Youki Itoh and Yoshikazu Sato
Reaction norm (RN) is defined as the form expressed by set of phenotypes that can be produced by a genotype exposed to different environmental conditions. To empirically examine genetic basis of RN under natural climates, quantitative trait locus (QTL) analysis was performed on genotypic mean under a condition and several phenotypic-plasticity (PP) indexes associated with density and/or year response of early vegetative plant architecture in rice. Recombinant inbred lines, derived from a cross between an annual-form-wild (AFW) and a cultivated rice, were grown under two-density conditions in two years. The present study provided three-significant results with some major theories of RN evolution. (1) Most of PP-type QTLs were associated with slope itself of RN rather than QTL responding to a specific condition regardless of genotype. (2) Further, three-fourth of estimated QTLs associated with density response behaved in year-condition-dependent manners. (3) In linkage analysis, QTLs that AFW-rice-derived allele contributed to an increase of PP tended to be linked each other, while QTLs that cultivated-rice-derived allele contributed to it tended to be scattered over several chromosomes. We discussed genetic mechanisms of RN evolution mainly based on the three results.
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