Submitted to: Idaho Winter Commodity School Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 1, 2001
Publication Date: N/A
Interpretive Summary: Internal Blackspot or Blackspot Bruise is a major problem for both the Tablestock and processing industries. Two of the major varieties grown in the Northwest, Russet Burbank and Ranger Russet, are very susceptible to the problem. This presentation outlines the causes of the problem and presents management strategies to reduce the potential for these varieties to develop blackspot. The grower can control to some extent the maturity of the vines in the field and the soil water content at the end of the growing season. Over mature tubers have high levels of the amino acid tyrosine which makes them much more susceptible to blackspot. Dry soils can dehydrate tubers to the point that impacts result in internal bruising. Harvest and handling temperature in also critical, Colder conditions result in more blackspot bruise.
Technical Abstract: The potential for Blackspot Bruise in potato tubers is controlled by a number of environmental conditions. Long, hot, and dry growing seasons, such as 2000, result in physiologically aged tubers and dryer soils during vine maturation. These two factors are the main contributors to increased susceptibility to Blackspot in sensitive varieties such as Russet Burbank and Ranger Russet. Over maturity of the tubers results in high tyrosine levels which in turn can lead to more severe blackening for any given level of impact bruise. Dry soils result in tuber dehydration, particularly at the stem end, leading to more internal tissue disruption for a given force of impact rather than a simple cleavage at the tuber surface. Other factors play an important role as well, larger tubers with higher solids content are more susceptible to both shatter and blackspot Bruise. Cold harvest and handling temperatures, around (40 degrees F) can increase bruise dramatically compared with temperatures above 50 degrees F. Insufficient potassium levels during the growing season can lead to increased sensitivity to blackspot. All of these factors interact to determine the potential of the the potato to react to an impact bruise by developing internal blackspot. Many of these factors can be managed by the grower.