| Cabbage (Brassica oleracea L. var. capitata L.) is an important vegetable crop of Cruciferous crops and is cultivated world-wide. It occupies an important position in vegetable production in China. In cabbage production, premature bolting occurred from time to time is the important issues that need to be addressed in the spring vegetable production. The most cost-effective solution to solve this problem is to develop bolting-resistant varieties and germplasms. Research on genetics and gene mapping helps to choose the appropriate breeding methods to select the target trait directionaly, to improve breeding efficiency and speed up the breeding process. This topic of genetics, physiology and related gene marker location on bolting time and flowering time was studied using different bolting-resistant cabbage inbred lines. Major conclusions are as follows:1. Analysis of major genes plus polygenes genetic segregation results show that the genetics of bolting time was controlled by two major gene and modified by polygenes; two major genes explained above 86% genetic variation, and 68%-88% of phenotype variation in segregation population. It showed that major genes played a decisive role of characteristics of the time of bolting. The bolting time character is a quantitative trait controlled by multiple genes. There is a most effective major gene, so the single cross or back cross can be used in breeding for premature bolting tolerance.2. Analysis of major genes plus polygenes genetic model segregation results showed that the genetics of flowering time was controlled by a pair of major genes modified by polygenes; major genes explained above 83% of genetic variation, and 44%-58% of phenotype variation in segregation population. It indicated that major genes played a decisive role in the characterization of flowering time. The flowering time and bolting time are simultaneously initiated. The same breeding technique could be used in cabbage variety development and selection.3. Six inbred lines from the cabbage breeding group of the Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, was used in analyzing the combining ability and heritability of bolting time and flowering time by Griffing complete diallel crossingâ…£, the results showed that the general combining ability of inbred lines 05521-2 and 04M9-2 was desirable, which can be used as bolting-resistant parental materials; the broad heritability ability and the narrow heritability of bolting time and flowering time separately are 92.6%, 50.04% and 92.09%, 67.28%, and mainly affected by additive genes. So, the selection of bolting and flowering characters in cabbage were effective in early generations.4. A F2 generation population derived from F1 self-cross from crosses between cabbage varieties was used for constructing a genetic linkage map of SSR and AFLP molecular markers. The map included 13 linkage groups with 113 markers (including 81 SSR markers, 31 AFLP markers and one CAPS marker), the length of each linkage group was 11 cM-146.6 cM, It covered a total length of 677.7 cM with an average interval distance for 6.0 cM, and including 3-19 molecular markers for each linkage group. The molecular marker linkage map could be used QTL location.5. Molecular marker analysis showed four QTL controlling bolting time by IM, single QTL explained 9.8%-18.7% of phenotype variation and 56.2% in total; two QTL showed positive additive effect, the remaining two showed negative additive effect. MQM method mapped one QTL, it explained 18.7% of phenotype variation, the additive effect was 5.4; 08c0954 marker was co-segregated with QTL, QTL was located on less than 10 cM interval and reached a preliminary location. So the markers can be used for MAS of breeding for bolting tolerance.6. Molecular marker analysis of flowering time showed four QTL controlling by IM, single QTL explained 14.5%-19.1% of phenotype variation and 66.2% in total; all four QTL showed positive additive effect. MQM method could map one QTL, it explained 15% phenotype variation, the additive effect was 3.14; 08c0784-2 marker was co-segregated with QTL, QTL was located on less than 1 cM interval and could process fine mapping and gene cloning. So the markers can be used for MAS of breeding for bolting tolerance.7. The process of flower bud differentiation and development was observed based on the growth point of cabbage. Flower bud differentiation of cabbage can be divided into five stages as follows: Stage 1: Vegetative growth stage, characterized by a curved stem apex surrounded by leaf primordia at the basal part; Stage 2: Flower bud initiation, stem apex is widening and surrounded by bract primordia and leaf primordia at the basal part; Stage 3: Flower bud differentiation stage, characterized by floral primordia and bract primordia formation, and more floral and bract primodia are formed; Stage 4: Floral organ differentiation stage, characterized by sepal primordia formation and floral organs formation;Stage 5: Flower bud appearing stage, flower bud is visible without microscope. These characteristics of cabbage flower bud differentiation provide a reference for identifying bolting and flowering time of cabbage indoor.8. The process of cabbage flower bud differentiation of endogenous hormones was determined by ELISA method. The results show that endogenous hormones concentration (low concentration of ABA/ZR and IAA/ZR) was downward trend in stage 3, that helped flower bud to differentiate; higher GA3 concentration promoted bolting. Lower ABA/ZR and IAA/ZR concentration and higher GA3/ZR concentration were beneficial to the completion of flower bud differentiation.The results of this study showed that the inbred lines 05521-2 and 04M9-2 could be used as bolting-resistant varieties directly; GA3 inhibitors could be applied to control bolting in cultivation as a quick solution to prevent premature bolting in the production. However research on the type of growth inhibitor and the concentration should be further studied; the growth inhibitor cost manpower, material and brought damage to the ecological environment, the application of premature bolting varieties was an economic and effective way to solve this issue. This study showed that flowering time and bolting time of cabbage were controlled by major gene, the single cross and back cross breeding methods could be applied in the breeding for the bolting tolerance and QTL could be used as a tool to assist the breeding. It could improve the breeding efficiency.
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