冠层温度在水稻抗旱性基因型筛选中的应用及其测定技术

本文综述了冠层温度在水稻抗旱性基因型筛选中的应用及其研究进展,并介绍了利用红外测温仪测定冠层温度的方法。作物不同基因型之间存在冠层温度的差异,并且从理论上讲,冠层温度与作物水分利用相关,因而把冠层温度用于作物基因型筛选是有价值而且是可行的。利用红外测温仪测定水稻冠层温度是一项非接触性测温法,为水稻抗旱性基因型的筛选提供了一种简便、快速、非破坏性的技术。     

施肥对小麦冠层温度的影响及其与生物学性状的关联

利用红外测温仪等研究了不同施肥处理对小麦冠层温度的影响。结果表明 :不同施肥处理可改变小麦基因型的冠层温度 ,对于同一基因型品种 ,养分胁迫越严重 ,冠层温度越高 ;籽粒灌浆期旗叶叶绿素含量、可溶性蛋白质含量、蒸腾速率、净光合速率及一些农艺性状与冠层温度呈显著负相关。这表明 ,优良的生物学性状和较低的冠层温度相联系 ,冠层温度的高低可能成为反映水、肥等栽培措施是否科学合理的便捷而较准确的指标     

旱地冬小麦灌浆期冠层温度与产量和水分利用效率的关系

利用红外测温仪,于2005～2006年在甘肃陇东旱原研究了我国北方冬麦区域的23个小麦品种(系)灌浆不同时期冠层温度的差异及其与产量和水分利用效率的关系。结果表明,不同基因型小麦在籽粒灌浆结实期存在着冠层温度高度分异的现象,其分异程度随灌浆过程的进行明显加大,到灌浆中后期达到最大。无论灌浆初期还是中期或中后期,旱地冬小麦产量、水分利用效率与冠层温度均呈极显著的负相关(R2=0.445-0.812),并且随着灌浆期推移,相关性增大,灌浆中后期冠层温度每升高1℃,旱地冬小麦产量减少近280 kg hm-2,水分利用效率下降约0.6 kg hm-2mm-1。灌浆中期以后不同基因型小麦冠层温度保持较高的一致性,冠层温度偏低的品种具有较高的产量和水分利用效率。灌浆中后期的冠层温度在评价小麦产量和水分利用效率上具有较高的可靠性,可作为一个田间选择指标应用。     

作物冠层温度的研究进展

作物冠层温度是作物遗传特性和环境条件共同作用的结果,它不仅影响叶片的功能期、蒸腾速率和光合能力,也影响籽粒蛋白质含量和淀粉合成。作物花后特别是灌浆中后期的冠层温度对产量具有较大影响。本文概述了冠层温度对作物产量的影响机理和影响因素的研究进展,并指出优良基因型的选育和合理的栽培管理措施是降低冠层温度、提高产量的有效途径。     

不同温度型花生品种的抗衰老特性

以我国北方4个大花生品种为研究材料,于花生结荚期到收获,用红外测温仪对各品种的冠层温度进行连续观测,并测定了花生主茎功能叶片中叶绿素、可溶性糖、可溶性蛋白、丙二醛（MDA）含量及硝酸还原酶（NR）、超氧化物歧化酶（SOD）和过氧化氢酶（CAT）活性。结果表明,不同品种花生冠层温度存在明显差异。冠层温度低的品种比冠层温度高的品种叶绿素、可溶性糖、可溶性蛋白含量及NR、SOD和CAT活性明显偏高,而MDA含量明显偏低,且越往生育后期越明显,说明冠层温度低的品种比冠层温度高的品种生活力更旺盛,抵抗衰老能力更强。因此,冠层温度可作为花生抗衰老能力的一个重要指标,用于指导花生育种和栽培等生产实践。     

水稻群体冠层光分布及光合作用模型

作物冠层光分布及光合作用模型,是作物栽培学、作物育种学研究的共同基础,对优化设计和评价作物株型、模拟作物生长发育与对环境变化的响应研究都有十分重要的价值.本文根据水稻群体冠层结构的特点,在虚拟切层法的基础上,建立了水稻群体冠层光分布及光合速率模型,模型包括冠层形态子模型、冠层光分布子模型和冠层光合速率子模型等.利用本模型,对设定的15625种水稻株型的光合速率进行了模拟计算,获得水稻最佳株型模型.结果表明,水稻群体光合速率与叶片数、叶含氮量、叶长、叶宽和叶倾角等5因素密切相关;最佳株型的上述5因素在冠层上部取值大,向下逐渐变小.     

开放式空气CO2浓度增高对水稻冠层微气候的影响

利用位于江苏省无锡市安镇的我国唯一的农田开放式空气CO₂浓度增高(FACE)系统平台,于2001年8月26日至10月13日(水稻抽穗至成熟期)进行水稻作物冠层微气候连续观测,以研究FACE对水稻冠层微气候特征的影响.结果表明,FACE降低了水稻叶片的气孔导度,FACE与对照水稻叶片气孔导度的差异上层叶片大于下层叶片,生长前期大于生长后期.FACE使白天水稻冠层和叶片温度升高,这种差异生长前期大于生长后期;但FACE对夜间水稻冠层温度的影响不明显.在水稻旺盛生长的抽穗开花期,晴天正午前后FACE水稻冠层温度比对照高1.2℃;从开花至成熟期,FACE水稻冠层白天平均温度比对照高0.43℃.FACE对冠层空气温度也有影响,白天水稻冠层空气温度FACE高于对照,这种差异随太阳辐射增强而增大且冠层中部大于冠层顶部;冠层中部空气温度FACE与对照的差异(T_face-T_ambient)日最大值在0.47～1.2℃之间,而冠层顶部的T_face-T_ambient日最大值在0.37～0.8℃之间.夜间水稻冠层空气温度FACE与对照差别不大,变化在±0.3℃之内.而FACE对水稻冠层空气湿度无显著影响,表明FACE使水稻叶片气孔导度降低,从而削弱了植株的蒸腾降温作用,导致水稻冠层温度和冠层空气温度升高,改变了整个水稻冠层的温度环     

开放式空气CO2浓度增高对水稻冠层微气候的影响

利用位于江苏省无锡市安镇的我国唯一的农田开放式空气CO2 浓度增高 (FACE)系统平台 ,于2 0 0 1年 8月 2 6日至 10月 13日 (水稻抽穗至成熟期 )进行水稻作物冠层微气候连续观测 ,以研究FACE对水稻冠层微气候特征的影响 .结果表明 ,FACE降低了水稻叶片的气孔导度 ,FACE与对照水稻叶片气孔导度的差异上层叶片大于下层叶片 ,生长前期大于生长后期 .FACE使白天水稻冠层和叶片温度升高 ,这种差异生长前期大于生长后期 ;但FACE对夜间水稻冠层温度的影响不明显 .在水稻旺盛生长的抽穗开花期 ,晴天正午前后FACE水稻冠层温度比对照高 1.2℃ ;从开花至成熟期 ,FACE水稻冠层白天平均温度比对照高 0 .4 3℃ .FACE对冠层空气温度也有影响 ,白天水稻冠层空气温度FACE高于对照 ,这种差异随太阳辐射增强而增大且冠层中部大于冠层顶部 ;冠层中部空气温度FACE与对照的差异 (Tface-Tambient)日最大值在 0 .4 7～ 1.2℃之间 ,而冠层顶部的Tface-Tambient日最大值在 0 .37～ 0 .8℃之间 .夜间水稻冠层空气温度FACE与对照差别不大 ,变化在± 0 .3℃之内 .而FACE对水稻冠层空气湿度无显著影响 ,表明FACE使水稻叶片气孔导度降低 ,从而削弱了植株的蒸腾降温作用 ,导致水稻冠层温度和冠层空气温度升高 ,改变了整个水稻冠层的温度环     

冬小麦不同生育期最上冠层阻力的估算

作物最小冠层阻力是研究农田蒸发和作物缺水的一个重要参数.使用作物的冠层红外温度信息,将作物在充分灌溉情况下冠层温度与空气温度之差与空气的饱和水汽压差的经验关系同其理论解释相结合,通过实验数据,估算了在华北平原气候条件下的冬小麦(Triticum aestivum L.)的平均最小冠层阻力,为基于这种阻力的应用提供基础.研究表明冬小麦最小冠层阻力随发育期而不同,并且抽穗前后差异明显,给出了冬小麦不同生育阶段的平均最小冠层阻力.     

冬小麦不同生育期最小冠层阻力的估算

作物最小冠层阻力是研究农田蒸发和作物缺水的一个重要参数。使用作物的冠层红外温度信息,将作物在充分灌溉情况下冠层温度与空气温度之差与空气的饱和水汽压差的经验关系同其理论解释相结合,通过实验数据,估算了在华北平原气候条件下的冬小麦（Triticum aestivum L.）的平均最小冠层阻力,为基于这种阻力的应用共基础,研究表明冬小麦最小冠层阻力随发育期而不同,并且抽穗前后差异明显,给出了冬小麦不同生育阶段的平均最小冠层阻力。     

Genetic analysis for drought resistance of rice at reproductive stage in field with different types of soil

Drought resistance of rice is a complex trait and is mainly determined by mechanisms of drought avoidance and drought tolerance. The present study was conducted to characterize the genetic basis of drought resistance at reproductive stage in field by analyzing the QTLs for drought response index (DRI, normalized by potential yield and flowering time), relative yield, relative spikelet fertility, and four traits of plant water status and their relationships with root traits using a recombinant inbred population derived from a cross between an indica rice and upland rice. A total of 39 QTLs for these traits were detected with individual QTL explained 5.1–32.1% of phenotypic variation. Only two QTLs for plant water status were commonly detected in two environments, suggesting different mechanisms might exist in two types of soil conditions. DRI has no correlation with potential yield and flowering time under control, suggesting that it can be used as a good drought resistance index in field conditions. The co-location of QTLs for canopy temperature and delaying in flowering time suggested a usefulness of these two traits as indexes in drought resistance screening. Correlation and QTL congruence between root traits and putative drought tolerance traits revealed that drought avoidance (via thick and deep root traits) was the main genetic basis of drought resistance in sandy soil condition, while drought tolerance may play more role in the genetic basis of drought resistance in paddy soil condition. Therefore, both drought mechanisms and soil textures must be considered in the improvement of drought resistance at reproductive stage in rice.     

Genotypic difference in canopy diffusive conductance measured by a new remote-sensing method and its association with the difference in rice yield potential

There have been few practical ways of measuring physiological determinants of rice yield. Rapid evaluation of yield determination traits may expedite breeding of high-yielding rice. Here, we report a new remote-sensing technique for the evaluation of canopy ecophysiological status under field conditions developed based on simultaneous measurements of sunlit and suddenly shaded canopy temperatures. This technique has the advantage of instantaneous estimation of aerodynamic resistance (r(a)) and canopy diffusive resistance (r(c) without measuring wind velocity. Canopy diffusive conductance (1 / r(c)) estimated by the remote sensing method was closely related to leaf stomatal conductance (g(s)) measured with a portable gas exchange system. This result supported the validity of this new method for quantitative estimation of canopy physiological characteristics. Significant genotypic differences were obtained in canopy-air temperature difference (Tc-Ta), r(c) and 1 / r(c) during the 2-week period preceding full heading for two years, and 1 / r(c) was highly correlated with crop growth rate (CGR), which was closely related to the final yield. These results suggest that 1 / r(c) can be an effective criterion for the selection of high-yielding rice genotypes, and the remote sensing technique proposed here can be a powerful tool for the rapid evaluation of 1 / r(c) under field conditions.     

Leaf morphology,rather than plant water status,underlies genetic variation of rice leaf rolling under drought

Soil drying causes leaf rolling in rice, but the relationship between leaf rolling and drought tolerance has historically confounded selection of drought‐tolerant genotypes. In this study on tropical japonica and aus diversity panels (170–220 genotypes), the degree of leaf rolling under drought was more affected by leaf morphology than by stomatal conductance, leaf water status, or maintenance of shoot biomass and grain yield. A range of canopy temperature and leaf rolling (measured as change in normalized difference vegetation index [ΔNDVI]) combinations were observed among aus genotypes, indicating that some genotypes continued transpiration while rolled. Association mapping indicated colocation of genomic regions for leaf rolling score and ΔNDVI under drought with previously reported leaf rolling genes and gene networks related to leaf anatomy. The relatively subtle variation across these large diversity panels may explain the lack of agreement of this study with earlier reports that used small numbers of genotypes that were highly divergent in hydraulic traits driving leaf rolling differences. This study highlights the large range of physiological responses to drought among rice genotypes and emphasizes that drought response processes should be understood in detail before incorporating them into a varietal selection programme.     

Advances in Drought Resistance of Rice

Water deficit is a serious environmental stress and the major constraint to rice productivity. Losses in rice yield due to water shortage probably exceed losses from all other causes combined and the extent of the yield loss depends on both the severity and duration of the water stress. Drought affects rice at morphological, physiological, and molecular levels such as delayed flowering, reduced dry matter accumulation and partitioning, and decreased photosynthetic capacity as a result of stomatal closure, metabolic limitations, and oxidative damage to chloroplasts. Small-statured rice plants with reduced leaf area and short growth duration are better able to tolerate drought stress, although the mechanisms are not yet fully understood. Increased water uptake by developing larger and deeper root systems, and the accumulation of osmolytes and osmoprotectants are other important mechanisms for drought resistance. Drought resistance in rice has been improved by using plant growth regulators and osmoprotectants. In addition, several enzymes have been found that act as antioxidants. Silicon has also improved drought resistance in rice by silicification of the root endodermis and improving water uptake. Seed priming improves germination and crop stand establishment under drought. Rice plants expressing HVA1, LEA proteins, MAP kinase, DREB and endo-1, 3-glucanase are better able to withstand drought stress. Polyamines and several enzymes act as antioxidants and reduce adverse effects of drought stress in rice. Drought resistance can be managed by developing and selecting drought-tolerant genotypes. Rice breeding and screening may be based on growth duration, root system, photosynthesis traits, stomatal frequency, specific leaf weight, leaf water potential, and yield in target environments. This review discusses recent developments in integrated approaches, such as genetics, breeding and resource management to increase rice yield and reduce water demand for rice production.     

Is xylem cavitation resistance a relevant criterion for screening drought resistance among Prunus species?

Fruit trees are likely to suffer from the effects of severe drought in the future; however, sound criteria for evaluating the species' ability to survive these extreme conditions are largely missing. Here, we evaluated the feasibility of using xylem cavitation resistance as a tool for screening Prunus species for drought resistance. Ten different Prunus species were selected to cover a large range of water requirements, from hydrophilic to xerophilic types. Shoot cavitation resistance was evaluated with the new Cavitron technique. At this inter-specific level, cavitation resistance was related to species drought resistance, with xerophilic species being less vulnerable to cavitation. The Cavitron technique enabled species characterization that required a short time and small amounts of plant material. This technique could be used to evaluate the drought resistance of a limited number of fruit tree genotypes. Genotype screening on a larger scale, however, would likely require another approach. Out of a number of anatomical traits tested, a significant correlation was found between cavitation resistance and inter-vessel wall thickness across species. This anatomical trait is, therefore, suggested as a possible alternative to direct cavitation estimates and could be included as a screening criterion in breeding programs for drought resistance of Prunus genotypes.     

Linking drought-resistance mechanisms to drought avoidance in upland rice using a QTL approach: progress and new opportunities to integrate stomatal and mesophyll responses

The advent of saturated molecular maps promised rapid progress towards the improvement of crops for genetically complex traits like drought resistance via analysis of quantitative trait loci (QTL). Progress with the identification of QTLs for drought resistance-related traits in rice is summarized here with the emphasis on a mapping population of a cross between drought-resistant varieties Azucena and Bala. Data which have used root morphological traits and indicators of drought avoidance in field-grown plants are reviewed, highlighting problems and uncertainties with the QTL approach. The contribution of root-growth QTLs to drought avoidance appears small in the experiments so far conducted, and the limitations of screening methodologies and the involvement of shoot-related mechanisms of drought resistance are studied. When compared to Azucena, Bala has been observed to have highly sensitive stomata, does not roll its leaves readily, has a greater ability to adjust osmotically, slows growth more rapidly when droughted and has a lower water-use efficiency. It is also a semi-dwarf variety and hence has a different canopy structure. There is a need to clarify the contribution of the shoot to drought resistance from the level of the biochemistry of photosynthesis through stomatal behaviour and leaf anatomy to canopy architecture. Recent advances in studying the physical and biochemical processes related to water use and drought stress offer the opportunity to advance a more holistic understanding of drought resistance. These include the potential use of infrared thermal imaging to study energy balance, integrated and online stable isotope analysis to dissect processes involved in carbon dioxide fixation and water evaporation, and leaf fluorescence to monitor photosynthesis and photochemical quenching. Justification and a strategy for this integrated approach is described, which has relevance to the study of drought resistance in most crops.     

Epigenetic responses to drought stress in rice (Oryza sativa L.)

Cytosine methylation polymorphism plays a key role in gene regulation, mainly in expression of genes in crop plants. The differential expression of cytosine methylation over drought stress response was analyzed in rice using drought susceptible but agronomically superior lines IR 20 and CO 43, and drought tolerant genotypes PL and PMK 3 and their F₁ hybrids. The parents and hybrids were subjected to two moisture regimes viz., one under drought condition and another under control condition. The cytosine methylation polymorphism in genomic DNA was quantified under both the conditions at the reproductive stage of the plant using the Methylation Sensitive Amplified Polymorphism (MSAP) technique devised by Xiong et al. (261:439–446, 1999). The results depicted that under drought condition, hyper-methylation was predominant in the drought susceptible genotypes while drought tolerant genotypes presented hypo-methylation behavior. While imposing drought, spikelet sterility per cent was positively correlated to percentage of methylation whereas, panicle length, number of seed per panicle, panicle weight, 100 seed weight, and yield/plant were negatively correlated indicating the role of epigenetic regulation in yield attributing traits in response to drought. Thus, methylation can be considered as an important epigenetic regulatory mechanism in rice plants to adapt drought situation. From this study, we speculate that the hyper- methylation may be an indicator of drought susceptibility and the hypo-methylation for drought tolerance and this methylation polymorphism can be effectively used in drought screening program.     

Drought resistance of bermudagrass (Cynodon spp.) ecotypes collected from different climatic zones

The objectives of this paper were to (1) evaluate drought resistance of a large number of bermudagrass ecotypes collected from different climatic zones of regional Australia and compare their performance to commercial cultivars, (2) describe the mechanisms of drought resistance observed, and (3) investigate the relationship between geographic origins of the ecotypes and their drought resistance. Fifty-two genotypes of bermudagrass were evaluated in two field experiments using lysimeters 40 cm deep. The grasses were grown in well-watered conditions and then a drought treatment was imposed by withholding water and excluding rainfall using a portable rain-out shelter. Two criteria were used to select for drought resistance, i.e. survival period (SP), defined as the number of days after water was withheld to the stage when 100% leaf firing had occurred and Days₅₀ defined as the days required to reach 50% green cover. These experiments suggested that genotypes with superior drought resistance had lower stomatal conductance in the earlier phases of the dry-down period as suggested by less water use and higher canopy temperature depression. Lower water use during the early stage of dry-down resulted in more soil available water at the end of the drought period to extend green-leaf cover. There was no correlation between root dry matter and survival period/Days₅₀. We also found some ecotypes performed better in drought conditions than popular commercial cultivars. There was no relationship between drought resistance and geographic origins, suggesting that drought resistant ecotypes could be obtained from any climatic zone sampled in this study.