28. Interaction between genes for panicle density in rice

Panicle density is a complex character which consists of many component characters such as number of spikelets, panicle length and number of branches.

In order to elucidate the interaction between two different genes controlling panicle density, the dense panicle mutant, carrying a single recessive gene, dn-3, was crossed with Soryuto which possesses a single recessive gene, lax, located on chromosome 1. The dense panicle mutant which was induced from a cultivar, Akibare, by ethylene imine treatment, is characterized by an increment in number of panicle branches and a reduced length of primary branches, thereby bringing

Fig. 1. Frequency distribution of panicle density and its related characters of four F2 genotype groups of a cross between Soryuto and Akibare-dense panicle mutant.

about dense panicle. Soryuto is characterized by a remarkable decrease in number of spikelets. Panicle density was evaluated by the number of spikelets/total length of rachis and primary branches in cm (Futsuhara et al. 1979a).

The F2 population segregated into 76 normal: 18 dense panicle: 25 lax pani- cle, giving a good fit to the 9 : 3 : 4 ratio (X2 = 2.82, 0.5 > P> 0.20). When 25 lax panicle-type plants were discriminated by using the pleiotropic action of dn-3 such as long empty glume (Futsuhara et al. 1979b), they can be classified into two genotype groups, 17 lax dn-3⁺ and 8 lax dn-3. This shows that both the genes lax and dn-3 behave independent of each other and lax is epistatic to dn-3.

As shown in Fig. 1, the order of magnitudes of 4 characters for 4 genotype groups in the segregation frequency of F2 were as follows:

It is worthwhile to note that despite the fact that panicle density did not differ significantly between the genotypes lax dn-3⁺ and lax dn-3, the lax dn-3 plants showed a considerable increase in number of primary branches and striking decreases in number of secondary branches and fertility, respectively, compared to the lax dn-3⁺ plants. This suggests that the promotive effect and depressive effect of dn-3 on number of primary branches and fertility, respectively, are enhanced in the presence of lax, and that the depressive effect of lax on number of secondary branches is enhanced when co-existed with dn-3.

Futsuhara, Y., S. Kondo and H. Kitano, 1979a. Genetical studies on dense and lax panicles in rice. i. Character expression and mode of inheritance of lax panicle rice. Jpn. J. Breed. 29: 151-158.

____, ____, and ____, 1979b. Ditto. II. Character expression and mode of inheritance of dense panicle rice. Jpn. J. Breed. 29: 239-247.