1641, all of which are moderately sensitive under field conditions, reduced most of the physiological characters evaluated. However, clone gg157 demonstrated increased root system growth, even during short periods of water stress. Clones i042 and i182 were deemed drought-susceptible, with large reductions in photosynthesis and growth, despite showing a high increase in abscisic acid content presumably as a defense mechanism. Interaction between A (photosyntetic rate), E (transpiration rate), ETR/A (electrons transport rate/photosynthetic rate) and SDM/ RDM (shoot dry matter/root dry matter) demonstrated the most significant differences between WD-treated clones and offer great potential for use as selection criterion for water deficit-tolerant genotypes.

Response of phreatophytes to short‐term groundwater pumping in a semiarid region: Field experiments and numerical simulations

AbstractBalancing the water demand between human usage and ecosystems remains a challenge in water‐limited regions where one of the main groundwater uses is short‐term pumping. A 23‐day pumping test was performed in a semiarid site of north‐west China to test the hypothesis that native phreatophytes can tolerate short‐term pumping. The monitoring indicated that sap flow velocity of groundwater‐dependent willow trees began to decrease on Day 4 after pumping and almost fully recovered on Day 9 after the cessation of pumping. Numerical simulations using HYDRUS‐1D were conducted for the period of 1954–2013 to assess the response of phreatophytes to groundwater withdrawal under various climatic conditions. The modelling results reveal that phreatophytes can recover from the stress induced by groundwater pumping because they can adapt to short periods of water stress using physiological and morphological traits and the degree of water stress depends on the amount and/or frequency of rainfall during and after pumping. Therefore, pulsed pumping, under particular climatic conditions, could be used to reduce negative impacts of groundwater extraction on phreatophytes, while still providing groundwater for socio‐economic activities in semiarid zones.

Short-term water stress affecting NO3− absorption by almond plants

Identifying the rates of nitrate absorption by almond plants under water stress is important for improving nitrogen use efficiency in almond orchards. This study aimed to determine the rates of nitrate absorption by almond plants subjected to short-term water stress and no water stress, and the kinetic NO3− absorption parameters in well-watered three-year-old almond plants. Two assays were performed. In the first, fourteen plants arranged in completely randomized design received nutrient solutions with water potentials (Ψw) of 0.0, −0.2, −0.4 and −0.7MPa and containing 1.2mmoll−1 KNO3. We accessed the NO3− depletion in these solutions over an 8-h interval and estimated regression curves of the quantity of nitrate in the nutrient solution (Q) as a function of time (t). Subsequently nitrate uptake rates were calculated. Water loss; nitrate reductase activity; nitrate and total N of the sap; nitrate concentration of leaf dry matter; and nitrate and nitrite concentration of root dry matter were, either, evaluated. The second assay was performed the same way of the first one, with four well-watered plants submitted to 0.3mmoll−1 KNO3 as initial concentration, and allowed estimating NO3− absorption parameters Vmax, Km and Cmin. We observed a linear decrease in the nitrate content of the containers receiving 1.2mmoll−1 of NO3− over a period of 8h. In this concentration, the rates of NO3− uptake ranged from 1.11 to 3.43μmolg−1h−1 and decreased in low water potentials at the root medium. Root nitrate reductase activity followed the same trend of nitrate absorption. In the low NO3− concentration range, the absorption showed a Michaelis–Menten pattern, being the kinetic parameters of NO3− absorption 1.15±0.27μmolg−1h−1, 28.81±4.12μmoll−1 and 17.93±1.1μmoll−1 for Vmax, Km, and Cmin, respectively. We concluded that NO3− uptake of almonds is affected by short periods of water stress, with harmful effects occurring at Ψw below −0.18MPa.

Irrigation scheduling based on CERES-Wheat model for spring wheat production in the Minqin Oasis in Northwest China

The Minqin County in Northwest China is known for its serious desertification and irrigation-dependent oasis farming that is mainly distributed along the Shiyang River. To answer some important hypothetical questions related to optimal irrigation scheduling for spring wheat (Triticum aestivum L.) production in the Minqin Oasis, the CERES-Wheat model in DSSAT V4.5 was used to simulate the spring wheat growth in irrigated farmland in this area. The results of model simulation indicate that if the soil water content is lower than 65% of field capacity (or about 190mm water) in the 1-m depth soil profile during the grain filling and milk ripe stages, the final grain yield can be remarkably reduced (e.g. more than 1000kgha−1 for some treatments in field experiment) even for a short period of water stress. The water stress in the early stages could be eliminated with luxurious water supply, but more nitrogen would be washed away from the soil profile and then the yield was impacted. The optimized irrigation dates played an important role in improving the water use efficiency of spring wheat. If there was only a single irrigation allowed by the limited water resources, the irrigation date should be at the end of booting or beginning of heading stage. If the second irrigation could be adjusted to the middle of heading stage, the 3-irrigation schedule (a total of three irrigations in the whole growth season, and so forth) could meet the water demand of spring wheat without losing too much yield (e.g. less than 20kgha−1 when compared with the 4-irrigation treatment). Furthermore, if the first irrigation of the 4-irrigation schedule could be delayed to the starting of jointing, the simulated yield could be increased from about 6500kgha−1 to the highest 7000kgha−1. Finally, the analysis of uncertainties of simulated dry yields across 58 years historical weather data showed that the schedules with fewer irrigation events cause larger uncertainties due to local weather variations. The 4-irrigation schedule seemed to be the best choice for spring wheat at the Minqin Oasis due to its relatively higher long-term average yields and lower uncertainties since it was under non-limited water conditions.

1-MCP partially alleviates dehydration-induced abscission in cut leaves of the fern Nephrolepis cordifolia

Fern leaves, also called fronds, are often used in bouquets. Leaves of the sword fern ( Nephrolepis cordifolia) consist of a central vascular tissue, with numerous leaflets (pinnae) at each side. Leaves that have been cut and immediately placed in water show abscission of the pinnae, starting from about day 4 of vase life, with 50% pinnae abscission on day 13. The onset of pinnae abscission was hastened by a period of dehydration (3, 6, 9 or 12 h at 25 °C). The time to 50% pinnae abscission was between 7.0 and 4.7 days after 3 h and 12 h of dehydration, respectively. Dehydration treatments might induce air emboli in the xylem, but in these experiments did not inhibit water uptake. Dehydration did increase the rate of ethylene production of the cut leaves throughout vase life. A 3 h treatment with 1-MCP at concentrations of 200 or 300 nL L −1 prior to the period of dehydration reduced the rate of ethylene production and reduced the rate of abscission. 1-MCP treatments were also effective if given after the period of dehydration. The data show that pinnae abscission limits the vase life of cut leaves of the sword fern, and that a short period of water stress drastically increases the rate of abscission. The increase in pinnae abscission was correlated with an increase in ethylene production. As 1-MCP alleviated the effect of dehydration on pinnae abscission, the dehydration effect involved ethylene perception. The data suggest that a small water stress induced an autocatalytic rise in ethylene production which was the direct cause of the increase in pinnae abscission.

Effects of Top Dressing on Growth and Panicle Dry Weight as Affected by Soil Water Stress at the Early Panicle-Development Stage in Rice (Oryza sativa L.)

Rice yield is reduced by a short period of water stress at the early panicle-development stage. This study was conducted to examine the factors that reduce the panicle dry weight of rice subjected to water stress and the alleviating effects of top dressing after the stress. Akihikari, Nipponbare and Akebono were grown in 4-L pots under submerged soil conditions. One half of the pots were subjected to the same degree of water stress during panicle development and the other half was grown without water stress. On the day after the stress treatment, chemical fertilizer was applied to one half of each water treatment. Panicle dry weight at maturity was decreased by water stress and the top dressing after the stress alleviated the decrease. The top dressing increased panicle dry weight under the two water treatments in all three cultivars. Increase of panicle dry weight was dependent on that of total dry weight from drainage to full heading, from full heading to maturity, and from drainage to maturity. Leaf area duration (LAD) and net assimilation rate (NAR) were responsible for changes in total dry weight. Effect of water stress was prominent before full heading, while that of top dressing after full heading. It was concluded that reduction of LAD and NAR may be involved in reduction of panicle dry weight by water stress at the early panicle-development stage, and that top dressing after the water stress may mitigate the effect of water stress on panicle dry weight through the improvement of LAD and NAR.

Effects of Water and Nutrient Availability in Pinus pinaster Ait. Open Pollinated Families at an Early Age: Growth, Gas Exchange and Water Relations

Growth and physiological responses of Pinus pinaster Ait. to water and nutrient availability were compared in four open pollinated families of Arenas de San Pedro provenance (Central Iberian Peninsula), looking for more useful parameters and growing conditions to be included in early selection programmes of forest trees. Young seedlings were grown in a greenhouse, subjected to high and low water and nutrient regimes, during 14 weeks. Interfamily differences were significant with regard to growth, nutrient content and water-use efficiency (WUE): differences in growth were higher under more favourable growing conditions; gas exchange differences were higher in the short term (9 weeks), indicating a faster reaction to water stress of the better adapted families to these conditions; the highest growth rates were found in the families with the largest plasticity, highest WUE and highest nutrient content. Water regime and nutrients had significant effects on growth, δ13C, gas exchange and water relation parameters. For these parameters the ranking of the families was kept regardless the water × nutrient supply combination and there was not a significant family × treatment interaction. In the long term (14 weeks) higher water supply and nutrient content significantly increased instantaneous WUE. The positive relationships between growth, intrinsic WUE (A/g wv) and δ13C demonstrate that it should be possible to use physiological parameters (e.g. g wv, δ13C) as a surrogate for the efficiency in the use of water, at least if short periods of water stress (up to 2 months long) were frequent, as it occurs in the Mediterranean basin. There was also some indication that the decrease in nitrogen or potassium supply led to increasing stomatal conductance and hence lower WUE.

Short Periods of Water Stress during Seed Filling, Leaf Senescence, and Yield of Soybean

The effects of short periods of water stress during seed‐filling on leaf senescence, seed‐fill duration, and yield of soybean [Glycine max (L.) Merrill] are not well understood. Short stress periods were investigated in two greenhouse experiments with cultivar Elgin 87 grown in soil‐filled pots. All pots received adequate water until the beginning of growth stage R6 when a continuous water‐stress treatment (pots received 40% of the water needed to bring controls to pot capacity) was initiated and maintained until maturity. Water stress was relieved in other pots (watered as the control) after 5 or 13 d in Exp. 1 and 3 or 6 d in Exp. 2. Each treatment was replicated six to eight times in a completely randomized design. The carbon exchange rate was rapidly reduced by continuous water stress resulting in earlier maturity, significantly lower yield (39%), and smaller seeds (25–33%). The carbon exchange rate rapidly increased to near control levels in the early stress‐relief treatment, but it was always less than the control for the rest of seed filling. These plants matured sooner and produced significantly lower yields (10–23%) and smaller seeds (9–17%) than control plants. Late stress relief also reduced yield and seed size relative to the control. Yield and seed size of both stress relief treatments, however, were greater than the continuous stress treatment. Water stress‐induced acceleration of senescence could not be stopped by eliminating the stress after a short period. Short periods of water stress during seed filling may, therefore, have larger than expected effects on yield.

Supplemental irrigation for dry-spell mitigation of rainfed agriculture in the Sahel

Unreliable and erratic rainfall combined with inherent low soil fertility in crust prone soils affect crop growth in the Sahel. Past efforts of agricultural water management have primarily focused on maximising rainfall infiltration through soil and water conservation. The challenge of how to cope with dry-spells, short periods of water stress during crop growth, remains largely unsolved. Small-scale water harvesting (WH) for supplemental irrigation may be a tool for small-holder farmers to stabilise crop water supply and thereby increase yields and create incentives for increased investments in fertilisation. Results are presented on the effects on Sorghum ( Sorghum Bicolor (L.)) yields under supplemental irrigation and soil nutrient application in an on-farm experiment in northern Burkina Faso. Focus is on dry-spell bridging and water and nutrient interactions on biomass productivity. The water harvesting system consisted of a low-cost manually dug farm pond with a storage volume of 150 m 3, collecting surface runoff as rill and small gully flow from a 1.8 ha catchment area. The on-farm experiment involved five repetitions of two levels of nutrient application (non-fertilised and fertilised) and two levels of supplemental irrigation (non-irrigated and irrigated) including: farmers’ traditional practices (TC), supplemental irrigation (I), fertiliser application (F) and supplemental irrigation combined with fertilisation (IF). This paper presents field results from three rainy seasons (1998–2000), receiving a cumulative seasonal rainfall ranging from 418 to 667 mm. Supplemental irrigation ranging from 60 to 90 mm per season was applied based on actual occurrence of dry-spell induced crop water stress. Supplemental irrigation had a significant effect on grain yield over the three crop seasons ( ∗∗ P<0.001). Similarly, fertiliser application (46.5 kg N ha −1) resulted in a significantly higher grain yield ( ∗∗∗ P<0.0001). Analysis of variance for interactions between supplemental irrigation and fertiliser application showed significant differences between treatments when analysing the 3 years together ( ∗∗∗ P<0.0001). The control grain yield’s (TC) average over the 3 years was 455 kg ha −1. Supplemental irrigation alone resulted in an average grain yield of 712 kg ha −1, while fertiliser application alone gave an average grain yield of 975 kg ha −1. Supplemental irrigation combined with fertiliser application resulted in an average grain yield of 1403 kg ha −1, which is higher than the farmer’s normal practice by a factor of three. Total above ground biomass yields followed the same pattern as the grain yields for respective years. All three seasons provided data systematically supporting supplemental irrigation as a dry-spell mitigating and yield gap reducing technology.

Water Transport Characteristics of Cotton as Affected by Drip Irrigation Layout

AbstractTo reduce drip irrigation equipment costs, dripper lines are laid in alternate interrow spaces. This study examined the effect of this practice on cotton (Gossypium hirsutum L.) water relations. Measurements of water uptake and water potential of plants grown in the field were conducted during four rainless summers at two locations. During the first summer, drippers in every interrow space delivered about 50 mm of water, the exact amount depending on estimated evapotranspiration (ET), every 10 d. The following summer, drip lines were laid in alternate interrow spaces, applying frequent (2‐4 d) and small (10‐20 mm) amounts of water, based on estimated ET. Treatments were repeated the following two summers. Measurements included water uptake (F), leaf water potential (ψ1, and soil water content. Whenever a linear relationship between diurnal ψ1 and F was found, we determined the hydraulic conductance (KT) of the plants as the line's slope reciprocal, and the intercept (ψ0) as the water potential at the root‐soil interface. A linear relation was found in the treatment with drippers in every interrow space. Water stress developed toward the end of the irrigation interval, causing KT to decrease without affecting ψ0. Irrigation restored KT to its initial value. With the alternate interrow‐space pattern, the relationship between ψ1 and F remained linear only until midday. Afternoon (ψ1, F) points were below those of the morning, suggesting a lowering of the soil water potential near the roots. It was concluded that drippers laid in alternate interrow spaces expose cotton to frequent short periods of water stress.

Effect of water stress on monoterpene emissions from young potted holm oak (Quercus ilex L.) trees.

We investigated the effects of a short period of water stress on monoterpene emissions from Quercus ilex, a common oak species of the Mediterranean vegetation and a strong emitter of monoterpenes. The experiment was carried out on two young saplings with a branch enclosure system under semi-controlled conditions. Under unstressed conditions, small qualitative (cis-β-ocimene, trans-β-ocimene, β-caryophyllene and 1,8-cineol) and large quantitative (as much as 40% for the main compounds emitted) differences were observed between the two apparently similar trees. Nevertheless these differences did not affect the short-and long-term responses to temperature and water stress. Daily courses of emissions and gas exchanges were similar before and after the stress. During the most severe stress, emissions were reduced by a factor of two orders of magnitude and the log-linear relationship between emissions and temperature no longer existed. Photosynthesis and transpiration rates decreased as soon as the soil started to dry, whereas monoterpene emissions slightly increased for few days and then dropped when the daily CO2 balance approached zero. We concluded that under water stress monoterpene emissions were highly limited by monoterpene synthesis resulting from a lack of carbon substrate and/or ATP. After rewatering, both emissions and gas exchanges recovered immediately, but to a level lower than the pre-stress level. These results have many implications for monoterpene emission modelling in the Mediterranean area, since the dry period generally extends from May to August. If our results are confirmed by field experiments, water stress could lead to a large overestimation of the emissions under summer conditions, when the algorithms based on light and temperature would give high emission rates.

Stomatal resistance and the ratio of intercellular to ambient carbon dioxide in container-grown yellow-poplar seedlings exposed to chronic ozone fumigation and water stress

One-year old container-grown seedlings of yellow-poplar ( Liriodendron tulipifera L.) were exposed to 0.15 ppm ozone (O 3) fumigation and water stress (two l-week drying cycles) in continuously stirred tank reactors prior to measuring stomatal resistance ( R s), intercellular carbon dioxide [CO 2 ( C i)], and the ratio of C i and ambient CO 2 ( C a) after 20 and 36 days. Water stress increased R s by more than 250% and reduced C i and the C i C a ratio by just over 20%. There were no significant effects of 0.15 ppm O 3 on C i and the C i C a ratio but R s was significantly increased by the interaction of water stress and O 3 fumigation. For water-stressed seedlings fumigated with charcoal-filtered air, C i and the C i C a ratio were significantly lower than those of the other treatments. The data show that interactions involving low levels of ozone and short periods of water stress may have a substantial influence on stomatal physiology.

Varietal differences in the response of potatoes to repeated short periods of water stress in hot climates. 2. Tuber yield and dry matter accumulation and other tuber properties

The effect of repeated short periods of water stress during the hot season on six potato cultivars was investigated. The number of tubers per plant tended to decrease in response to water stress in cultivars which had more than 9.8 tubers per control plant (Desiree, Alpha, Elvira). In the other cultivars, no consistent effect of water stress on tuber number per plant was observed. Except for Spunta, the percentage of large tubers (>60 g/tuber) was reduced in the water-stressed plants. Consequently, the average weight of these tubers was greater than that of tubers harvested from the unstressed plants, indicating that the sink force of the individual tuber was not impaired by drought. However, tuber yield per plant was reduced due to drought in all cultivars tested. The smallest decrease in dry matter accumulation as well as the greatest lowering of the osmotic potential in the tuber tissue was found in Alpha. No consistent effect of water stress on the percentage of misshapen and sprouting tubers was observed, indicating the marked effect of the high temperature on these traits.

Varietal differences in the response of potatoes to repeated short periods of water stress in hot climates. 1. Turgor maintenance and stomatal behaviour

The response of six potato cultivars, Desiree, Up-to-Date, Alpha, Elvira, Spunta and Troubadour, to water stress under high ambient temperatures was investigated. Osmotic regulation in the leaves of all six cultivars was highest in Alpha and the lowest in Troubadour. Concomitantly, Alpha maintained the highest turgor potential under water stress while Troubadour had the lowest values indicating a relationship between the degree of osmotic regulation and maintenance of turgor. The highest stomatal conductance under water stress was exhibited by Desiree while both stressed and non-stressed plants of Up-to-Date had the lowest values. In addition, Up-to-Date had a larger root system than Desiree. The association of these traits with tolerance to short periods of drought in the potato is discussed.

Effects of water stress on the chlorophyll content, nitrogen level and photosynthesis of leaves of two maize genotypes

The dynamics of leaf chlorophyll level, nitrogen content, photosynthesis and stomatal conductance were followed in detail in two cultivars of maize (Zea mays) during a short period of water stress, applied at tasseling, and during the subsequent recovery phase. Plants used in the experiment were grown in sand-nutrient solution culture under field weather conditions. Water stress reduced chlorophyll levels, stomatal conductance and photosynthesis, but the nitrogen content of the leaves was not affected. It is concluded that the stress-induced loss of chlorophyll is not mediated by a lack of nitrogen. Considerable differences were observed between genotypes in the rate of post-stress recovery of chlorophyll level. Recovery, upon rewatering, of stomatal conductance and photosynthesis preceded that of chlorophyll level. Losses of up to 40% of leaf chlorophyll content were insufficient to affect rates of photosynthesis measured at mid-day.

Stem pithiness in tomato plants: The effect of water stress and the role of abscisic acid

The pith parenchyma in tomato (Lycopersicum esculentum) stems was found to be disrupted in response to water stress (stem pithiness). The process of the degradation starts at the upper part of the stem and proceeds downwards as the stress is prolonged. The damage to the stem tissue was found to be irreversible upon rehydration of the stressed plants. Scanning electron microscopy revealed that the protoplast of the affected cells is disrupted first, followed by degradation of the cell wall.Application of abscisic acid (ABA) induced pithiness in non‐stressed plants and also enhanced the effect of a short period of dehydration. Kinetin, although causing severe wilting, did not induce pithiness. However, when given after a short period of water stress or within the period of stress, kinetin enhanced pithiness development.In the course of the stress, ABA levels in the upper part of the stem and in the young leaves were higher than the levels found in the lower parts of the plant shoot. The increase in ABA levels was detected before any sign of pithiness.It is suggested that ABA might be the triggering agent of the cellular degradation process initiated by water stress.

Relationship between Leaf Water Status and Endogenous Ethylene in Detached Leaves

The pattern of changes in the internal concentration of ethylene in response to water stress was investigated in species with leaves that do abscise and leaves that do not abscise. When leaves which abscise were detached and exposed to dry air for up to 6 hours, a continuous increase of internal ethylene was observed. In water-stressed leaves which do not abscise only a transient rise in ethylene occurred. The peak, which was attained after 30 to 120 minutes, depending on the species studied, was followed by a sharp decline to the initial level. The principal site of ethylene production in response to a short period of water stress was in the blades rather than the petioles in both types of leaves. The internal ethylene level in leaves was reduced by pretreatment with the ethoxy analog of rhizobitoxine (an inhibitor of ethylene biosynthesis) or by maintaining the leaves under subatmospheric pressure. The results obtained by these methods showed that ethylene was not involved in the mechanism of stomatal movement in either turgid or in stressed leaves. Also, the increase in leaf abscisic acid content and the depletion of gibberellins induced by water stress were not related to the internal concentration of ethylene in the detached leaf. The different patterns of drought-induced ethylene production observed in the blades of leaves which exhibit abscission compared with those which do not exhibit abscission may indicate the involvement of ethylene in a primary event in the process of leaf abscission induced by water stress.

Yield responses of two maize cultivars following short periods of water stress at tasseling

Two maize ( Zea mays L.) double-hybrids, Abati No. 2 and DeKalb F880, were grown outdoors to maturity in sand-water culture. At tasseling, both cultivars were subjected to drought by withholding water from the plants for 0 (control), 3, 5, or 6 days. Water was supplied thereafter and till harvest. Leaf water potential (LWP) at the end of each droughting treatment was usually higher in DeKalb than in Abatí, particularly at the 5- and 6-day droughting treatments. There was no differential effect of drought on the mean proportion of fully green leaves of each hybrid as recorded one week after the termination of the droughting treatments. Both the total dry matter and grain yields per plant in both hybrids were directly related to LWP at tasseling in plants droughted for 0, 3, or 5 days. Six days of drought decreased the total dry-matter yield of DeKalb F880 to a value below that of Abatí but the grain yield of the former hybrid was much higher than that of the latter. This was the result of drought-induced changes (absent in DeKalb F880 plants) in the pattern of dry-matter distribution in Abatí No. 2: the decrease in the proportion of grain (−32%) was compensated by increases in the proportions of roots (25%), leaf blades (4%) and barren ears (2%). It is concluded that the responses exhibited by DeKalb F880 represent an important advantage for maize cultivars grown in areas where drought spells are likely to occur during the early growth of the ears.

The effect of high temperature regimes or short periods of water stress on development of small fruiting saltana vines

Poor fruit set of sultanas in the Murray Valley is sometimes attributed to excessively high temperatures around flowering time. Experiments with small fruiting sultana vines in pots suggest that water stress is the more important factor. Fruit set was significantly less when a 3-day period of water stress was imposed at flowering or 1, 2, or 4 weeks after flowering, but not when it was imposed 6 weeks after flowering. Three days with maximum temperatures above 45°C at or 1 week after flowering did not reduce fruit set when ample water was supplied. When controlled environments combining day temperatures between 21 and 30°C with night temperatures between 19 and 25° were used, no significant differences in fruit set were found, although shoot growth increased with increasing night temperature. Shoot elongation slowed down during periods of applied water stress but recovered, when the stress was ended, to a rate greater than that of plants which had not been stressed.