Abstract
Broccoli (Brassica oleracea L. var. italica) is one of the most important vegetable crops cultivated worldwide. The market demand for broccoli is still increasing due to its richness in vitamins, anthocyanins, mineral substances, fiber, secondary metabolites and other nutrients. The famous secondary metabolites, glucosinolates, sulforaphane and selenium have protective effects against cancer. Significant progress has been made in fine-mapping and cloning genes that are responsible for important traits; this progress provides a foundation for marker-assisted selection (MAS) in broccoli breeding. Genetic engineering by the well-developed Agrobacterium tumefaciens-mediated transformation in broccoli has contributed to the improvement of quality; postharvest life; glucosinolate and sulforaphane content; and resistance to insects, pathogens and abiotic stresses. Here, we review recent progress in the genetics and molecular breeding of broccoli. Future perspectives for improving broccoli are also briefly discussed.
Highlights
We review the recent progress on the genetics and molecular breeding of broccoli, focusing on desirable agronomic traits, male sterility, abiotic stress resistance, disease resistance, secondary metabolites and genetic transformation
In the dominant genic male sterility (DGMS)-based breeding system, this marker was used for identifying homozygous DGMS plants from selfing progenies of heterozygous plants as an alternative to test crossing, which requires at least two years and additional labor in tissue culture [61]
Li et al isolated two tryptophan synthase beta subunit (TSB) genes from broccoli and generated overexpression lines of BoTSB1 or BoTSB2 in Arabidopsis, which showed accumulation of tryptophan, indole-3-acetic acid (IAA) and indole glucosinolates; this study provides a target for improving glucosinolates, but no broccoli transgenic plants were generated [147]
Summary
Broccoli production faces challenges of demand to extend plant areas and maintain production security under extreme weather brought by climate change [13,15]. Branham et al constructed a high-density genetic map by genotyping-by-sequencing of a DH broccoli segregating population for heat tolerance and identified five QTLs and one positive epistatic interaction between QHT_C03 and QHT_C05, explaining 62.1% of phenotypic variation [15]. Using a new DH population of broccoli, Branham et al performed whole-genome resequencing of bulked segregants and identified two novel heat tolerance QTLs, of which QHT_C09.2 may explain the negative correlation between maturity and heat tolerance [13]. A heat-stress-related broccoli catalase gene was cloned, and ectopic expression of this gene in Arabidopsis can enhance heat tolerance, but whether it plays a role in maintaining a high-quality head under high temperatures is still unknown [24,25]. Benefiting from improved sequencing techniques and the release of reference genomes, some researchers performed omics-related studies and identified differentially expressed microRNAs/genes and potential pathways involved in heat tolerance [26,27]
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