NKJ 134 - Bedømmelse af lagringsevne og biologisk bekjæmpelse til forebyggelse af råd og kvalitetstab af kartofler

Rotting of fruit and vegetables (including potato tubers) in storage, causes great economic losses in addition to being an environmental- and bioresource problem. A number of different fungal and bacterial pathogens, which originate from the environment (e.g. soil) or from infected plants during harvest, packing or transport, causes the post-harvest diseases. Many of the postharvest pathogens do not cause diseases in the fields, but the plants or the crop often weakens during storage, which make them more susceptible to diseases. One of the goals of the project was to develop a test for quality control of potato tubers, so that it will be possible to predict which lots should be used immediately and which could be stored for longer periods. In addition, we wanted to investigate whether selected biocontrol agents can be used to control important post-harvest diseases, and study mechanisms for these. In the Norwegian part of this joint Nordic project, we focused on infection and development of potato late blight disease and silver scurf in storage. We have performed a series of infection experiments with late blight (Phytophthora infestans) and silver scurf (Helminthosporium solani) under conditions that either promotes (high humidity) or inhibits (low humidity) disease development. In addition, we have tested a so-called biocontrol agent (originally isolated by our Swedish collaborators) against both diseases in infection experiments with stored tubers. The biocontrol agent had only a small effect on the late blight pathogen in vitro, but no effect during infection in stored potato tubers. However, the biocontrol agent effectively stopped all development of silver scurf during the six weeks that the tubers were stored. During the last year, we have performed two large-scale field experiments with the biocontrol agent. The potatoes were harvested in September, but evaluation of the results remains to be done after the standard 6-8 incubation in storage. We have sampled tubers during the infection experiments for both late blight and silver scurf including the biocontrol agent, and RNA (trancriptome) have been sequenced used so-called next generation sequencing technology that have given millions of sequences per sample. We have used an Illumina HiSeq instrument (localized at Aalborg University= Danish NKJ partner, and at The Norwegian Sequencing Centre in Oslo) for the sequencing. The large number of sequences for each sample enables us to quantify RNA activity or gene expression with much higher resolution than other methods, which gives potential for discovering the small changes that often are associated with important biological processes. After sequencing, we have linked the RNA sequences to the publically available genomes of potato, silver scurf and the biocontrol agent so that we know which genes are expressed during infection. Results from the late blight studies indicates that the potato defense responses are weakened in response to lack of oxygen that occur at high humidity due to water film on the surface of the tuber. For the silver scurf, results indicate that the biocontrol agent has a dual effect, as it seem to have a direct negative effect on the silver scurf as well as triggering the defense responses in the potato. We have simultaneously detected several potential pathogenicity genes of the silver scurf fungus. These could be potential targets for future management of silver scurf.

Rotting of vegetables and fruit in storage by microbes is a world-wide problem that causes big losses in agriculture, industry and trade. The goal of this project is to use potato as a model to develop diagnostic test for quality control and to apply biol ogical control for prevention of post harvest diseases of potato. Interaction of potato tubers with fungal pathogens causing dry rot (Fusarium), potato blight (Phytophthora) and silver scurf (Helminthosporium), and soft rot (Pectobacterium and Dickeya) wi ll be used as model systems. The gene expression in the host and the pathogens will be studied with deep sequencing in two conditions; in high humidity that promote the diseases and in low humidity suppressing them. The gene expression profiling of intere sting genes in the host and in the pathogens during interactions in different conditions will be verified with real-time PCR. The goal is to understand, how the various processes in the host and the pathogens are affected by humidity, and identify process es which can be linked to the onset of rotting. Based on this information, real-time PCR or ELISA test will be developed for the identification of the lots that have the highest risk of rotting. Furthermore, biological control organisms will be evaluated for the ability to prevent rotting and skin blemishes in harvested potato tubers. The interaction of the control organisms with the pathogens will be evaluated and studied in the conditions either promoting or suppressing the post-harvest diseases. Financ ing is applied for three years. Potato cDNA sequencing and laboratory testing of the biocontrol agents is scheduled for the first year, analysis and verification of the sequencing results and performance of the biocontrol agents in plant tissue for the se cond, and the final evaluation of the methods for the third year.