Studies On Intersubgenomic Heterosis Between Brassica Napus And B.rapa

Brassica napus (AnAnCnCn2n=38), a worldwide important oilseed crop, originated from a few spontaneous interspecfic hybrid plants between B. rapa (AA, 2n=20) and B. oleracea (CC, 2n=18) some centuries ago. In compared with parental B. rapa, B. napus exhibited narrow germplasm due to short history of domestication. Introgression of gene pool from B. rapa into B. napus is an important breeding program. The main purposes of this study were to estimate the triploid intersubgenomic heterosis between B. napus and B. rapa for biomass, to synthesize new formed B. napus (ArArCnCn) by genome manipulation and to estimate the potential of tetroploid intersubgenomic heterosis between synthesized and natural B. napus for seed yield. A pathway of utilization intersubgenomic heterosis was advanced.1 .The hybrids between B. napus and B. rapa exhibited strong heterosis. The hybrids between 6 cultivars (lines) of B. napus and 20 cultivars (lines) of B. rapa were estimated for biomass in the end of flowering stage over two years. It was found that 90% combinations exhibited positive mid-heterosis, and that the superior resulted from the combinations between Chinese B. napus and B. rapa. The analysis of combining ability showed that the gene additive effects weighed none additive effects in contribution to biomass although they both played role to.2. Fifty of the 120 triploid combinations (ArA"Cn) with higher biomass yield were chosen to introduce Ar subgenomic components into B. napus in two ways. Twenty-nine plants of F2 (BC1F2) with high fertility and 38 chromosomes, were gained by extensive phenotypic selecting and cytological screening of large segregating populations. Molecular marker analysis showed that Ar subgenomic component was partially introgressed into synthesized B. napus.90 advantageous lines were screened out by the analysis of quality.3.The new-typed B. napus possessed strong potential of heterosis for yield. One hundred and twenty-nine intersubgenomic hybrids (ArAnC"Cn) were made between the synthesized B. napus and the natural B. napus to test the intersubgenomic heterosis potential in seed yield. Strong intersubgenomic heterosis was observed in seed yield since three quarters of the tested hybrids exceeded the elite cultivar (Zhongyou 821), and one quarter of tested hybrids surpassed the elite commercial hybrid (Huaza 6). In 2002, two combinations which possessed strong heterosis in 2001, still exhibited high potential of seed yield in big plot, with exceeding ckl (Zhongyou 821) and ck2 (Huaza 6)upto 28.6% and 15.1%,respectively.4. The introgression from B. rapa into B. napus can improve the heterosis potential. Four lines of synthesized B. napus were compared with their corresponding parental B. napus cultivars for heterosis potential. Two of them synthesized B. napus lines exhibited good combining performance. The best intersubgenomic hybrid exceeded the corresponding intraspecific hybrid up to 36.6%. The seed yield of intersubgenomic hybrids was positively correlated with their biomass yield and biomass yield of corresponding triploid hybrids as well.5. The intraction between Ar and A" genomes played important role in subgenomicheterosis between new-typed and natural B. napus. A BC1F6 popular ((Huashuang 3 X Tianmen Youcaibai) X Tianmen Youcaibai) were analysized for genetic construction, and the potential subgenomic heterosis among hybrids between them and parental B. napus was anatomied.lt was found that those new-typed B. napus possessed the part genetic matterial of parental B. rapa, and that some new bands were found with the average of 5.1%.The interactions between Ar and A" subgenomes and between Ar and Cn subgenomes both contributed to subgenomic heterosis, and the former weighed the latter.