Abstract
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.
Highlights
Domesticated carrot (Daucus carota L. subsp. sativus (Hoffm.) Schubl. & G
Four types of symptoms were observed in many different different fields: black scurf, greyish-white felt-like mycelium, crown rot and brown wilted fields: black scurf, greyish-white felt-like mycelium, crown rot and brown stem stem bases/leaves
The results indicate that the disease occurrence of Rhizoctonia solani inducing these symptoms have increased over the period of time (Figure 2)
Summary
Domesticated carrot (Daucus carota L. subsp. sativus (Hoffm.) Schubl. & G. Martens) is a biennial plant belonging to the Apiaceae family [1]. It is cultivated worldwide for the fresh market and processing industry for its nutritive taproot. In Sweden, carrot and potato are the most cultivated root and tuber crops. In 2019, carrots and potatoes were produced on approximately 1700 ha (109,000 tons) and 23,650 ha (846,900 tons), respectively, in Sweden. The main Swedish production areas of carrots are Scania (57%) and Gotland (25%). Potatoes are mainly grown in the southern provinces of Scania, Halland and Blekinge (62%) [2]
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