| Sugarbeet (Beta vulgaris L.) is one of the most important sugar crops in the world.Polygerm varieties of sugarbeet have been forbidded to be grown in developed countriesfor their lower yield. Meanwhile, monogerm hybrids of sugarbeet are widely cultivated.The production of hybrids is mainly based on cytoplasmic male sterile (CMS) lines inheterosis breeding. However, the study and its application of male sterility in sugarbeet inChina greatly lag behind that in other countries. Also, some results of the study oncytoplasmic male sterility in sugarbeet differ from that in other crops and amongresearchers. In the present study, we investigate the morphology, physiology, molecularbiology, genetic diversities and systematic breeding of 2 pairs of monogerm CMS linesand maintainer (O-type) lines of sugarbeet. The results here provide a basis for the studyof the mechanism of cytoplasmic male sterility, such as characteristics and stage of thepollen abortion, physiology and biochemistry during the male sterility development. Weprovided also information of the genetic diversity in sugarbeet which is of high value notonly for the breeding monogerm varieties, but also for germplasm introduction andparent selection of sugarbeet.Results and conclusions1. Studies on morphology and cytology of monogerm CMS lines and its O-type linesof SugarbeetWe compared the development of anthers, pollen and pistil of CMS lines with that ofO-type lines, based on the data of field investigation, optical and electronic microscopicobservation. The results showed that the development of the anther and pollen of CMSlines was abnormal. The callose wall was thick. No Ubisch bodies were observed on thesurface of the tapetum. The pollen became abortive when tapetum was not in contactwith middle layer at tetrad stage, rather than after the tetrad stage as reported previously.Microspore mother cell was clearly vacuolized. There was little difference in themorphology of pistil, ovule and embryo sacs between CMS lines and O-type lines. Insummary, the abortion process of anther and pollen of CMS lines could be divided into 4phases. The results provided a first survey on pistil structure of sugarbeet in China, whichrevealed some news traits.2. Relationships between endogenous hormone contents and cytoplasmic malesterility in Monogerm of SugarbeetThis study was designed to elucidate the relationship between endogenous hormonecontents and cytoplasmic male sterility of sugar beet. Enzyme-linked immunosorbentassays (ELISA) was used to determine indoleacetic acid (IAA), cytokinin, abscisic acid (ABA) and gibberellin (GA3) contents and the ratio of these endogenous hormones toABA respectively. These endogenous hormones were taken from functional leaf and budof two pair of monogerm cytoplasmic male sterile (CMS) lines with significant differentphenotype and O-type line sugar beet during vegetative and reproductive period. Theresults showed that ABA, IAA and GA3 contents in leaves of O-type line weresignificantly higher than those of CMS lines, except DHZR, IPA, ZR, during vegetativeperiod, to the early stage of flower, IAA, ABA, DHZR, ZR, GA3 contents of CMSlines were higher than those of O-type line, except IPA; while in bud IAA, ABA, ZR andGA3 contents of CMS lines were lower than those of O-type line. The regular changes oftheses endogenous hormones contents in organs were found in leaves during vegetativeperiod and at early stage of flower, and in bud during florescence. For the three periods,compared with O-type line, the ratio of IAA, ZR and GA3 to ABA for CMS lines were0.55, 1.43,1.64; 2.66, 1.55, 1.49; 1.14, 1.60, 1.53 times respectively. The changes ofendogenous hormones contents and CMS are closely connected. Differently fromprevious report, in the present study we found the CMS in sugarbeet was related to thedecreased contents ofABA, IAA and GA3 and balances of the hormones.3. Comparison of enzyme activity in CMS lines and O-type lines of Monogerm ofSugarbeetWe measured the activity of ascorbate oxidase (ASO), superoxidedismutase (SOD),peroxidase (POD) and catalase (CAT) in flowers and leaves of monogerm CMS lines andO-type lines during reproductive growth period. The result indicated that decrease inASO and POD and SOD activities affected the occurrence of cytoplasmic male sterilityin sugarbeet. Mean ASO activities in leaves of the O-type lines was 2.62 times higherthan that of MS lines during florescence, 1.19 times higher for mean POD activities inflower bud, and 0.10 times higher for mean SOD activities in flower bud. The CATactivities had no significant difference between CMS lines and O-type lines duringreproductive growth period.4. Analysis of the Genetic Diversity of Different Types of Monogerm of Sugar beetsby SRAP and SSR MarkersSRAP and SSR markers were employed to investigate the genetic diversity of 49 sugarbeet accessions, including monogerm male sterilities and maintainers. A total of 199SRAP bands were amplified. The average ratio of polymorphic SRAP bands was 43.7ï¼….The selected SSR primers yielded 35 bands and the ratio of polymorphism was as high as100ï¼…. Our cluster analysis divided the 49 accessions into A, B, C and D group. Thegenetic diversity was high. The results indicated that sugar beet had a high level ofheterogeneity. There was definite difference between foreign genetic background andnative genetic background, and the varieties in practice exhibit closer relationships andnarrower genetic basis. 5. Study on the yield and resistance of monogerm CMS lines of sugarbeet based onsynchronous improvement, recurrent selection and interaction effect betweengenotype and environment.We used foreign introduced monogerm CMS accessions and domestic polygerm O-typelines to synchronously replace the nuclei of CMS lines and O-type lines. It increased thecontent of sugar by 2ï¼…than that of their parent. The resistance was also increased by 1.5class. Based on that, the recurrent selection and interaction effect between genotype andenvironment were further employed to screen populations. The result showed that theroot yield of test-cross populations and full-sib populations were increased by 14ï¼…and7ï¼…respectively, compared with that of base populations in non-infected areas, 35ï¼…and3ï¼…in infected ones. It implied that the program was an efficient way to improvegermplasm of sugarbeet. |
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