title: QTLs for tolerance of drought and breeding for tolerance of abiotic and biotic stress: an integrated approach.
abstract: BACKGROUND
  The coupling of biotic and abiotic stresses leads to high yield losses in rainfed rice (Oryza sativa L.) growing areas. While several studies target these stresses independently, breeding strategies to combat multiple stresses seldom exist. This study reports an integrated strategy that combines QTL mapping and phenotypic selection to develop rice lines with high grain yield (GY) under drought stress and non-stress conditions, and tolerance of rice blast.
  
  
  METHODS
  A blast-tolerant BC2F3-derived population was developed from the cross of tropical japonica cultivar Moroberekan (blast- and drought-tolerant) and high-yielding indica variety Swarna (blast- and drought-susceptible) through phenotypic selection for blast tolerance at the BC2F2 generation. The population was studied for segregation distortion patterns and QTLs for GY under drought were identified along with study of epistatic interactions for the trait.
  
  
  RESULTS
  Segregation distortion, in favour of Moroberekan, was observed at 50 of the 59 loci. Majority of these marker loci co-localized with known QTLs for blast tolerance or NBS-LRR disease resistance genes. Despite the presence of segregation distortion, high variation for DTF, PH and GY was observed and several QTLs were identified under drought stress and non-stress conditions for the three traits. Epistatic interactions were also detected for GY which explained a large proportion of phenotypic variance observed in the population.
  
  
  CONCLUSIONS
  This strategy allowed us to identify QTLs for GY along with rapid development of high-yielding purelines tolerant to blast and drought with considerably reduced efforts. Apart from this, it also allowed us to study the effects of the selection cycle for blast tolerance. The developed lines were screened at IRRI and in the target environment, and drought and blast tolerant lines with high yield were identified. With tolerance to two major stresses and high yield potential, these lines may provide yield stability in rainfed rice areas.
authors.affiliation: International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
authors.forename: Shalabh
authors.initials: S
authors.lastname: Dixit
authors.affiliation: Computational Informatics, CSIRO, Dutton Park, Queensland, Australia.
authors.forename: B Emma
authors.initials: BE
authors.lastname: Huang
authors.affiliation: International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
authors.forename: Ma Teresa
authors.initials: MT
authors.lastname: Sta Cruz
authors.affiliation: International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Maturan
authors.affiliation: International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
authors.forename: Jhon Christian E
authors.initials: JC
authors.lastname: Ontoy
authors.affiliation: International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
authors.forename: Arvind
authors.initials: A
authors.lastname: Kumar
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D001947:Breeding; D003681:Dehydration; D055864:Droughts; D017343:Genes, Plant; D056726:Genetic Association Studies; D012275:Oryza / Q000235:genetics* / Q000254:growth & development; D010641:Phenotype; D040641:Quantitative Trait Loci; D013312:Stress, Physiological