Blast resistance R genes pyramiding in temperate japonica rice

A major issue in rice production is the control of Pyricularia oryzae, the causal agent of rice blast. Genotypes with R resistant leucine-rich repeat genes control specific races of the parasite. However, the resistance is overcome by the pathogen, over a sufficiently long time. In temperate areas, current cultivated varieties have a largely insufficient field resistance. This prompted us to undertake the pyramiding of the R resistance genes Pib, Piz, Pik, Pita2, and Piz-t in temperate japonica materials. Two lines were produced, SJKK and SJKT-2, that have each four pyramided genes. They are fully resistant to rice blast when tested in the field and in greenhouse. However, the tropical origin of the R donor genotypes added complexity to the pyramiding exercise. The results point to a lack of fitness costs in pyramided lines.