Development of cytoplasmic male sterile lines derived from three cytoplasm sources and its use on hybrid rice breeding

Abstract

Hybrid rice is an alternative technology to increase lowland rice productivity. In Indonesia, hybrid rice was developed through three line system that involved three parental lines i.e. cytoplasmic male sterile lines (CMS), maintainer (B) and Restorer (R). CMS as seed parent should have high pollen sterility, be stable, easy to restore, good in agro-morphology and flower behavior, high in combining ability and resistant to pest and diseases. Intensive use of single source of male sterile cytoplasm (i.e. wild abortive or WA) in developing rice hybrids might lead to genetic vulnerability associated with susceptibility to pests and diseases.A series of experiments were conducted to identify new CMS from three cytoplasm sources (WA, Gambiaca and Kalinga) with high pollen sterility, stable and easy to restore. CMS efectivity on seed production and hybrid rice breeding were studied. The results showed that among doubled haploid population,panicle weight had thelargest contribution to grain weight per hill, as shown by high and positive direct effect value (0.7739) and indirect effect value through number of filled grain per panicle (0.6556), therefore the characters could be usedfor selection of good maintainer lines. H36-3-Mb, H36-3-Mc, H36-4-M, H45-3-Da, B1-2-Pb and B2-2-Pb were suitable to be used as new maintainer candidates related to their high number of filled grain and yield. Doubled haploid of B1-1-Mb, B2-1-Db and B2-1-M were resistant to Bacterial Leaf Blight (BLB) strain III. B4-1-Dc line was very resistant (score 0) to BLB strain IV and VIII. Six CMS of wild abortive types, one CMS of Gambiaca and three Kalinga types were bred through successive backcrosses. The three types of CMS lines were semi dwarf and having better flowering characters than the check line. The good flowering behavior of the new CMS lines improved seed set up to 25.90% compared to 2.98% of seed set in IR58025A. The new CMS were more effective and easier in its seed production. Phenotype obstacles such as low panicle exertion and short panicle length were improved through GA3 spraying. It increased the yield of seed. The three types of CMS had spesific combining ability to many restorers and yielded high yielding hybrid combination with good heterosis. The results indicated that the yield of hybrids were controlled by overdominant, dominant x dominantor epistasis gene activity. The best hybrid was derived from WA cytoplasm i.e. BI485A/IR53942 (10.21 t/ha), while the best hybrid derived from Gambiaca cytoplasm was BI625A/SMD11 (9.88 t/ha). BI665A/IR53942 was the best hybrid derived from Kalinga cytoplasm, yielded up to 9.15 t/ha. It can be concluded that new CMS derived from WA, Gambiaca and Kalinga cytoplasm were more efective on seed production and hybrid rice development because of their good flower behaviour, resistance to BLB and good specific combiner with restorers.

Teknologi padi hibrida merupakan salah satu alternatif dalam usaha peningkatan produktivitas padi sawah.Perakitan padi hibrida di Indonesia menggunakan sistem tiga galur yang melibatkan tiga galur tetua yaitu galur mandul jantan (GMJ), galur pelestari (B) dan galur pemulih kesuburan (R).GMJ merupakan kunci utama dalam pengembangan padi hibrida sistem tiga galur, karena berfungsi sebagai seed parent. GMJ yang baik harus memiliki sterilitas polen sempurna, stabil, mudah dipulihkan fertilitasnya, memiliki karakter agromorfologi dan bunga baik, memiliki daya gabung baik dan tahan terhadap satu atau lebih hama penyakit tropis. GMJ yang digunakan di Indonesia masih didominasi oleh GMJ dengan latar belakang sitoplasma wild abortive (WA). Penggunaan satu tipe GMJ dalam area luas dikhawatirkan dapat menimbulkan kerapuhan genetik, sehingga hibrida menjadi lebih rentan terhadap hama, penyakit maupun perubahan lingkungan yang ekstrim. Serangkaian penelitian dilakukan untuk memperoleh GMJ baru dengan tiga sitoplasma berbeda (WA, Gambiaca dan Kalinga) yang memiliki sterilitas polen sempurna, stabil dan mudah dipulihkan. Efektivitas GMJ dalam produksi benih dan perakitan padi hibrida menjadi target berikutnya dalam penelitian ini.