Polyploidization is a basic feature of plant evolution. Nearly all of the main food, cotton and oil crops are polyploid. When ploidy levels increase, yields double; this phenomenon suggested a new strategy of rice breeding that utilizes wide crosses and polyploidization dual advantages to breed super rice. Because low seed set rates in polyploid rice usually makes it difficult to breed, the selection of Ph-liked gene lines was emphasized. After progenies of indica-japonica were identified and selected, two polyploid lines, PMeS-1 and PMeS-2 with Polyploid Meiosis Stability (PMeS) genes were bred. The procedure included seven steps: selecting parents, crossing or multiple crossing, back-crossing, doubling chromosomes, identifying the polyploid, and choosing plants with high seed set rates that can breed themselves into stable lines. The characteristics of PMeS were determined by observing meiotic behaviors and by cross-identification of seed sets. PMeS-1 and PMeS-2, (japonica rice), have several characteristics different from other polyploid rice lines, including a higher rate of seed set (more than 65%, increasing to more than 70% in their F1 offspring); and stable meiotic behaviors (pairing with bivalents and quarivalents nearly without over-quarivalent in prophase, nearly without lagging chromosomes in metaphase and without micronuclei in anaphase and telophase). The latter was obviously different from control polyploid line Dure-4X, which displayed abnormal meiotic behaviors including a higher rate of multivalents, univalents and trivalents in prophase, lagging chromosomes in metaphase and micronuclei in anaphase and telophase. There were also three differences of the breeding method between PMeS lines and normal diploid lines: chromosomes doubling, polyploidism identifying and higher seed set testing. The selection of PMeS lines is the first step in polyploid rice breeding; their use will advance the progress of polyploid rice breeding, which will in turn offer a new way to breed super rice.

Oryza punctata, a wild relative of cultivated rice, belongs to the BB genome of Oryza. Interspecific hybrids (CW008, AB) between Oryza sativa (2n = 24 AA) and O. punctata (2n = 24 BB) were obtained using embryo rescue technique. Synthetic allopolyploid (DCW008, AABB) were produced through chromosome doubling by colchicine. Hybrids overcame many wild traits except the shattering and awn. The synthetic amphiploid plants showed obvious superiority in growth and production. Interspecific hybrids CW008 were completely infertile but DCW008 had better seed set after selfing. Genomic in situ hybridization investigations were performed on DCW008. The result indicated that the A genome was closed to the B genome and translocations occurred between some chromosomes of cultivated and wild rice. Meiosis was nearly normal in the amphiploid hybrid but was disrupted in the diploid hybrid, which resulted in different fertility of them.

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