ORIGINAL PAPER Genetic mapping and validation of QTLs associated with resistance to Calonectria leaf blight caused by Calonectria pteridis in Eucalyptus Talyta Gafassi Zarpelon & Lúcio Mauro da Silva Guimarães & Danielle Assis Faria & Marcelo Magalhães Coutinho & Braz Cápua Neto & Ramon Ubirajara Teixeira & Dario Grattapaglia & Acelino Couto Alfenas Received: 29 May 2014 /Revised: 23 September 2014 /Accepted: 24 October 2014 /Published online: 15 November 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract Calonectria leaf blight (CLB) caused by Calonectria pteridis is one of the main leaf diseases in Brazilian Eucalyptus plantations in warm climates with prolonged periods of rain. The main symptoms are leaf spots followed by intense defoliation in highly susceptible plants. Exploiting the existing inter- and intraspecific variability for defoliation is the best option to control this disease. Nevertheless, nothing is known about the genetic architecture of resistance to CLB in Eucalyptus. We built microsatellite- based genetic maps for E. urophylla × E. camaldulensis (EU11×EC06) F1 family of 89 plants. Four or five clonal replicates per individual offspring were clonally propagated, totalling 445 plants which were phenotyped for defoliation in the basal third of the branches at 30 days following controlled inoculation with a single-spore isolate. Genetic mapping was performed using a pseudo-testcross, and QTLs detected using composite interval mapping. Five QTLs were detected for resistance to CLB; of them, only one could be validated in two unrelated pedigrees, and its effect was conservatively estimated as controlling between 5 and 10 % of the phenotypic variation when the bias derived from the limited size of the mapping population was taken into account. This work pro- vides a starting point for future studies of the genetics of resistance to CLB, and adds further evidence to the challenge of ascertaining the effects of QTLs detected in a single bipa- rental background across unrelated families. Keywords Genetic resistance . Forest pathology . Genetic map . Microsatellite markers Introduction Calonectria leaf blight (CLB) caused by Calonectria pteridis Crous, M.J. Wingf. & Alfenas (=Cylindrocladium pteridis F.A. Wolf) is one of the main leaf diseases in Brazilian eucalypt plantations in warm climates with prolonged periods of rain (Alfenas et al. 2009). The first report of C. pteridis in eucalypts in Brazil occurred in 1995 in 1-year-old plants of E. grandis Hill ex Maid. in southeastern Bahia (Ferreira et al. 1995). Since then, C. pteridis has become one of the most common diseases in commercial plantations in northeastern and northern Brazil, occurring primarily on E. camaldulensis Dehnh., E. cloeziana F. Muell., E. grandis, E. saligna Smith, E. tereticornis Smith, E. urophylla S.T. Blake and the hybrid E. grandis × E. urophylla (“urograndis”) (Alfenas et al. 2009). For most Eucalyptus species under field conditions, the disease is characterized by spots that are initially small, circu- lar or elongated, and light-gray to light-brown but progress and extend throughout the leaf blade and cause blight and intense defoliation (Alfenas and Ferreira 1979). Intense defo- liation caused by the fungus may decrease the tree growth rate Communicated by R. Burdon T. G. Zarpelon : M. M. Coutinho Clonar Resistência a Doenças Florestais, Cajuri, MG 36560-000, Brazil T. G. Zarpelon : L. M. da Silva Guimarães : B. Cápua Neto : R. U. Teixeira : A. C. Alfenas (*) Departamento de Fitopatologia, Universidade Federal de Viçosa, Viçosa, MG 36571-000, Brazil e-mail: aalfenas@ufv.br D. A. Faria : D. Grattapaglia EMBRAPA Genetic Resources and Biotechnology, Brasilia, DF 70770-970, Brazil D. Grattapaglia Graduate Program in Genomic Sciences, Universidade Católica de Brasilia, Brasilia, DF 70790-160, Brazil Tree Genetics & Genomes (2015) 11:803 DOI 10.1007/s11295-014-0803-4