On the other hand, binucleate Rhizoctonia spp. To date, 14 AGs have been defined within multinucleate R. Commonly observed symptoms are pre- and post-emergence damping-off, root and stem rot, stem canker and black scurf. This highly destructive soil-borne fungus can attack several distinct plant parts such as seedlings, roots, tubers, stems, leaves and fruits. įrom all groups, multinucleate Rhizoctonia solani Kühn (teleomorph: Thanatephorus cucumeris) is the most extensively studied and widely recognized species. Moreover, these AGs can be subdivided in subgroups on the basis of high similarity in pathogenicity, genetic characteristics or the frequency of fusion between isolates. Each major group is taxonomically further divided into different anastomosis groups (AGs) based on the fusion of touching hyphae. Rhizoctonia isolates are currently classified into three major groups based on differences in the number of nuclei per hyphal cell: uninucleate Rhizoctonia (teleomorph: Ceratobasidium), binucleate Rhizoctonia (teleomorph: Ceratobasidium and Tulasnella) and multinucleate Rhizoctonia (teleomorph: Thanetophorus and Waitea). Only occasionally, under specific environmental conditions, sexual basidiospores are formed. are found in nature primarily as vegetative mycelium and sclerotia. The genus Rhizoctonia is a highly complex and heterogeneous group of basidiomycete fungi, which does not produce any asexual conidia. Damping-off and root rot can induce serious disease problems on carrot in Sweden and are caused by a species complex of three genera: Pythium species (spp.), Fusarium spp. A wide range of disease symptoms have been described worldwide during carrot cultivation, including root and stem rot, seedling damping-off, leaf spot and blight. There are also carrots stored under straw that are harvested during the winter from December to May. Carrots for direct consumption and cold storage are harvested between early July and late October. Cultivated carrots are mainly grown in open fields and are mostly sown in Swedish areas from March to mid-June. Potatoes are mainly grown in the southern provinces of Scania, Halland and Blekinge (62%). The main Swedish production areas of carrots are Scania (57%) and Gotland (25%). In 2019, carrots and potatoes were produced on approximately 1700 ha (109,000 tons) and 23,650 ha (846,900 tons), respectively, in Sweden. In Sweden, carrot and potato are the most cultivated root and tuber crops. It is cultivated worldwide for the fresh market and processing industry for its nutritive taproot. Martens) is a biennial plant belonging to the Apiaceae family. This information is of high importance to reduce Rhizoctonia inoculum in soils, since avoiding carrot-potato crop rotations needs to be considered.ĭomesticated carrot ( Daucus carota L. Due to a widely used carrot-potato crop rotation in Swedish areas, a possible cross-over from potato to carrot is suggested. solani AG 3, and the less observed AGs: AG 1-IB and AG 5 can induce black scurf symptoms on the taproot of carrots. Secondly, we report for the first time that R. 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. 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%). An overall increase in disease incidence in all studied fields over time was observed for both symptoms. 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. Carrots with different Rhizoctonia-like symptoms were found in the main Swedish carrot production areas from 2001–2020.
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