Developmental and postharvest physiological phenotypes of engineered potatoes (Solanum tuberosum L.) grown in the Columbia Basin
Introduction
Russet Burbank, Ranger Russet, and Atlantic are important industry-standard cultivars for frozen French fry and chip production in North America (Belyea et al., 2010; NASS, 2013). These cultivars often dominate their respective markets because of superior processing and culinary attributes; however, they also have major weaknesses and are targets for replacement by breeding programs in the United States. One of the primary deficiencies in the three cultivars is their susceptibility to low temperature sweetening (LTS), an accumulation of sucrose and/or reducing sugars at storage temperatures below 8 °C. As Maillard substrates (Maillard, 1916), reducing sugars are responsible for dark, undesirable process color and, in the presence of asparagine, elevated acrylamide in chips and fries (Mottram et al., 2002; Muttucumaru et al., 2014; Rosen et al., 2018). Russet Burbank (frozen processing) is susceptible to bruising, external and internal defects, LTS, stress-related physiological disorders, and various pathogens (Bethke, 2014; Love et al., 2003). Ranger Russet (frozen processing) is highly sensitive to blackspot bruise, LTS, and cannot be stored for long periods because of short dormancy (Love et al., 2003; Pavek et al., 1992; Woodell et al., 2004). Atlantic (chip processing) is also sensitive to environmental stressors, various defects (e.g., internal brown spot), many diseases, and sugar accumulation during storage, rendering it typically a straight-to-process cultivar (Cropwatch (University of Nebraska), 2019; Love et al., 2003; Pavlista and Ojala, 1997).
While breeding programs have successfully developed new cultivars with superior traits, these mainstay cultivars continue to dominate many production areas. This is partly due to the slow pace of adoption by processors and the quick service restaurant (QSR) industry. The Pacific Northwest leads the nation in production of Russet Burbank and Ranger Russet for the frozen French fry process industry (NASS, 2019).
As an alternative to conventional breeding, genetic engineering enables trait improvement for cultivars that already enjoy robust market share. Using genes from wild and domesticated potato, the J.R. Simplot Co. (Boise, ID) used Agrobacterium to transform cvs Russet Burbank, Ranger Russet, and Atlantic for improved traits. The first generation Innate® cultivars, approved for production in 2014, have increased resistance to blackspot bruise and acrylamide formation during frying by virtue of silenced polyphenol oxidase (PPO) and asparagine synthetase, respectively, and silencing of α-1,4 glucan phosphorylase L and α-glucan water dikinase to preserve starch (Clark and Collinge, 2013). The second generation Innate® cultivars (Glaciate, Acclimate, Hibernate) added an R-gene for increased resistance to Late Blight (Phytophthora infestans), along with silenced vacuolar acid invertase to prevent cold-induced reducing sugar buildup (Clark et al., 2014; Pence et al., 2016). The U.S. Environmental Protection Agency approved these Innate® cultivars for commercial production in 2017.
Developing new cultivars entails extensive phenotyping, including evaluation of plant performance and yield potential in major production regions. As a part of this effort, we compared the developmental and postharvest physiological phenotypes of Acclimate, Hibernate (both commercialized in 2017) and Glaciate (not commercialized) to their respective parental cultivars, Ranger Russet, Atlantic, and Russet Burbank. Growth profiling studies were designed to reveal cultivar-dependent differences in the timing of critical growth-stage ‘windows’ (emergence and plant establishment, tuberization, bulking, foliar senescence, tuber maturation), estimate the attainment of tuber physiological maturity (PM), and identify potential consequences of delayed harvest beyond PM for subsequent retention of process quality for each cultivar. Harvest indices (a measure of source/sink relationships) and bulking rates were compared, along with developmental changes in tuber specific gravity, sugars, and free amino acid composition. In addition to PM, differences in the relative concentrations and distributions of Suc and reducing sugars in tubers during bulking and maturation were compared as indicators (Knowles et al., 2015) of propensity to develop physiological disorders such as sugar or translucent (jelly) ends during storage (Thompson et al., 2008), which adversely affect process and nutritional qualities.
The project was conducted in the Columbia Basin of Washington, a region responsible for 65 % of the U.S. fall crop of potatoes (total tonnage basis) (NASS, 2013). Environmental and edaphic conditions in this area are ideal for potato production, resulting in the highest average yield (ca. 70 MT ha−1) of potatoes worldwide. Yields of late-season frozen processing cultivars are even higher in this area, with 75–90 MT ha−1 routinely produced. While these yields remain well below the estimated theoretical yield of 160 MT ha−1 for late season cultivars in this region (Haverkort and Struik, 2015; Kunkel and Campbell, 1987), in-season and postharvest management have been optimized for these late-season cultivars through many decades of production, making the Columbia Basin ideal for phenotyping the Innate® cultivars. The trials reveal how the unique characteristics of Innate® cultivars lead to differences in crop productivity and postharvest quality compared to their parental cultivars.
Section snippets
Summary of trials
Differences in crop growth and development, yield, postharvest physiology, and process quality were evaluated for the potato (Solanum tuberosum L.) cultivars, Russet Burbank, Ranger Russet, and Atlantic, versus their respective Innate®-engineered counterparts, Glaciate, Acclimate, and Hibernate. Crop growth profiling and final yield phenotyping were accomplished in a series of field trials conducted during the 2015–17 growing seasons at the Washington State University (WSU) Irrigated Research
Crop development, tuber carbohydrate, specific gravity, and amino acid profiles
Trends in plant emergence, foliar growth, and tuber growth of cvs Russet Burbank and Glaciate were similar over the 2015 and 2016 growing seasons. Data were thus averaged over years to characterize and compare the developmental phenotypes of each cultivar. Emergence of Glaciate plants was slightly (1–2 days) delayed (P < 0.05) compared with Russet Burbank but both cultivars had reached 94–100% emergence by 32 days after planting (DAP) in both years (data not shown). Seasonal foliar growth
Discussion
We characterized the developmental and postharvest phenotypes of three Innate® potato cultivars in the Columbia Basin of Washington by: (1) modeling foliar and tuber physicochemical development over time and in relation to accumulated degree days from planting, (2) comparing tuber physiological responses to low temperature sweetening and reconditioning during storage, and (3) evaluating how heat stress modulates subsequent cold-induced sweetening and process quality.
Consistent with Pence et al.
CRediT authorship contribution statement
Graham D. Ellis: Methodology, Investigation, Formal analysis, Data curation, Writing - original draft. Lisa O. Knowles: Conceptualization, Methodology, Validation, Investigation, Resources, Writing - review & editing, Supervision. N. Richard Knowles: Conceptualization, Funding acquisition, Methodology, Formal analysis, Supervision, Visualization, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by grants from the USDA ARS Federal-State Partnership Potato Program (2092-21220-001-00D), the USDA National Institute of Food and Agriculture Hatch project (Accession No. 1005995), “Physiological and agronomic studies to maximize the productivity and postharvest quality of new potato cultivars”, and through a sponsored research agreement with the J.R. Simplot Co.
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