Evaluation of Tendency to Blackspot Bruising and Enzymatic Discoloration of Potato Tubers

Enzymatic discoloration of potato tubers initiated by mechanical impact bruising and the discoloration which appears after tuber cutting are crucial quality traits of the cultivated potato. The presented determination of blackspot bruise susceptibility includes evaluation of the trait with two impact methods - the rotating drum and the falling bolt. These two methods affect both the physical and the biochemical properties of tubers. Evaluation of the discoloration potential after tuber cutting (ED) is also discussed. Evaluating the discoloration potential of tubers is one of the most important points in determining potato quality.

The evaluation method of potato genotype resistance to blackspot bruise

In 2001–2003 a method for the evaluation of potato genotype (genetic resource) resistance to blackspot bruise was verified. Thirty tubers of 25 varieties and hybrids of Solanum tuberosum L. were evaluated using electronic pendulum MIDAS 88P. The analysis of variance showed a significant difference among the individual varieties and hybrids and among years as well. An evaluation scale was established for the assessment of potato genotype (genetic resource) resistance to blackspot bruise. Varieties and hybrids were included in the new designed evaluation scale in scores of 7 (high resistance) up to 9 (very high resistance), which could be regarded as suitable genetic resources in breeding for the improvement of this character. From the evaluated set, the suitable varieties are: Carmona, Agria, Annabelle, Futura, Impala, Adora, Granola and Inova and the suitable hybrids: YP 91-123 and VDW 94-76.

Enhancing Tuber Calcium Concentration May Reduce Incidence of Blackspot Bruise Injury in Potatoes

Our previous research has provided evidence that in-season calcium applications can increase tuber calcium and improve tuber quality with reduced internal defects. To determine if increasing the tuber calcium concentration also mitigates tuber bruise incidence, five commercially relevant potato (Solanum tuberosum L.) cultivars (`Russet Burbank', `Atlantic', `Snowden', `Superior', and `Dark Red Norland') were grown during three seasons, 1999–2001. Three split applications of a calcium/nitrogen water soluble blend totaling 168 kg·ha–1calcium were made starting at hilling. All plots, including controls, received an equal amount of total nitrogen in a season. Tubers were allowed to be bruised during normal machine harvest standard to commercial production in Wisconsin. Over 100 tubers from each replication (5–10 replications/treatment) were cut and examined for the incidences of bruise and internal brown spot. Paired samples of medullary tissue were taken for measuring calcium concentration. As expected, tuber tissue calcium concentration increased significantly, in all cultivars and in all years, with in-season calcium application. Bruise incidence varied among cultivars and seasons. Although tuber calcium concentration varied among seasons, `Atlantic' and 'Snowden' consistently had the lowest calcium concentration, whereas `Superior' and `Dark Red Norland' consistently had the highest calcium concentration. Meta-analysis of pooled data for three years showed that blackspot bruise incidence was significantly reduced with calcium application in `Atlantic', `Burbank', and `Snowden'. On the other hand, `Dark Red Norland' and `Superior' had low incidence of bruise and were unaffected by calcium applications. Regression analyses of pooled data from all cultivars for three years revealed a significant quadratic relationship between blackspot bruise and tuber tissue calcium as well as between blackspot bruise and internal brown spot. A linear to plateau plot of medullary calcium concentration versus blackspot bruise incidence revealed that bruise incidence is minimized between 200 and 250 μg/kg (dry wt)–1 tuber calcium concentration. To our knowledge, ours is the first study providing evidence for reducing bruise by improving tuber calcium. Variations in the bruise incidences among cultivars generally followed tuber calcium concentration suggesting a genetic control. Given the role of calcium in improved membrane health and enhanced wall structure, and as a modulator of physiological responses, it is not surprising that internal brown spot and bruise incidences are reduced by in-season application to calcium-deficient cultivars.