Characterization of interploid hybrids from crosses between Brassica juncea and B. oleracea and the production of yellow-seeded B. napus

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Abstract
Yellow-seeded Brassica napus was for the first time developed from interspecific crosses using yellow-seeded B. juncea (AABB), yellow-seeded B. oleracea (CC), and black-seeded artificial B. napus (AACC). Three different mating approaches were undertaken to eliminate B-genome chromosomes after trigenomic hexaploids (AABBCC) were generated. Hybrids (AABCC, ABCC) from crosses AABBCC × AACC, AABBCC × CC and ABCC × AACC were advanced by continuous selfing in approach 1, 2 and 3, respectively. To provide more insight into Brassica genome evolution and the cytological basis for B. napus resynthesis in each approach, B-genome chromosome pairing and segregation were intensively analyzed in AABCC and ABCC plants using genomic in situ hybridization methods. The frequencies at which B-genome chromosomes underwent autosyndesis and allosyndesis were generally higher in ABCC than in AABCC plants. The difference was statistically significant for allosyndesis but not autosyndesis. Abnormal distributions of B-genome chromosomes were encountered at anaphase I, including chromosome lagging and precocious sister centromere separation of univalents. These abnormalities were observed at a significantly higher frequency in AABCC than in ABCC plants, which resulted in more rapid B-genome chromosome elimination in the AABCC derivatives. Yellow or yellow-brown seeds were obtained in all approaches, although true-breeding yellow-seeded B. napus was developed only in approaches 2 and 3. The efficiency of the B. napus construction approaches was in the order 1 > 3 > 2 whereas this order was 3 > 2 > 1 with respect to the construction of yellow-seeded B. napus. The results are discussed in relation to Brassica genome evolution and the development and utilization of the yellow-seeded B. napus obtained here.

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