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FFL-JA-Forskningsmidlene for jordbruk og matindustri

Understanding the causal agent(s) of tip rot to reduce carrot loss and waste within the supply chain

Alternative title: Identifikasjon av årsaker til og tiltak for å redusere tap i norsk gulrotproduksjon som følge av tuppråte

Awarded: NOK 2.1 mill.

Carrot is the main field vegetable in Norway, and it contributes over 886 million NOK per annum, where 94.5% of the market share is covered by locally produced carrots. It is stored in cold storage for up to 8 months. It has been claimed that tip rot of carrot is an increasing problem in Norway, but there was limited information about the extent of the tip rot problem and its causal agent(s). The primary objective of the project is to reduce carrot loss and waste caused by tip rot to ensure sustainable carrot production in Norway. A typical symptom of tip rot is discoloration and necrosis starting from the tip of the tap root and progressing upwards. The focus group interview results indicate that producers seem to have several different definitions of the tip rot symptoms. However, they do agree that symptoms are rarely seen at harvest but common after 10-12 weeks in storage. The prevalence of tip rot and other post-harvest diseases were assessed at the end of the storage period of carrots in four regions. The incidence of postharvest diseases was 58% and that of tip rot alone was close to 30%. The pathogen identification results showed that tip rot is caused by four or more pathogens such as Mycocentrospora acerina, Cylindrocarpon spp. Fusarium species. Carrots with tip rot develop brownish symptom few hours after removing the infected part, polishing, and packaging. This is due to the production of phenolic compounds and oxidation. Tip rot of carrot is caused by several fungi and symptom can be light, brown, and dark brown with dry or wet rot, so the diseases is called tip rot diseases complex. The pathogenicity of candidate organisms was conducted. The effect of temperature on latent period were determined by storing inoculated carrot at 0+1°C, 3±1°C and 6±1°C. The pathogenicity of the candidate pathogens was confirmed. The latent period varied among pathogens and storage temperature. The higher the storage temperature, the shorter the latent period. Nematode population analysis results showed that some of the nematode species were increased at the harvesting time compared to the sowing time. Controlled high plastic tunnel trials on the effect of drought stress on tip rot development showed an increasing tendency in the incidence of tip rot in drought stress treatments during the last part of the growth period. The effect of sowing times, two weeks between each sowing (early, normal, and late), we saw a tendency to a higher percentage of roots with tip rot following storage in roots sown at the delayed sowing time (youngest roots). The incidences of tip rot were more on immature than mature carrot. High soil pH gave a higher proportion of roots with fingers at harvest, but a lower proportion of roots with tip rot and more fresh roots after storage. Experiments showed that boron deficiency had a negative effect on how well cells in the carrot tissue were attached to each other. A brief daily UV treatment in combination with cold storage temperature (4 °C) can suppress the colony growth of the candidate pathogens (M. acerina, F. avenaceum, and C. destructans). Blue light in combination with cold storage showed significant suppression of colony growth for all three candidate pathogens. Experiments conducted with carrots harvested at commercial maturity and inoculated with candidate pathogens showed that there were no symptoms of tip rot when the inoculated carrots were exposed to brief UV at cold storage temperature compared to room temperature. Hot water treatment against latent pathogens is challenging as carrots can withstand 60 s at 50 °C before being damaged on the surface. In the packaging experiments, gas development in the packages was followed, and the number of roots that had developed disease was recorded at the end of the storage period. The results showed that exposure at room temperature in the grocery store stimulates the growth of pathogens and that roots infected with M. acerina developed the most visible rot. Browning at the tips within a few hours after washing, polishing, and packaging is a problem for packaging houses and leads to returns (food waste) and extra work (repackaging) at the packaging plants. Chemical analyses were carried out on selected samples of diseased and healthy carrots. Increased levels of phenolic compounds were found in carrots infected by M. acerina, the rapid development of browning of the tip of the carrots just a few hours after washing and polishing could be due to the combined effect of the pathogens that cause tip rot disease complex and predisposition of the infected tissue for phenolic oxidation. In conclusion, the tip rot disease complex is caused by pathogens. The knowledge of identification of the causal agents of tip rot disease complex is important to take appropriate control measures. Control measures should focus on tip rot disease complex prevention measures.

The overall goal of RootCause is to reduce losses and waste of carrots along the value chain through improved knowledge of the causal agent of tip rot, increase the market share of locally produced carrots and develop effective management strategies. Accurate identification of the causal agent(s) of tip rot whether biotic (caused by fungi) or abiotic is crucial to manage the disease more effectively. The project identified the root cause of the tip rot of carrots, and it is caused by several pathogens among which Mycocentrospora acerina, Cylindrocarpon spp., Fusarium spp were the dominant pathogens. The disease is called tip rot disease complex. It was found that the development of tip rot disease complex is affected by the storage temperature and the causal pathogen. The knowledge of identification of the causal agents of tip rot disease complex and the effect of storage temperature on tip rot development is important to take appropriate control measures. Control measures should focus on tip rot disease complex prevention measures both in the growing season and in storage. Year-round availability of quality carrots is important for consumers. When the project started about 80% of carrots consumed in Norway were produced domestically, but in 2021 the market share by domestically produced carrots increased to 94.5% of the market demand (Opplysningskontoret for Frukt og Grønt (OFG), 2022). One of Norway’s targets is to increase domestic market shares in food production. This will have a positive impact on the economy of the value chain actors (producers, processors, retailers, and consumers) because the need for foreign currency to import carrots can significantly reduce. Results from the project are disseminated in different channels to the industry. As indicated in the performance indicator tables, there were 73 dissemination measures during the project period. There will be further dissemination after the project period among which 2-3 scientific publications and NIBIO report.

Carrot is the main field vegetable in Norway, and it contributes over 461 million NOK per annum. Carrots are stored for up to 8 months in Norway. However, carrot quality is deteriorating due to post-harvest diseases and disorders, and postharvest yield losses reach 40%. A symptom called tip rot has been observed with increasing frequency over the last 10 years. Tip rot significantly reduce root quality and contributes to the high level of carrot rejection during sorting and packaging. The causal agent of tip rot is not well known and it is important to identify the primary causal agents and how it is influenced by abiotic factors in the field and in the storage. To tackle the tip rot problem, there are five major research priorities: 1. A survey among carrot supply chain actors will provide information about the extent of the problem and their perception about the possible causal agent of tip-rot and its relation to different agronomic practices and environmental conditions. 2. biotic agents (fungi, bacteria and plant parasitic nematodes) that may cause tip rot will be identified using molecular and classical methods, and their pathogenicity and latent period will be determined. 3. Controlled experiments will be conducted to determine the effect of abiotic factors (soil type, water logging, drought stress, mineral nutrients (boron and calcium)) as a predisposing factors of tip rot. 4. Postharvest disease management strategies (UV and hot water) that may induce carrot defense mechanisms against tip rot will be tested. 5. The effect of packaging materials and storage conditions on tip rot development will be tested to reduce losses in the retail market. In RootCause, proper identification of the causal agent(s) of tip rot and coordinated management of preharvest and postharvest tip rot development is emphasized and deemed critical to maintain the 80% domestic market share of carrot and for the sustainability of carrot production in Norway.

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FFL-JA-Forskningsmidlene for jordbruk og matindustri