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Title: A Heat Unit Model for Predicting Blackberry Flowering Time

item Black, Brent
item Frisby, James
item Lewers, Kimberly
item Takeda, Fumiomi - Fumi

Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2007
Publication Date: 7/19/2007
Citation: Black, B.L., Frisby, J.W., Lewers, K.S., Takeda, F. 2007. A heat unit model for predicting blackberry flowering time. HortScience. Poster 337.

Interpretive Summary:

Technical Abstract: Spring temperature fluctuations are often the cause of crop loss in blackberry. The maximum sensitivity to cold temperatures occurs at or near bloom, when temperatures only a few degrees below freezing will damage the pistils. The ability to predict bloom date and identify genotypes that are consistently late flowering may help reduce the risk of crop loss due to spring frost. Potted plants of 'Navaho' and 'Apache' blackberry were held in cold storage to fulfill their chilling requirement. Chilled plants were then placed in growth chambers maintained at 10, 15, 20, 25, 30 or 35C, and flowering dates were recorded. Trend analysis indicated that the optimum temperature (fewest days to flowering) was between 25 and 30C. In a separate experiment, a collection of 120 blackberry and raspberry-blackberry hybrid genotypes was established in 2000 at the Henry A. Wallace Beltsville Agricultural Research Center in Beltsville, Maryland. Flowering dates were observed each spring from 2002 to 2005, and weather data were collected at a nearby automated weather station. Using these weather and bloom date records, linear and curvilinear heat unit models with a range of minimum, optimum and maximum temperatures were compared to find the model with the minimum error variance. The best fit for the field data was an asymmetric curvilinear model defined by minimum, optimum and maximum temperatures of 6, 28 and 36C. Among named cultivars in the collection, heat units to bloom varied from 7,900 growing degree hours (GDH) for 'Chickasaw' to 17,600 GDH for 'Merton Thornless'.