Post‐harvest diseases cause significant economic losses in the carrot production chain. In this study, storage losses and fungal pathogens causing them were analysed in the carrot yield from 52 different field plots in four areas in Finland in 3 years (2016–2018). Over 30,000 carrots were sampled and analysed at three time points during cold storage at 0–1°C. In March, after 5–6 months' storage, the average loss due to diseases was 20%–21% every year. Decay of the root tip was the most common disease symptom, followed by pits on the side and black rot in the crown, detected in 69.2%, 15.0% and 9.0% of the symptomatic samples, respectively. Both intensive carrot cultivation practice and early timing of harvest increased storage losses. Pathogens in 3057 symptomatic carrot tissue samples were isolated by culturing, and fungal species were identified. The most common fungal species detected were Mycocentrospora acerina, Botrytis cinerea and Fusarium spp., especially F. avenaceum. However, the frequency of different pathogens varied between the different years and time points during storage. Species‐specific PCR tests revealed that M. acerina and F. avenaceum were present in many early time‐point samples where they could not yet be detected by the culturing method. In Finland, this study on carrot post‐harvest diseases is the first large‐scale survey in which the fungal pathogens were isolated and identified by laboratory tests. In comparison with the previous studies, Fusarium spp. were detected more frequently in this study, while grey mould and Sclerotinia rot were less frequent.

Potato onion (Allium cepa var. aggregatum G. Don) remained the most widely grown onion type in Finland up to the 1950’s, after which the more productive cultivars of common onion replaced this vegetatively propagated onion type. The Finnish accessions have been maintained in two national plant genetic resources (PGR) collections since 1990’s but new samples have been obtained still later. In this research, we analysed the genetic diversity of potato onions and shallots, grown in home gardens and in PGR collection, and compared the uniformity of the two PGR collections. One hundred ten onion samples were analysed using eight microsatellite loci, which amplified 83 alleles in total. There was a large number of genetically different samples, forming four major groups in the dendrogram. The results show that there is still a lot of genetic diversity among the Finnish potato onions, even though they are propagated vegetatively. The rich diversity in the samples obtained from citizens reflects a valuable source of genetic resources maintained by home gardeners. The national collection has been updated on the basis of the results. To ensure the preservation of the rich onion heritage, efforts are needed to increase the availability of potato onion to home gardeners and commercial growers.

Fungal pathogens often cause severe post-harvest losses in stored carrot yields. In 2020 and 2021, carrot samples were collected in Finland from 26 fields with different soil types. The proportion of symptomatic carrots was assessed at two time points during the cold storage period. To analyse the occurrence of different fungal pathogens in the symptomatic carrots, DNA samples were prepared and tested for the presence of fungal pathogens by species-specific PCR. The most frequently detected pathogens were Cylindrocarpon spp. with 61% occurrence, followed by Fusarium avenaceum (44%), Mycocentrospora acerina (42%), Botrytis cinerea (12%), and Alternaria spp. (0.8%). B. cinerea and F. avenaceum were more common in carrots grown on organic soil, while M. acerina was more common in carrots grown on mineral soils. Mixed fungal infections were overrepresented in the symptomatic samples, in particular, Cylindrocarpon spp. often occurred together with F. avenaceum and M. acerina in the same samples. Amplicon sequencing of the fungal internal transcribed spacer region from the DNA of symptomatic tissues revealed that in addition to the pathogens— B. cinerea , M. acerina, Cylindrocarpon spp. and Sclerotinia sclerotiorum —the hyphomycete fungi Tetracladium spp. and the yeast Leucosporidium intermedium were abundant, and that Tetracladium spp. were more abundant in the carrots infected with M. acerina . A pathogenicity test confirmed that F. avenaceum is pathogenic to both the new season and old season carrots.

Postharvest diseases can cause significant losses in carrot ( Daucus carota ) yield during storage. In this study, the effects of soil quality and microbial diversity in the field bulk soil and rhizosphere on the development of postharvest diseases were investigated. Microbial genera in bulk soil and rhizosphere samples were identified by Illumina Miseq amplicon sequencing of bacterial 16S and fungal ITS regions. Disease symptoms in the stored carrots were monitored after six months of cold storage, and the main pathogens were identified. The field sites with mineral soils, which had a higher pH, had a higher bacterial and fungal diversity than organic soils. The organically managed fields had a higher bacterial diversity than the conventionally managed fields. Community structure of both bacteria and fungi was largely driven by field site including its main chemical characteristics, with rhizosphere and bulk soil samples from the same site displaying comparable assemblages. Higher soil microbial diversity was associated with higher postharvest storability in the stored carrots. The weather during the growing season also had an effect on the observed fungal biodiversity, which was higher at sites that had lower temperatures and less rain prior to harvest.