Fundamental studies on rice breeding through hybridization between Japanese and foreign varieties. XII, Results of testcrosses showing C-gene locus duplication in an Indian variety, Surjamkhi.

Abstract

In a previsus paper (Kondo and Mizushima, 1964) the authors suggested that an Indian variety “Surjamkhi” has a doubled C-loci, having two douninant C-gene, C^B₁ and C^B₂, each of which is located in a different chrmosome. In this paper further evidence (for the fact) is given from the results of testcrosses made between the pragenies (F₃ and F₅) of the cross, Surjamkhi (C^B₁C^B₂AP) xNorin No. 1 (C^BA^aP), and some tester varieties of known genotype. Each plant was randonily taken from five colorless F₃ Strains and crossed with two tester varieties. From the phenotype of the F₁ hybrids as well as from the mode of segregation in their F₂ strains it was proved that all the parental F₃ Plants lacked the dominant P-gene and two of them dominant A-gene and had either the genbtype C^B₂AP^- or C^B₂A^-P^-Here A^- or P^- represents the lack of dominant A-or P-gene respectively, which had been contributed to the hybrids from both sides of the parental varieties, Surjamkhi and Norin No. 1. Five plants randomly taken from five colored F₅ strains were crossed with another tester variety. The result showed that the gametes from the F₅ plants were either of three genotypes, C^BC^B₁AP, C^BA^aP or C^BAP. The authors refer to the mechanism that causes the lack of dominant P- and A-gene in the hybrids elsewhere. However, the occurrence of F₃ plants having the second C-gene (C^B₂) of Surjarnkhi and of F₅ gametes with the genotype C^B₁C^BAP confirmed in the present experiment is considered to afford clear evidence for the existence of doubled C-loci in Surjamkhi. Since Surjamkhi has been identified to be C^B₁C^B₂AP, the question as why don't such segregants show the phenotype of C^B₂AP appear in F₂ Surjamkhi x Norin No, 1 naturally arises. As a brief discussion we concluded from the present results that perhaps it might be due to a lack of the dominant P-gene and presented no effect of C^B-gene, making identification difiicult.