35. A dense panicle mutant producing adventitious roots from spikelets

1) Institute of Radiation Breeding, Omiya-machi, Ibaraki-ken, 319-22 Japan

2) Faculty of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464 Japan

A dense panicle mutant induced in cultivar Akibare after a treatment with 0.2% solution of ethylene imine for two hours at 30 degrees C, was found to be due to a recessive gene, dn-3 (Futsuhara et al. 1979). This mutant bears small panicles shorter than 5 cm with often malformed spikelets like those having long empty glumes, and produces a few adventitious roots at the base of spikelet with a frequency of less than 2 percent.

To elucidate the pleiotropic effect of gene dn-3 on root induction, the mutant line was crossed with Jodon's tester L-16 carrying the clustered spikelet gene, Cl (linkage group I). The F\2\ population segregated into 73 Cl dn-3⁺:29 Cl dn-3 : 25 cl dn-3⁺:11 cl dn-3, giving a good fit to the 9:3:3:1 ratio (X²=0.087, P>0.7). Among the four phenotypic classes, Cl dn plants developed a considerable number of adventitous roots on the panicle, the frequency of spikelets producing adventitous roots being 80 percent (Figs. 1 and 2). The total number of roots per panicle was 66.8, and the number of roots per spikelet ranged from 0 to 3. Most of the roots (88.6%) were shorter than 5cm, but 8.4% of them were 5 to 10 cm long and 3.0% of them were longer than 10 cm. This suggests that the root-developing effect of dn-3 is enhanced in the presence of Cl.

A similar phenomenon was reported by Jones and Pope (1942) that the panicle of an American cultivar, Nira, produced adventitious roots emerging above and below the second glume.

In the present material, a treatment with 20 ppm of Ga\3\ from tillering to heading had no effect on the occurrence and elongation of adventitious roots on the panicles. Cytohistological observations demonstrated that the adventitious roots emerged in the region between empty glume and rudimentary glume (Fig. 3), and had a structure characteristic of aerial roots (Fig. 4). Gene dn-3 will be useful in studies of the genetic control of root development.

Fig. 1. Adventitous roots emerging from a panicle of Cl dn plant.

Fig. 2. Spikelets of a panicle producing adventitious roots.

Fig. 3. Longitudinal section of the base of spikelet showing that the adventitious roots (stained darkly) occur between the empty glume (eg) and rudimentary glume (rg).

Fig. 4. Longitudinal section of an adventitous root.

References

Futsuhara, Y., S. Kondo and H. Kitano, 1979. Genetical studies on dense and lax panicles in rice II. Character expression and mode of inheritance of dense panicle rice. Jpn. J. Breed. 29: 239-247.

Jones, J.W. and M.N. Pope, 1942. Adventitious roots on panicles of rice. J. Hered. 33:55-58.