13. The genetic basis of hybrid chlorosis found in a cross between two Japanese native cultivars


Y. I. SATO1, S. MATSUURA2 and K. HAYASHI2

1) National Institute of Genetics, Misima, 411 Japan and

2) Faculty of Agriculture, Kochi University, Nankoku, Kochi, 783 Japan


We incidentally found a case of hybrid chlorosis in the F\2\ population of a cross between two Japanese native cultivars, J-147 and J-321. Its first symptom was a change in color of the third or fourth leaf-blade to yellowish. The chlorotic plants died within 30 days after germination, hence no seed was obtainable from them.

The F\2\2 population segregated into 849 normal and 63 chlorotic plants, giving a good fit to the 15 : 1 ratio. The F\3\ lines showing segregation ratios of 1 : 0, 3 : 1 and 15 : 1 numbered 72, 35 and 37, respectively. This F\3\ ratio fitted 7 : 4 : 4, which was expected on the assumption of two independent recessive genes (Table 1). The data thus indicated that there was a set of duplicate genes independent of each other whose double-recessive combination causes chlorosis. They were symboled ch-1-d and ch-1-a, tentatively.


Table 1. Segregation ratios of F\2\ plants and F\3\ lines into normal and chlorotic phenotypes in J-147 x J-321

=============================================================================
Generation            No. of plants or lines        X2              P
=============================================================================
F\2\,               Normal    Chlorotic   Total
  Observed           849         63        912
  Exp. (15:1)        855         57        912      0.67            >0.3

F\3\,                1:0     3:1   15:1     Total
  Observed            72      35     37      144
  Exp. (7:4:4)      67.2    38.4   38.4      144    0.69            >0.7
=============================================================================

Sato and Hayashi (1983) reported the presence of a set of complementary lethal genes, L-2-a and L-2-b causing F\1\ weakness, and that the distibution of L-2-a was suggestive of the phylogenetic relationship among varietal groups and the mode of dissemination of rice varieties. The distribution of the hybrid chlorosis genes may also be useful for such studies.


Reference

Sato, Y. I. and K. Hayashi, 1983. Distribution of the complementary genes causing F\1\ weakness in the common rice and its wild relatives, I. L-2-a gene in Asian native cultivars. Jpn. J. Genet. 58:411-418.