ABERDEEN, Idaho — University of Idaho researchers are studying reflections of various light wavelengths off of zebra chip-infected potatoes, seeking to devise a quicker and more precise method of quantifying disease prevalence.
Zebra chip — caused by the Liberibacter bacterium and spread by tiny, winged insects called potato psyllids — creates bands in tuber flesh that darken during frying. The disease first surfaced in the Northwest in 2011.
UI Extension entomologist Arash Rashed explained processors have been slicing random samples from truckloads of potatoes to check for zebra chip. Spuds are subjectively scored from zero, representing no signs of infection, to 3 based on zebra chip severity.
Rashed said the approach is far from foolproof and can sometimes result in the rejection of spuds that would meet quality specifications, or the acceptance of tubers with latent infections that exhibit poor quality in processing.
For the past two months, Rashed and his collaborators have been using a spectrometer — a device that records signatures of reflected light wavelengths — to evaluate infected tubers from other UI zebra chip experiments for comparison with healthy tubers. Xi Liang, a UI cropping systems agronomist, is assisting with spectrometer analysis, and Zhiguo Zhao, a visiting scientist from China, is developing a computer model, based on the data, to predict the progression of zebra chip infection without frying.
“In research, I can see giving a more meaningful measure of disease,” Rashed said. “For industry, the short-term benefit is to predict quality loss after storage and processing based on tubers that are just harvested.”
Rashed said Zhao’s software should also enable the industry to estimate the growth stage in which infections occurred and predict the further development of zebra chip symptoms in storage.
Rashed said the research has been funded mostly from his general laboratory budget, and he hopes to have initial results in October to justify a larger grant. He anticipates working with UI Extension storage specialist Nora Olsen on storage trials using Zhao’s model. Sean Prager, with the University of Saskatchewan, Rodney Cooper, a research entomologist with USDA’s Agricultural Research Service in Wapato, Wash., and Rashed’s Ph.D. student, Karin Cruzado, have also been involved in the research.
Cooper trained Rashed’s team to use infrared imaging equipment. The researchers hope thermal infrared signatures will also enable them to detect zebra chip in uncut tubers.
“It looks like it’s going to be really promising technology to be able to identify diseased tubers in a batch,” Cooper said. “It could be extremely useful to both growers and researchers.”