• quantitative trait loci (QTL);
  • QTL × E (environment);
  • R-genes;
  • partial resistance;
  • nitrogen (N);
  • Oryza sativa (rice);
  • Magnaporthe grisea (blast)


  • • 
    Plant disease susceptibility is often increased by nitrogen (N) application. Therefore, it is important to know if resistance loci are effective in different plant N environments.
  • • 
    One-hundred lines of the Bala × Azucena rice (Oryza sativa) mapping population were grown in two N treatments and tested for partial resistance to blast (Magnaporthe grisea) isolate CD100. Disease severity (DS), the number and size of lesions and plant N and C concentrations were measured and the results subject to quantitative trait loci (QTL) and QTL × environment analysis.
  • • 
    There was a 66% higher plant N concentration in the high N treatment and DS increased significantly, mostly as a result of increased numbers of lesions. Nine regions contained QTL for disease traits but only one showed evidence of statistically significant QTL × treatment interaction. This was a large effect quantitative trait locus at marker R1933 on chromosome 12 which was less effective at high N.
  • • 
    Apparently, blast disease is increased by higher plant N, but the efficacy of partial resistance genes is not greatly affected by N application.