10. A new gene for spreading panicle in rice

A.C. SANCHEZ and G.S. KHUSH

International Rice Research Institute, P.O. 933, 1099 Manila, Philippines

Two rice accessions from Malaysia, Padi Keriting (Acc. 14385) and Pontianak Puteh (Acc. 44114) planted for bacterial blight resistance screening showed spreading panicle phenotype. The mutant is characterized by perpendicular growth of the primary branches of the panicle relative to the primary axis. This growth gives the panicle a spreading appearance (Fig. 1).

The F2 population from the cross of the two mutant accessions did not show any segregation for normal panicle. Thus, the two accessions have the same gene for spreading panicel character. The inheritance of this mutant trait was investigated by crossing both accessions with IR36 which has the normal panicle phenotype. Both F1's showed spreading panicle. The F2 of the cross with Acc. 14385 segregated into 185 spreading panicle: 46 normal panicle and the F2 of the cross with Acc 44114 segregated into 68 spreading: 29 normal panicles. The segregation data of both populations fit the ratio of 3 spreading panicle: 1 normal panicle with χ2 values of 3.04 and 1.12, respectively. These data show that the spreading panicle trait in these rice accessions is due to a single dominant gene.

Two spreading panicle mutants of rice were reported earlier; the recessive gene spr1,(Kinoshita and Takamure 1986) and the dominant gene Spr2 (Mitra and Ganguli, 1932). Eiguchi and Sano (1990) reported a third gene for spreading panicle tentatively designated as Spr3 (t). We obtained seeds of Spr3 from Dr. Y. Sano for allele tests. The Pi plants between Spr3 and Padi Keriting had spreading panicle and F2 population segregated in a ratio of 15 spreading: 1 normal panicle.

Our data suggests a single dominant gene for spreading panicle, in which case, the dominant gene detected in this study may not correspond to Spr2. We could not make the allele test between our mutant and Spr2 as the seeds of Spr2 are not available. We designated this new gene as Spr4(t).

References

Kinoshita, T. and I. Takamure, 1986. Linkage studies by the use of backcross data in rice. Genetical studies on rice plant, LXXXVIII. J. Fac. Agr. Hokkaido Univ. 61(4): 445-455.

Mitra, S.K. and P.M. Ganguli, 1932. Some observations on the characters of wild rice hybrids. Ind. J. Agr. Sci. 2:271-279.

Eiguchi, M. and Y. Sano, 1990. A gene complex for seed shattering and panicle spreading found in common wild rices. RGN 7: 105-107.