Effects of the two most common Wx alleles on different genetic backgrounds in rice

Wx^a and Wx^b are the most common alleles of the Wx gene in Asian cultivated rice. The difference between them is responsible for differences in the levels of the Wx gene product in the endosperm, as well as in amylose content, which is an important determinant of the quality of edible rice. Since Indica rice mostly carries the Wx^a allele, we introduced the Wx^b allele into Indica‐type rice (IR36) from a Japonica‐type rice (T65) by repeated backcrossing. In the near‐isogenic line (IR36 Wx^b), the level of the Wx gene product was reduced and, as expected, the level of amylose. However, IR36Wx^b had a lower amylose content than the recurrent parent of T65 with the Wx^b allele. The results suggest that the Indica (IR36) background might lower the amylose content more than the Japonica (T65) background when the Wx allele is the same. The possible importance of modifiers that regulate expression of the Wx gene is also discussed in relation to improvements in the grain quality of rice.