Potato Progress

Volume 22 Number 6

15 August 2022 

Postharvest Potato Physiology Research Updates from Washington State University

Jacob M. Blauer, Department of Horticulture, Washington State University

The WSU potato postharvest laboratory continues to march forward despite changes and challenges.  In April 2020, Dr. N. Richard (Rick) Knowles retired from the postharvest physiologist position leaving behind a legacy of research excellence.  Dr. Knowles had been in the position since 1999 and had trained ten graduate students while at WSU, partnered with the Northwest Potato Variety Development Program (NPVDP) to develop novel varieties for the marketplace, developed the sprout inhibitor Smartblock®, and produced numerous publications aimed at helping growers improve production and storage quality.  His well-earned retirement left an important void to be filled for research in the industry.  In August of 2020, Rick and his wife (and partner in research), Dr. Lisa Knowles, stepped up from retirement to continue the research critical to the variety development program while WSU conducted a candidate search for a suitable replacement for Rick’s position.  At the same time during 2020, the world was in turmoil with shutdowns and economic disruptions stemming from the COVID-19 outbreak.  This pandemic created disruptions which we are still feeling in today’s supply chain and yet despite this, WSU and the broader potato research group were able to recruit me as a new faculty member to continue research to support hard working growers and processors in the Columbia Basin and Pacific Northwest.

‍WSU maintained this vital research program during the COVID challenges with continued support from the Washington State Potato Commission (WSPC), who worked hard behind the scenes to advocate for structural improvements at WSU.  Their efforts were realized with the announcement in early 2021 that the federal government would sponsor the construction of a new USDA research building where Johnson Hall currently sits on the WSU campus.  Once completed, this building will house the WSU potato research program with new and improved storages, and pilot lab for postharvest and culinary evaluations.  While these facilities are essential to the program, Dr. Mark Pavek and I have invested considerable effort working with administrators to develop temporary solutions for the infra-structure needed to support continued research during the demolition of Johnson Hall and construction of the new building.

‍To achieve research goals during the next 2-4 years of transition between buildings, we partnered with WSU and the WSPC to arrange for temporary facilities on the WSU campus.  The WSPC generously secured and loaned four refrigerated shipping containers to support storage of potato samples at different temperatures through the storage season (see photo).  Additionally, WSU has retrofitted the old honey processing facility to support the potato processing and associated analytical equipment for postharvest evaluations.  As with any transition, there have been challenges, but there has been great support from WSU, WSPC, and other key stakeholders.  With these temporary facilities in place, the Northwest Potato Variety Development Program will continue successfully for years to come.  

‍Photo of refrigerated storage containers for postharvest research provided by the WSPC at WSU.

‍Ongoing Research:

Beyond variety development for the fresh and process industries, the WSU Postharvest program has continued to work towards meaningful research over the past two years.  While there are multiple projects in progress, several notable projects are as follows.

‍First, research to better understand the ideal wound healing timing in Clearwater Russet, Alturas, and Russet Burbank between seed cutting and planting.  While this research is in the second season of evaluation, we observed that allowing between 24-48 hours of wound healing prior to planting results in optimum emergence rates, stand establishment, and maximum yield.  Early indicators suggest this is especially important for Clearwater Russet.  Lab analyses of enzymes involved in the wound healing response demonstrate Clearwater Russet has good wound healing potential, but initial wound response is attenuated when compared to Russet Burbank.  These early data indicate a potential for attenuating disease incidence by allowing additional time for wound healing between seed cutting and planting.

‍Second, tuber maturation at the end of the growing season is a critical time for periderm development (skin set).  A combination of endogenous and exogenous factors influences native periderm development.  Understanding genotypic differences and their associated environmental interactions will potentially improve variety development and grower management practices.  To understand these interactions, we conducted a series of evaluations during the 2021 season and are repeating several evaluations this season.  The first evaluation consisted of hand digs in 2021 to track native periderm development.  Generally, it was found that periderm shear strength begins increasing approximately 71 days after planting (DAP) and continues to increase (approximately 2.5x) over the next 83 days until vine-kill.  Shear strength continues to increase throughout the remainder of the storage interval observed.  Prior greenhouse evidence suggested that soil moisture content could alter the thickness of the periderm in some genotypes (Tyner, et. al., 1997), which might reduce weight loss in storage.  To investigate this hypothesis, available soil moisture (ASM) was altered during the tuber maturation period in the field.  Treatments included green harvest at vine-kill and 60%, 70%, and 80% ASM treatments during tuber maturation.  Tubers were then harvested and observed for postharvest quality and weight loss.  While only preliminary, the first season’s data suggests increased soil moisture at maturation correlates to increased yield by approximately 4%, though this does subject the crop to increased disease risk.  Additionally, increased soil moisture correlated with improved harvest fry color and more fry color uniformity during the storage season, though all treatments produced acceptably light color fries.  Observation of soil temperatures demonstrated increased soil moisture buffered the crop from temperature fluctuations better than the lower moisture treatments, possibly reducing stress which promoted improved fry color.  Postharvest weight loss suggests lower water treatments reduced weight loss in storage compared to the higher soil moisture treatment.  While this data is intriguing, it only represents a single year of observations; we will continue investigations this season.

‍Third, previous research has demonstrated seed tuber heat stress in storage alters the tuber set to size distribution in the subsequent crop (Blauer, et. al., 2013).  Seasonal fluctuations in temperature can alter soil temperature which has been shown to alter yield and the physiological maturity of the tubers at harvest with in-season heat stress reducing postharvest quality (Zommick, et. al. 2014; Herman, et. al., 2017).  Growing a crop during different stress periods over the growing season has the potential to alter physiological maturity thus impacting the relative physiological age of tubers.  It is hypothesized that plants grown from seed tubers with increased heat stress will produce more smaller tubers when compared to seed tubers grown under more favorable conditions the same year in the same location.  To investigate this hypothesis, Shepody and Russet Norkotah potatoes were planted for their early- to mid-maturing phenotype.  Tubers were planted early season, mid-season, and late season and were allowed to grow for 120 DAP before vine-kill and subsequent harvest post tuber maturation.  Soil and ambient temperatures were monitored and harvest yields were obtained.  Harvested potatoes were then stored under standard conditions for seed storage or heat treated at 40°C for 21 days before storage at 4°C the remainder of the season.  Generally, tubers planted early season had lower respiration rates than tubers planted late season.  Additionally, tubers subjected to postharvest heat stress had significantly higher respiration rates than non-heat treated tubers during storage.  Elevated respiration rates suggest advance physiological age which has been demonstrated to increase stem numbers and tuber set the following year (Blauer, et. al., 2013).  Stored potatoes from the 2021 study were then back planted in 2022 and the corresponding phenotype is currently under observation.  The ability to alter seed production growth timing has the potential to improve size distribution for subsequent crop performance the following year depending on end use.

‍While these research projects represent a small number of ongoing projects, they demonstrate the WSU Postharvest program’s intent to continue research with practical applications.  Feedback from growers and processors alike will further support ongoing and future projects to ensure effort is relevant and useful to our stakeholders.  While the broad WSU potato program and the postharvest program has a history of excellence, I hope to continue that legacy in the years to come.  I would like to thank WSU, the WSU potato research team, the Department of Horticulture, the Washington State Potato Commission, the USDA, and the Northwest Potato Research Consortium for their support today and future support of our research initiatives.

‍Literature cited:

Blauer, J.M., L.O. Knowles, & N.R. Knowles. 2013. Evidence that Tuber Respiration is the Pacemaker of Physiological Aging in Seed Potatoes (Solanum tuberosum L.). Journal of Plant Growth Regulation. 32 (4): 708-720.

Herman, D.J., L.O. Knowles, & N.R. Knowles. 2017. Heat stress affects carbohydrate metabolism during cold-induced sweetening of potato (Solanum tuberosum L.). Planta. 245: 563-852.

Tyner, D.N., M.J. Hocart, J.H. Lennard, & D.C. Graham. 1997. Periderm and lenticel characterization in relation to potato cultivar, soil moisture and tuber maturity. Potato Research. 40: 181-190.

Zommick, D.H., L.O. Knowles, M.J. Pavek, & N.R. Knowles. 2014. In-season heat stress compromises postharvest quality and low-temperature sweetening resistance in potato (Solanum tuberosum L.). Planta. 239: 1243-1263.

‍Suggest Topics for the WA/OR Potato Conference General Session

‍January 2023 will be the 14th Washington/Oregon Potato Conference in Kennewick, WA. Each year the general sessions take place throughout the Wednesday and Thursday of conference week. Speakers and topics are selected based on suggestions from industry members, commission employees, and our regional research and extension experts. This month we are seeking topic and speaker suggestions for the 2023 conference. To avoid promoting products or services from some private companies over others, our speakers are almost always from nonprofit industry groups, universities, USDA, and state agencies. Only rarely will we host speakers from private companies in the general session. A few years ago the conference board initiated the "Industry Innovation Session" at the conference, which is the venue for private companies to talk about their technological advances.

‍If you would like to suggest a topic or speaker for the conference general session, please email your idea to Andy Jensen (ajensen@potatoes.com) by September 1st. 

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