BIOLOGIA PLANTARUM 57 (1): 184-188, 2013 DOI: 10.1007/s10535-012-0267-z 184 BRIEF COMMUNICATION Frost tolerance in winter wheat cultivars: different effects of chromosome 5A and association with microsatellite alleles G. GANEVA 1 , T. PETROVA 2 , S. LANDJEVA 1 *, E. TODOROVSKA 3 , S. KOLEV 3 , G. GALIBA 4 , F. SZIRA 4 , and A.F. BÁLINT 4 Institute of Plant Physiology and Genetics, Bulgarian Academy of Sciences, BG-1113 Sofia, Bulgaria 1 Dobrudzha Agricultural Institute, BG-9200 General Toshevo, Bulgaria 2 AgroBioInstitute, BG-1164 Sofia, Bulgaria 3 Agricultural Institute, Hungarian Academy of Sciences, H-2462, Martonvásár, Hungary 4 Abstract Frost tolerance of ten Bulgarian winter wheat (Triticum aestivum L.) cultivars (Milena, Pobeda, Sadovo-1, Enola, Kristal, Laska, Svilena, Russalka, No301, and Lozen) and five foreign cultivars (Mironovskaya 808, Bezostaya-1, Rannaya-12, Skorospelka-35, and Chinese Spring) was studied in two experimental seasons following natural cold acclimation and in one experiment carried out in controlled acclimation conditions. Considerable intercultivar variability in plant survival was observed after freezing at -21 ºC following sufficient cold acclimation, or at -18 ºC following insufficient or controlled acclimation. In seven cultivars, the effects of chromosome 5A on frost tolerance were investigated in their F 2 hybrids with chromosome 5A monosomic lines of cultivars with high, intermediate, and low frost tolerance. The effects of chromosome 5A depended on the stress severity and the genetic background of the hybrids and varied even in cultivars of similar frost tolerance and vernalization requirements. Effects of other chromosomes besides 5A on frost tolerance were assumed. The analysis of six microsatellite loci located in the interval from centromere to Vrn-1 on chromosomes 5AL, 5BL, and 5DL showed that the major loci determining frost tolerance in Bulgarian winter wheats were Fr-A2 on chromosome 5AL and, to a lesser extent, Fr-B1 on chromosome 5BL. A strong association of the 176 bp allele at locus wmc327 tightly linked to Fr-A2 with the elevated frost tolerance of cvs. Milena, Pobeda, Sadovo-1, Mironovskaya-808, and Bezostaya-1 was revealed. Relatively weaker association between frost tolerance and the presence of the 172 bp allele at locus Xgwm639 tightly linked to Fr-B1 was also observed. Additional key words: cold acclimation, genetic variability, PCR, QTL, Triticum aestivum. ⎯⎯⎯⎯ In hexaploid wheat, almost all chromosomes contribute to plant response to low temperature stress (Sutka 2001). Frost tolerance is determined by major loci (Fr) and genes controlling plant response to acclimation and vernalization (Vrn), both located on the long arms of homoeologous group 5 of chromosomes (Sutka 2001, Tóth et al. 2003). The most potent loci, Fr-A1 and Fr-A2, were mapped on chromosome 5AL in close proximity (2 and 30 cM, respectively) to the gene Vrn-A1 (Galiba et al. 1995, Vágújfalvi et al. 2003). Orthologous frost tolerance loci were identified on chromosomes 5B and 5D (Tóth et al. 2003). The evaluation of plant genetic resources for variation in frost tolerance and the examination of the association between phenotypic variation and variation at frost tolerance loci could accelerate modern wheat breeding. The presented study aimed at 1) assessment of frost tolerance of Bulgarian bread wheat cultivars under different cold acclimation conditions and freezing temperatures; 2) estimation of the effects of chromosome 5A on frost tolerance, and ⎯⎯⎯⎯ Received 24 February 2012, accepted 14 June 2012. Abbreviations: CBF - C-repeat binding factor; PCR - polymerase chain reaction; QTL - quantitative trait locus. Acknowledgements: The research was performed under the bilateral agreements between the Bulgarian Academy of Sciences and the Hungarian Academy of Sciences (No. 37 and No. 25). This work was also partially supported by the Hungarian National Office for Research and Technology (GVOP-3.1.1.-2004-05-0441/3.0). The technical assistance of Mrs K. Prokopova is gratefully acknowledged. * Author for correspondence; fax: (+35) 92 8739952, e-mail: s_landjeva@mail.bg