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Plant function and evolutionary biology
RESEARCH ARTICLE

Chlorophyll fluorescence parameters allow the rapid detection and differentiation of plant responses in three different wheat pathosystems

Olubukola O. Ajigboye A , Louise Bousquet B , Erik H. Murchie A and Rumiana V. Ray A C
+ Author Affiliations
- Author Affiliations

A Plant and Crop Sciences Division, School of Biosciences, The University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, LE12 5RD, UK.

B BASF Plc, E-APE-, Cheadle, SK8 6QG, UK.

C Corresponding author. Email: rumiana.ray@nottingham.ac.uk

Functional Plant Biology 43(4) 356-369 https://doi.org/10.1071/FP15280
Submitted: 8 September 2015  Accepted: 14 December 2015   Published: 14 January 2016

Abstract

The present study was undertaken to identify chlorophyll fluorescence (CF) parameters that can quantify changes in PSII associated with plant responses in three different wheat pathosystems of foliar, stem-base and ear diseases. The pathosystems included powdery mildew caused by Blumeria graminis, eyespot caused by Oculimacula yallundae or Oculimacula acuformis and Fusarium head blight (FHB) caused by Fusarium culmorum, F. avenaceum or F. langsethiae. Fast CF transients (OJIP) were analysed with the JIP-test to determine changes in PSII photochemistry. Measurements on asymptomatic leaves showed that electron transport related parameters (ETo/RC, ψo and ϕEo) were important to identify varietal differences in resistance to powdery mildew during early stages of infection. The same parameters also allowed differentiation between F. langsethiae and other Fusarium spp. Where infections were caused by the necrotrophic pathogens, Oculimacula spp., F. culmorum or F. avenaceum, changes related to maximum efficiency of PSII photochemistry (Fvʹ/Fmʹ) as well as flux of dissipated (DIo/RC), trapped (TRo/RC), or absorbed (ABS/RC) energy per active reaction centers were significant in detecting biotic stress and the effectiveness of fungicide treatment for disease control. Our results demonstrated that Fvʹ/Fmʹ correlated significantly with visual disease and pathogen DNA of different wheat pathosystems. OJIP was shown as a sensitive technique that can be explored as diagnostic tool in future crop disease management and varietal breeding programs.

Additional keywords: Blumeria graminis, chlorophyll fluorescence, Fusarium spp., Oculimacula spp., OJIP, wheat.


References

Ajigboye OO, Murchie EH, Ray RV (2014) Foliar application of isopyrazam and epoxiconazole improves photosystem II efficiency, biomass and yield in winter wheat. Pesticide Biochemistry and Physiology 114, 52–60.
Foliar application of isopyrazam and epoxiconazole improves photosystem II efficiency, biomass and yield in winter wheat.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXht1GkurjF&md5=1b98968c71cbe5b5c29cfcb1defe358aCAS | 25175650PubMed |

Bassanezi RB, Amorim L, Bergamin Filho A, Berger RD (2002) Gas exchange and emission of chlorophyll fluorescence during the monocycle of rust, angular leaf spot and anthracnose on bean leaves as a function of their trophic characteristics. Journal of Phytopathology 150, 37–47.
Gas exchange and emission of chlorophyll fluorescence during the monocycle of rust, angular leaf spot and anthracnose on bean leaves as a function of their trophic characteristics.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38Xis1ertbc%3D&md5=a87d866c3003c1c1a494a2ce8b91cce6CAS |

Bauriegel E, Herppich WB (2014) Hyperspectral and chlorophyll fluorescence imaging for early detection of plant diseases, with special reference to Fusarium spec. infections on wheat. Agriculture 4, 32–57.
Hyperspectral and chlorophyll fluorescence imaging for early detection of plant diseases, with special reference to Fusarium spec. infections on wheat.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXhvVWru7nO&md5=4ac37c26f2ac32aa4a102c86fd318ec1CAS |

Bauriegel E, Giebel A, Herppich WB (2010) Rapid Fusarium head blight detection on winter wheat ears using chlorophyll fluorescence imaging. Journal of Applied Botany and Food Quality 83, 196–203.

Berger S, Sinha AK, Roitsch T (2007) Plant physiology meets phytopathology: plant primary metabolism and plant–pathogen interactions. Journal of Experimental Botany 58, 4019–4026.
Plant physiology meets phytopathology: plant primary metabolism and plant–pathogen interactions.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXitlymtLg%3D&md5=cb7e09d8b65beaec1711811c543a5329CAS | 18182420PubMed |

Bürling K, Hunsche M, Noga G (2010) Quantum yield of non-regulated energy dissipation in PSII (Y(NO)) for early detection of leaf rust (Puccinia triticina) infection in susceptible and resistant wheat (Triticum aestivum L.) cultivars. Precision Agriculture 11, 703–716.
Quantum yield of non-regulated energy dissipation in PSII (Y(NO)) for early detection of leaf rust (Puccinia triticina) infection in susceptible and resistant wheat (Triticum aestivum L.) cultivars.Crossref | GoogleScholarGoogle Scholar |

Burnett FJ, Oxley SJP, Harling R (1997) The use of PCR diagnostics to monitor development of eyespot in winter wheat. HGCA Project Report 150.

Burnett F, Butler-Ellis C, Hughes G, Knight S, Ray R (2012) Forecasting eyespot development and yield losses in winter wheat. HGCA Project Report 491.

Chaerle L, Pineda M, Romero-Aranda R, Van Der Straeten D, Baron M (2006) Robotized thermal and chlorophyll fluorescence imaging of pepper mild mottle virus infection in Nicotiana benthamiana. Plant & Cell Physiology 47, 1323–1336.
Robotized thermal and chlorophyll fluorescence imaging of pepper mild mottle virus infection in Nicotiana benthamiana.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XhtFCgur%2FF&md5=1583bab5da7386927f086da20d1a1876CAS |

Christen D, Schonmann S, Jermini M, Strasser RJ, Defago G (2007) Characterization and early detection of grapevine (Vitis vinifera) stress responses to esca disease by in situ chlorophyll fluorescence and comparison with drought stress. Environmental and Experimental Botany 60, 504–514.
Characterization and early detection of grapevine (Vitis vinifera) stress responses to esca disease by in situ chlorophyll fluorescence and comparison with drought stress.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXntFyhtbY%3D&md5=5fe866198635c81c4ad2b42224b72c39CAS |

Cornic G, Massacci A (1996) Leaf photosynthesis under drought stress. In Photosynthesis and the Environment (Ed. Baker NR). Netherlands: Kluwer Academic Publishers, The Netherlaands, pp. 347–366.

Delaye L, García-Guzmán G, Heil M (2013) Endophytes versus biotrophic and necrotrophic pathogens – are fungal lifestyles evolutionarily stable traits? Fungal Diversity 60, 125–135.
Endophytes versus biotrophic and necrotrophic pathogens – are fungal lifestyles evolutionarily stable traits?Crossref | GoogleScholarGoogle Scholar |

Demetriou G, Neonaki C, Navakoudis E, Kotzabasis K (2007) Salt stress impact on the molecular structure and function of the photosynthetic apparatus: the protective role of polyamines. Biochimica et Biophysica Acta 1767, 272–280.
Salt stress impact on the molecular structure and function of the photosynthetic apparatus: the protective role of polyamines.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXkt1aqurc%3D&md5=807e74244d296537669507b03d6d1bdeCAS | 17408588PubMed |

Divon HH, Razzaghian J, Udnes-Aamot H, Klemsdal SS (2012) Fusarium langsethiae (Torp and Nirenberg) investigation of alternative infection routes in oats. European Journal of Plant Pathology 132, 147–161.
Fusarium langsethiae (Torp and Nirenberg) investigation of alternative infection routes in oats.Crossref | GoogleScholarGoogle Scholar |

Edwards SG, Pirgozliev SR, Hare MC, Jenkinson P (2001) Quantification of trichothecene-producing Fusarium species in harvested grain by competitive PCR to determine efficacies of fungicides against Fusarium head blight of winter wheat. Applied and Environmental Microbiology 67, 1575–1580.
Quantification of trichothecene-producing Fusarium species in harvested grain by competitive PCR to determine efficacies of fungicides against Fusarium head blight of winter wheat.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXis1egsbc%3D&md5=ee9fb0fb92d8d1fdca3ce6b4c5d0e4a3CAS | 11282607PubMed |

Edwards SG, Imathiu SM, Ray RV, Back M, Hare MC (2012) Molecular studies to identify the Fusarium species responsible for HT-2 and T-2 mycotoxins in UK oats. International Journal of Food Microbiology 156, 168–175.
Molecular studies to identify the Fusarium species responsible for HT-2 and T-2 mycotoxins in UK oats.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XlvFKhtrw%3D&md5=8e74f3cc666fb4744909929b0d84846cCAS | 22521800PubMed |

Fofana B, Banks TW, McCallum B, Strelkov SE, Cloutier S (2007) Temporal gene expression profiling of the wheat leaf rust pathosystem using cDNA microarray reveals differences in compatible and incompatible defence pathways. International Journal of Plant Genomics 2007, 17542
Temporal gene expression profiling of the wheat leaf rust pathosystem using cDNA microarray reveals differences in compatible and incompatible defence pathways.Crossref | GoogleScholarGoogle Scholar | 18288238PubMed |

Fulton ND, Bollenbacher K, Templeton GE (1965) A metabolic from Alternaria tenuis that inhibits chlorophyll production. Phytopathology 55, 49–51.

Ghotbi-Ravandi A, Shahbazi M, Shariati M, Mulo P (2014) Effects of mild and severe drought stress on photosynthetic efficiency in tolerant and susceptible barley (Hordeum vulgare L.) genotypes. Journal Agronomy & Crop Science 200, 403–415.
Effects of mild and severe drought stress on photosynthetic efficiency in tolerant and susceptible barley (Hordeum vulgare L.) genotypes.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXhvVCgsbjN&md5=b40f0e9f16d4aa3aafca1f4b1410dc65CAS |

Gorbe E, Catalayud A (2012) Applications of chlorophyll fluorescence imaging technique in horticultural research: a review. Scientia Horticulturae 138, 24–35.
Applications of chlorophyll fluorescence imaging technique in horticultural research: a review.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38Xltlantr0%3D&md5=ed907bc6d94f2725e17aac2fc747773aCAS |

Hawkesford MJ, Araus J, Park R, Calderini D, Miralles D, Shen T, Zhang J, Parry MAJ (2013) Prospects of doubling global wheat yields. Food and Energy Security 2, 34–48.
Prospects of doubling global wheat yields.Crossref | GoogleScholarGoogle Scholar |

HGCA (2009/2010) ‘Recommended list.’ (Home-Grown Cereals Authority, Agricultural and Horticulture Development Board: Stoneleigh Park, UK)

Imathiu SM (2008) Fusarium langsethiae infection and mycotoxin production in oats. PhD thesis. Department of Crop and Environment Sciences, Harper Adams University College, UK.

Imathiu SM, Ray RV, Back M, Hare MC, Edwards SG (2009) Fusarium langsethiae pathogenicity and aggressiveness towards oats and wheat in wounded and unwounded in vitro detached leaf assays. European Journal of Plant Pathology 124, 117–126.
Fusarium langsethiae pathogenicity and aggressiveness towards oats and wheat in wounded and unwounded in vitro detached leaf assays.Crossref | GoogleScholarGoogle Scholar |

Imathiu SM, Edwards SG, Ray RV, Back MA (2013) Fusarium langsethiae – a HT-2 and T-2 toxins producer that needs more attention. Journal of Phytopathology 161, 1–10.
Fusarium langsethiae – a HT-2 and T-2 toxins producer that needs more attention.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XhvVajtLrN&md5=3e98920eadc26396b61f6972f9d0ae8bCAS |

Kocal N, Sonnewald U, Sonnewald S (2008) Cell wall-bound invertase limits sucrose export and is involved in symptom development and inhibition of photosynthesis during compatible interaction between tomato and Xanthomonas campestris pv. vesicatoria. Plant Physiology 148, 1523–1536.
Cell wall-bound invertase limits sucrose export and is involved in symptom development and inhibition of photosynthesis during compatible interaction between tomato and Xanthomonas campestris pv. vesicatoria.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXhsVSnurnI&md5=901a9883039cc189baf8e6cc5ab1ac66CAS | 18784281PubMed |

Kuckenberg J, Tartachnyk I, Schmitz-Eiberger M, Noga G (2007) Early detection of leaf rust and powdery mildew infections on wheat leaves by PAM fluorescence imaging. Precision Agriculture 8, 515–521.

Leroux P, Gredt M, Remuson F, Micoud A, Walker A (2013) Fungicide resistance status in French populations of the wheat eyespot fungi Oculimacula acuformis and Oculimacula yallundae. Pest Management Science 69, 15–26.
Fungicide resistance status in French populations of the wheat eyespot fungi Oculimacula acuformis and Oculimacula yallundae.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XhsFWiurfO&md5=09cdca9c3d0a87399852773d54a61debCAS | 23073993PubMed |

Maxwell K, Johnson GN (2000) Chlorophyll fluorescence: a practical guide. Journal of Experimental Botany 51, 659–668.
Chlorophyll fluorescence: a practical guide.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXjtF2js74%3D&md5=b2079d1ff209536207d91054c5b02220CAS | 10938857PubMed |

Mengiste T (2012) Plant immunity to necrotrophs. Annual Review of Phytopathology 50, 267–294.
Plant immunity to necrotrophs.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XhsVWht73O&md5=9918fbe5847009a64055d9a44316de12CAS | 22726121PubMed |

Murchie EH, Lawson T (2013) Chlorophyll fluorescence analysis: a guide to good practice and understanding some new applications. Journal of Experimental Botany 64, 3983–3998.
Chlorophyll fluorescence analysis: a guide to good practice and understanding some new applications.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhs1SmtLbJ&md5=8b721e3e9d9bbcbce496be3070f4c2b1CAS | 23913954PubMed |

Nielsen LK, Cook DJ, Edwards SG, Ray RV (2014) The prevalence and impact of Fusarium head blight pathogens and mycotoxins on malting barley quality in UK. International Journal of Food Microbiology 179, 38–49.
The prevalence and impact of Fusarium head blight pathogens and mycotoxins on malting barley quality in UK.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXms1Cqsro%3D&md5=91aaf7118b78c614da694d3af208bcdcCAS | 24727381PubMed |

Oerke EC (2006) Crop losses to pests. Journal of Agricultural Science 144, 31–43.
Crop losses to pests.Crossref | GoogleScholarGoogle Scholar |

Oukarroum A, Madidi SE, Schansker G, Strasser RJ (2007) Probing the responses of barley cultivars (Hordeum vulgare L.) by chlorophyll a fluorescence OLKJIP under drought stress and re-watering. Environmental and Experimental Botany 60, 438–446.
Probing the responses of barley cultivars (Hordeum vulgare L.) by chlorophyll a fluorescence OLKJIP under drought stress and re-watering.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXntFyhtb0%3D&md5=4d746f81450ebb724ad8f3a2474da825CAS |

Perfect SE, Green JR (2001) Infection structures of biotrophic and hemibiotrophic fungal plant pathogens. Molecular Plant Pathology 2, 101–108.

Pinto LSRC, Azevedo JL, Pereira JO, Vieira MLC, Labate CA (2000) Symptomless infection of banana and maize by endophytic fungi impairs photosynthetic efficiency. New Phytologist 147, 609–615.
Symptomless infection of banana and maize by endophytic fungi impairs photosynthetic efficiency.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXnsVKqsLs%3D&md5=845018092f99cec18ee85ee5bce4f64cCAS |

Rasmussen JB, Scheffer RP (1988) Effects of selective toxin from Helminthosporium carbonum on chlorophyll synthesis in maize. Physiological and Molecular Plant Pathology 32, 283–291.
Effects of selective toxin from Helminthosporium carbonum on chlorophyll synthesis in maize.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL1cXktlemtrw%3D&md5=2bb9539d49bda9a9e8b760e2c43ecad8CAS |

Ray RV, Jenkinson P, Edwards SG (2004) Effects of fungicides on eyespot, caused predominantly by Oculimacula acuformis, and yield of early-drilled winter wheat. Crop Protection 23, 1199–1207.
Effects of fungicides on eyespot, caused predominantly by Oculimacula acuformis, and yield of early-drilled winter wheat.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXpsFemsrY%3D&md5=037063ffbb3bf0f17fe22e029a934e25CAS |

Ray RV, Crook MJ, Jenkinson P, Edwards SG (2006) Effect of eyespot caused by Oculimacula yallundae and O. acuformis, assessed visually and by competitive PCR, on stem strength associated with lodging resistance and yield of winter wheat. Journal of Experimental Botany 57, 2249–2257.
Effect of eyespot caused by Oculimacula yallundae and O. acuformis, assessed visually and by competitive PCR, on stem strength associated with lodging resistance and yield of winter wheat.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XnvF2mu7w%3D&md5=2aae8dea39b8d89a3beeb4f9abbc0a69CAS | 16720606PubMed |

Robbertse B, Campbell GF, Crous PW (1995) Revision of Pseudocercosporella-like species causing eyespot disease of wheat. South African Journal of Botany 61, 43–48.
Revision of Pseudocercosporella-like species causing eyespot disease of wheat.Crossref | GoogleScholarGoogle Scholar |

Rolfe SA, Scholes JD (2010) Chlorophyll fluorescence imaging of plant-pathogen interactions. Protoplasma 247, 163–175.
Chlorophyll fluorescence imaging of plant-pathogen interactions.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXhsVGrsbzM&md5=bdc94e825fd0d661537195bcdba23c8aCAS | 20814703PubMed |

Rousseau C, Belin É, Bove E, Rousseau D, Fabre F, Berruyer R, Guillaumès J, Manceau C, Jacques M, Boureau T (2013) High throughput quantitative phenotyping of plant resistance using chlorophyll fluorescence image analysis. Plant Methods 9, 17
High throughput quantitative phenotyping of plant resistance using chlorophyll fluorescence image analysis.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhtVOhtrvI&md5=37f58e2c1cf8626cc7142ad075612941CAS | 23758798PubMed |

Sagaram M, Burns JK (2009) Leaf chlorophyll fluorescence parameters and huanglongbing. Journal of the American Society for Horticultural Science 134, 194–201.

Scholes JD, Rolfe SA (1996) Photosynthesis in localized regions of oat leaves infected with crown rust (Puccinia coronata): quantitative imaging of chlorophyll fluorescence. Planta 199, 573–582.
Photosynthesis in localized regions of oat leaves infected with crown rust (Puccinia coronata): quantitative imaging of chlorophyll fluorescence.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28XltlWiurw%3D&md5=a4b17464cc6fccfbcc18e46d92aad1aaCAS |

Scott PR, Hollins TW (1974) Effects of eyespot on yield of winter-wheat. Annals of Applied Biology 78, 269–279.
Effects of eyespot on yield of winter-wheat.Crossref | GoogleScholarGoogle Scholar |

Silvestre S, Araújo SS, Vaz Patto MC, Marques da Silva J (2014) Performance index: an expeditious tool to screen for improved drought resistance in the Lathyrus genus. Journal of Integrative Plant Biology 56, 610–621.
Performance index: an expeditious tool to screen for improved drought resistance in the Lathyrus genus.Crossref | GoogleScholarGoogle Scholar | 25126659PubMed |

Strange RN, Scott PR (2005) Plant disease: a threat to global food security. Annual Review of Phytopathology 43, 83–116.
Plant disease: a threat to global food security.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXhtVOksr3O&md5=058be9414442d6366427d569840acfc5CAS | 16078878PubMed |

Strasser RJ, Srivastava A, Govindjee (1995) Polyphasic chlorophyll a fluorescence transients in plants and cyanobacteria. Photochemistry and Photobiology 61, 32–42.
Polyphasic chlorophyll a fluorescence transients in plants and cyanobacteria.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXjtFWmtr0%3D&md5=b78170ad28ac0d0510bdbeb24d940a58CAS |

Strasser RJ, Srivastava A, Tsimilli-Michael M (2000) The fluorescence transient as a tool to characterize and screen photosynthetic samples. In ‘Probing photosynthesis: mechanisms, regulation and adaptation’. (Eds M Yunus, U Pathre, P Mohanty) pp. 445–483. (Taylor & Francis: London)

Strasser RJ, Tsimilli-Michael M, Srivastava A (2004) Analysis of the chlorophyll a fluorescence transient. In ‘Chlorophyll a fluorescence: a signature of photosynthesis’. (Eds GC Papageorgiou, Govindjee) pp. 321–362. (Kluwer Academic Publishers, Dordrecht, the Netherlands)

Swarbrick PJ, Schulze-Lefert P, Scholes JD (2006) Metabolic consequences of susceptibility and resistance in barley leaves challenged with powdery mildew. Plant, Cell & Environment 29, 1061–1076.
Metabolic consequences of susceptibility and resistance in barley leaves challenged with powdery mildew.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XlvFaktbk%3D&md5=4b1ca7964cb542f60b7686591d8cfcccCAS |

Walsh K, Korimbocus J, Boonham N, Jennings P, Hims M (2005) Using real-time PCR to discriminate and quantify the closely related wheat pathogens Oculimacula yallundae and Oculimacula acuformis. Journal of Phytopathology 153, 715–721.
Using real-time PCR to discriminate and quantify the closely related wheat pathogens Oculimacula yallundae and Oculimacula acuformis.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xns1M%3D&md5=a580342734070048dfd4aaec64bcb526CAS |

Wang X, Zhang ZW, Tu SH, Feng WQ, Xu F, Zhu F, Zhang DW, Du JB, Yuan S, Lin HH (2013) Comparative study of four rice cultivars with different levels of cadmium tolerance. Biologia 68, 74–81.
Comparative study of four rice cultivars with different levels of cadmium tolerance.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XhvFSnsLjM&md5=0f9ece0ea37391b8997340a29af3b454CAS |

Zadoks JC, Chang TT, Konzak FC (1974) A decimal code for growth stages of cereals. Weed Research 14, 415–421.
A decimal code for growth stages of cereals.Crossref | GoogleScholarGoogle Scholar |

Živčák M, Brestič M, Olšovská K, Slamka P (2008) Performance index as a sensitive indicator of water stress in Triticum aestivum L. Plant, Soil and Environment 54, 133–139.