Induction of apomixis and fixation of heterosis in Egyptian rice Hybrid1 line using colchicine mutagenesis

Abstract

It is known that hybrid rice yields 15–20% over inbred varieties in first generation because of heterosis. However, heterosis is normally broken due to segregation. Applying apomixis produces plants as a clone of mother plant and overcomes the problem of breaking heterosis. In order to fix heterosis in the Egyptian rice Hybrid1, their seeds were mutagenized in 0.2% colchicine for two time periods 24 and 50h. After colchicine mutagenesis, rice seedlings were grown in the field till maturation and the resulted M1 seeds were sown in season 2 and plants were selected based on yield and homogeneity. Then, seeds were sown to be evaluated in season 3. Pollen fertility test, esterase isozyme analysis, and flow cytometry seed screening were performed to confirm the results of field selection of populations identical to control. Pollen fertility examination was performed on the populations of the third season. Pollens of populations 304, 298, 292, 284, 281, 154 and 149 were found to be completely sterile. However, these plants had high seed set percentage. The flow cytometry screening of the six yield-based identical populations and the control seeds showed that populations 220, 339, 351 and 298 have higher nuclear DNA content (C2) than untreated hybrid (C2 & C3). Results of flow cytometry clearly showed that population 298 has one peak (C2) and its endosperm was formed autonomously without fertilization. Although its pollen grains were sterile, it showed high seed set percentage. This indicates that heterosis was completely fixed by apomixis in this population.