September 25, 2025
Japan International Research Center for Agricultural Sciences (JIRCAS)
Hokkaido University

A joint research group from JIRCAS and Hokkaido University has established a new method for efficiently producing interspecific hybrids between Asian cultivated rice (Oryza sativa, “Asian rice”) and African cultivated rice (Oryza glaberrima, “African rice”) that carry nearly equal genetic contributions from both species and exhibit seed fertility.

African rice is a cultivated species valued highly as a breeding resource because it possesses useful traits not found in Asian rice, such as resistance to diseases and environmental stresses and strong competitiveness against weeds. However, when the two species are crossed, the F₁ hybrids become almost completely male-sterile and do not produce seeds, representing a major breeding constraint known as the “hybridization barrier.” This pollen sterility occurs when the alleles of the hybrid sterility gene (HS gene) become heterozygous. Previous studies had shown that in F₁ hybrids in which the genomes of both species were doubled to become tetraploids, the effect of the HS gene was reduced and pollen fertility was partially restored.

Based on this knowledge, the present study produced diploid hybrids by culturing pollen from tetraploid hybrids, then further cultured and doubled their pollen to obtain 22 doubled haploid diploid plants in which all HS genes were fixed in the homozygous state. Among these, 10 plants showed stable seed fertility through self-pollination and retained intermediate genomic compositions of Asian and African rice.

This achievement is the first to demonstrate that combining tetraploidization with two rounds of pollen culture enables the stable development of interspecific hybrids that maintain an intermediate genetic composition of the two species while enduring seed fertility. Going forward, the researchers will evaluate traits of the obtained hybrid materials and identify useful genes, with the expectation of advancing breeding strategies that combine the strengths of both Asian and African rice.

The results of this research have been published as an open-access article in the online edition of the international scientific journal Theoretical and Applied Genetics on June 27, 2025 (Japan time).
 

Related Information

Funding

Operating Expenses Grant Project: "Advancement of tropical crop genetic resources utilization through the development of database, technologies and research networking (Tropical crop genetic resources)"
KAKENHI Grants Nos. JP19H00937、JP23H02180

Authors

KUNIYOSHI Daichi and KISHIMA Yuji

Paper Title

Fertile interspecific diploid hybrids between the Asian and African rice species facilitated by tetraploidization and its reduction

Journal Title

Theoretical and Applied Genetics
DOI: https://doi.org/10.1007/s00122-025-04901-3

JIRCAS (Tsukuba HQ, Ibaraki)
President: KOYAMA Osamu

Program Director:

IIYAMA Miyuki

Research Staff:

KUNIYOSHI Daichi (Researcher, Tropical Agriculture Research Front)

Press Coordinator:

OMORI Keisuke (Head, Information and Public Relations Office)
Press email: koho-jircas@ml.affrc.go.jp

Hokkaido University (Sapporo, Hokkaido)
President: HOUKIN Kiyohiro

Research Staff:

KISHIMA Yuji (Professor, Graduate School of Agriculture)

Press Coordinator:

Hokkaido University Public Relations Division
Press email: jp-press@general.hokudai.ac.jp