Construction Of A Molecular Genetic Map And Mapping QTL Controlling Agronomic Traits In Chinese Cabbage (Brassica Campestris L.ssp.pekinensis)

To Chinese cabbage, the most important economic crop, it is more meaningful to construct a molecular genetic map. A population of Fe generation including 102 recombinant inbred lines was derived from the cross of two advanced lines 177 and 276 of cultivated Chinese cabbage (Brassica. campestris L. ssp. pekinensis), using single seed descendant method. In this paper, the AFLP and RAPD markers were employed in constructing a molecular genetic map and mapping QTL controlling heat tolerance and some agronomically important traits in Chinese cabbage.In this RIL population, Distorted segregation is a universal phenomenal, and the frequency of distorted segregation markers was similar for AFLP or RAPD. Out of 492 markers, the number of markers came from male parent and female parent agrees with the Mendel ratio 1:1. To single marker, the frequency of band from two parents was closely, and not deflected to either parent. It could be concluded that no obvious distorted segregation in the population.A molecular genetic map of Chinese cabbage was constructed using AFLP and RAPD markers. 352 markers including 265 AFLP markers and 87 RAPD markers were integrated into 17 linkage groups. It covered a total of 2665.7 cM with an average interval of 7.6 cM. Number of markers in linkage groups varied from 6 to 43, average interval distance from 3.4 cM to 13.0 cM and the total map distance from 20.3 to 400.7cM. A total of 13.92% distorted markers distributed in the map. The molecular genetic map is fundamental for gene localization, comparative genomics, and QTL mapping of agronomically important traits.Composite interval mapping method was employed in mapping and analysis QTL controlling heat tolerance and some important agronomical traits in Chinese cabbage.These results will provide useful information for molecular assistant selection of some important agronomic traits in breeding programmes of Chinese cabbage.Heat damage index in seedlings was used as phenotypic value to detect QTL cntrolling heat tolerane in Chinese cabbage. Five putative QTL were mapped in three linkage groups. Three loci including ht-\, ht-3 and ht-5 showed positive additive effect, while ht-2 and ht-4 showed negative additive effect. Phenotypic variation explained by the putative QTL varied from 7.00% to 18.53%. ht-2 had the highest contribution to heat tolerance, and it may be a major gene locus.Forty-four QTL controlling agronomic traits related to head were mapped on 16 linkage groups. These QTL included three for days to harvesting, three for number of non-wrapper leaves, seven for head length, five for head diameter, eleven for head length /head diameter ratio, four for number of head-forming leaves, seven for head weight and seven for gross weight There was unequal gene effects on the expression of many agronomic traits related to head, and the variation explained ranged from 4.72% to 21.04%.The number, location, variation explained and additive effect of QTL underlying nine morphological traits were also determined. Fifty putative QTL, including five for plant growth habit, six for plant height, five for plant diameter, seven for leaf length, four for leaf width, six for leaf length/leaf width ratio, seven for petiole length, four for petiole width and six for bolting character, were mapped on 14 linkage groups. There was unequal gene effects on the expression of many morphological traits, and the variation explained ranged from 5.17% to 21.50%.