Rice Genetics Newsletter, Vol. 18

Rgn18

14.	Two dominant complementary genes controlling rhizomatous expression in Oryza longistaminata
	F.-Y. HU^1,2, D.-Y. TAO², P. XU², J. LI², Y. YANG², E. SACKS¹, K. MCNALLY¹, T.S. CRUZ^1., J. ZHOU¹ , Z.-K.LI¹ 1)Plant Breeding, Genetics and Biochemistry Division, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines 2)Food Crops Research Institute, Yunnan Academy of Agricultural Sciences, Kunming 650205, P.R. China

Oryza longistaminata is a perennial wild rice that is reproductively isolated from all other Oryza species. The reproductive barrier between O. longistaminata and O. sativa is reportedly due to the action of two complementary lethal genes, D1 and D2, which cause abortion of the embryo in the interspecific hybrid (Chu and Oka, 1970). The perennial habit of O. longistaminata is characterized by the presence of rhizomes and is reportedly associated with D1 and D2 (Ghesquiere, 1992). However, the control of rhizome expression by the two complementary loci remains a hypothesis to be tested (Ghesquiere, 1991). In addition, Maekawa et al. (1998) reported that rhizome expression in an O. sativa/ O. longistaminata F₂ population was controlled by a single gene loosely linked to the lg locus on chromosome 4 and the rhizome phenotype varied considerably among F₂ plants, suggesting the presence of modifying gene(s).

To understand the inheritance of rhizome expression in O. longistaminata an F₂ population and two backcross populations were developed from the hydrid between O. sativa (RD23) and O. longistaminata. RD23 is an indica cultivar from Thailand. The accession of O.

longistaminata was collected from Niger and kindly supplied by Dr. Hiroshi Hyakutake (Ministry of Agriculture, Fisheries and Forestry, Japan). The F₁ plant from the RD23/O. longistaminata cross was obtained by direct hybridization followed by embryo rescue and has 32.53% pollen fertility, indehiscent anthers, and rhizomes that were intermediate between the two parents (Tao and Scripichitt, 2000). The F₁ plant was grown in Hainan Province, China, and produced 381 normally developed F₂ seeds by compulsive self-pollination. The F₁ plant was also backcrossed to the parents, RD23 and O. longistaminata, to produce two BC₁F₁ populations. The F₂ seeds were germinated on 1/4 MS medium (3% sucrose = 0.7% agar, pH 5.8)from which 258 seedlings were obtained and transplanted to the irrigated field for investigation of rhizome production in Sanya, China. In the phenotyping experiment, 238 randomly selected F₂ plants, the F₁ plant and its parents were planted in the field according to randomized complete block design and 3 replications (cutting population) on September 15, 2000. All plants were dug up and the roots were washed free of soil and evaluated for the presence and absence of rhizomes in December, 2000.

The numbers of F₂ plants with or without rhizomes was 152 and 86, respectively. This figure deviates slightly from the expected 9:7 ratio (chi² =5.98), suggesting that two dominant complementary genes were a possible genetic model for rhizome expression in O. longistaminata (Fig. 1). The hypothesis was supported by the results from the backcross populations. In the BC₁ population (F₁ x O. longistaminata), all 41 BC₁F₁ plants had rhizomes, while in the BC₁ population (F₁ x RD23), the rhizomatous and non-rhizomatous individuals segregated in the ration of 1:3 expected from the hypothesis (data not shown). Here we tentatively assign the two dominant complementary genes controlling rhizome expression in O. longistaminata as Rhz2 and Rhz3, respectively, since Rhz was used to designate a dominant gene for rhizomatous stems in rice (Maekawa et al , 1998). Further investigations to map Rhz2/Rhz3 and QTLs associated with rhizome growth in O. longistminata using molecular markers are underway at IRRI.

This study was supported by grants from National Natural Science Foundation of China, Agricultural Department of Yunnan Province, China, and to IRRI from BMZ/GTZX of the German Government.

References

Chu, Y.E., and Oka, H.I. 1970. The genetic basis of crossing barriers between Oryza perennis subsp. Barthii and its related taxa. Evolution 24: 135-144.

Ghesquiere, A. 1991. Re-examination of genetic control of the reproductive barier between Oryza longistaminat and O. sativa and relationship with rhizome expression. In: G.S. Khush, ed, Rice Genetics II. International Rice Research Institute (IRRI). Los Banos, Philippines. pp. 729-730.

Ghesquiere, A., and Causse, M. 1992. Linkage study between molecular markers and genes controlling the reproductive barrier in interspecific backcross between O. sativa and O. longistaminata. RGN 9: 28-31.

Maekawa, M., Inukai, T., Rikiishi, K., Matsuura, T. and Govidaraj, K. G. 1998. Inheritance of the rhizomatous traits in hybrid of Oryza longistaminata Chev. et Roehr. and O. sativa L. SABRAO J. Breeding Genet. 30: 69-72.

Tao, D., Sripichitt, P. 2000. Preliminary report on transfer of vegetative propagation from wild rices to O. sativa via distant hybridization and embryo rescue. Kasetsart J. (Nat. Sci.) 34: 1-11.