|Stark, Jeff - UNIVERSITY OF IDAHO|
|Thornton, Mike - NATUREMARK INC.|
Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 1999
Publication Date: N/A
Interpretive Summary: Blackspot bruise is a major problem in the fresh market and frozen French fry industry. This study was a two-year survey of Idaho potato fields to determine what factors were the major causes of the blackspot bruise problem. The most consistent factor that could be used to predict blackspot susceptibility was the maturity of the tubers. Potatoes from fields that were "over mature" or mostly dead had a much higher blackspot potential. Low soil moisture at the end of the growing season also increased blackspot sensitivity presumably by partially dehydrating tubers. Tubers with higher solids content were also more susceptible. There did not appear to be a direct relationship between soil fertility and blackspot in the group of fields surveyed.
Technical Abstract: The blackspot bruise potential of Russet Burbank and Ranger Russet in Idaho potato fields was determined by surveying commercial fields during 1993 and 1994. Management factors were monitored to determine what practices were contributing to blackspot susceptibility in addition to mechanical damage. The survey included 17 Russet Burbank and 3 Ranger Russet fields in 1993, and 28 Russet Burbank and 8 Ranger Russet fields in 1994. Blackspot bruise potential was determined at different stages of tuber physiological maturity by collecting samples several weeks prior to normal harvest, immediately before harvest, and after storing sub-samples for several months. Field maturity was the factor most consistently related to blackspot potential both years. In 1994 a multiple regression of 3 independent variables - field maturity index, specific gravity, and percent available soil water at tuber sampling, compared with the blackspot potential as the dependent variable gave a correlation coefficient of r = 0.73 (p = 0.001). The available fertility data indicated no direct relationship between N, P, or K fertilization and blackspot potential. Preharvest samples in late August had lower blackspot potential than harvest samples in mid September, and storage samples in February had the highest susceptibility. There was a consistent increase in blackspot severity when tubers were equilibrated at 4 C compared with 10 C prior to bruising.