Inheritance And Cytological Studies On A New Type Of CMS In Brassica Rapa L.

Brassica rapa L., originated in China, is one of the most important oil crops in China.Heterosis is an important approach to improve yield and quality of rapeseed. Cytoplasmicmale sterility is an effective pollination control system in breeding hybrid B. rapa.Thediscovery and characterization of new male sterile sources is the basic work for utilizationof heterosis breeding. Our group has discovered several male sterile plants in a B. rapaaccession0A193collected from Binxian, Shaanxi province in2011. In the presentinvestigation anther development of the male sterile accession was studied bymicrostructure observation. The inheritance of this male sterile accession was investigatedby observing segregation ratios of male sterile plants to male fertile plants in F1, F2and BC1population derived from this male sterile accession with its restorers, and by one stepmultiple PCR and gene cloning techniques. Finally, its thermo-sensitive characters wasinvestigated by the growth chamber experiment and the field growth experiment. The mainresults are as following:(1) The microstructure observation showed that the main abortion stage of the malesterile accession is archesporial cell differentiation；only cells in a few individual cornerscould differentiate into pollen sacs and eventually produced fertile pollen；In addition, a lotof abnormalities, not reported before, were observed including most abnormally dehiscencepollen sacs, adhesive pollens, no connective, concrescent anthers, multiple connectives.After male fertility of this accession transformed normally, its anther’s development andpollen restored as normally as that of the fertile materials.(2) Fertility investigation of the testcrosses of this male sterile accession with18B.rapa accessions and9B. napus accessions indicated that it has a different maintainingand restoring relationship with Pol CMS. The F1populations between this male sterileaccession and its restorers Binxian Yimen Youcai and Binxian Beiji Youcai were all malefertile, the F2population segregated at a3:1ratio for fertility to sterility, and the BC1population segregated at a1:1ratio for fertility to sterility. These results suggested thatfertility of this male sterile accession was controlled by both cytoplasmic gene and a pair ofgenic recessive genes. (3) Multiple PCR result demonstrated that this male sterile accession could amplify aspecific fragment about1102bp in length, the specific band for Nap CMS gene orf222.Cloning and sequence analysis of this specific fragment indicated that its sequence totallymatched to that of orf222. These results suggested that the fertility of this male sterileaccession is related to male sterile gene orf222.(4) Fertility investigation of this male sterile accession in field and growth chamberexperiment revealed that this male sterile accession is temperature-sensitive and it is sterileunder low temperature, and when temperature increases to a certain high it turns into fertile.The range of fertility sensitivity of this accession is between10℃to15℃. The fertility ofthis male sterile accession is not only affected by a range of certain temperatures but alsodid by the cumulative effect of temperature.