Image-based phenotyping for non-destructive screening of different salinity tolerance traits in rice
© Hairmansis et al.; licensee springer. 2014
Received: 3 March 2014
Accepted: 16 July 2014
Published: 14 August 2014
Soil salinity is an abiotic stress wide spread in rice producing areas, limiting both plant growth and yield. The development of salt-tolerant rice requires efficient and high-throughput screening techniques to identify promising lines for salt affected areas. Advances made in image-based phenotyping techniques provide an opportunity to use non-destructive imaging to screen for salinity tolerance traits in a wide range of germplasm in a reliable, quantitative and efficient way. However, the application of image-based phenotyping in the development of salt-tolerant rice remains limited.
A non-destructive image-based phenotyping protocol to assess salinity tolerance traits of two rice cultivars (IR64 and Fatmawati) has been established in this study. The response of rice to different levels of salt stress was quantified over time based on total shoot area and senescent shoot area, calculated from visible red-green-blue (RGB) and fluorescence images. The response of rice to salt stress (50, 75 and 100 mM NaCl) could be clearly distinguished from the control as indicated by the reduced increase of shoot area. The salt concentrations used had only a small effect on the growth of rice during the initial phase of stress, the shoot Na+ accumulation independent phase termed the ‘osmotic stress’ phase. However, after 20 d of treatment, the shoot area of salt stressed plants was reduced compared with non-stressed plants. This was accompanied by a significant increase in the concentration of Na+ in the shoot. Variation in the senescent area of the cultivars IR64 and Fatmawati in response to a high concentration of Na+ in the shoot indicates variation in tissue tolerance mechanisms between the cultivars.
Image analysis has the potential to be used for high-throughput screening procedures in the development of salt-tolerant rice. The ability of image analysis to discriminate between the different aspects of salt stress (shoot ion-independent stress and shoot ion dependent stress) makes it a useful tool for genetic and physiological studies to elucidate processes that contribute to salinity tolerance in rice. The technique has the potential for identifying the genetic basis of these mechanisms and assisting in pyramiding different tolerance mechanisms into breeding lines.
KeywordsRice (Oryza sativa L.) Salinity tolerance Phenotyping Image analysis Growth Senescence
Salinity is a major abiotic stress that threatens the sustainability of global rice production. Rice yield can be reduced significantly by the addition of as little as 50 mM NaCl (Yeo and Flowers ), making it one of the crop species most susceptible to salt stress (Grattan et al. ; Munns and Tester ). It has been estimated that about 48 million ha of potentially useful agricultural land is unusable for growing rice in Southern Asia and South East Asia due to saline soils (Ponnamperuma and Bandyopadhya ; Vinod et al. ). The cultivation of salt-tolerant rice is important to maintain the sustainability of rice production in such areas. However, progress with breeding programmes to develop salt-tolerant rice has been slow (Gregorio et al. ; Flowers ; Yamaguchi and Blumwald ). One of the limiting factors in the breeding of salt tolerant rice is the availability of efficient and reliable screening techniques to select tolerant plants (Gregorio et al. ).
A number of screening methods for different morpho-physiological traits have been used to measure salinity tolerance in rice, including shoot weight (Yeo et al. ; Aslam et al. ), shoot Na+ concentration, the ratio of shoot Na+/K+ (Yeo et al. ; Gregorio and Senadhira ; Asch et al. ), leaf injury and survival rate (Yeo et al. ; Gregorio et al. ), leaf area (Akita and Cabuslay ; Zeng et al. ) and bypass flow in the root (Faiyue et al. ). Of these traits, shoot weight was shown to be closely related to overall plant performance (Yeo et al. ) and to the performance of the plant in the field (Aslam et al. ). However, most protocols that measure plant biomass are destructive, thus making it difficult to measure dynamic responses in plant growth in response to salt application and to collect seed from the individuals being measured. Recent developments in image-based phenotyping have enabled the non-destructive assessment of plant responses to salinity over time and allows determination of shoot biomass measurements without having to harvest the whole plant (Rajendran et al. ; Furbank and Tester ; Berger et al. [2012a]; Jansen et al. ).
When plants are exposed to salt, their growth immediately slows due to the shoot ion independent stress, the so-called osmotic component of salt stress, and plants produce fewer tillers (Munns and Tester ; Rajendran et al. ; Horie et al. ). Over time, Na+ and Cl- will accumulate to toxic concentrations in the shoot, resulting in premature leaf senescence and death – the ionic component of salt stress (Tester and Davenport ; Munns and Tester ; Munns ; Horie et al. ). Importantly, image-based phenotyping can differentiate between the effects of the osmotic and ionic components of salt stress in growing plants. This can be done by measuring growth responses immediately after salt application, before the accumulation of toxic concentrations of ions in the shoot. This allows for at least some dissection of salinity tolerance mechanisms (Rajendran et al. ; Sirault et al. ).
Several studies have used image based phenotyping to measure salinity tolerance in crops, in particular wheat and barley (Rajendran et al. ; Sirault et al. ; Harris et al. ), where digital colour images were used to quantify plant biomass, leaf area and health (Rajendran et al. ; Harris et al. ; Golzarian et al. ). The measurement of senescent leaf area in combination with the measurement of shoot Na+ concentration enabled the quantification of shoot tissue tolerance in salt stressed einkorn wheat (Triticum monococcum) (Rajendran et al. ). Infrared thermography has also been used to measure leaf temperature, as a surrogate for stomatal conductance, to screen the osmotic tolerance of barley and durum wheat seedlings (Sirault et al. ) and rice (Siddiqui et al. ). In the current study, high-throughput image acquisition and analysis was used to study the salinity tolerance traits of two rice cultivars (IR64 and Fatmawati) under different levels of salt stress. The use of this technology for screening individual salt tolerance traits in rice, as well as whole plant salt tolerance, is demonstrated here. These methods can now be used in genetic studies to inform breeding programs of approaches to improve the salinity tolerance of rice.
Results and discussion
Imaging as a surrogate for rice shoot biomass measurements
Non-destructive imaging of plants allows multiple measurements of plant growth and plant health on the same individual over time, without having to harvest plant material for analysis (Rajendran et al. ; Furbank and Tester ; Berger et al. [2012b]; Fiorani and Schurr ). Non-destructive imaging is important when measuring the dynamic response of individual plants to the onset of an environmental stress such as salinity and water deficit. It is also important to use non-destructive techniques when plants are unique, such as early generation transgenics, which need to be phenotyped but also maintained for seed collection. Key to the success of this technique is that the measurements obtained are quantitative, quick to obtain and a good surrogate for important traits, such as determination of plant biomass.
A number of studies have used projected shoot area to estimate the shoot biomass of different crops, such as wheat and barley under conditions of salinity stress (Rajendran et al. ; Harris et al. ; Golzarian et al. ).
IR64 and Fatmawati differ in their response to salt stress
IR64 and Fatmawati were grown in soil under moderate (0, 50, 75 and 100 mM NaCl) and high (0, 100, 150 and 200 mM NaCl) salt stress. Digital images were taken through time, at 0, 10, and 20 d after salt application.
Measurements of plant growth are important to permit an understanding of the physiological mechanisms underlying the plant response to salt stress over time (Munns ), particularly to separate the effects of the osmotic and ionic stress components, which dominate plant growth at different times (Munns and Tester ).
After 20 d of salt treatment, however, the projected shoot area of salt stressed rice was clearly reduced compared with that of the non-stressed plants, even at 50 mM NaCl. The reduction in shoot area was more pronounced under the higher concentrations of salt with the shoot area of Fatmawati and IR64 reduced by 37% and 30%, respectively, after 20 d of growth in 100 mM NaCl when compared with non-stressed plants (Figure 3). There was a slight difference in response of rice plants to 100 mM NaCl treatment between two subsequent experiments, which might be attributed to soil batches of different age being used (Figures 3 and 4). In the second experiment (high salt stress; Figure 4), after 20 d of growth under 100 mM NaCl the shoot area of Fatmawati and IR64 was reduced by 49% and 54% compared to control plants, respectively (Figure 4). However, the 0 mM NaCl plants in the second experiment (Figure 4) grew bigger than in the first experiment (low salt stress; Figure 3) for both Fatmawati and IR64, while the plants grown in 100 mM NaCl reached a similar size in both experiments. The increase in biomass reduction is therefore primarily a result of the control plants growing bigger in the second experiment. The late reduction in growth rate in response to salinity in both experiments suggests that the plants experience ionic stress, which can be determined by measurements of leaf senescence and leaf ion concentration.
Fatmawati exhibits greater shoot senescence under salinity stress than IR64
The cultivar Fatmawati appears to be significantly more salt sensitive than IR64, showing considerable shoot senescence (23%) when exposed to 200 mM NaCl for 20 d (Figure 5A). IR64, in contrast, exhibited little shoot senescence (4%), even under very high NaCl concentrations (Figure 5B). While there was an increase in shoot senescent area that corresponded to increasing salt concentrations, both cultivars had little senescence at moderate salinity levels (Figure 5A and 5B).
IR64 plants accumulate sodium in the shoot while exhibiting low levels of shoot senescence
Shoot Na + and K + accumulation and K + /Na + ratio of rice cv. Fatmawati and IR64 at 20 d after application of a moderate salt stress (50, 75 and 100 mM NaCl)
Salt stress (mM NaCl)
1.6 ± 0.1 a
297.4 ± 6.6 a
196.8 ± 16.6
2.4 ± 0.3 b
343.0 ± 6.6 b
151.0 ± 14.1
3.3 ± 0.2 c
362.0 ± 5.6 bc
111.0 ± 5.4
3.4 ± 0.2 c
365.6 ± 7.2 c
111.8 ± 6.6
2.5 ± 0.1 b
345.1 ± 7.4 b
137.4 ± 5.1
4.8 ± 0.3 d
357.3 ± 10.0 bc
76.7 ± 4.4
5.7 ± 0.4 e
365.4 ± 3.5 c
66.4 ± 4.7
6.1 ± 0.4 e
385.5 ± 7.2 d
65.0 ± 4.3
Salt stress (S)
C x S
Shoot Na + and K + accumulation and K + /Na + ratio of rice cv. Fatmawati and IR64 at 20 d after application of a high salt stress (100, 150 and 200 mM NaCl)
Salt stress (mM NaCl)
1.3 ± 0.1
265.3 ± 5.5
208.3 ± 12.3 b
3.8 ± 0.1
326.1 ± 8.2
85.8 ± 2.1 c
8.2 ± 1.0
346.3 ± 9.8
46.3 ± 6.1 d
0.6 ± 0.1
284.4 ± 4.8
465.2 ± 48.0 a
5.9 ± 0.4
320.0 ± 7.0
55.4 ± 4.8 cd
11.6 ± 1.1
325.7 ± 6.0
29.1 ± 2.5 d
12.5 ± 1.3
366.4 ± 11.0
31.2 ± 2.9 d
Salt stress (S)
C x S
A role for non-destructive phenotyping in screening for rice salinity tolerance
Automation of the phenotyping process in combination with automated plant handling and watering allows large numbers of plants to be screened efficiently with limited handling. Entire populations of plants can be grown in soil media, emulating field conditions (at least for the earlier stages of growth), thus facilitating the transfer of knowledge from controlled environment to growth conditions in the field. An increasing number of phenotyping facilities are now accessible globally, such as the Australian Plant Phenomics Facility (http://www.plantphenomics.org.au), used in this study, or the centres of the European Plant Phenomics Network (http://www.plant-phenotyping-network.eu). The process described here has the potential to be scaled to phenotype large numbers of rice breeding lines and mapping populations allowing the evaluation of the effect of different salt tolerant mechanisms on plant growth and yield. Screening of hundreds of mapping lines and/or rice accessions for bi-parental or association mapping studies can now be done relatively quickly for traits that require time course measurements of growth. The use of such populations has the potential to identify the underlying genetic mechanisms of salinity tolerance in a forward genetics screen.
The main limitation for the widespread adoption of this approach is the cost, but this is decreasing very rapidly as imaging technologies decrease in price and, as knowledge of phenotyping improves, short-cuts and pragmatic compromises can be more confidently undertaken. This will be accompanied by an increasing ability to phenotype cheaply in the field – although this inevitably comes with a reduced ability to control and manipulate environmental conditions. As costs decrease, so the power of this approach will also increase, to enable more detailed physiological characterization of rice genotypes (e.g. stomatal behaviour) in response to salinity (e.g. by combination of infrared (IR), RGB and fluorescence techniques).
An efficient and high-throughput screening protocol to select salt-tolerant rice is required to accelerate the development of salt-tolerant rice cultivars. A non-destructive image-based phenotyping method to analyse the responses of rice to different levels of salinity stress has been developed and revealed differences in the effects of salt stress in two cultivars of rice, IR64 and Fatmawati. Use of non-destructive imaging technologies, such as those described here, in combination with measurements of tissue ion concentration, allow the differentiation between the ionic and osmotic components of salt stress in growing rice. This will enable the identification of new traits and sources of salinity tolerance genes that can be used to pyramid different salinity tolerance mechanisms into elite rice breeding lines.
Plant material and growth conditions
Two Indica rice cultivars, IR64 and Fatmawati, were used in this study. IR64 was developed at the International Rice Research Institute (IRRI) in the Philippines and is known as a “mega variety” because of its wide adoption and cultivation in large areas (Mackill ). Fatmawati is a new plant type of rice from Indonesia (Abdullah et al. ) which has new morphological traits, such as fewer tillers, sturdy culms and higher number of seed per panicle compared to traditional rice cultivars (Khush ; Abdullah et al. ). IR64 and Fatmawati seeds were obtained from the Indonesian Centre for Rice Research, Sukamandi, Indonesia.
Rice seeds were sorted for uniform size and then dehusked and surface sterilised with 70% (v/v) ethanol for one min followed by a 30 min bleach treatment (30% (v/v) commercial Domestos bleach solution, sodium hypochlorite 49.9 g/L). The seeds were then washed with RO water five times to remove all traces of bleach. Surface sterilised seeds were germinated by placing them on sterile wet filter paper in dishes. The dishes were sealed to prevent evaporation and contamination and placed in a growth chamber with 12 h light and a constant temperature of 28°C. After seven days, uniformly germinated seedlings were transferred into white plastic pots (150 mm diameter × 200 mm height) containing 3 kg dry University of California (U.C.) soil mix (Matkin and Chandler ), composed of sand and peat moss (volume ratio 1.6:1) and fertiliser (1.5 kg Mini Osmocote® per 600 litre UC soil base). The soil surface was covered by blue plastic pellets to reduce development of algae, reduce evaporation and to provide a favourable background colour for image analysis. Three rice seedlings were transplanted into each pot but were thinned to a single plant per pot after one week.
The plastic pots had drainage holes in their base, allowing watering from underneath (Figure 1A). The pots were placed in a deep white plastic saucer (160 mm × 160 mm × 90 mm) to which a volume of 600 mL of water was applied to each pot via the saucer. Water levels were monitored daily by weighing the pots using a digital scale, and pots were adjusted to the target weight by adding water to maintain a constant salt concentration in each pot.
The rice plants were placed in a growth chamber (Conviron, Model PGC20) at The Plant Accelerator® (Australian Plant Phenomics Facility, University of Adelaide, Adelaide, Australia) with a sinusoidal 12 hr/12 hr day/night cycle. Growth chambers were fitted with Osram FQ54W/840 HO fluorescence lights (Osram Australia, Pennant Hills, Australia) providing an average photon irradiance of 200 - 300 μmol/m2/s over a 24 h period. Humidity was maintained at 70% with day/night temperatures of 28°C/26°C, respectively.
Two separate salt experiments (moderate salt stress and high salt stress) were carried out sequentially in 2012. The moderate salt experiment was conducted from 15 February to 26 March 2012 and the high salt experiment was from 23 March to 3 May 2012. In the moderate salt stress experiment, the rice cultivars were subjected to four levels of salt, 0 mM, 50 mM, 75 mM and 100 mM NaCl. In the high salt stress experiment the salt levels were 0 mM, 100 mM, 150 mM and 200 mM NaCl. Seven biological replicates were used for each treatment. Salt treatments were imposed 14 d after seedling transplantation in 50 mM increments every 12 h until the desired level was reached to minimise the osmotic shock to the plants. For each increment, 60 mL of a 0.5 M NaCl solution was applied to the saucer in which the pots sat. Additional CaCl2 was added to prevent Na+ induced Ca2+deficiency with the ratio of Na+:Ca2+ molar concentration of 30:1 (3.3 mM CaCl2 for 100 mM NaCl (Genc et al. )). The concentrations of NaCl in the soil were maintained at constant levels by watering each pot to weight, as described in the previous section.
Image capture and image analysis
Shoot images were taken using the LemnaTec 3D Scanalyzer system (LemnaTec GmbH, Aachen, Germany) at The Plant Accelerator® at 14 d after seedling transplantation (before the start of salt application), 10 d and 20 d after the start of salt application. The pots were manually loaded onto the conveyer belt and automatically moved to the image capture stations. Three 5 mega pixel colour images (RGB images) were taken per plant, two from the side at 90° from each other and one from the top. Three fluorescent images were taken in a separate imaging chamber with constant blue light excitation (400 nm to 500 nm) and a 1.4 mega pixel colour camera with a 500 nm high pass filter capturing steady-state fluorescence emission from 500 nm to 750 nm of light-adapted plants. The images captured allow detection of senescence, necrosis and chlorosis but are not suitable for measuring photosynthetic activity since the lighting system is not pulsed. After image capture, all images were analysed using the LemnaTec Grid software package (LemnaTec GmbH, Aachen, Germany).
In brief, the plant was separated from the imaging background using a nearest-neighbour colour classification. Noise was removed from the images using erosion and dilation steps as well as a size filter. Subsequently, all objects identified as being part of the plant were composed to one single object. The visible RGB images were used to measure size and height of the object (Berger et al. [2012a]). The summed area of all three images per plant was used as an approximation for shoot biomass (Rajendran et al. ; Golzarian et al. ; Berger et al. [2012a]). The top view fluorescent images were used to quantify the level of shoot senescence. After object separation from the background and noise reduction, nearest-neighbour colour classification was used to separate the shoot into healthy leaf area (red chlorophyll fluorescence) and senescent leaf area (yellow fluorescence; Figure 1D). The level of senescence was calculated as the percentage of senescence pixels relative to total shoot area.
Measurement of shoot biomass and shoot ion concentration
Shoots were harvested 20 d after salt application and the fresh weight was measured using a digital scale. Leaf tissue for shoot Na+ and K+ measurements were taken from the youngest fully expanded leaf at 20 d after salt application. The leaves were weighed immediately after harvest to determine their fresh weight and then dried in an oven at 70°C for 24 h. The dry weight was measured to determine the tissue water content. Dried leaf samples were placed in 50 mL Falcon tubes and digested in 20 mL1% (v/v) nitric acid (HNO3) for 5 h in a heat block at 70°C. The samples were shaken every hour to ensure complete digestion. The concentrations of Na+ and K+ were determined using a flame photometer (model 420; Sherwood Scientific Ltd., Cambridge, UK).
AH is financially supported by an Australian Development Scholarship, AusAID. SR and MT would like to thank the Australian Research Council and the Grains Research and Development Corporation for funding. The authors would like to thank the staff of The Plant Accelerator® for the support in undertaking this study and analysing the image results. The Plant Accelerator®, Australian Plant Phenomics Facility, was funded under the National Collaborative Infrastructure Strategy. We would also like to thank Dr Julian Taylor for statistical assistance. We are grateful to Dr Christina Morris for editing the manuscript.
- Abdullah B, Tjokrowidjojo S, Sularjo : Development and prospect of new plant type of rice in Indonesia (in Indonesian with English abstract). Jurnal Litbang Pertanian 2008, 27(1):1–9.Google Scholar
- Akita S, Cabuslay G: Physiological basis of differential response to salinity in rice cultivars. Plant Soil 1990, 123(2):277–294.View ArticleGoogle Scholar
- Asch F, Dingkuhn M, Dörffling K, Miezan K: Leaf K/Na ratio predicts salinity induced yield loss in irrigated rice. Euphytica 2000, 113(2):109–118.View ArticleGoogle Scholar
- Aslam M, Qureshi RH, Ahmed N: A rapid screening technique for salt tolerance in rice ( Oryza sativa L.). Plant Soil 1993, 150(1):99–107.View ArticleGoogle Scholar
- Berger B, de Regt B, Tester M: High-throughput phenotyping of plant shoots. In High-Throughput Phenotyping in Plants. Edited by: Normanly J. Methods in Molecular Biology. Humana Press, New York, USA; 2012:9–20.View ArticleGoogle Scholar
- Berger B, de Regt B, Tester M: Trait dissection of salinity tolerance with plant phenomics. In Plant Salt Tolerance. Edited by: Shabala S, Cuin TA. Methods in Molecular Biology. Humana Press, New York, USA; 2012:399–413.View ArticleGoogle Scholar
- Blumwald E, Aharon GS, Apse MP: Sodium transport in plant cells. Biochim Biophys Acta Biomembranes 2000, 1465(1–2):140–151.View ArticleGoogle Scholar
- Castillo EG, Tuong TP, Ismail AM, Inubushi K: Response to salinity in rice: Comparative effects of osmotic and ionic stresses. Plant Prod Sci 2007, 10(2):159–170.View ArticleGoogle Scholar
- Faiyue B, Al-Azzawi MJ, Flowers TJ: A new screening technique for salinity resistance in rice ( Oryza sativa L.) seedlings using bypass flow. Plant, Cell Environ 2012, 35(6):1099–1108.View ArticleGoogle Scholar
- Fiorani F, Schurr U: Future scenarios for plant phenotyping. Annu Rev Plant Biol 2013, 64: 17.11–17.25.View ArticleGoogle Scholar
- Flowers TJ: Improving crop salt tolerance. J Exp Bot 2004, 55(396):307–319.View ArticlePubMedGoogle Scholar
- Furbank RT, Tester M: Phenomics – technologies to relieve the phenotyping bottleneck. Trends Plant Sci 2011, 16(12):635–644.View ArticlePubMedGoogle Scholar
- Garbarino J, DuPont FM: Rapid induction of Na+/H+ exchange activity in barley root tonoplast. Plant Physiol 1989, 89(1):1–4.PubMed CentralView ArticlePubMedGoogle Scholar
- Genc Y, Tester M, McDonald GK: Calcium requirement of wheat in saline and non-saline conditions. Plant Soil 2010, 327(1–2):331–345.View ArticleGoogle Scholar
- Golzarian M, Frick R, Rajendran K, Berger B, Roy S, Tester M, Lun D (2011) Accurate inference of shoot biomass from high-throughput images of cereal plants. Plant Methods 7(1):2 Golzarian M, Frick R, Rajendran K, Berger B, Roy S, Tester M, Lun D (2011) Accurate inference of shoot biomass from high-throughput images of cereal plants. Plant Methods 7(1):2
- Grattan SR, Zeng L, Shannon MC, Roberts SR: Rice is more sensitive to salinity than previously thought. Calif Agric 2002, 56(6):189–195.View ArticleGoogle Scholar
- Gregorio GB, Senadhira D: Genetic-analysis of salinity tolerance in rice ( Oryza-sativa L). Theor Appl Genet 1993, 86(2–3):333–338.PubMedGoogle Scholar
- Gregorio GB, Senadhira D, Mendoza RD: Screening rice for salinity tolerance. International Rice Research Institute, Manila; 1997.Google Scholar
- Gregorio GB, Senadhira D, Mendoza RD, Manigbas NL, Roxas JP, Guerta CQ: Progress in breeding for salinity tolerance and associated abiotic stresses in rice. Field Crops Res 2002, 76(2–3):91–101.View ArticleGoogle Scholar
- Harris B, Sadras V, Tester M: A water-centred framework to assess the effects of salinity on the growth and yield of wheat and barley. Plant Soil 2010, 336(1–2):377–389.View ArticleGoogle Scholar
- Horie T, Karahara I, Katsuhara M (2012) Salinity tolerance mechanisms in glycophytes: An overview with the central focus on rice plants. Rice 5(1):11 Horie T, Karahara I, Katsuhara M (2012) Salinity tolerance mechanisms in glycophytes: An overview with the central focus on rice plants. Rice 5(1):11
- James RA, Munns R, Von Caemmerer S, Trejo C, Miller C, Condon T: Photosynthetic capacity is related to the cellular and subcellular partitioning of Na+, K+ and Cl- in salt-affected barley and durum wheat. Plant, Cell Environ 2006, 29(12):2185–2197.View ArticleGoogle Scholar
- James RA, Sv C, Condon AG, Zawrt AB, Munns R: Genetic variation in tolerance to the osmotic stress component of salinity stress in durum wheat. Funct Plant Biol 2008, 35: 111–123.View ArticleGoogle Scholar
- Jansen M, Pinto F, Nagel KA, Dusschoten D, Fiorani F, Rascher U, Schneider HU, Walter A, Schurr U: Non-invasive phenotyping methodologies enable the accurate characterization of growth and performance of shoots and roots. In Genomics of Plant Genetic Resources. Edited by: Tuberosa R, Graner A, Frison E. Springer Netherlands, Dordecht, Netherlands; 2014:173–206.View ArticleGoogle Scholar
- Khush GS: Breaking the yield frontier of rice. GeoJournal 1995, 35(3):329–332.View ArticleGoogle Scholar
- Mackill DJ: Breeding for resistance to abiotic stresses in rice: The value of quantitative trait loci. In Plant Breeding: The Arnel R. Hallauer International Symposium. Blackwell Publishing, Oxford, England; 2008:201–212.View ArticleGoogle Scholar
- Matkin OA, Chandler PA: The U.C.-type soil mixes. In The U.C. system for producing healthy container-grown plants. Edited by: Baker KF. The University of California College of Agriculture, Berkeley, California, USA; 1957:332.Google Scholar
- Møller IS, Gilliham M, Jha D, Mayo GM, Roy SJ, Coates JC, Haseloff J, Tester M: Shoot Na+ exclusion and increased salinity tolerance engineered by cell type-specific alteration of Na+ transport in Arabidopsis . Plant Cell 2009, 21(7):2163–2178.PubMed CentralView ArticlePubMedGoogle Scholar
- Moradi F, Ismail AM: Responses of photosynthesis, chlorophyll fluorescence and ROS-Scavenging systems to salt stress during seedling and reproductive stages in rice. Ann Bot 2007, 99(6):1161–1173.PubMed CentralView ArticlePubMedGoogle Scholar
- Munns R: Approaches to identifying genes for salinity tolerance and the importance of timescale. In Plant Stress Tolerance. Edited by: Sunkar R. Methods in Molecular Biology. Humana Press, New York, USA; 2010:25–38.View ArticleGoogle Scholar
- Munns R, Tester M: Mechanisms of salinity tolerance. Annu Rev Plant Biol 2008, 59: 651–681.View ArticlePubMedGoogle Scholar
- Nakhoda B, Leung H, Mendioro MS, Mohammadi-nejad G, Ismail AM: Isolation, characterization, and field evaluation of rice ( Oryza sativa L., Var. IR64) mutants with altered responses to salt stress. Field Crops Res 2012, 127: 191–202.View ArticleGoogle Scholar
- Negrão S, Courtois B, Ahmadi N, Abreu I, Saibo N, Oliveira MM: Recent updates on salinity stress in rice: From physiological to molecular responses. Crit Rev Plant Sci 2011, 30(4):329–377.View ArticleGoogle Scholar
- Plett D, Safwat G, Gilliham M, Møller IS, Roy S, Shirley N, Jacobs A, Johnson A, Tester M (2010) Improved salinity tolerance of rice through cell type-specific expression of AtHKT1;1. PLoS ONE 5(9), doi:10.1371/journal.pone.0012571Google Scholar
- Ponnamperuma FN, Bandyopadhya AK: Soil salinity as a constraint on food production in the humid tropics. In Priorities for alleviating soil-related constraints to food production in the tropics, Los Banos, Philippines, 1980. International Rice Research Institute and Cornel University, Los Banos, Laguna, Philippines; 1980:468.Google Scholar
- Rahnama A, James RA, Poustini K, Munns R: Stomatal conductance as a screen for osmotic stress tolerance in durum wheat growing in saline soil. Funct Plant Biol 2010, 37(3):255–263.View ArticleGoogle Scholar
- Rahnama A, Poustini K, Tavakkol-Afshari R, Ahmadi A, Alizadeh H: Growth properties and ion distribution in different tissues of bread wheat genotypes ( Triticum aestivum L .) differing in salt tolerance. J Agron Crop Sci 2011, 197(1):21–30.View ArticleGoogle Scholar
- Rajendran K, Tester M, Roy SJ: Quantifying the three main components of salinity tolerance in cereals. Plant, Cell Environ 2009, 32(3):237–249.View ArticleGoogle Scholar
- Siddiqui ZS, Cho J-I, Park S-H, Kwon T-R, Ahn B-O, Lee G-S, Jeong M-J, Kim K-W, Lee S-K, Park S-C: Phenotyping of rice in salt stress environment using high-throughput infrared imaging. Acta Bot Croat 2014, 73(1):149–158.Google Scholar
- Sirault XRR, James RA, Furbank RT: A new screening method for osmotic component of salinity tolerance in cereals using infrared thermography. Funct Plant Biol 2009, 36(10–11):970–977.View ArticleGoogle Scholar
- Tester M, Davenport R: Na+ tolerance and Na+ transport in higher plants. Ann Bot 2003, 91(5):503–527.PubMed CentralView ArticlePubMedGoogle Scholar
- Ueda A, Kathiresan A, Bennett J, Takabe T: Comparative transcriptome analyses of barley and rice under salt stress. Theor Appl Genet 2006, 112(7):1286–1294.View ArticlePubMedGoogle Scholar
- Vinod KK, Krishnan SG, Babu NN, Nagarajan M, Singh AK: Improving salt tolerance in rice: Looking beyond the conventional. In Ahmad P. Edited by: Azooz MM, Prasad MNV. Salt Stress in Plants, Springer New York; 2013:219–260.Google Scholar
- Yamaguchi T, Blumwald E: Developing salt-tolerant crop plants: challenges and opportunities. Trends Plant Sci 2005, 10(12):615–620.View ArticlePubMedGoogle Scholar
- Yeo AR, Flowers TJ: Salinity resistance in rice ( Oryza-Sativa -L) and a pyramiding approach to breeding varieties for saline soils. Aust J Plant Physiol 1986, 13(1):161–173.View ArticleGoogle Scholar
- Yeo AR, Yeo ME, Flowers TJ: Selection of lines with high and low sodium transport from within varieties of an inbreeding species; rice ( Oryza sativa L.). New Phytol 1988, 110(1):13–19.View ArticleGoogle Scholar
- Yeo AR, Yeo ME, Flowers SA, Flowers TJ: Screening of rice ( Oryza sativa L.) genotypes for physiological characters contributing to salinity resistance, and their relationship to overall performance. Theor Appl Genet 1990, 79(3):377–384.View ArticlePubMedGoogle Scholar
- Zeng L, Poss J, Wilson C, Draz A-S, Gregorio G, Grieve C: Evaluation of salt tolerance in rice genotypes by physiological characters. Euphytica 2003, 129(3):281–292.View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.