18. Association between grain shattering and semidwarfness in rice

Masao Yokoo-National Agriculture Research Center, Yatabe, Tsukuba, 305 AND Shigeru Saito-Tohoku National Agricultural Experiment Station, Yotsuya, Ohmagari, 014-01 Japan


A Korean rice variety, Milyang 23, has been extensively used as parent in breeding programs at Tohoku National Agricultural Experiment Station, as a possible source of semidwarf plant type and high yielding capacity. However, Milyang 23 had a grain shattering habit, which was in close association with semidwarfness in its crosses with Japanese varieties.

Ten F\1\ and 300 F\2\ plants for each of five crosses were grown in a field, and grain shattering of individual plants at maturity was evaluated by firmly grasping three panicles. Shattering was dominant over non-shattering and was found to be controlled by a single gene in both F\2\ and B\1\F\2\ populations (Table 1).


Table 1. Segregation for grain shattering in F\2\ and B\1\F\2\

=============================================================================
   Cross                  No. of plants            X2      Probability
                   ============================
                   Non-shatte.     Shattering
=============================================================================
F\2\:                                              (1:3)
Milyang 23/Reimei       71            225          0.16        >0.5
     "    /Akihikari    71            227          0.22        >0.5
     "    /Toyonishiki  78            220          0.22        >0.5
     "    /Rikuu 132    62            228          2.03        >0.1   
     "    /Somewake     87            212          2.68        >0.1
B\1\F\2\                                           (1:1)
Milyang 23/2* Akihikari 95             96          0.005       >0.9
=============================================================================


The variation in culm length of F\2\ plants was continuous and transgressive in both tall and short direction (Fig. 1). In any cross, almost all semidwarf plants with stiff straw and erect leaves like Milyang 23 had the easy shattering habit. This affected the selection efficiency in breeding programs, although some recombinants were obtained in later generations.

The semidwarf type of Milyang 23 is due to sd-1, although the transgressive segregation would be due to the action of modifiers. The dominant gene for shattering would differ from sh carried by H-21 of Hokkaido University. It should be identified and its linkage with ad-1 should be investigated.


Fig. 1 Relationships between grain shattering and culm length in the F\2\ populations of the crosses Milyang 23/Akihikari and Milyang 23/Somewake.