Polyploidization is the evolution trend of many crops, and the yield increased obviously after polyploidization. The polyploidization of rice often brings "gigas" of both vegetative organs and seeds. Howevere, in rice breeding, it is required for restoring lines to have not only big anthers but also abundant pollens. People often doubt that the enlargement of the floral organ may just be enlargement of cell size in polyploid rice. So, it is of significance to study characteristics of floral organs and pollens of several tetraploid rice varieties or lines. Floral organ and pollen characteristics of Sg99012 and HN2026 were studied comparatively by stages and different ploidy levels, with the materials 9311, HD9802S, and PA64S as the control. The results showed that chromosome doubling had much more influence on floral characteristics of every lines than seeding by stages, and the tetraploids of every lines displayed "gigas". In correlation analysis, spikelet length, spikelet width, and anther length had significant correlation; spikelet width and anther width had significant correlation, too. Both seeding by stages and chromosome doubling made the correlations of characters between every floral organ changed to some extent. Seeding by stages had little effect on pollen diameter and fertility of HN2026-4X and Sg99012-4X. But chromosome doubling increased pollen size of every lines remarkably, and also increased the pollen quantity of PMeS (polyploid meiosis stability) restoring line HN2026-4X and gene map restoring line 9311-4X remarkably, whereas only had little effect on that of sterile lines. Moreover, chromosome doubling changed pollen fertility and made the number of fertility pollen of 9311 reduced significantly, but the pollen fertility of HN2026 (PMeS restoring line) and PA64S (sterile line) almost had no change after chromosome doubling. The results showed that tetraploid restoring lines had advantage of abundant and big size pollens, and tetraploid sterile lines had the characters of big size pollens, few
LIU Jian-xinCHEN Jian-guoCHEN Dong-lingSONG Zhao-jianDAI Bing-chengCAI De-tian
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 poly- ploid lines, PMeS-1 and PMeS-2 with Polyploid Meiosis Stability (PMeS) genes were bred. The proce- dure 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 be- haviors 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 bi- valents and quarivalents nearly without over-quarivalent in prophase, nearly without lagging chromo- somes 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.
CAI DeTian1, 2, CHEN JianGuo1, CHEN DongLing1, DAI BingCheng1, ZHANG Wei1, SONG ZhaoJian1, YANG ZhiFan1, DU ChaoQun1, TANG ZhiQiang1, HE YuChi1, ZHANG DaoSheng1, HE GuangCun2 & ZHU YingGuo2 1 College of Life Science, Hubei University, Wuhan 430062, China
