Management of potato tuber water status to reduce bruising

There was significant blackspot bruising in all experiments involving Lady Rosetta. In three out of four seasons, irrigation regime had no effect on bruising at final harvest when the crops were fully senesced. In one season, crops kept fully irrigated throughout the season had more bruising at final harvest than crops kept unwatered. Short or more prolonged periods of water stress increased bruising early in the season compared with maintaining soils with a low soil moisture deficit but this was transitory and once re-hydrated, tubers generally bruised similarly at the end of the season than if they had been maintained closer to hydrated for most of the season by full irrigation. In experiments with Maris Piper, where blackspot bruising was less prevalent than in Lady Rosetta, there was no consistent effect of irrigation regime on bruising at final harvest.

When tuber hydration status was studied over shorter time periods (e.g. 1 week down to every 2 hours), the directional changes in tuber turgor were reflected in similar changes in bruising. However, the magnitude of the change in bruising with changes in turgor varied over time when the period between measurement was greater than weekly. Sampling tuber turgor frequently (every 2 hours) during the day demonstrated that changes approximately equivalent to the range encountered across the season can occur within one day if the evapotranspiration demand is high. Point measurements of tuber water status of an individual crop are unlikely to be able to predict the incidence and severity of blackspot bruising during the season. Dehydration of tubers over a short period of time can increase the risk of bruising considerably.

Mechanically defoliating a crop just prior to the onset of senescence following a period of high evapotranspiration demand caused a significant increase in blackspot bruising compared with crops allowed to senesce naturally and this occurred in all crops, irrespective of the soil moisture deficit at the time of defoliation. There was a smaller, but still significant, effect from defoliating when ground covers had decreased to 50 %. This effect appeared to be totally unrelated to changes in tuber turgor and the differences in bruising were still evident several weeks later.