Abstract
Tuber tissue discolorations caused by impact (blackspot bruising) and enzymatic discoloration (ED) after tuber cutting are crucial quality traits of the cultivated potato. To understand the complex genetics of the traits, quantitative trait locus (QTL) analysis using diploid mapping population and diversity array technology (DArT) markers was performed. The phenotypic assessment included the complex evaluation of blackspot bruising susceptibility through two methods: rotating drum (BRD) and falling bolt (BFB) in combination with the evaluation of enzymatic discoloration. Because of observed in-practice relationship between bruising susceptibility and tuber starch content (TSC), analysis of starch content-corrected bruising susceptibility (SCB) was performed. QTLs for bruising were detected on chromosomes I, V with both test methods. The rotating drum method enabled the detection of additional QTLs on chromosomes VIII and XII. Analysis of SCB enabled the identification of the major QTL on chromosome V and two weaker QTLs on chromosomes VIII and XII, independently of starch content. The QTL for bruising detected on chromosome I overlapped with the most significant QTL for tuber starch content. This QTL was not significant for starch content-corrected bruising susceptibility, and the effect of the QTL on chromosome V was enhanced for this trait. The QTL analysis of ED revealed the contribution of seven QTLs for the trait, located on six chromosomes, including these detected for the first time: a major locus on chromosome V and minor QTLs on chromosomes VII and X, which were specific for the trait. The QTL for ED on chromosome VIII was co-localized with the marker for polyphenol oxidase (POT32). The phenotypic correlation between bruising and ED was confirmed in QTL analyses of both traits, and the QTLs detected for these traits overlapped on chromosomes I, V, and VIII. Our results should provide a basis for further studies on candidate genes affecting blackspot bruise susceptibility and enzymatic discoloration.
Highlights
Enzymatic discoloration (ED) and blackspot bruising affect potato tuber quality via the formation of dark pigments from phenolic compounds and the action of polyphenol oxidase (PPO) (Cobb 1999)
The maternal clone DG 06-5 was highly susceptible to bruising with high tuber starch content (TSC)
The genotype × year interaction effects were larger than year effects for bruising susceptibility and enzymatic discoloration, but this trend was not found for starch content
Summary
Enzymatic discoloration (ED) and blackspot bruising affect potato tuber quality via the formation of dark pigments from phenolic compounds and the action of polyphenol oxidase (PPO) (Cobb 1999). The ED that appears after peeling and cutting the tuber leads to undesirable colours and flavour changes and loss of nutritional quality (Vitti et al 2011). Blackspot bruising of potatoes is an internal defect of tubers caused by mechanical impact and is observed only after peeling of the tuber skin and short exposure to the air. Bruising leads to rejection of the crop by consumers and the processing industry, resulting in considerable economic losses (Storey 2007). Potato bruising is estimated to cost the U.S potato industry at least $298 million each year, as deduced from a total
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