10. Location of a floury endosperm gene in the second linkage group

Masahiko Maekawa

Experiment Farm, Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan

In order to obtain more useful gene markets for linkage analysis, I am collecting spontaneous and induced mutants of rice. An endosperm mutant named "MA2-50" was obtained from the M2 generation of gamma-ray treated Shiokari, a rice cultivar of Hokkaido. The grain is normal in shape but white in color. The endosperm stained strongly blue black with iodine. The brown rice is soft and floury. These characteristics suggest that this endosperm mutant is comparable to the floury mutants reported by Satoh and Omura (1981).

Genetic analysis of this mutant was conducted first in the cross between MA2- 50 and Shiokari. The F2 population segregated into 3 normal : 1 floury, and the F3 families segregated in a 1:2:1 ratio (Table 1). The floury endosperm is thus controlled by a recessive gene, which is tentatively symbolized as flo-3(t).

The F2 population from a cross between MA2-50 and MA1-274 (a line homozygous for lg and ga-6) showed an excess of floury endosperm suggesting the linkage of flo-3(t) with ga-6, a gametic gene for certation. Both Shiokari and MA2-50 are homozygous for ga-6+. In the F3 of MA1-274xMA2-50, the recombination value between flo-3(t) and ga-6 was estimated to be 11.0±1.5%. In the same cross, linkage between flo-3(t) and 1 g was also detected. From the data for 12 F3 lines giving normal segregation ratios, the maximum likelihood estimate of recombination value between the two loci was 10.4±2.9% (Table 2). The distance between lg and ga-6 was earlier calculated to be approximately 4% (Maekawa 1982). The location of flo-3(t) may be assumed as flo-3(t)-lg-ga-6 although this must be confirmed by crossing MA2-50 with a strain with Pl.

Table 1. F2 and F3 segregation patterns for floury endosperm

============================================================================
Cross comb.            Endosperm character                        Chi-square
                   ---------------------------------
                     Normal  Segre. Floury     Total           (3:1 or 1:2:1)
============================================================================
ShiokarixMA2-50  F2  231            65        296               1.46
                 F3   77    154     65        296               1.46
MA1-274xMA2-50   F2  251           168        419              50.92**
============================================================================

Table 2. Recombination between flo-3(t) and lg in F3 of MA1-274xMA2-50 (pooled data for 12 F3 lines not showing segregations distortion)

============================================================================
       Normal            Floury
      ----------        ---------
      +     lg           +    lg     Total    Recombination (%)    Chi-square
                                                                    (9:3:3:1)
------------------------------------------------------------------------------
Obs. 613    297         278    3      1191                           111.1**
Exp. 598.7  294.5       294.5  3.2               10.4±2.9              1.3a  
============================================================================
** Significant at 1% level.
a Repulsion of the two genes with the given recombination value assumed.

References

Maekawa, M., 1982. Studies on genetical differences between distantly related rice varieties. Mem. Fac. Agr. Hokkaido Univ. 13: 146-177.

Satoh, H. and T. Omura, 1981. New endosperm mutations induced by chemical mutagens in rice. Jpn. J. Breed. 31: 316-326.