Abstract
BackgroundHeterosis or hybrid vigour is a phenomenon in which hybrid progeny exhibit superior performance compared to their parental inbred lines. Most commercial Chinese cabbage cultivars are F1 hybrids and their level of hybrid vigour is of critical importance and is a key selection criterion in the breeding system.ResultsWe have characterized the heterotic phenotype of one F1 hybrid cultivar of Chinese cabbage and its parental lines from early- to late-developmental stages of the plants. Hybrid cotyledons are larger than those of the parents at 4 days after sowing and biomass in the hybrid, determined by the fresh weight of leaves, is greater than that of the larger parent line by approximately 20 % at 14 days after sowing. The final yield of the hybrid harvested at 63 days after sowing is 25 % greater than the yield of the better parent. The larger leaves of the hybrid are a consequence of increased cell size and number of the photosynthetic palisade mesophyll cells and other leaf cells. The accumulation of plant hormones in the F1 was within the range of the parental levels at both 2 and 10 days after sowing. Two days after sowing, the expression levels of chloroplast-targeted genes in the cotyledon cells were upregulated in the F1 hybrid relative to their mid parent values. Shutdown of chlorophyll biosynthesis in the cotyledon by norflurazon prevented the increased leaf area in the F1 hybrid.ConclusionsIn the cotyledons of F1 hybrids, chloroplast-targeted genes were upregulated at 2 days after sowing. The increased activity levels of this group of genes suggested that their differential transcription levels could be important for establishing early heterosis but the increased transcription levels were transient. Inhibition of the photosynthetic process in the cotyledon reduced heterosis in later seedling stages. These observations suggest early developmental events in the germinating seedling of the hybrid may be important for later developmental vigour and yield advantage.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0734-3) contains supplementary material, which is available to authorized users.
Highlights
Heterosis or hybrid vigour is a phenomenon in which hybrid progeny exhibit superior performance compared to their parental inbred lines
Hybrid vigour or heterosis refers to the superior performance of hybrid progeny relative to their parents, and this phenomenon is important in the production of many crops and vegetables
We found that increased production of photosynthesis in the first week after germination is critical for heterosis and that upregulation of chloroplast-targeted genes at 2 days after sowing (DAS) might contribute to this process
Summary
Heterosis or hybrid vigour is a phenomenon in which hybrid progeny exhibit superior performance compared to their parental inbred lines. Most commercial Chinese cabbage cultivars are F1 hybrids and their level of hybrid vigour is of critical importance and is a key selection criterion in the breeding system. Hybrid vigour or heterosis refers to the superior performance of hybrid progeny relative to their parents, and this phenomenon is important in the production of many crops and vegetables. The genus Brassica includes important vegetables (Brassica rapa L. and Brassica oleracea L.) and oilseed crops (Brassica napus L.), and is related to A. thaliana. B. rapa vegetables such as Chinese cabbage Most cultivars of B. rapa are self-incompatible, preventing self-fertilization, some oilseed cultivars In Japan, most B. rapa commercial varieties are F1 hybrid cultivars which have increased yields relative to their parents. Self-incompatibility or cytoplasmic male sterility is utilized in producing the F1 hybrid seeds [14]
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