Then & Now

Published online: Nov 10, 2021 Articles James Woodhall, University of Idaho
Viewed 513 time(s)
This article appears in the November 2021 issue of Potato Grower

This year, as I received some of the first tubers from the 2021 harvest into the lab for diagnosis, I realized it’s been 20 years since I received my very first potato diagnostic sample, when I was a Ph.D. student studying Rhizoctonia potato disease. After a couple of hours’ reflection (and maybe depression) of wondering how time has flown by, I started to give some thought to how we diagnosed things back then and maybe what things will look like in another 20 years.

What was the world of potato diagnostics like in 2001? I remember using a lot of books, and there seemed to be less expectation of a quick turnaround like there is now. The internet has really changed things: Nowadays there are some great websites like, and I’ve found that the Google image search is a great tool to assist with a diagnosis. It is also so much easier to text or email a photo to an expert now. In 2001 most cameras were still film; I must admit I still miss the excitement of getting your photos back from being developed and seeing them for the first time. Now, I just take a snap with my phone in seconds and usually forget about it.

In 2001, molecular testing was still in its early days. Tests did not exist for all pathogens, and where they did it was largely conventional PCR, which lacks the speed and sensitivity of the tests primarily in use today. Today in my lab, we have real-time PCR tests for over 20 pathogens that can cause tuber blemish diseases. These tests can usually provide a result in just a few hours. DNA sequencing used to take weeks for just a few hundred base pairs; now, whole genomes can be sequenced in hours. Our understanding of pathogens is much greater now. However, this has increased the complexity of the task as new species and strains have been discovered. There is also a lot more scientific literature to keep up with these days.

So what developments can we expect in the next 20 years? We are already seeing a range of non-targeted testing technologies being developed. “Non-targeted” means we are not testing for a pathogen we know, but for everything including the unknowns—which should really help with new discoveries. High-throughput DNA sequencing is already being used in research and will filter down into use as a frontline tool. We are also seeing new methods based on imaging—such as hyperspectral—being used, as well as methods to screen volatiles. Hopefully we will see technologies deployed at an early stage to prevent a problem as opposed to reacting to one. It’s likely these technologies will one day be automated as well, with big data approaches also being used.

What will stay the same, though? Diagnosing potato blemishes will still be a challenge as the interaction between grower practices, various pathogens, varieties and the environment can present a vast array of symptoms. It’s also worth pointing out that testing is not always helpful for tuber blemishes, as sometimes the damage is done in the field long before symptoms are seen on the tuber. (Such is often the case with some Streptomyces and Rhizoctonia blemishes). Because of these challenges, I am confident that even with a range of fancy new toys giving us lots of data, there will always be the need for somebody with the right kind of knowledge to interpret the information.

James Woodhall is an assistant professor and plant pathologist at the University of Idaho’s Parma Research & Extension Center. He can be contacted at