Pia Heltoft

Research Scientist

(+47) 920 80 939


Visiting address
Nylinna 226, 2849 Kapp


I am a scientist and expert on potatoes and vegetables. My research is mainly concentrated on storage and postharvest where I focus on product quality, physiology and pathology.


2010-2016: PhD. Norwegian University of Life Science
2008-2010: Cand. Agro, University of Copenhagen
2004-2007: Bachelor i naturressourcer, University of Copenhagen

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After harvesting, the Norwegian root vegetables are normally stored at refrigerated temperatures for 5 to 7 months. During this period, up to 30% of the products are lost. The goal is to reduce the diseases, the product loss and energy consumption, in addition to increase shelf-life and storage period. Twenty-eight commercial root vegetable cold-stores were instrumented to measure air temperature, relative humidity and product temperature. The study was done over two years. The cold-stores were located in four different regions of Norway. The three focus-products carrot, swede and celeriac were harvested from one field in each region in open wire nets. The nets were placed in the various cold-stores in the respective regions and put in the wooden bins together with the producer's own products. The quality and yield of the products were determined and correlated to the storage condition. The various storage condition negatively affects the respiration and quality of the root vegetables, storage-life, and influence on the cooling capacity of the refrigeration systems.


Important factors for development of quality defects are the physical, physiological and chemical state of the tubers, which is also described as the maturity status of the crop. The use of maturity indicators as predictors of quality in potato tubers during and after storage was explored in cvs. Asterix and Saturna with three different maturity levels during three years (2010, 2012 and 2013). The maturity indicators measured 1–3 weeks before harvest and at harvest included haulm senescence (haulm maturity), skin set (physical maturity), dry matter content (physiological maturity) and contents of sucrose, glucose and fructose (chemical maturity). Potato quality parameters were measured three times during storage (December, February and April) and included dry matter content, sucrose, glucose and fructose contents, weight loss and fry colour. Cultivar and maturity level were included as categorical predictors in a linear regression model and contributed significantly (P < 0.001) to the models predicting reducing sugars during storage. Dry matter, sucrose, glucose and fructose were included as continuous predictors in the linear regression models and contributed significantly (P < 0.01) to the sucrose, glucose and fructose models and these models explained a high proportion of the variation (R2 ≥ 0.88). Skin set contributed significantly to the weight loss models (P < 0.01) but the models showed low R2 -values (R2 < 0.48). Sucrose contents contributed significantly (P = 0.05) to the fry colour model for Asterix and the fry colour models for both Asterix and Saturna had R2 -values of 0.50 and 0.51 respectively. This study provides new information about the influence of maturity on potato quality during storage and the potential of using field measurements of maturity as predictors of storage potential for processing potato cultivars Asterix and Saturna in Norway.


Optimization of produce quality and storage conditions to reduce loss during long-term storage of root vegetables in Norway (OPTIROOT, 2016-2019) Authors: Thomsen, M.G., Indergaard, E., Asalf, B., Heltoft, P., Wold, A.B., Nordskog, B., Guren, G, Dyste, J. & Larsen, H. Author’s affiliation: Key words: carrot, swede, celeriac, storage technology, diseases, physiological disorder, packaging, nutrition Reducing yield loss along the supply chains is important for resource sustainability in vegetable production. Norwegian root vegetables are typically stored 6 to 8 months before consumption, often resulting in 20-30% loss post harvest. In OptiRoot 26 producers, refrigeration-technology companies, sensor developer, grower’s organisation, agricultural advisory service, and four research institutes are cooperating and conducting research to improve storage quality of carrot, swede and celeriac. The research focuses on: i) Fertilizer/Boron deficiency affects the storage quality of root vegetables and amount, methods of application, and timing of boron are studied in swede and celeriac. ii) Interaction between storage conditions/functions and produce quality of the root vegetables through mapping of technical features of 27 storages. The storage conditions recorded are relative humidity, air movement, temperature in boxes and storages, and physical features of storages. In addition, the physiological and health status of the produces are assessed one week before harvest, postharvest and post-storage. The prevalence of fungal diseases or disorders varied from region to region and between storages. iii) Effects of pre-storage wound healing are tested using seven different temperature strategies (direct to 0° C vs. down 0.2° C per day vs. 1° C per day) and low/high humidity in carrot (2016/17/18), celeriac and swede (2017/18/19). Preliminary results show that wound healing reduced loss due to fungal infections in carrot iv) CO2 concentration, temperature and relative humidity were recorded over time inside carrot storage bin liners with different numbers of perforations. An initial screening indicated a positive correlation between number of holes and number of fresh roots. As a post storage method, coating of swede with chitosan oligomers will be tested to inhibit growth of post-harvest pathogens. In conclusion, OptiRoot have gained good progress and promising preliminary results by connecting data on biology and technology for reduction of loss during long-term storage.


Ventilation management and the tuber maturity at harvest are essential factors in maintaining potato quality during long-term storage. The aim of this study was to examine the effect of ventilation strategy on storage quality of potato tubers with three different maturity levels at harvest. Two potato cultivars, Saturna and Asterix, were stored in small-scale experimental stores and large-scale commercial stores. Both storage categories were ventilated by both low continuous air rates (natural ventilation) and intermittent high air rates (forced ventilation). The different maturity levels were obtained by a combination of pre-sprouting strategy, planting date and level of nitrogen fertilization of the seed tubers, where pre-sprouting, early planting date and low amount of nitrogen resulted in the most mature tubers. Storage quality parameters investigated during and after long-term storage (6 months in small-scale and 4 months in large-scale stores) included weight loss, respiration, dry matter, sucrose, glucose/fructose content and fry colour. In average over three years natural ventilation resulted in higher weight losses in small- and large-scale stores (1.36 and 3.93%), lower content of reducing sugars (glucose + fructose) in large-scale stores (2.35 mg g 1) and lighter fry colour than did forced ventilation. Immature potatoes had higher weight losses (4.16%), higher respiration rates (1.68 mg CO2 kg 1 h 1) and lower dry matter content (22.3–22.5%) than more mature potatoes. This study show that both maturity and ventilation strategy affects storage quality of potatoes as measured by weight loss, sugar content and fry colour.


The prevalence of Fusarium dry rot in potatoes produced in Norway was investigated in a survey for three consecutive years in the period 2010 to 2012. A total of 238 samples (comprising 23,800 tubers) were collected, representing different cultivars and production regions in Norway. Fusarium spp. were detected in 47% of the samples, with one to three species per sample. In total, 718 isolates of Fusarium spp. were recovered and identified to seven species. The most commonly isolated species was Fusarium coeruleum, comprising 59.6% of the total Fusarium isolates and found in 17.2% of the collected samples, followed by Fusarium avenaceum (27.2% of the isolates and found in 27.7% of the samples). Fusarium sambucinum was the third most prevalent species (6.4% in 8.8% of the samples) and Fusarium culmorum the fourth (5.2% in 6.3% of the samples). Less prevalent species included Fusarium cerealis, Fusarium graminearum, and Fusarium equiseti (<1% in 0.4 to 1.3% of the samples). F. coeruleum was the most prevalent species in northern and southwestern Norway, whereas F. avenaceum was dominating in eastern Norway. The potato cultivars Berber and Rutt were susceptible to all Fusarium spp. A new TaqMan real-time PCR assay specific for F. coeruleum was developed, which successfully identified Norwegian isolates. This and other previously developed real-time PCR assays targeting different Fusarium species were evaluated for their ability to detect latent infections in potatoes at harvest. This study provides new information on the current occurrence of different Fusarium species causing Fusarium dry rot in potatoes in Europe including areas far into the arctic in the north of Norway.

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A glasshouse experiment was carried out with the aim of quantifying the relative contribution of seed- and soil-borne inoculum of three Fusarium spp. (F. coeruleum, F. sambucinum and F. avenaceum) in causing dry rot in two potato cultivars, Asterix and Saturna. Different concentrations of inoculum; control (water only), low (102 conidia ml−1) and high (105 conidia ml−1) were used to inoculate seed and infest soil and disease severity on progeny tubers was subsequently assessed following an 8-week post-harvest storage period. Overall, F. sambucinum caused significantly (P < 0.05) larger rots than F. avenaceum, with the severity of rots caused by F. coeruleum being intermediate, and disease severity was greater in cv. Asterix than cv. Saturna (P < 0.01). None of the seed inoculation treatments resulted in dry rot development on progeny tubers. In contrast, soil infested with Fusarium species resulted in significantly more severe tuber rots on progeny tubers compared with controls (P < 0.01). Soil infested with F. sambucinum (low and high levels) resulted in significantly more severe rots than control treatments (P < 0.001), whilst only high levels of F. avenaceum soil inoculum increased the severity of tuber rots compared with control treatments (P < 0.05). Increased disease severity observed as a result of the addition of inoculum of F. coeruleum to soil was not significant.