Flax is an important crop cultivated for its seeds and fibers. It is widely grown in temperate regions, with an increase in cultivation areas for seed production (linseed) in the past 50 years and for fiber production (fiber flax) in the last decade. Among fiber-producing crops, fiber flax is the most valuable species. Linseed is the highest omega-3 oleaginous crop, and its consumption provides several benefits for animal and human health. However, flax production is impacted by various abiotic and biotic factors that affect yield and quality. Among biotic factors, eukaryotic diseases pose a significant threat to both seed production and fiber quality, which highlights the economic importance of controlling these diseases. This review focuses on the major eukaryotic diseases that affect flax in the field, describing the pathogens, their transmission modes and the associated plant symptoms. Moreover, this article aims to identify the challenges in disease management and provide future perspectives to overcome these biotic stresses in flax cultivation. By emphasizing the key diseases and their management, this review can aid in promoting sustainable and profitable flax production.

Carrots with different Rhizoctonia-like symptoms were found in the main Swedish carrot production areas from 2001–2020. The most commonly observed symptoms were a greyish-white felt-like mycelium and black scurf, the latter often associated with Rhizoctonia solani anastomosis group (AG) 3-PT on potato. An overall increase in disease incidence in all studied fields over time was observed for both symptoms. The majority of Rhizoctonia isolates sampled from carrot in the period 2015–2020 were identified as AG 3 (45%) and AG 5 (24%), followed by AG 1-IB (13%), AG 11 (5%), AG-E (5%), AG BI (3%), AG-K (3%) and AG 4-HGII (2%). To our knowledge, this is the first report describing AG 5 in Sweden as well as AG 3, AG 11 and AG-E inducing Rhizoctonia-like symptoms on carrot. Secondly, we report for the first time that R. solani AG 3, and the less observed AGs: AG 1-IB and AG 5 can induce black scurf symptoms on the taproot of carrots. Due to a widely used carrot-potato crop rotation in Swedish areas, a possible cross-over from potato to carrot is suggested. This information is of high importance to reduce Rhizoctonia inoculum in soils, since avoiding carrot-potato crop rotations needs to be considered.

The burrowing nematode Radopholus similis is considered a major problem of intensive banana cultivation. It can cause extensive root damage resulting in the toppling disease of banana, which means that plants fall to the ground. Soaking R. similis in double-stranded (ds) RNA of the nematode genes Rps13, chitin synthase (Chs-2), Unc-87, Pat-10 or beta-1,4-endoglucanase (Eng1a) suppressed reproduction on carrot discs, from 2.8-fold (Chs-2) to 7-fold (Rps13). The East African Highland Banana cultivar Nakitembe was then transformed with constructs for expression of dsRNA against the same genes, and for each construct, 30 independent transformants were tested with nematode infection. Four months after transfer from in vitro culture to the greenhouse, the banana plants were transferred to a screenhouse and inoculated with 2000 nematodes per plant, and thirteen weeks later, they were analyzed for several parameters including plant growth, root necrosis and final nematode population. Plants with dsRNA constructs against the nematode genes were on average showing lower nematode multiplication and root damage than the nontransformed controls or the banana plants expressing dsRNA against the nonendogenous gene. In conclusion, RNAi seems to efficiently protect banana against damage caused by R. similis, opening perspectives to control this pest.

Rhizoctonia solani is a soil-borne pathogen with a broad host range and considerable genetic diversity, yet little is known about its population structure in Sweden or Northern Europe. This study presents the most comprehensive survey to date of R. solani and related fungi across major field crops in Sweden, focusing on the southern agricultural region Scania. A total of 202 isolates were collected and characterized using rDNA-ITS sequencing for anastomosis group (AG) identification, geographic mapping, and multivariate analysis. The isolates primarily belonged to multinucleate AG-5 (81), followed by AG-3 (32), AG-2-1 (30), and AG-1 IB and AG-4 HGII (both 13), among other AGs, binucleate isolates, and Waitea species. AG-5 was clearly dominant, particularly on legumes, showing mild aggressiveness on pea and faba bean and high intraspecific ITS diversity. In contrast, AG-4 HGII and AG-2-1 displayed higher virulence, while AG-3 was non-pathogenic on the same hosts. Multivariate analyses revealed crop- and region-specific AG distributions. AG-3 was strongly associated with carrot and potato in Northeastern Scania, whereas across the rest of the region, AG-5 dominated legumes and was also found on sugar beet, together with AG-4 HGII and AG-2-1, while AG-2-1 occurred mainly on Brassicaceae. These findings have direct implications for crop rotation planning and disease management, highlighting potential risks in rotations involving legumes, Brassicaceae, and sugar beet, while rotations with carrot or potato may present lower risk. Overall, this study underscores the ecological complexity of Rhizoctonia in Swedish agroecosystems, emphasizing the need for localized surveillance and tailored management strategies to mitigate disease risk.