Analysis Of Root Swelling In Turnip(Brassica Campestris L.ssp.rapifera Matzg.)Using AFLP Markers

Product of turnip in cruciferae is swelling root, which has enriched nourishment and is one of the vegetables liked by many people. The character of root swelling is controlled by polygenes and belongs to quantitative trait inheritance. However, for a long period of time, the research only localized on celluar and dissentional levels because of limited research ways. It hasn抰 reported about its genetic mechanism and molecular research. The F2 cross progeny between turnip (Brassica campestris L. ssp. rap fera Matzg, syn. B. rapa L.) and bird rape (Brassica campestris L.) were used as experimental materials in this study. F2 lines were distributed into large, middle and small pools through bulked segregant analysis. Three pools were screened using 64 AFLP markers and amplified 2903 bands, probably 45 bands per primer combination. Primer combinations E-ACA/M-CAG, E-ACA/M-CTG and E-ACC/M-CAG amplified polymorphic fragments in swelling pool. Only E-ACC/M-CAG amplified a 220-bp fragment linked to root swelling genes with a distance of 14.6 cM through genetic test between parents and F2 progenies. The polymorphic fragment was denominated EM220 and is the first molecular marker linked to root swelling genes. We localized it on linkage group 4 of genetic map. The inheritable mode of this locus carrying EM220 mainly is dominant and additive effects, and may be the major QTL controlling root swelling because 65.2% of the phenotypic variance was explained by this region. Southern hybridization showed that this molecular marker is single copy sequence. Based on the sequence we designed two specific primers and converted it to SCAR markers. Dissecting structure of turnip belongs to radish type. Our result provide molecular evidence for molecular-assistanted selection in breeding programs of root swelling in radish type. Molecular markers linked more closely can be found combining linkage disequilibrium based on the result and related genes may be coloned with map-based cloning. Besides, we also use leaves and roots of turnip in different period for SDS-PAGE. The result showed that the 32th days after seeding is the critical period of root swelling. Related genes may be cloned using cDNA-AFLP or DD-PCR technology. We also can research regular and transcription of root swelling based on the result.