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FFL-JA-Forskningsmidlene for jordbruk og matindustri

Improved potato seed tuber quality through better disease control methods

Alternative title: POTTIFRISK - Bedre settepotetkvalitet gjennom økt kunnskap og metodeutvikling knyttet til problematiske skadegjørere

Awarded: NOK 0.77 mill.

Diseases are a major constrain in potato production, leading to a great reduction in yield and quality. Contaminated seed tubers are the most important source of inoculum for many potato diseases. Particularly challenging is the fact that many of the important pathogens can be difficult to detect as they give rise to symptomless (latent) infections. A first step towards management of plant diseases is identification and detection. In the project, we focused on bacterial soft rot diseases, late blight, gangrene and skin blemish diseases (silver scurf, skin spot, black dot). We have implemented DNA-based testing methods for all diseases and have tested 15 seed lots of potato in 2015, 12 in 2016 and 2017, including the cultivars Asterix, Lady Claire, Innovator, before planting, after uptake and after 3 months in storage. We did not find any late blight pathogen, which indicates that the seed potato growers have a good control regime for this pathogen. Silver scurf was detected in all lots already at uptake and regardless of symptoms. A small amount of black dot was detected in some lots using the DNA-based test (only tested in 2015), but symptoms were not observed. The amount of skin spot increased during storage and was found in most lots with the DNA- test, although visible symptoms were rare. Phoma were observed in single lots all years, more often after storage than at harvest, which correlated well with the DNA-test. The soft rot bacteria were found to be near-ubiquitous, regardless of potato cultivar or seed quality, except for seed of the highest quality. These tubers quite reliably tested low in infection prevalence and disease was rarely observed compared to lower quality seed. Climate, particularly precipitation, seemed to play the most important role in infection prevalence. Disease incidence for blackleg was partially determined by the host, as demonstrated by one cultivar (Innovator), which seemed less susceptible to this disease. It also performed best in a test, where tubers from 15 different cultivars were infected with two Pectobacterium species. In this test, it was also shown that temperature was the factor that had the overall largest influence on rot outcome. In addition to testing seed tuber lots, we have sampled symptomatic plants from different fields in Norway, and isolated and characterized soft rot bacteria from these. Several different species of soft rot bacteria have been detected in Norway the last few years, and some of the isolates that were particularly aggressive have been studied in detail and their genomes sequenced. These were significantly different from other described species, and we have consequently described and published them as a new species (Pectobacterium polaris). We also studied the possible role of insects in dissemination of soft rot bacteria, by setting up sticky traps in potato fields with soft rot infection and tested captured insects with the DNA based tests. We discovered that ca 19 % of 2142 tested insects in 2015-2016 contained a high level of soft rot bacteria and the majority of these insects belonged to a Delia species. This indicates that insect play a role during infection of potatoes. The factors that trigger outbreak of soft rot are not know. For increased understanding of the disease, one of the goals of the project was to identify genes, gene products and regulatory mechanisms that are involved in pathogenicity. As part of this, we have performed infection experiments with two new bacterial isolates and RNA sequence analysis to study genes that are expressed during infection. In both examined strains, important virulence genes, encoding e.g. the enzymes that degrade host cell walls, as well as several bacterial secretion systems, decreased in expression over time. This, indicated a shift in prioritized function in the investigated bacteria. A better understanding of the molecular processes and their trajectory in progressing infection may help in devising and optimizing counterstrategies. A total of seven field trials were planted with Asterix, Innovator and Lady Claire 2015-2017, to investigate the effects of different strategies for planting and harvest on diseases after storage. Treatments were normal and late planting dates, and harvest 2 and 4 weeks after vine desiccation. In 2015 and 2017, three different treatment strategies after harvest were also used. Most powdery scab were detected in the later harvest dates and when combining wound healing and rapid cooling. Fast and direct cooling generally resulted in lower levels of silver scurf and black dot. The levels of skin spot were affected by the desiccation period, but different among years. There were only low levels of tuber rots in the samples, even after incubation. In cultivar Asterix somewhat more soft rot was found after prolonged desiccation. Most rot diseases were found after direct and fast cooling. Wound healing before cooling reduced the levels of infections.

Prosjektet har bidratt til kompetanseoppbygging hos deltagende forskningsinstitusjoner, Norsk landbruksrådgivning og industripartnere i form av økt forståelse av viktige bakterie- og soppskadegjørere i potet. Prosjektet har gitt innføring av nye metoder for påvisning og kvantifisering av skadegjørere i potet. Utvikling og implementering av DNA-baserte tester har gjort det mulig å undersøke potetpartier og andre smittekilder, slik som insektvektorer. Stengelråte/bløtråtetestingen er implementert i rutinetestingen til NIBIO Planteklinikken, og har blitt benyttet de siste årene av industripartnere i prosjektet. De utviklede testene har gitt og vil fortsette å gi ny kunnskap om spredningsveier for bløtråte og stengelråte, og det vil på sikt kunne bidra til reduserte avlingstap, økt salgbar produksjon og forbedret lønnsomhet i næringen. I tillegg har prosjektet ført til publisering av vitenskapelig artikler, utdanning av PhD student, økt internasjonalt samarbeid (Nederland og Skottland).

Potatoes are the most important food crop with respect to first hand value in Norway. Diseases are a major constrain in potato production, leading to a significant reduction in yield and quality. Contaminated seed tubers are the most important source of inoculum for many potato diseases. Particularly challenging is the fact that many of the important pathogens can be difficult to detect as they give rise to symptomless (latent) infections. There is a great knowledge need in how to detect and control all of the potato diseases. A first step towards management of plant diseases is appropriate identification and detection methods. Consequently, one of the major goals of the project is to develop / implement DNA based methods for rapid and sensitive detection and quantification of latent infection of bacteria and fungi in seed tubers. We will particularly focus our work on bacterial soft rot diseases, late blight, gangrene and skin blemish diseases such as silver scurf, skin spot and black dot. The target pathogens, selected in collaboration with Norwegian potato industry, are the ones currently causing most damage to Norwegian potato production. The development and implementation of methods to quantify infection in tubers will also give us a powerful tool for studying the epidemiology of these diseases. In addition, the methods will be used for testing the effect of potential control-measures and regime for using these, as well as different cultivation and storage strategies. The project will be organized by Bioforsk and Norwegian Agricultural Extension Service with scientific support from leading international scientists in the area and is financially supported by a large part of the companies in the potato industry. The project aims at building knowledge on major potato diseases and methods to control them. This will help Norwegian potato production to answer significant challenges concerning increased import and a weaker production economy.

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FFL-JA-Forskningsmidlene for jordbruk og matindustri