The progression of internal heat necrosis (IHN) of `Atlantic' potato was studied in seven plantings in two locations (Virginia and New Jersey) over 3 years. The incidence (percentage of tubers with necrosis), severity (rating), and distribution (percentage of 1/8 pieces with necrosis per tuber) of IHN increased with successive harvests, but varied with year and location. Significant but weak linear correlation coefficients were found for the IHN variables of incidence, rating, and distribution with either time in days after planting (DAP), yield, or percentage of tubers >64 mm in diameter. Models were developed using stepwise regression to relate IHN variables with DAP, yield, percentage of large tubers, and various temperature and rainfall measurements. Time (DAP), penalty (DAP to first occurrence of three consecutive days of negative accumulated heat units), and rainfall (1 to 60 DAP) were significant variables in regression models for incidence and rating. While DAP and penalty were significant variables in the regression model for distribution, the variable rainfall was not included in the model. These findings indicate that the potential of IHN in `Atlantic' varies with the growing season, and is influenced by more than one environmental

In `Atlantic' potato (Solanum tuberosum L.) the onset and development of internal heat necrosis (IHN) varied with planting date and location in 1989. Symptoms of IHN (first trace) took fewer days to appear in the later plantings in Virginia and New Jersey. However, the interval from first trace to offgrade was extended in the later plantings. Data from successive harvests in these two locations over the past 4 years were used to develop a two-stage model to predict first trace and offgrade by stepwise regression techniques. The predictive model for first trace included rainfall and variables calculated from a heat-sum model that reflected maximum and minimum air temperatures during tuber initiation and early enlargement. The addition of variables reflecting size distribution and rainfall events at first trace resulted in a strong predictive model for offgrade (R2 = 0.98, Mallow's criterion = 2.97). These models indicate that onset and development of IHN are influenced by environmental stress during more than one stage of growth. A delay in the development of offgrade tubers would be expected in years with a cool, wet spring, fewer tubers >64 mm in diameter at first trace, and more rain events during the 10 days immediately after first trace.