Panicle Water Potential, a Physiological Trait to Identify Drought Tolerance in Rice

Two upland rice varieties (IRAT109, IAPAR9) and one lowland rice variety (Zhenshan 97B) were planted in summer and treated with both normal (full water) and drought stress in the reproductive stage. Panicle water potential (PWP) and leaf water potential (LWP) were measured every 1.0-1.5 h over 24 h on sunny days. Both PWP and LWP of upland varieties started to decrease later, maintained a higher level and recovered more quickly than that of the lowland variety. The results show that PWP can be used as an indicator of plant water status based on the parallel daily changes, and the high correlation between PWP and LWP. Similar correlations were also observed between PWP, LWP and eight traits related to plant growth and grain yield formation. PWP seemed to be more effective for distinguishing the upland rice varieties with different drought-tolerant ability. Differences in PWP and LWP between upland and lowland rice varieties were also observed at noon even under normal water conditions, implying the incorporation of the drought-tolerant mechanism to improve the photosynthesis and yield of traditional paddy rice.     

The role of aquaporin RWC3 in drought avoidance in rice

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and drought resistance still remains elusive. From an agronomic viewpoint, upland rice is traditionally considered as showing drought avoidance. In the investigation of different morphological and physiological responses of upland rice (Oryza sativa L. spp indica cv. Zhonghan 3) and lowland rice (O. sativa L. spp japonica cv. Xiushui 63) to water deficit, we observed young leaf rolling and the remarkable decline of cumulative transpiration in the upland rice. The expression of water channel protein RWC3 mRNA was increased in upland rice at the early response (up to 4 h) to the 20% polyethylene glycol (PEG) 6000 treatment, whereas there was no significant expression changes in lowland rice. Protein levels were increased in upland rice and decreased in lowland rice at 10 h after the water deficit. The up-regulation of RWC3 in upland rice fits well with the knowledge that upland rice adopts the mechanism of drought avoidance. The physiological significance of this RWC3 up-regulation was then explored with the over-expression of RWC3 in transgenic lowland rice (O. sativa L. spp japonica cv. Zhonghua 11) controlled by a stress-inducible SWPA2 promoter. Compared to the wild-type plant, the transgenic lowland rice exhibited higher root osmotic hydraulic conductivity (Lp), leaf water potential and relative cumulative transpiration at the end of 10 h PEG treatment. These results indicated that RWC3 probably played a role in drought avoidance in rice.     

Sensitivities of rice grain yield and other panicle characters to late-stage drought stress revealed by phenotypic correlation and QTL analysis

A lowland rice variety (Zhenshan97B) was crossed with an upland variety (IRAT109) to construct a set of recombinant inbred lines (RILs). The population was evaluated under both well-watered (control) and drought-stress (drought) conditions for 2 years. Panicle water potential (PWP), panicle length (PL), grain number per plant (GNP), primary branch number (PBN), second branch number (SBN), spikelet density (SPD), and dry grain weight per plant (DGW) were measured. Phenotypic correlation and path analysis were used to interpret the ranking of importance of other panicle traits to grain yield. Comparison of such rankings under control and drought conditions showed varied responses of panicle traits to drought stress. It was indicated that GNP was an important contributor to DGW under control, and even more important under drought. Thirty-two quantitative trait loci (QTLs) for panicle traits and dry grain weight were identified, with contribution rates ranging from 3.33% to 22.66%. Eleven epistatic QTLs were detected. Cases of collocated QTLs under control and drought were found for PL, SPD, GNP, PBN, and SBN, but not for DGW and PWP. The effectiveness of selection under normal and stressed conditions is discussed.     

Upland rice and lowland rice exhibited different PIP expression under water deficit and ABA treatment

Aquaporins play a significant role in plant water relations. To further understand the aquaporin function in plants under water stress, the expression of a subgroup of aquaporins, plasma membrane intrinsic proteins （PIPs）, was studied at both the protein and mRNA level in upland rice （Oryza sativa L. cv. Zhonghan 3） and lowland rice （Oryza sativa L. cv. Xiushui 63） when they were water stressed by treatment with 20% polyethylene glycol （PEG）. Plants responded differently to 20% PEG treatment. Leaf water content of upland rice leaves was reduced rapidly. PIP protein level increased markedly in roots of both types, but only in leaves of upland rice after 10 h of PEG treatment. At the mRNA level, OsPIP1,2, OsPIP1,3, OsPIP2;1 and OsPIP2;5 in roots as well as OsPIP1,2 and OsPIP1;3 in leaves were significantly up-regulated in upland rice, whereas the corresponding genes remained unchanged or down-regulated in lowland rice. Meanwhile, we observed a significant increase in the endogenous abscisic acid （ABA） level in upland rice but not in lowland rice under water deficit. Treatment with 60 μM ABA enhanced the expression of OsPIP1;2, OsPIP2;5 and OsPIP2;6 in roots and OsPIP1;2, OsPIP2;4 and OsPIP2;6 in leaves of upland rice. The responsiveness of PIP genes to water stress and ABA were different, implying that the regulation of PIP genes involves both ABA-dependent and ABA-independent signaling oathways during water deficit.     

Comparison on physiological adaptation and phosphorus use efficiency of upland rice and lowland rice under alternate wetting and drying irrigation

As one of the most widely promoted water-saving irrigation strategies for rice, alternate wetting and drying irrigation (AWD) can not only save water but also increase mineral nutrient use efficiency. In this study, we compared the growth conditions of four rice varieties (two lowland and two upland varieties) under three irrigation regimes: continuously flooded (CF), alternate wetting and moderate soil drying (AWD15) and alternate wetting and severe soil drying (AWD30). AWD15 and AWD30 enabled the plants to receive fewer irrigation events and less irrigation water than CF, thereby saving both water resources and labor. AWD15 reduced redundant vegetative growth, promoted root growth, and increased the root-shoot ratio and harvest index. AWD15 increased the grain yield, water use efficiency (WUE) and phosphorus use efficiency (PUE) of upland rice and maintained the grain yield while increasing the WUE and PUE of lowland rice. More developed root systems under AWD helped upland rice to maintain a higher water status than lowland rice when plants were subjected to soil drying, which resulted in superior performance in grain yield in upland rice. AWD30 could not reconcile the demands of higher yield and the desire to reduce irrigation water use because it decreased grain yield. The results indicate that AWD15 irrigation of rice can not only increase rice yield and WUE but also enhance PUE, which can potentially reduce the use of phosphorus fertilizers. The results provide theoretical and technical support for improving rice cultivation.     

Rice leaf growth and water potential are resilient to evaporative demand and soil water deficit once the effects of root system are neutralized

Rice is known to be sensitive to soil water deficit and evaporative demand, with a greatest sensitivity of lowland‐adapted genotypes. We have analysed the responses of plant water relations and of leaf elongation rate (LER) to soil water status and evaporative demand in seven rice genotypes belonging to different species, subspecies, either upland‐ or lowland‐adapted. In the considered range of soil water potential (0 to ?0.6 MPa), stomatal conductance was controlled in such a way that the daytime leaf water potential was similar in well‐watered, droughted or flooded conditions (isohydric behaviour). A low sensitivity of LER to evaporative demand was observed in the same three conditions, with small differences between genotypes and lower sensitivity than in maize. The sensitivity of LER to soil water deficit was similar to that of maize. A tendency towards lower sensitivities was observed in upland than lowland genotypes but with smaller differences than expected. We conclude that leaf water status and leaf elongation of rice are not particularly sensitive to water deficit. The main origin of drought sensitivity in rice may be its poor root system, whose effect was alleviated in the study presented here by growing plants in pots whose soil was entirely colonized by roots of all genotypes.     

Leaf gas exchange of upland and lowland rice cultivars

Leaf gas exchange of upland and lowland rice cultivars were measured during late vegetative and during grain filling stages in the field under upland and lowland growth conditions. The rate of photosynthesis and water use efficiency (the rate of photosynthesis/the rate of transpiration) under upland conditions decreased with ageing, but generally varied little among four cultivars. At mid-grain filling under lowland conditions, upland cultivars showed lower rates of photosynthesis and transpiration than the lowland cultivars with concomitant reduction in whole plant conductance. At this stage, water use efficiency was higher under upland conditions than under lowland conditions, particularly in the upland cultivars. Water stress reduced the rate of photosynthesis without altering water use efficiency.     

Evaluating the resistance of six rice cultivars to drought: restriction of deep rooting and the use of raised beds

Soil water deficits reduce rice (Oryza sativa L.) productivity under upland field conditions. In this study, we constructed screening facilities to evaluate the performance of rice cultivars under drought conditions and to assess the roles of deep roots. Two experiments were conducted with six rice cultivars, including drought-tolerant and drought-susceptible cultivars, grown in two root environments: a root-restricted treatment that restricted rooting depth with water-permeable sheets, and a raised bed that reduced water availability in the surface soil by inserting a gravel layer between the topsoil and subsoil layers to interrupt capillary transport of water. In the root-restricted treatment, in which root growth was restricted to the surface 25-cm layer, leaf water potential decreased faster in cultivars with a large canopy during drought stress, and there was little difference in panicle weight among cultivars. With a normal (unrestricted) root environment, the deepest-rooting cultivar (‘IRAT109’) maintained higher leaf water potential during drought, although panicle weight under drought stress was affected by yield potential as well as by deep rooting. Under the intermittent drought stress in the raised bed, deep-rooting cultivars accumulated more nitrogen and produced more biomass, and the difference in panicle weight between deep-rooting drought-tolerant and shallow-rooting drought-susceptible cultivars was magnified by the raised bed compared with the yield differences under drought in a normal root environment. These results demonstrate that the drought screening facilities we developed can help to identify superior cultivars under upland field conditions without time-consuming measurement of deep root systems.     

Alleviating soil sickness caused by aerobic monocropping: responses of aerobic rice to soil oven-heating

“Aerobic rice” system is the cultivation of nutrient-responsive cultivars in nonflooded and nonsaturated soil under supplemental irrigation. It is intended for lowland areas with water shortage and for favorable upland areas with access to supplementary irrigation. Yield decline caused by soil sickness has been reported with continuous monocropping of aerobic rice grown under nonflooded conditions. The objective of this study was to determine the growth response of rice plant to oven heating of soil with a monocropping history of aerobic rice. A series of pot experiments was conducted with soils from fields where rice has been grown continuously under aerobic or anaerobic (flooded) conditions. Soil was oven heated at different temperatures and for various durations. Plants of Apo, an upland variety that does relatively well under the aerobic conditions of lowland, were grown aerobically without fertilizer inputs in all six experiments. Plants were sampled during vegetative stage to determine stem number, plant height, leaf area, and total biomass. Heating of soil increased plant growth greatly in soils with an aerobic history but a relatively small increase was observed in soils with a flooded history as these plants nearly reached optimum growth. A growth increase with continuous aerobic soil was already observed with heating at 90°C for 12 h and at 120°C for as short as 3 h. Maximum plant growth response was observed with heating at 120°C for 12 h. Leaf area was most sensitive to soil heating, followed by total biomass and stem number. We conclude that soil heating provides a simple and quick test to determine whether a soil has any sign of sickness that is caused by continuous cropping of aerobic rice.     

Hydraulic properties of rice and the response of gas exchange to water stress

We investigated the role of xylem cavitation, plant hydraulic conductance, and root pressure in the response of rice (Oryza sativa) gas exchange to water stress. In the field (Philippines), the percentage loss of xylem conductivity (PLC) from cavitation exceeded 60% in leaves even in watered controls. The PLC versus leaf water potential relationship indicated diurnal refilling of cavitated xylem. The leaf water potential causing 50 PLC (P(50)) was -1.6 MPa and did not differ between upland versus lowland rice varieties. Greenhouse-grown varieties (Utah) were more resistant to cavitation with a 50 PLC of -1.9 MPa but also showed no difference between varieties. Six-day droughts caused concomitant reductions in leaf-specific photosynthetic rate, leaf diffusive conductance, and soil-leaf hydraulic conductance that were associated with cavitation-inducing water potentials and the disappearance of nightly root pressure. The return of root pressure after drought was associated with the complete recovery of leaf diffusive conductance, leaf-specific photosynthetic rate, and soil-leaf hydraulic conductance. Root pressure after the 6-d drought (61.2 +/- 8.8 kPa) was stimulated 7-fold compared with well-watered plants before drought (8.5 +/- 3.8 kPa). The results indicate: (a) that xylem cavitation plays a major role in the reduction of plant hydraulic conductance during drought, and (b) that rice can readily reverse cavitation, possibly aided by nocturnal root pressure.     

水稻叶片水势的QTL定位与候选基因分析

为探究叶片水势(LWP)相关基因在水稻(Oryza sativa)抗旱中的作用及其遗传机制, 以热研2号(Nekken2)和华占(HZ)为亲本以及构建的120个重组自交系(RILs)群体为实验材料, 对水稻分蘖期叶片水势进行检测, 并利用前期基于高通量测序构建的分子遗传连锁图谱进行数量性状基因座(QTL)分析。结果表明, 共检测到5个与水稻分蘖期叶片水势相关的QTLs, 分别位于第2、3、4、11和12号染色体上, LOD值均达2.5以上, 其中位于4号染色体物理距离24 066 261- 30 847 136 bp内QTL的LOD值高达5.15。对这些QTL区间内与水势相关的候选基因进行定量分析, 发现LOC_Os02g56630、LOC_Os02g57720、LOC_Os02g57580、LOC_Os04g43730、LOC_Os04g46490、LOC_Os04g44570和LOC_Os04g44060这7个基因在双亲间表达量差异显著。位于4号染色体QTL区间内LOC_Os04g46490基因的表达在两亲本间存在显著差异。对基因LOC_Os04g46490进行测序分析, 发现该基因在两亲本间共存在6处差异, 从而导致氨基酸序列的改变。通过QTL挖掘及相关基因表达分析, 发现这些基因与水稻叶片水势调控相关, 可能间接影响水稻的抗旱性。检测到的QTL位点对水势相关基因精细定位和克隆具有重要参考价值, 有助于进一步理解水稻叶片水势的遗传基础, 并为培育耐旱水稻新品种提供有利的基因资源。     

树锦鸡儿、柠条锦鸡儿、小叶锦鸡儿和鹰嘴豆干旱适应能力比较

对1年生豆科作物鹰嘴豆Rupali品种和Almaz品种以及多年生植物树锦鸡儿、柠条锦鸡儿和小叶锦鸡儿叶相对含水量和叶水势对逐渐干旱胁迫的响应进行了分析,比较了两类植物的干旱适应能力。结果表明鹰嘴豆叶相对含水量随叶水势的下降线性下降,树锦鸡儿、柠条锦鸡儿和小叶锦鸡儿叶相对含水量在叶水势分别下降到-2.4MPa、-2.5MPa和-1.5 MPa之前没有下降,之后随水势的下降线性下降。树锦鸡儿、柠条锦鸡儿和小叶锦鸡儿这种叶相对含水量下降的滞后性表明该类植物叶具有较硬而弹性较差的细胞壁,使得植物在干旱胁迫下叶具有良好的保水能力。鹰嘴豆叶具有的最低水势为-4.5MPa,对应的土壤相对含水量为14％,锦鸡儿植物叶具有的最低水势可达-6.7MPa,对应的土壤相对含水量为6％,说明锦鸡儿植物比鹰嘴豆具有更好的干旱适应能力,这种能力可能取决于锦鸡儿植物体内大量渗透调节物质的累积。     

新疆策勒绿洲外围四种多年生植物的水分生理特征

对新疆策勒绿洲外围多年生植物胡杨、柽柳、沙拐枣和骆驼刺的水分生理特性进行了试验研究.结果表明：4种植物在生长季内没有受到严重的水分胁迫,灌溉对植物水分生理指标变化的影响不显著(P＞0.05).4种植物水分生理特性的季节变化各不相同.其中,骆驼刺的清晨水势和日均茎流量最高,但其平均水分利用效率最低;沙拐枣的平均水分利用效率最高,而且其清晨水势与日均茎流量的变化最为稳定,季节变幅不大;柽柳的清晨水势最低,具有较好的环境适应性;胡杨水分生理指标的季节变化相对平稳.在新疆策勒绿洲外围的极端干旱环境中,4种植物通过深根系和地下水相连接,并利用地下水来维持其生存与生长.     

Whole plant responses, key processes, and adaptation to drought stress: the case of rice

Most high-yielding rice cultivars developed for irrigated conditions, including the widely grown lowland variety IR64, are highly susceptible to drought stress. This limits their adoption in rainfed rice environments where there is a risk of water shortage during the growing season. Mapping studies using lowland-by-upland rice populations have provided limited information about the genetic basis of variation in yield under drought. One approach to simultaneously improve and understand rice drought tolerance is to generate backcross populations, select superior lines in managed stress environments, and then evaluate which features of the selected lines differ from the recurrent parent. This approach was been taken with IR64, using a range of tolerant and susceptible cultivars as donor parents. Yields of the selected lines measured across 13 widely contracting water environments were generally greater than IR64, but genotype-by-environment effects were large. Traits expected to vary between IR64 and selected lines are plant height, because many donors were not semi-dwarf types, and maturity, because selection in a terminal stress environment is expected to favour earliness. In these experiments it was found that some lines that performed better under upland drought were indeed taller than IR64, but that shorter lines with good yield under drought could also be identified. In trials where drought stress developed in previously flooded (lowland) fields, height was not associated with performance. There was little change in maturity with selection. Other notable differences between IR64 and the selected backcross lines were in their responses to applied ABA and ethylene in greenhouse experiments at the vegetative stage and in leaf rolling observed under chronic upland stress in the field. These observations are consistent with the hypothesis that adaptive responses to drought can effectively allow for improved performance across a broad range of water environments. The results indicate that the yield of IR64 under drought can be significantly improved by backcrossing with selection under stress. In target environments where drought is infrequent but significant in certain years, improved IR64 with greater drought tolerance would be a valuable option for farmers.     

直播旱作水稻的吸氮特征与土壤氮素表观盈亏

水稻旱作是水稻节水栽培中最有效的方式。通过田间试验研究旱作直播条件下水稻对氮素的吸收利用特征以及土壤矿质氮的动态变化 ,并对土壤氮素的表观盈亏量进行了估算。结果表明 ,直播旱作水稻较水作水稻更注重中后期对氮素养分的吸收 ,尤其是对土壤氮素的吸收 ;幼穗分化后水稻的土壤吸氮量占阶段吸氮总量的 6 9.5 % ,比水作水稻多 17.8%。对 0～ 4 0 cm土层土壤矿质氮含量时空变化的研究表明 ,直播旱作水稻生育前期土壤表层矿质态氮大量累积 ,在灌水和降雨的影响下 ,向下层的迁移增加 ,基肥施用后裸地处理 2 0～ 4 0 cm土层的矿质氮高达 10 4 kg N/hm2 。对水稻各生育期土壤氮素盈亏的计算结果表明 ,自分蘖盛期后旱作各处理都表现出土壤氮素不同程度上的表观亏缺 ,然而就全生育期土壤氮素盈余量而言 ,旱作处理平均高达 12 7kg N/hm2 ,生育前期氮肥的大量投入是氮素盈余的主要原因。本试验结果表明 ,直播旱作水稻生育前期对施用的肥料氮吸收很少 ,提高直播旱作水稻氮肥利用效率的关键在于减少生育前期肥料氮的投入     

Transfer of water from roots into dry soil and the effect on wheat water relations and growth

This investigation was performed to study the effect on plant water relations and growth when some of roots grow into dry soil. Common spring water (Triticum aestivum) plants were grown from seed in soil in 1.2 m long PVC (polyvinyl chloride) tubes. Some of the tubes had a PVC partition along their center so that plants developed a split root system (SPR). Part of the roots grew in fully irrigated soil on one side of the partition while the rest of the roots grew into a very dry (-4.1 MPa) soil on the other side of the partition. Split root plants were compared with plants grown from emergence on stored soil moisture (STOR) and with plants that were fully irrigated as needed (IRR). The experiment was duplicated over two temperature regimes (10°/20°C and 15°/25°C, night/day temperatures) in growth chambers. Data were collected on root dry matter distribution, soil moisture status, midday leaf water potential (LWP), leaf relative water content (RWC) and parameters of plant growth and yield.Some roots were found in the dry side of SPR already at 21 DAE (days after emergence) at a soil depth of 15 to 25 cm. Soil water potential around these roots was -0.7 to -1.0 MPa at midday, as compared with the initial value of -4.1 MPa. Therefore, water apparently flowed from the plant into the dry soil, probably during the night. Despite having most of their roots (around 2/3 of the total) in wet soil, SPR plants developed severe plant water stress, even in comparison with STOR plants. Already at 21 DAE, SPR plants had a LWP of -1.5 to -2.0 MPa, while IRR and STOR had a LWP of -0.5 MPa or higher. As a consequence of their greater plant water stress, SPR as compared with IRR plants were lower in tiller number, ear number, shoot dry matter, root dry matter, total biomass, plant height and grain yield and had more epicuticular wax on their leaves.It was concluded that the exposure of a relatively small part of a plant root system to a dry soil may result in a plant-to-soil water potential gradient which may cause severe plant water stress, leading to reduced plant growth and yield.     

Silicon deficiency and the adaptation of tropical rice ecotypes

Although silicon (Si) is found at much higher concentrations in healthy rice crops than N, P or K, it has received far less study, particularly for upland rice. There are few reports on the existence, causes, and effects of varying Si supplies in different environments. Chemical analyses of soil, water and plant tissue samples from experiments grown on a typical weathered, acidic upland soil in Colombia found concentrations of Si which were 80-90% lower than those in a typical lowland environment. These results corroborate published findings from West Africa and Hawaii, and lend support to a conclusion that acid-soil upland rice environments in the tropics tend to be deficient in Si, increasing disease damage, among other effects. Critical values for diagnosis of Si deficiency in soils, water and rice husk tissue are suggested. These are reasonably consistent with, but extend the application of previously published values derived from lowland rice studies to upland environments, and use simpler sampling and analysis methods. A strong correlation was found (r = -0.91) between high husk Si concentration and low husk discoloration disease damage, among diverse rice genotypes grown in the uplands. These genotypic differences were mainly explained by their ecotypic affinities: those belonging to the tropical japonica ecotype exhibited 93% higher husk Si concentrations than indica ecotypes (ecotypic means of 23 vs. 12 mg kg^-1 ). This is consistent with a hypothesis that the tropical japonicas may have adapted to Si deficiency in their native upland environment by evolving mechanisms to attain relatively higher tissue Si concentrations than indicas, which are believed to have evolved in the lowlands, where the Si supply is generally ample. Increased understanding of Si-mediated disease resistance in different rice environments and ecotypes could help breeders combine the high yield potential of indica types with the more durable disease resistance of the japonicas, and could contribute to the development of integrated disease management strategies.     

干旱胁迫对水稻水分利用效率的影响

通过特殊自然干旱胁迫的方法,研究不同干旱胁迫对水稻的水分利用效率（ＷＵＥ）的影响,在一定供水量时,水稻的ＷＵＥ随供水量的增加而下降,但水稻旱种时,却因供水量过低,干旱胁迫严重,ＷＵＥ值为最低。不同品种的水稻ＷＵＥ存在较大的差异,抗旱性强的品种具有较高ＷＵＥ,因此选用具有较高ＷＵＥ的品种,是水稻节水栽培的关键。     

Development and application of gene-based markers for the major rice QTL Phosphorus uptake 1

Marker-assisted breeding is a very useful tool for breeders but still lags behind its potential because information on the effect of quantitative trait loci (QTLs) in different genetic backgrounds and ideal molecular markers are unavailable. Here, we report on some first steps toward the validation and application of the major rice QTL Phosphate uptake 1 (Pup1) that confers tolerance of phosphorus (P) deficiency in rice (Oryza sativa L.). Based on the Pup1 genomic sequence of the tolerant donor variety Kasalath that recently became available, markers were designed that target (1) putative genes that are partially conserved in the Nipponbare reference genome and (2) Kasalath-specific genes that are located in a large insertion-deletion (INDEL) region that is absent in Nipponbare. Testing these markers in 159 diverse rice accessions confirmed their diagnostic value across genotypes and showed that Pup1 is present in more than 50% of rice accessions adapted to stress-prone environments, whereas it was detected in only about 10% of the analyzed irrigated/lowland varieties. Furthermore, the Pup1 locus was detected in more than 80% of the analyzed drought-tolerant rice breeding lines, suggesting that breeders are unknowingly selecting for Pup1. A hydroponics experiment revealed genotypic differences in the response to P deficiency between upland and irrigated varieties but confirmed that root elongation is independent of Pup1. Contrasting Pup1 near-isogenic lines (NILs) were subsequently grown in two different P-deficient soils and environments. Under the applied aerobic growth conditions, NILs with the Pup1 locus maintained significantly higher grain weight plant^?1 under P deprivation in comparison with intolerant sister lines without Pup1. Overall, the data provide evidence that Pup1 has the potential to improve yield in P-deficient and/or drought-prone environments and in diverse genetic backgrounds.     

Organic manure additions and the leaf water potential and yield of barley

The effect of adding organic manure to three soils with differing textures on changes in leaf water potential (LWP) and yield of barley (cv. Loyola) was investigated under controlled growth-chamber conditions. Cattle manure was applied to the soils in pots at rates equivalent to 0, 15, 25, 50 and 100 t ha^-1. Plants were subjected to water stress by withholding water at three different stages of grwoth.The results show that the addition of cattle manure significantly increased (p<-0.05) the organic carbon (OC) content of all the soils. LWP remained consistently high during the entire growing period in the control plants. As stress progressed, LWP in the stressed plants decreased. However, treatments with high OC contents had significantly higher LWP compared to those which had less. The former plants experienced less water stress than the latter.Yields were higher in the control than stressed plants. Within the stressed plants however, treatments with high OC content had significantly higher yields. An effect of soil texture was also noted. Generally, the influence of manure application on LWP and yields were more pronounced in sand and loam than clay soils.