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Physiological characteristics of cassava tolerance to prolonged drought in the tropics: implications for breeding cultivars adapted to seasonally dry and semiarid environments
El-Sharkawy, Mabrouk A.;
Brazilian Journal of Plant Physiology , 2007, DOI: 10.1590/S1677-04202007000400003
Abstract: the paper summarizes research conducted at international center for tropical agriculture (ciat) on responses of cassava to extended water shortages in the field aided by modern gas-exchange and water-relation techniques as well as biochemical assays. the aim of the research was to coordinate basic and applied aspects of crop physiology into a breeding strategy with a multidisciplinary approach. several physiological characteristics/traits and mechanisms underpinning tolerance of cassava to drought were elucidated using a large number of genotypes from the ciat core germplasm collection grown in various locations representing ecozones where cassava is cultivated. most notable among these characteristics are the high photosynthetic capacity of cassava leaves in favorable environments and the maintenance of reasonable rates throughout prolonged water deficits, a crucial characteristic for high and sustainable productivity. cassava possess a tight stomatal control over leaf gas exchange that reduces water losses when plants are subjected to soil water deficits as well as to high atmospheric evaporative demands, thus protecting leaves from severe dehydration. during prolonged water deficits, cassava reduces its canopy by shedding older leaves and forming smaller new leaves leading to less light interception, another adaptive trait to drought. though root yield is reduced (but much less than the reduction in top growth) under water stress, the crop can recover when water becomes available by rapidly forming new canopy leaves with much higher photosynthetic rates compared to unstressed crops, thus compensating for yield losses with final yields approaching those in well-watered crops. cassava can extract slowly water from deep soils, a characteristic of paramount importance in seasonally dry and semiarid environments where deeply stored water needs to be tapped. screening large accessions under seasonally dry and semiarid environments showed that yield is significantly cor
Analysis of Natural Variation in Bermudagrass (Cynodon dactylon) Reveals Physiological Responses Underlying Drought Tolerance  [PDF]
Haitao Shi, Yanping Wang, Zhangmin Cheng, Tiantian Ye, Zhulong Chan
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0053422
Abstract: Bermudagrass (Cynodon dactylon) is a widely used warm-season turfgrass and one of the most drought tolerant species. Dissecting the natural variation in drought tolerance and physiological responses will bring us powerful basis and novel insight for plant breeding. In the present study, we evaluated the natural variation of drought tolerance among nine bermudagrass varieties by measuring physiological responses after drought stress treatment through withholding water. Three groups differing in drought tolerance were identified, including two tolerant, five moderately tolerant and two susceptible varieties. Under drought stress condition, drought sensitive variety (Yukon) showed relative higher water loss, more severe cell membrane damage (EL), and more accumulation of hydrogen peroxide (H2O2) and malondialdehyde (MDA), while drought tolerant variety (Tifgreen) exhibited significantly higher antioxidant enzymes activities. Further results indicated that drought induced cell injury in different varieties (Yukon, SR9554 and Tifgreen) exhibited liner correlation with leaf water content (LWC), H2O2 content, MDA content and antioxidant enzyme activities. Additionally, Tifgreen plants had significantly higher levels of osmolytes (proline level and soluble sugars) when compared with Yukon and SR9554 under drought stress condition. Taken together, our results indicated that natural variation of drought stress tolerance in bermudagrass varieties might be largely related to the induced changes of water status, osmolyte accumulation and antioxidant defense system.
Physiological and molecular insights into drought tolerance
Sagadevan G Mundree, Bienyameen Baker, Shaheen Mowla, Shaun Peters, Saberi Marais, Clare Vander Willigen, Kershini Govender, Alice Maredza, Samson Muyanga, Jill M Farrant, Jennifer A Thomson
African Journal of Biotechnology , 2002,
Abstract: Water is a major limiting factor in world agriculture. In general, most crop plants are highly sensitive to even a mild dehydration stress. There are however, a few genera of plants unique to Southern Africa, called "resurrection plants" which can tolerate extreme water loss or desiccation. We have used Xerophyta viscosa, a representative of the monocotyledonous resurrection plants to isolate genes that are associated with osmotic stress tolerance. Several genes that are differentially expressed, and that confer functional sufficiency to osmotically-stressed Escherichia coli are being studied at the molecular and biochemical levels. In this review, we use this as a basis to discuss the physiological and molecular insights into drought tolerance. (African Journal of Biotechnology: 2002 1(2): 28-38)
Phenotypic and physiological aspects related to drought tolerance in sorghum
J Mutisya, JK Sitieney, ST Gichuki
African Crop Science Journal , 2010,
Abstract: Drought is one of the major limitations to crop productivity worldwide. Identifying suitable screening tools and quantifiable traits would facilitate the crop improvement process for drought tolerance in sorghum. This study evaluated phenotypic characteristics and physiological parameters determine which cultivars are more drought tolerant. Signs of drought intolerance in sorghum include leaf rolling, death of lower leaves, stunted growth and low yields. Experiments were conducted using 8 and 25 sorghum accessions planted at two sites in Kenya, namely; Biotechnology Centre and Kiboko Research site, respectively, for evaluation and seeds maintenance. Based on phenotypic characteristic of the 25 cultivars evaluated, the best drought tolerant cultivars were, IS.13615, KAK1950, KBM078, E-36.1, B-35, KBM-003 and IE SV 92036. These observations were specifically deduced from their performance, root characteristics, tillering ability and leaf parameters as drought tolerance indicators. B 35 and E-36 ranked the highest relative water content in leaves, hence more drought tolerant.
Physiological and Biochemical Responses to Drought Stress and Subsequent Rehydration in the Symbiotic Association Peanut-Bradyrhizobium sp.  [PDF]
Ana Furlan,Analía Llanes,Virginia Luna,Stella Castro
ISRN Agronomy , 2012, DOI: 10.5402/2012/318083
Abstract: Drought stress is one of the most important environmental factors that regulate plant growth and development and limit its production. Peanut (Arachis hypogaea L.) is an agriculturally valuable plant with widespread distribution in the world serving as a subsistence food crop as well as a source of various food products. The aims of this work were to evaluate growth and nodulation as well as some physiological and biochemical stress indicators in response to drought stress and subsequent rehydration in the symbiotic association peanut-Bradyrhizobium sp. SEMIA6144. Drought stress affected peanut growth reducing shoot dry weight, nodule number, and dry weight as well as nitrogen content, but root dry weight increased reaching a major exploratory surface. Besides, this severe water stress induced hydrogen peroxide production associated with lipid and protein damage; however, the plant was able to increase soluble sugar and abscisic acid contents as avoidance strategies to cope with drought stress. These physiological and biochemical parameters were completely reversed upon rehydration, in a short period of time, in the symbiotic association peanut-Bradyrhizobium sp. Thus, the results provided in this work constitute the initial steps of physiological and biochemical responses to drought stress and rehydration in this nodulated legume. 1. Introduction Peanut (Arachis hypogaea L.) is grown as an important crop in a wide range of environments between latitudes of 40°N and 40°S. Two-thirds of the global production occurs in rain-fed areas of the semiarid tropics which are characterized by unpredictable periods of water deficit [1]. Along with the United States and China, Argentina is one of the major exporters of peanut for human consumption [2]. However, the crop production area suffers intermittently water deficit periods almost every year [3]. Peanut flowering and pod filling are quiet sensitive to drought stress [4], thus water deficit periods affecting these phenological stages may have a large negative impact on yield. Drought stress causes cellular dehydration as a consequence of water release from cytosol and vacuoles to the apoplast. The plant responses to water stress include changes in stomatal conductance, growth, osmolyte accumulation, and expression of specific genes. In these processes, the abscisic acid (ABA) is defined as the major stress hormone due to its rapid accumulation in severe conditions and participation in physiological and biochemical processes that allow plants to survive to this challenge [5]. Sharp and LeNoble [6] suggested that
Physiological traits for drought phenotyping in cotton
Brito, Giovani Greigh de;Sofiatti, Valdinei;Lima, Marleide Magalh?es de Andrade;Carvalho, Luiz Paulo de;Silva Filho, Jo?o Luiz da;
Acta Scientiarum. Agronomy , 2011, DOI: 10.4025/actasciagron.v33i1.9839
Abstract: the objective of this study was to identify physiological traits that could distinguish between cotton genotypes that were tolerant or sensitive to water deficits. the experiment was conducted in a completely randomized design through a factorial combination to analyze four genotypes (brs 187 8h and acala sj-4 - water deficit tolerant; cnpa 7h and su-0450/8909 - water deficit sensitive) and two water regimes (watered/always irrigated and stressed/with a water deficit imposed at flowering). irrigation was suspended for the plants in the water deficit treatment groups when their first flowers appeared. leaf water potential (ψpd) was monitored until the plants reached -3.0 mpa predawn, at which point leaf samples were collected for analysis. the plants were re-irrigated and monitored for a recovery to 50% of leaf water potential. the maximum photochemical efficiency (fv/fm), chlorophyll content (spad index), relative water content (rwc), disruption of the cell membrane via membrane leakage, carbon isotope composition (δ13c), seed cotton yield and fiber quality were evaluated. the trends in membrane leakage and carbon isotope composition were different between the tolerant and sensitive genotypes under a water deficit, which makes these physiological traits suitable for screening for tolerance to water deficits in cotton.
Genetic, Physiological, and Gene Expression Analyses Reveal That Multiple QTL Enhance Yield of Rice Mega-Variety IR64 under Drought  [PDF]
Mallikarjuna Swamy B. P., Helal Uddin Ahmed, Amelia Henry, Ramil Mauleon, Shalabh Dixit, Prashant Vikram, Ram Tilatto, Satish B. Verulkar, Puvvada Perraju, Nimai P. Mandal, Mukund Variar, Robin S., Ranganath Chandrababu, Onkar N. Singh, Jawaharlal L. Dwivedi, Sankar Prasad Das, Krishna K. Mishra, Ram B. Yadaw, Tamal Lata Aditya, Biswajit Karmakar, Kouji Satoh, Ali Moumeni, Shoshi Kikuchi, Hei Leung, Arvind Kumar
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0062795
Abstract: Background Rice (Oryza sativa L.) is a highly drought sensitive crop, and most semi dwarf rice varieties suffer severe yield losses from reproductive stage drought stress. The genetic complexity of drought tolerance has deterred the identification of agronomically relevant quantitative trait loci (QTL) that can be deployed to improve rice yield under drought in rice. Convergent evidence from physiological characterization, genetic mapping, and multi-location field evaluation was used to address this challenge. Methodology/Principal Findings Two pairs of backcross inbred lines (BILs) from a cross between drought-tolerant donor Aday Sel and high-yielding but drought-susceptible rice variety IR64 were produced. From six BC4F3 mapping populations produced by crossing the +QTL BILs with the ?QTL BILs and IR64, four major-effect QTL - one each on chromosomes 2, 4, 9, and 10 - were identified. Meta-analysis of transcriptome data from the +QTL/?QTL BILs identified differentially expressed genes (DEGs) significantly associated with QTL on chromosomes 2, 4, 9, and 10. Physiological characterization of BILs showed increased water uptake ability under drought. The enrichment of DEGs associated with root traits points to differential regulation of root development and function as contributing to drought tolerance in these BILs. BC4F3-derived lines with the QTL conferred yield advantages of 528 to 1875 kg ha?1 over IR64 under reproductive-stage drought stress in the targeted ecosystems of South Asia. Conclusions/Significance Given the importance of rice in daily food consumption and the popularity of IR64, the BC4F3 lines with multiple QTL could provide higher livelihood security to farmers in drought-prone environments. Candidate genes were shortlisted for further characterization to confirm their role in drought tolerance. Differential yield advantages of different combinations of the four QTL reported here indicate that future research should include optimizing QTL combinations in different genetic backgrounds to maximize yield advantage under drought.
Physiological Integration Ameliorates Negative Effects of Drought Stress in the Clonal Herb Fragaria orientalis  [PDF]
Yunchun Zhang, Qiaoying Zhang, Marek Sammul
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044221
Abstract: Clonal growth allows plants to spread horizontally and to establish ramets in sites of contrasting resource status. If ramets remain physiologically integrated, clones in heterogeneous environments can act as cooperative systems – effects of stress on one ramet can be ameliorated by another connected ramet inhabiting benign conditions. But little is known about the effects of patch contrast on physiological integration of clonal plants and no study has addressed its effects on physiological traits like osmolytes, reactive oxygen intermediates and antioxidant enzymes. We examined the effect of physiological integration on survival, growth and stress indicators such as osmolytes, reactive oxygen intermediates (ROIs) and antioxidant enzymes in a clonal plant, Fragaria orientalis, growing in homogenous and heterogeneous environments differing in patch contrast of water availability (1 homogeneous (no contrast) group; 2 low contrast group; 3 high contrast group). Drought stress markedly reduced the survival and growth of the severed ramets of F. orientalis, especially in high contrast treatments. Support from a ramet growing in benign patch considerably reduced drought stress and enhanced growth of ramets in dry patches. The larger the contrast between water availability, the larger the amount of support the depending ramet received from the supporting one. This support strongly affected the growth of the supporting ramet, but not to an extent to cause increase in stress indicators. We also found indication of costs related to maintenance of physiological connection between ramets. Thus, the net benefit of physiological integration depends on the environment and integration between ramets of F. orientalis could be advantageous only in heterogeneous conditions with a high contrast.
Evaluation of morpho-physiological characters in sorghum (Sorghum bicolor (l.) Moench) genotypes under post-flowering drought stress
N. Kumari Vinodhana and K. Ganesamurthy
Electronic Journal of Plant Breeding , 2010,
Abstract: Post-flowering drought adaptation in sorghum is associated with the stay-green phenotype. Plants with stay green resist droughtinducedpremature plant senescence. Sorghum varietal improvement for drought conditions could be achieved moreefficiently if the trait associated with drought resistance could be identified and utilized as selection criteria. Hence, fieldstudies were carried out in a randomized block design with two replications during the post-rainy season to evaluate responsesamong 100 sorghum genotypes under post-flowering drought stress which include B35 and CO26 as a drought resistant andsusceptible check respectively. A total of 15 morpho-physiological characters putatively related with crop performanceunder drought were studied. Significant variations were found in all the traits among the sorghum genotypes studied.Based on the per se performance the genotypes MS73, CO21, CO22, Tenkasi1, AS2059, AS5078, AS2752, AS5057,AS4289, MS7819, IS5379, AS8038, AS6616, K3, MS7837, Murungapatti local, Uppam chloam, VS1564, VS1560,CO24 and CO1 exhibited high mean values for relative water content, SPAD chlorophyll reading, root length, rootvolume, root dry weight, 1000 grain weight, grain yield, and lower score for stay-green when compared to othergenotypes under stress. These genotypes also recorded low drought susceptibility index, high relative yield, stresstolerance index and yield stability ratio and they can be used as the parents for future breeding programmes.
The Physiological Response of Soybean Genotypes to VAM Inoculation on Selected Drought Stress Levels  [cached]
HAPSOH,SUDIRMAN YAHYA,TEUKU MUHAMMAD HANAFIAH OELIM,BAMBANG SAPTA PURWOKO
HAYATI Journal of Biosciences , 2006,
Abstract: Present research was aimed to study physiological changes of soybean which were inoculated with vesicular arbuscular mycorrhizal fungi (VAM). Glomus etunicatum was exposed to moderate and severe drought condition. Symbiotic association with VAM improved adaptability as it was shown by the increasing leaf proline content. The MLG 3474 and Sindoro are the more tolerant genotypes while the responses of plant to VAM on improving the adaptability to drought were larger on Lokon.
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