10. Allelic relationships among floury and opaque endosperm mutants in rice

R. P. KAUSHIK and G. S. KHUSH

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

Recently various types of mutants affecting amylose content and appearance of rice endosperm have been induced by mutagenic treatments (Omura and Satoh 1985; Okuno et al. 1983; Rutger et al. 1986). Among these, floury mutants are characterized by white endosperm like waxy mutants, but unlike waxy strains they stain strongly blue-black by I-KI solution. As the name suggests, the grains of floury mutants break easily into a fine powder as the compound starch granules are very weakly attached. An opaque mutant ESD8-3(o), reported by Rutger et al. (1986) appeared to be similar to the floury mutants in endosperm characteristics.

In order to test the allelic relationships among the various floury mutants and the opaque mutant (Table 1) we crossed them in a diallel fashion (without reciprocals), during 1986 wet season at the International Rice Research Institute. The F1 hybrids along with the parents were grown during 1987 dry season to obtain F2 seeds.

In crosses involving 2047, EM 17, EM 28 and ESD7-3(o), the F1 (crossed) seeds were white in appearance and floury in texture. No segregation was observed in the F2 and all the seeds were white and floury, suggesting that the four mutants have allelic genes (Table 2). The floury gene in EM 36 is non-allelic to the floury gene of four other mutants mentioned above. The F1 seeds of the crosses of EM 36 with these four floury mutants had normal endosperm and F2 segregated into 9 normal: 7 floury.

Floury genes in EM 17 and EM 36 have been designated flo-1 and flo-2, respectively (Omura and Satoh, 1985; Satoh, Yano and Omura, 1984). Hence 2047, EM 28 and ESD7-3(o) also carry the flo-1 gene. Thus, the gene for opaque endospesm (o) is allelic to flo-1.

                    
Table 1. Rice endosperm mutants used in the study
_______________________________________________________________
Mutant designation  Gene symbol  Parent variety    Source
_______________________________________________________________
EM 17                 flo-1         Kinmaze     Dr.  H.  Satoh
EM 36                 flo-2         Kinmaze     Dr.  H.  Satoh
EM 28                  __           Kinmaze     Dr.  H.  Satoh
2048                   __           Sasanishnki Dr.  K.   Okuo
ESD7-3(o)              o            ESD-3       Dr.J.N. Rutger
_______________________________________________________________

          
Table 2. Allelic relationships among the floury and obaque 
mutants based on F1 endosperm appearance and F2 segregation
_______________________________________________________________
            EM 17       EM 28       EM 36       ESD7-3(o)
_______________________________________________________________
2047          flo        flo          +            flo
EM 17                    flo          +            flo
EM 28                                 +            flo
EM 36                                               +
_______________________________________________________________
+ = normal, flo = floury

References

Okuno, K., H. Fuwa and M. Yano, 1983. A new mutant gene lowering amylose content in endosperm starch of rice, Oryza sativa L. Jpn. J Breed. 33: 387-394.

Omura, T. and H. Satoh, 1985. Mutagenesis by treating fertilized egg cells with nitroso compounds in rice. In Rice Genetics. pp. 707-717. IRRI, P. O. Box 933, Manila.

Rutger, J. N., L. E. Azzini and P. J. Brookhouzen, 1986. Inheritance of semi-dwarf and other useful mutants genes in rice. In Rice Genetics. pp. 261-271. IRRI, Manila.

Satoh, H., M. Yano and T. Omura, 1984. Endosperm mutants of rice induced by N-methyl-nitroso urea treatment of fertilized egg cells. RGN 1: 113.