| Broccoli (Brassica oleracea var. Italica) which is a variant of cabbage , belongs to Cruciferae family, Brassica species. Its head is edible . It's a cross-pollinated crop, which possesses heterosis. Quality, disease and insect pest resistance and yield potential are usually improved by the use of F1 hybrid. However the prerequisite is to obtain the genetically stable and pure inbred lines to produce F1 hybrid as soon as possible. Homozygous diploid can be directly obtained by haploid, that can speed up the homozygosis of genotypes and greatly enhance the selection efficiency, and shorten the breeding cycle. Broccoli originated from the Mediterranean, and some European countries have rich germplasm resources. But we have a later start to collect the resource and breeding,and the superior germplasm resources for using are very scarce. For example, only 2 resources are stored in the germplasm library of China. Microspore culture is a very effective way to create new germplasm. Breeding materials with quite different characters from the DH population are important in the use of the hybrid breeding to develop the new varieties. Obtaining of breeding material largely depends on the richness of genetic diversity. At present, the study also focuses on the microspore culture which is how to improve microspore embryo rate and the rate of embryo seedlings, but genetic diversity study evaluation of its potential utilization have not been initiated yet.and evaluated the potential value. So hybrid breeding by Microspore Culture of DH lines is affected to some extent.In this study, the Institute of Vegetables and Flowers CAAS built up two populations, a DH population and a F2 population, which are derived from the same F1. The DH population (includes 176) was isolated microspore culture technology, which include 176 DH lines. DH groups of genetic diversity were studied for 13 agronomic traits, using the markers of EST-SSR and gSSR.The DH population and the F2 population, were compared for their agronomic traits. The main conclusions are as follows:1 For 13 agronomic traits of the DH population, genetic analysis shows that: Most of the agronomic traits are correlated. All the leaf traits are related and the average correlation coefficient is 0.80, the head leaves and pods are not related to other traits. DH group was divided into nine sub-groups, of which the first three sub-groups included 161 DH lines, accounting for 91.48% overall in the cluster from 6.1270. DH group was divided into three clusters by principal component analysis, and cluster analysis was similar. The result of principal component analysis shows that, the first six principal components explained 89.13% of the genetic variation.2 Genetic diversity of DH population was analyzed by using 97 gSSR markers, 550 bands were amplified by 97 pairs of primers, 6.37 bands per primer. Polymorphism ratio was 89.42 % of which 63.25% of primers were seriously segregated. The average expected heterozygosis which was revealed by the gSSR was 0.77. The clustering distance of DH based on gSSR was 0~0.52. In the cluster of 0.3842, the DH group was divided into 8 sub-groups, but the distribution was even.3 Population genetic diversity of Broccoli's DH was analyzed by using 79 EST-SSR molecular markers. 285 bands were amplified by 79 pairs of primers, 3.61 bands per primer. Polymorphism ratio was 85.96 % , of which 69% of primers were seriously segregated. The average expected heterozygosis which was revealed by the EST-SSR was 0.58. The clustering distance of DH based on EST-SSR was 0.04~0.69. In the cluster of 0.5789, the DH population was divided into six sub-groups, but the distribution was uneven.4 The amplification by gSSR was higher than the EST-SSR, however there was little difference between their percentage of polymorphic fragments. There was no significant correlation between the genetic distance and the type and number of markers. It does make no sense to compare the Diversity by different index and groups. In this study, the correlation coefficient between agronomic traits and molecular markers was not high, the correlation coefficient between agronomic traits and EST-SSR markers was 0.12587, between agronomic traits and gSSR was 0.12435, but between EST-SSR markers with gSSR was as high as 0.63861.5 Average value of all traits, the coefficient of variation, the analysis and comparison of segregating interval of DH and F2 populations were studied. The results showed that the 13 major agronomic traits were controlled by multiple quantitative genes. The positive and negative transgress genotypes can be generated in DH population groups and F2. The CVs and genetic diversity index of the same trait were similar between DH and F2 population. |
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