Molecular Marker Analysis Of Chimerism And Cytogenetical Study On Seedlessness Of Hongjiang Cheng

Hongjiang Cheng, originated form Guangdong province, is an excellent local orange cultivar with early mature time, high productivity, and high quality. It is one of the minor orange cultivars that compares favorably with foreign excellent ones and still shows high value in Citrus production. However, Hongjiang Cheng shows chimerism with some important character segregations that affected its competitive strength, especially, the unstable proportion of red fruits and yellow ones. Furthermore, too many seeds also lowered its market value. Though, lines of few seeds were selected through bud mutation, their seedless mechanisms were still unknown which instructs the application of these lines. Thus, it is very meaningful for making further selection and purification of Hongjiang Cheng to make clear the origin and chimeric type of Hongjiang Cheng and study the stability and seedless mechanism of these lines. Furthermore, it is important for the spread of Hongjiang Cheng and the improvement of characteristic Citrus production.In resent years, molecular marker technique progresses so greatly that it was possible to study the origins of chimeras and their chimeric types in DNA level. Meanwhile, cytogenetical method is useful for finding clues of Citrus seedless mechanisms. In this research, different organs and tissues of Hongjiang Cheng and leaves of its possible donor cultivars were studied by RAPD analysis, for the purpose of studying its origin and their chimeric type in DNA level. Meiosis behavior of pollen mother cells (PMC) of 9 seedless lines bred by Zhanjiang Agricultural institute of Guangdong and Guangdong Hongjiang farm was also observed. to find the possible cytogenetical mechanism of their seedlessness. The main results are as follows:1. DNA extracted through CTAB method established by our laboratory has high quality. RAPD method, modified in this research, showed clear bands, low nonspecific amplification and high repeatability. This method fit well the need of RAPD analysis of leaf and fruit samples of Hongjiang Cheng.2. According to the RAPD analysis of Hongjiang Cheng and its possible donor cultivars, it could be concluded that Hongjiang Cheng was an uncompleted periclinal chimera of Xinhui Cheng and Hongju. Chimeral happened in layer LI with genetic variety, while layer LII and layer LIII were originated from Xinhui Cheng. As a result, it is impossble to make purification through pathways already existed.3. Seed number pur fruit of the check æ™®₂ was 17 and that of the 9 seedless lines varies between 2 and 7 while their weighths per fruit and juice sugar concentrations were similar. Out of the 9 seedless lines, K_东1, E_西2, E_西1, D_中1, Q_北1, and K_东2 showed high frequency of chromoses ofabnormal pairing and separation in PMC meiosis, which could subsequently conducted pollar sterility. Thus, it was the major cause of the seedlessness of these lines.4. K *i, E B2> E a i, D +1, Q jti, and K *2 showed higher frequency of chromosal reversion and chromosomal translocation that could be reserved through somatic multiplication. It could be conluded that seedlessness of these 6 lines was easy to stablize. Thus, these lines have high value in further selection and usage.