Hybrid incompatibility in F 1 hybrids or later generations is often observed as sterility or inviability. This incompatibility acts as postzygotic reproductive isolation, which results in the irreversible divergence of species. Here, we show that the reciprocal loss of duplicated genes encoding mitochondrial ribosomal protein L27 causes hybrid pollen sterility in F 1 hybrids of the cultivated rice Oryza sativa and its wild relative O. glumaepatula. Functional analysis revealed that this gene is essential for the later stage of pollen development, and distribution analysis suggests that the gene duplication occurred before the divergence of the AA genome species. On the basis of these results, we discuss the possible contribution of the "founder effect" in establishing this reproductive barrier.

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ABSTRAK Potensi Pemuliaan Mutasi untuk Perbaikan Varietas Padi Lokal Indonesia.Padi (Oryza sativa L.) merupakan tanaman sereal penting dalam memenuhi kebutuhan nutrisi manusia. Padi terbagi kedalam dua sub-spesies yaitu Indika dan Japonika. Sub-spesies Japonika terdiri dari Temprate dan Tropical Japonika (disebut dengan Javanika). Sebagian besar Javanika berasal dari Indonesia yaitu sebagai varietas lokal dengan jumlah lebih dari 8000 varietas. Tulisan ini bertujuan untuk membahas potensi pemuliaan mutasi, keberhasilan dan kegiatan yang sedang berjalan untuk perbaikan genetik varietas padi lokal Indonesia. Secara alami varietas lokal telah teruji ketahanannya terhadap berbagai cekaman biotik dan abiotik sehingga merupakan kumpulan sumberdaya genetik yang sangat bermanfaat. Varietas lokal biasanya beradaptasi baik pada daerah asalnya dengan rasa nasi dan aroma sesuai selera masyarakat setempat. Namun demikian padi lokal memiliki kekurangan seperti umur dalam, batang tinggi sehingga mudah rebah, tidak responsif terhadap pemupukan dan produksi rendah. Pengadaan benih biasanya dilakukan dengan menyisihkan dari hasil panen petani sendiri sehingga mutu benih, terutama tingkat kemurniannya sangat rendah. Perbaikan mutu benih diupayakan melalui pemurnian dan pelepasan varietas. Bahkan beberapa varietas diperbaiki terlebih dahulu melalui pemuliaan mutasi radiasi sebelum dilepas, seperti varietas Pandan Putri yang lebih genjah dibandingkan varietas asalnya Pandan Wangi dari Kabupaten Cianjur. Keberhasilan memperbaiki varietas Pandan Wangi telah memicu Pemerintah Daerah lainnya untuk ikut memperbaiki sifat-sifat agronomis padi lokal mereka melalui teknologi nuklir, karena diyakini pemuliaan mutasi radiasi mampu memperbaiki kelemahan varietas padi lokal tanpa merubah sifat lain yang disukai. Kata Kunci : Pemuliaan mutasi, varietas padi lokal, Indonesia ABSTRACT Potential of Mutation Breeding in Improving Indonesian Local Rice Varieties.Rice (Oryza sativa L.) is an important cereal crops for human nutrition, this spesies can be divided into sub-species i.e. Indica and Japonica. Japonica sub-species consists of Temprate and Tropical Japonica (it is called as Javanica) groups. Mostly Javanica group originated from Indonesia, the people mentioned as Indonesian local varieties, it was covering more than 8000 varieties. This paper aims is to discuss the potential of mutation breeding, success stories and on going activities improved genetically the selocal rice varieties. Indonesian local varieties have been tested naturally for resistance to biotic and abiotic stresses so that they become useful collections of genetic resources. They usually adapted well toa specific environment where they grow largely, having good aroma and eating quality, but they have some weakness such very long growth duration, susceptible to lodging, unresponsive to fertilizer, and low yield. Seed multiplication is usually conducted by collecting seeds from farmer's fields so that the seed quality, especially for seeds purity levelis very low. Improvements...

The development of rice genotype is vital to guarantee food security to cope with global climate changes and increasing population growth. Biodiversity is spread throughout the Indonesian archipelago. Many Indonesian local varieties are resistant to biotic and abiotic stresses that may be useful for rice breeding program. They are well-adapted to specific environment and have good aroma and eating quality, but have some weaknesses, such as late maturity, susceptible to lodging, unresponsive to fertilizer and low yield. Induced mutation breeding is useful for increasing genetic variability to develop genotypes with several interesting agronomical characters and yield. Center for Isotope and Radiation Application, National Nuclear Energy Agency (CIRA-NNEA) has been conducting the induced mutation technique for genetic improvement of rice. Pandan Putri, an early maturing mutant variety that was derived from irradiated Pandan Wangi variety from Cianjur area, is one of successful improvements of traditional rice varieties using mutation technique. The other success stories are described in this paper. It is concluded that nuclear technology can be applied for induced mutation breeding to improve several agronomical traits.

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