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Abstract

Hybrid necrosis is a phenomenon that is often observed in intra/inter-specific plant crosses and characterized by elevated immune responses. This phenomenon has been suggested to serve as an effective postzygotic gene flow barrier in plant species (1). Here we report cases of hybrid necrosis that result from the incompatible epistatic interaction involving a complex disease resistance (r) gene cluster. the r gene cluster that carries rECoGnition oF pEronosporA pArAsitiCA 1 (rpp1)-like r genes on chromosome 3 is highly divergent both in sequence and number in different accessions. We identified a single r gene in the cluster that is sufficient to cause hybrid incompatibility in one case. however, this particular r gene allele does not manifest necrotic symptoms in the other cases involving this cluster. furthermore, epistatically interacting loci of this r gene cluster differ in all cases. this indicates that the r gene cluster evolved under different evolutionary trajectory among different accessions yet carries numerous potential alleles that would contribute to gene flow barrier. Population genetic structure of this cluster both in local and global accessions as well as investigation on incompatible substitutions will be presented at the meeting. this study will shed light on our understanding of evolutionary forces that lead to hybrid incompatibility and speciation.