Location: Potato, Pulse and Small Grains Quality Research
2024 Annual Report
Objectives
Objective 1: Resolve the underlying changes in transcriptome and metabolome profiles, and identify regulatory genes, gene-networks and metabolic pathways responsible for wound-healing and tuber sprouting in potato during postharvest storage.
Sub-objective 1.A: Determine the effects of exogenous ethylene treatment on tuber dormancy progression and identify molecular mechanisms regulating dormancy/sprout growth by utilizing integrated transcriptome, phytohormone, and metabolome analyses.
Sub-objective 1.B: Determine the effects of exogenous DMN and CIPC treatment on tuber dormancy progression and identify genes and metabolic pathways regulating dormancy/sprout growth by utilizing integrated transcriptome, phytohormone, and metabolome analyses.
Sub-objective 1.C: Determine changes in transcriptome and metabolome profiles in tuber tissues following mechanical wounding to identify regulatory genes and metabolic pathways involved in periderm development and wound-healing processes.
Objective 2: Evaluate and report the effects of postharvest storage on intrinsic processing quality and nutritional composition of advanced breeding lines in collaboration with public breeding programs, as a USDA-ARS direct mission of research support (non-hypothesis driven).
Sub-objective 2.A: Determine cold storage (< 7°C) potential and processing characteristics of advanced breeding lines.
Sub-objective 2.B: Screen advanced potato breeding lines for vitamin C and anti-quality compounds impacting food end-use.
Approach
Potato (Solanum tuberosum) ranks fourth among major food crops with annual global production exceeding 368 million metric tons (FAOSTATS, 2018). United States potato production exceeds 450 million hundredweight (cwt; USDA-NASS, 2018), of which 400 million cwt (~90%) with an estimated value of over $2 billion, are harvested in the fall. Because postharvest losses through physiological and disease-related processes routinely reach 10-15%, maintenance of postharvest quality is of prime concern to the potato industry. Current management strategies employed to combat these problems are several decades old and do not effectively meet today’s consumer or industry demands to control physiological deteriorations. Moreover, chemistries utilized to manage storage issues are under regulatory scrutiny and may not be available in coming years. Two physiological processes that adversely affect postharvest tuber quality are dormancy/sprouting and wound-healing. Further improvements in postharvest storage technologies are hindered by limited empirical information on biological processes underlying tuber meristem dormancy and wound-healing. Thus, the proposed research project is essential to identify the critical molecular, biochemical, and physiological mechanisms controlling tuber dormancy/sprouting and wound-healing and, ultimately, to manipulate these rate-limiting processes to reduce postharvest deteriorations of potato (Figure 1). Studies will be conducted to achieve the following objectives: (a) investigate effects of exogenous postharvest treatments (i.e., ethylene, 1,4-dimethylnaphthalene, and isopropyl-N-(3-chlorophenyl) carbamate) on tuber dormancy progression and sprouting using distinct cultivars for dormancy characteristics and utilize transcriptome and metabolome profiling to determine changes induced by these treatments, (b) identify the molecular mechanisms associated with mechanical wounding and wound-healing processes by utilizing transcriptome and metabolome profiling, and using a natural elicitor (water soluble chitosan) and distinct cultivars for periderm development and wound-healing characteristics. Equally important to the potato industry is development of superior germplasm for introducing new varieties with proven storage characteristics. Effective evaluation of new clones requires high-throughput screening facilities, specialized equipment, and resources. Therefore, we collaborate with public breeding programs to screen advanced breeding material for the postharvest storage potential, food quality and safety characteristics.
Progress Report
In Fiscal Year 2024, significant progress was made towards Objective 1. Collaborative research with multiple institutions across the U.S. continued, and grant proposals were submitted to attain external funding for complementing the Objective 1. Biological samples collected from the Fiscal Year 2023 research were processed for transcriptome, phytohormone, and metabolome analysis. Biochemical analysis pertaining to oxidative stress regulation, which is a key indicator of tuber dormancy progression and sprouting, were also conducted. For one experiment with continuous ethylene treatment (Sub-objective 1.A) as a sprout suppressor, 136 tuber tissue samples were collected and processed for transcriptome and phytohormone analysis. From a second experiment, which included chlorpropham and dimethylnapthalene as sprout suppressor treatments (Sub-objective 1.B), 99 tuber tissue samples were also processed for transcriptome and phytohormone analysis. RNA sequencing datasets for transcriptome analyses for both experiments were obtained. Currently, data is being analyzed for understanding the underlying mechanisms of sprout suppression involving genes, gene network, and phytohormones. Data from phytohormone analysis of primary bud tissues revealed changes in cytokinin, abscisic acid, jasmonic acid, and salicylic acid content during different dormancy stages and with sprout suppressor treatment. A third experiment with single application of dimethylnapthalene and methyl jasmonate as sprout suppressor treatments (complementing Sub-objective 1.B) was completed and data related to sprout growth, abundance of transcripts for phytohormones, cell-cycle, and dormancy regulation and biochemical analysis for stress responses were analyzed and recently published. Results revealed higher efficacy of methyl jasmonate as a sprout suppressor treatment. In Fiscal Year 2024, partnering with potato stakeholders, potato tubers of agronomically relevant cultivars were obtained and research related to tuber dormancy and sprout growth was conducted under different postharvest storage temperatures. Research related to determination of efficacy of natural elicitor treatments (Sub-objective 1C) to improve potato tuber wound healing was also continued in Fiscal Year 2024. One experiment was conducted with certified seed tubers of two agronomically relevant potato cultivars. Mechanically wounded tuber tissues were treated with different nitric oxide and related chemical treatments; tuber tissue samples were collected at different time points (0, 1, 3, 6, 9 days) after wounding for histological, biochemical, and molecular analysis. Histological and biochemical analysis revealed essential role of nitric oxide in wound healing of potato tubers. External application of nitric oxide was optimized to improve wound healing of potato tubers at postharvest storage. A second study to determine the critical role of abscisic acid in wound healing of potato tuber was also conducted with certified seed tubers of two agronomically relevant potato cultivars. Another experiment to determine potential variability in wound healing responses among different cell layers of potato tubers was also conducted for improving our understanding on impact of different types of wounding on healing of potato tubers and to complement with the Sub-objective 1C. Additionally, biochemical assays were performed for biological tissues collected from Fiscal Year 2023 research, to investigate wound-induced defense responses, specifically to determine critical control points in biochemical pathways that are relevant for wound healing of potato tuber tissues. Data analysis was conducted for biochemical assays, and natural elicitors with higher efficacy to improve tuber wound healing was identified. Agronomically relevant potato cultivars with contrasting wound healing traits (fast and slow healers) were also determined. Research results from natural elicitor experiment and nitric oxide experiment were published in Fiscal Year 2024. Currently, research on impact of healing of cut potato seed tuber pieces before planting on sprout emergence and performance of potato crop is being conducted in the field and under controlled greenhouse environment. This research was initiated to support potato growers’ need to optimize pre-planting practices for improved crop performance by identifying alternative best practices suitable for fluctuating environmental conditions.
Significant progress was made in Objective 2. Cooperative research has been fostered among university breeding programs, USDA-ARS potato breeding programs, and potato industry growers and processing stakeholders. Annual processing quality evaluations were performed throughout storage among advanced breeding clones and new potato varieties representing public breeding programs. Potato clones possessing improved processing quality and cold storage potential were identified (Sub-Objective 2.A). Processing quality of fry and chip clones was assessed among Potatoes USA sponsored National Chip and Fry field and processing trials (Sub-Objective 2.A). Tuber components (glycoalkaloids and acrylamide) impacting food end-use quality were quantified among new potato clones at harvest and throughout storage (Sub-Objective 2.B). This cooperative evaluation process has streamlined the introduction of new potato cultivars with superior processing characteristics in storage, and has been considered gold-standard by the potato industry and stakeholders in the U.S.
Accomplishments
1. Methyl jasmonate is an effective sprout inhibitor of potato tuber during long-term storage. After harvest, the majority of potato tubers are placed in storage for year-round use. As potato tubers age, they develop sprouts and lose their nutritional quality. Commercial storage facilities usually integrate cold storage and sprout inhibitors to prevent premature sprouting. The potato industry in the United States is in need of effective sprout inhibitors as the most commonly used chemical has been under regulatory scrutiny and already banned in several countries. ARS scientists in Fargo, North Dakota, identified methyl jasmonate as an effective sprout inhibitor treatment during long-term storage of potato tubers. The results of the lab assays also elucidated how this chemical regulates sprout growth at the molecular level. Additional research in the future will focus on the optimization of commercial application and potential use of this sprout inhibitor in the potato industry.
2. Natural elicitors improve wound healing of potato tubers. Potato growers face serious challenges due to wounding-related loses of tubers after harvest. Finding safe and effective postharvest strategies to minimize these losses is critical for the potato industry. ARS scientists in Fargo, North Dakota, have optimized two natural elicitor treatments to accelerate wound healing of potato tubers. Several agronomically relevant cultivars were used to determine the impact of these elicitor treatments on their wound healing performances. Results of this study also revealed critical information regarding biochemical regulations of wound healing. The researchers further elucidated the critical role of nitric oxide in wound healing, and optimized a treatment to accelerate the healing response of tubers. Further research will be conducted for potential use of the natural elicitors and nitric oxide to minimize wounding-related postharvest crop losses.
3. Evaluation of potato processing quality in storage among new potato cultivars. Acceptable processing quality after storage is an essential attribute of a successful potato variety. The standardized evaluation procedures developed and used by ARS scientists in East Grand Forks, Minnesota, have been an important component of the overall process evaluation and release of new cultivars by federal and state cooperators nationwide. In the past year, in support of federal and non-federal public breeding/screening programs, 139 advanced breeding lines from 11 public potato breeding programs were analyzed for storage/processing quality at multiple storage temperatures and durations. Data from these analyses will contribute to the release of new potato varieties. These improved varieties offer significant benefits to both producers and processors and should be widely adopted by the potato industry.
4. Potato cultivars with reduced acrylamide. . Acrylamide is an unwanted and potentially toxic by-product produced when carbohydrate-rich foods are processed at high temperatures. Among entries in National Fry Processing Trials, more than 20 clones exhibiting excellent processing characteristics and very low acrylamide levels were identified by ARS scientists in East Grand Forks, Minnesota. These clones will be evaluated in more detailed trials and may be candidates to replace currently used varieties in the commercial production of processed potato products. Eventual adoption of these clones and consequent reduction in the acrylamide concentration of potato products will benefit both producers and consumers.
5. Examining glycoalkaloid concentrations of new potato varieties. Glycoalkaloids are a naturally occurring secondary metabolite found in potato tissues, but tuber concentrations exceeding 20 mg/100 g fw-1 are not safe for human consumption (bitterness). In 2023, glycoalkaloid concentrations were measured from 349 cultivars from 11 public breeding programs. Variability in tuber glycoalkaloid concentrations was also quantified from 75 advanced chip breeding lines sampled from North Dakota, Wisconsin, and Michigan potato chip production locations. Data reported to breeders and potato processing stakeholders will help ensure new potato varieties meet glycoalkaloid concentrations safe for human consumption.
Review Publications
Dogramaci, M., Sarkar, D., Lulai, E.C. 2024. Modulatory role of nitric oxide in wound healing of potato tubers. Frontiers in Horticulture. 3. https://doi.org/10.3389/fhort.2024.1345461.
Dogramaci, M., Sarkar, D., Finger, F., Shetty, K., Fugate, K.K. 2024. Natural elicitors enhanced suberin polyphenolic accumulation in wounded surface of potato tuber tissues. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2024.1384602.
Dogramaci, M., Dobry, E.P., Fortini, E., Sarkar, D., Eshel, D., Campbell, M. 2024. Physiological and molecular mechanisms associated with potato tuber dormancy. Journal of Experimental Botany. https://doi.org/10.1093/jxb/erae182.
Dogramaci, M., Sarkar, D., Datir, S., Finger, F., Shetty, K., Fugate, K.K., Anderson, J.V. 2024. Methyl jasmonate and 1,4-dimethylnaphthalene differentially impact phytohormonal and stress protective pathway regulation involved in potato tuber dormancy. Postharvest Biology and Technology. 213. https://doi.org/10.1016/j.postharvbio.2024.112931.
