Interspecific Hybridization Of Vegetable Brassica Juncea With B. Nigra And B. Rapa

Vegetable Brassica juncea(AABB,2n=36) originating from Asia is very popular in China. Different types with variations in leaves, roots, stems and shoots are the natural genetic mutants, which are probably controlled by the genes in A-genome chromosomes. In this study, crosses between B. nigra (L.) Koch (2n=16, BB) as male and three types of B. juncea vegetables (B. juncea var. megarrhiza Tsen et Lee, B. juncea var. tsatsai Mao and B. juncea var. gemmifera Lee Lin) were made, and the hybrids are further backcrossed with B. nigra, to dissect the A genome and obtain the B. nigra-B. rapa addition lines, with the purpose of locating the specific phenotypic genes for the mutant roots, stems and shoots, and also providing new knowledge and materials for the evolution and breeding of Brassica crops. The main results were described below:1. In the crosses between B. nigra and three vegetables (B. juncea var. megarrhiza, var. tsatsai and var. gemmifera) as female parents,3223flowers were emasculated and pollinated,378young embryos were rescued on medium,223plantlets regenerated, among which79plants transferred to the field and49true hybrid plants identified. Three combinations produced hybrid plants (designated as F.A B, F.A1B and F.A2B)(2n=26), with the crossability of under3%, and only one hybrid plant for F.A2B,15for F.A B and33for F.A1B.2. The hybrid plants (F.A B, F.A1B and F.A2B) showed strong growth vigor and whole morphology biased to male parent B. nigra, while the roots of F.A B, the stem of F.A1B and the shoots of F.A2B were not enlarged as their vegetable parents. The height of hybrid plants was higher than their female parents, especially for F.A B and F.A1B. The stems of hybrids were thicker than female parent and the stems of F.AB and F.A’B were also thicker than their male parent, but F.A2B was thinner. As the female parent, the hybrid plants were susceptible to aphids and stem rot (Sclerotinia sclerotiorum). Besides, their flowering time was delayed, especially F.A2B flowered after1April (2011) with only the period of10days. The pollen fertility was5%-10%, maximally for F.AB.3. Selfed plants (F2) of F.AB had strong vegetative growth, but had2n=22-23,3to 4chromosomes fewer than F.AB. The roots of F2plants expanded, but different from B. juncea var. megarrhiza. The main stems’ diameter of F2plants was three to four times thicker than F.AB and the stems were fleshy. Their pollen fertility was16%-38%, higher than F.AB(10%).4. Both hybrids between B. rapa and B. juncea var. megarrhiza or var. tsatsai were produced, the hybrid seeds were well developed, with seed-set being up to60%. The plant height of F.BA was about230-240cm, much higher than the female and male parents. Also its main stems’diameter was1-2times thicker than that of female parent and3-5times thicker than male parent. The seed-set of backcrossing (30%-47%) of F.BA with B. rapa was2-4times higher than its selfing (<10%). The F3plants between B. juncea var. megarrhiza and B. rapa still showed vegetative vigor, and had2n=23-25. The roots were obviously expanded and lager than B. juncea var. megarrhiza, but the shape was different from its fleshy roots. The stem parts about10-20cm over the roots were dramatically thickened and the roots were fleshy. Their pollen fertilitywas up to23%-29%.5. Cytogenetic analysis of hybrids from B. juncea var. tsatsai×B. nigra. The labeled DNA of B. nigra was used as probe. In F.A1B, autosyndetic bivalent could be formed in A and B genomes, allosyndetic bivalent appearde between A and B, most of chromosomes from A genome are present ad unvalents. The BBA show abnormal pairing with laggards at anaphase Ⅰ and Ⅱ. At metaphase Ⅰ and Ⅱ,6-11chromosomes segregated ahead of time or lagged.