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Research Helps Produce Elongated Grapes

February 18, 2009

Round, oblong, and in-between: the shapes of the fruits we eat are not always coincidental or, for that matter, thanks to nature. Before fruit arrives in local groceries, a lot of time and effort may have gone into creating the varieties found in the produce section.

In the mid-1960s, Dr. James N. Moore of the University of Arkansas began a grape breeding program, working toward developing varieties with elongated shapes. Now, 40 years later, Dr. John R. Clark continues this effort. One of these unique-shaped developments has been researched further, first to characterize the shape variation, with subsequent work to find genetic markers that could help breeders produce elongated grapes without waiting years to see the actual fruit on the vine.

Classifying fruit as elongated or other shapes can be challenging, as visual observations can be highly subjective and ratings often variable among observers.

Recently, a digital method for analyzing shapes has been used for tomatoes, but this method requires each fruit to be cut in half and scanned to take the measurements, making the fruit unusable for additional studies or for eating.

Another digital analysis method, called SigmaScan®, is in use at the University of Arkansas’ turfgrass science program. SigmaScan® selects colors within a given range of a photograph to analyze turf quality mechanically, eliminating human error.

The university’s fruit breeding program borrowed this technology for a study of grape shapes led by Clark and graduate student Andrew P. Wycislo. The study, published in the American Society for Horticultural Science journal HortScience, began with digital photos of grapes developed specifically for the project. The seedlings exhibited wide variation of shape””from round to very elongated. Using a special application of the SigmaScan® technology that measures the area of the grape by differentiating it from the background color, calculations were made about the shape of each grape. Every grape was also manually rated based on elongation.

“Visual inspection supported the SigmaScan® analysis,” reported the researchers.

The grapes used for the study were frozen at the time of harvest and did not need to be thawed or cut to be photographed. Ten grapes were photographed at one time, but more grapes could be shot and studied in a single photo in the future to further the speed of study. In this way, SigmaScan® improves efficiency, and because the fruit is still intact, it can also be used for additional studies or consumption.

This method has potential for future breeders by helping them to select grapes based on degree of elongation, and can also be applied to studies of other fruits. Although none of the elongated grapes have been released for public use as yet, it is hoped that in the future these new and unique grapes will be an addition to the expanding fresh fruit profile for American consumers.

Image Caption: Digital analysis is used to characterize the shapes of grapes. Credit: Photo by John R. Clark

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