MN Fruit & Vegetable IPM News - Vol. 2, No. 15

At the St. Paul Farmers Market recently, I saw ‘Honeycrisp’ apples being sold for $1.50 apiece or $5 for a quarter peck. Anyone who has eaten a ‘Honeycrisp’ apple knows that it usually lives up to its name. The fruit is crispy and makes an audible “crunch” sound when bitten into. This distinctive texture, along with the fruit’s sweetness and rarity are what brings the high prices. The local supply is still lower than the demand for ‘Honeycrisp’, so most growers near the Twin Cities sell their stock quickly and don’t have to store them for very long. If you did store ‘Honeycrisp’ fruit under refrigeration, however, you’d find out that the apples stay crisp for months after harvest. The ability of ‘Honeycrisp’ to maintain its crispness after months of cold storage is the subject of research in our laboratory.

The first thing we did was determine if we could find objective measurements of “crispness”. Normally, when testing different varieties of apples, we ask people to bite into pieces of apple fruit and rate them on a scale of 1 to 15 for crispness. This takes a lot of time, and after several months of storage many apple varieties get soft, so we have to PAY people to taste the apples, or they’ll stop talking to us. Finding a machine to measure crispness saves us money and friends. We found that we could take cylindrical cores of flesh from the equator of the fruit, put the cylinders on vertical supports (like miniature gymnasts’ parallel bars), and break the cylinders with a probe that comes down perpendicular to the cylinders at a controlled speed. We record the force and time it takes to break the cylinders. The force multiplied by the time equals the amount of work it takes to break a cylinder. We found that work values are highly correlated to whether or not apple varieties were judged by people to maintain crispness, meaning that we can now measure work needed to break cylinders and not torture people with mealy apples.

Now that we have an objective measurement of crispness maintenance, we can use this to test many different apple varieties, including ‘Honeycrisp’ offspring. David Bedford and Jim Luby, apple breeders at the University of Minnesota, have crossed ‘Honeycrisp’ with a lot of different apple varieties. These crosses have now started to produce fruit, so we will be testing the fruit of some of these crosses to see if the presence of certain genes correlate well with crispness maintenance. So far, we’ve found that some ‘Honeycrisp’ offspring do produce fruit that stay crisp after months of cold storage, but most do not. Whether or not those that do produce fruit that stay crisp will do so year after year is another question that needs to be answered.

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jeanne Ciborowski, 651-297-3217, jeanne.ciborowski@state.mn.us , MDA, 90 W. Plato Blvd., St. Paul, MN 55107-2094. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: www.mda.state.mn.us/biocon/fruitreports/

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA). These institutions are equal opportunity providers.

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