Is an egg-killer present in rice?

The genetic model for hybrid sterility that an allelic interaction at the S ₅ locus induces the abortion of megaspores has been proposed as partial clarification of the wide compatibility in Asian rice cultivars; this model predicts the presence of an egg-killer. The present study was carried out in order to confirm that the proposed S ₅ ⁱ allele acts as an egg-killer against its counterpart, the S ₅ ^j allele, in the Indica-Japonica hybrid. A conspicuous feature of an egg-killer is the high rate of its transmission into the progeny through the egg. Backcrossing experiments were conducted using the Indica-Japonica hybrid in which the S ₅ ⁱ and S ₅ ^j alleles were assumed to be involved. Although an egg-killer was easily identified by these backcross experiments, it was not detected in the Indica-Japonica hybrid, which suggests that the proposed genetic mechanism for hybrid sterility in Asian rice should be viewed with caution.