Location: Sugarbeet and Potato Research
2018 Annual Report
Objectives
Objective 1: Delineate and integrate the molecular processes that control cytokinin content and their biological activities during tuber dormancy progression and wound-healing.
Sub-Objective 1-1: Determine changes in tuber meristem cytokinin content and expression of genes encoding cytokinin biosynthetic enzymes during dormancy progression.
Sub-Objective 1-2: Determine changes in the expression of cytokinin-responsive histidine kinase genes and the acquisition of cytokinin sensitivity during tuber dormancy progression.
Sub-Objective 1.3: Determine changes in cytokinin content and the expression of genes encoding key cytokinin metabolic enzymes in tuber tissues following mechanical wounding.
Objective 2: Quantify nitric oxide release during potato storage and handling and determine nitric oxide involvement in tuber dormancy progression and wound-healing.
Sub-Objective 2.1: Determine the release and role of NO in potato tuber dormancy exit.
Sub-Objective 2.2: Determine the release and role of NO in the potato tuber wound-healing response.
Objectives 1 and 2 build upon research findings secured during the previous project cycle and address current knowledge gaps in the regulatory processes controlling tuber dormancy progression and wound healing.
Approach
Worldwide, the potato ranks fourth among the major food crops. Global potato production exceeds 364 million metric tons (FAOSTAT, March, 2013) and U.S. production exceeds 437 million cwt (USDA-NASS, January, 2013) of which over 400 million cwt worth an estimated $2.01 billion are harvested in the fall. Over 70% of the fall potato crop is placed into storage for year-round use. Unlike other major food crops, potatoes are stored in a fully hydrated and highly perishable form. Postharvest losses routinely approach 10% of the stored crop and occur through both physiological and disease-related processes. Two of the most important physiological processes affecting potato storage and market quality are dormancy/sprouting and wound-healing. Despite the severity of these losses, management strategies and technologies employed to combat these problems were empirically derived, are several decades old and do not effectively meet today’s consumer or industry demands to control damage, minimize physiological deteriorations, and reduce disease problems. Further improvements in postharvest storage technologies are hindered by ignorance of the biological mechanisms underlying these physiological processes. The goals of this project are to identify critical molecular, biochemical and physiological mechanisms controlling tuber dormancy/sprout growth and wound-healing and, ultimately, to genetically, chemically, or physically manipulate these rate-limiting processes to develop improved methods to maintain potato nutritional and processing quality during storage. Specific goals are: 1) Identify the cognate processes that control cytokinin content and activity during postharvest storage/wound-healing, and 2) Determine the involvement of nitric oxide in tuber dormancy progression and wound-healing.
Progress Report
The biosynthesis and release of nitric oxide (NO) are import plant wound-responses which appear to be critical in modulating tuber wound-healing (WH) and reducing associated costly rot, defects and nutritional losses of potatoes damaged at harvest/handling into storage and at seed cutting. Methods are being developed and refined to determine: 1) the production time-course and amount of NO and nitric oxide synthase (NOS- the enzyme producing NO) induced in response to tuber wounding, and 2) the effects of NO on wound healing processes. Electronic probes to detect and quantify the presence of wound-induced NO and the stable NO breakdown products (nitrate and nitrite) were found to lack the required sensitivity. However, specially formulated colorimetric assays were found to be effective measures of NO and NOS in wound-responding tuber tissue. These assay methods, in conjunction with established wound-healing assays, facilitate determination of the effects of NO donors and NO and NOS inhibitor treatments to wound-responding tuber tissues. Nitric oxide donors and inhibitors continue to be included in these studies to formulate environments that are: 1) artificially supplemented with nitric oxide, and 2) blocked of nitric oxide accumulation. Results from this project will be used in the development of new approaches to safely treat freshly stored potatoes to enhance wound-healing and reduce costly rot and nutritional losses (> $330 m/yr.). Objective 2; Sub-objective 2.2.
Accomplishments
1. Nitric oxide (NO) is essential in potato tuber wound healing to protect harvested tubers from infection and deterioration. Potato tuber infections cause defects in development and nutritional losses that account for $330 million in in lost revenue per year. The development of technologies to prevent potato tuber infection is severely hampered by the lack of information surrounding the regulation and modulation of potato tuber wound healing. ARS scientists in Fargo, North Dakota found that the wound-induced formation of NO in potato tuber is essential for protective wound healing processes. Laboratory analysis showed that NO and nitric oxide synthase (NOS) naturally increased within 24 h of wounding. Importantly, treatment of tuber tissues with specific scavengers of NO totally blocked the formation of new barriers to infection. These results suggest that NO is essential to wound healing processes and the formation of barriers to pathogens. These results, and further related experimentation, hold promise in the development of innovative technologies to reduce potato disease and associated losses through enhanced NO formation and possible treatment in potato storage facilities.
2. “Periderm Disorder Syndrome”: a new name for the costly syndrome formerly referred to as pink eye. The costly problem of potato tuber “pink eye” had been mistakenly hypothesized to be caused by a combination of unknown pathogens. This mistake resulted in much confusion by growers and many fruitless research efforts to solve the problem. ARS and North Dakota State University scientists (Fargo, North Dakota) and University of Idaho scientists (Idaho Falls, Idaho) resolved this problem by condensing new information with their previous research results and showed that the problem was caused by a “periderm disorder syndrome” and as such published research proving that the disorder/syndrome was physiological in origin and resulted in broad ranging susceptibility to tuber infection. This concerted research and official renaming of the malady to “periderm disorder syndrome” clarifies the cause of this costly problem for growers and researchers and correctly directs future efforts for the control this costly disorder.
