| Abstract | The potato crop is one of the four most important food crops. Since it is a cross-fertilizing, highly heterozygous, and vegetatively-propagated tetraploid species, genetic improvements through traditional breeding are slow, expensive and relatively imprecise. Also, the genetic base in existing cultivars is narrow, making them difficult to use for genetic and genomic analyses. After-cooking darkening (ACD) and enzymatic browning are the major tuber quality defects for both tablestock and processing. This study examined two candidate genes encoding cinnamic acid 4-hydroxylase (C4H) and polyphenol oxidase (PPO), and their functions in relation to ACD. The gene encoding C4H was first cloned from the processing cultivar 'Russet Burbank'. Its gene expression level was shown to be positively related to ACD in a variety of diploid and tetraploid samples tested. Through QTL mapping analysis, we confirmed that the c4h gene, located on chromosome 6, was in one of four QTL regions identified for ACD. PPO is well-known for its involvement in enzymatic browning. This protein was identified through our comparative proteomics study, based on its significant correlation to ACD in a diploid population. This relationship was further examined by real-time qRT-PCR in a larger genetic mapping population. A SNP marker was designed in the coding region of the ppo gene and the association mapping was successfully completed. We believe these two genes are effective candidate markers for breeding for both low ACD and enzymatic browning varieties in potatoes. |
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