POTATO GENETICS, CYTOGENETICS, DISEASE RESISTANCE, AND PRE-BREEDING UTILIZING WILD AND CULTIVATED SPECIES
Location: Vegetable Crops Research Unit
Title: Have your chip and eat it too!
Submitted to: Common Tater
Publication Type: Trade Journal
Publication Acceptance Date: July 18, 2011
Publication Date: August 1, 2011
Citation: Bethke, P.C., Jiang, J. 2011. Have your chip and eat it too!. Common Tater. 63:26-27.
Potatoes used for chips and fries need to have low contents of reducing sugars in order to have acceptable fry color, yet high sugars are frustratingly common. Part of the reason for this is that high sugars can result from numerous in-field and in-storage events including heat or water stress prior to harvest, immaturity or over maturity of tubers at harvest, improper preconditioning in storage, exposure of tubers to ethylene, senescent sweetening, and storage at too low a temperature. The later is referred to as cold-induced sweetening or low-temperature sweetening. Recent research findings from the Jiang and Bethke labs have demonstrated one way that low sugars can be maintained during storage at temperatures as low as 39°F. Because the same sugars that contribute to dark color formation in chips and fries also contribute to acrylamide formation in finished products, a single approach can be used to address the cold-induced sweetening and acrylamide problems simultaneously.
The approach was to use the RNAi interference techniques to “turn off “the gene for vacuolar acid invertase (see accompanying boxes “How to ‘turn off’ a gene” and “Invertase is the key enzyme in cold-induced sweetening” for additional information). We hypothesized that if activity of the invertase enzyme decreased by a similar amount, then potato tubers might be much less prone to cold-induced sweetening. To test this hypothesis, the Jiang lab made genetically modified lines of several potato cultivars. Katahdin was used for initial studies, and those were followed up with additional research using Snowden, Atlantic, MegaChip and Dakota Pearl. In all cases, when the RNA interference approach was highly successful at turning off the gene for vacuolar acid invertase, the resulting lines showed greatly improved resistance toward cold-induced sweeting. Chips made from tubers stored at 39°F for one to four months were light colored when made from low-invertase lines, but dark colored and unacceptable when made from unmodified checks. Remarkably, we have not observed other differences between these low-invertase lines and the cultivar checks in our greenhouse and early generation field trials. Plant emergence, growth, tuber yield and specific gravity all appear to be comparable to that of the original cultivars.
The initial work with chipping potatoes is being extended in several directions. Low-invertase lines of Russet Burbank are being developed, in part with funding to WPVGA through DATCP and the Specialty Crop Block Grant program. When these lines get into the field, we’ll be able to find out if the low-invertase approach is sufficient to greatly reduce sugar end defects and sugar tips, as well as to allow for storage of tubers for processing at lower temperatures than those currently used. Scientists at other sites have used the RNA interference approach to turn off the two genes that produce the amino acid asparagine. Along with reducing sugars, asparagine contributes to acrylamide formation, and funding from the AFRI ARS State Partnership program will be used to develop low-invertase, low-asparagine lines of Atlantic. We hope that these lines will tell us what the lower limit is for acrylamide in potato chips. The low-invertase lines have demonstrated a clear goal for tubers with improved processing quality, but we are not restricted to using molecular approaches to meeting this goal. It is likely that conventional potato breeding, perhaps in combination with targeted selection using molecular markers, can also be used to generate low-invertase lines. In ongoing work with the Jansky lab we have shown that the low-invertase trait exists in wild species relatives of potato and can be transferred to cultivated potato using conventional crosses.