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Date: 28 Apr 2011
Source: Horticulture Week [edited]
Carrot crops may need closer monitoring, following the results of an Horticultural Development Council (HDC) project.
The study concluded that internal browning did not appear to be associated with _Parsnip yellow fleck virus_ (PYFV), a semi-persistent virus carried by aphids and against which most current aphid control measures in carrots are aimed. Instead, it found that internal browning appeared to be associated with viruses from the carrot motley dwarf complex (CMD), most commonly in combinations including _Carrot mottle virus_ (CMoV).
Growers began to experience significant crop losses from the condition. Crop advisers found that it was evident in regional virus "hot spots" and appeared in addition to the textbook foliar symptoms and root stunting. The project, therefore, aimed to determine the extent of the problem and which viruses were associated with it.
Root crops consultant Howard Hinds said the finding was significant because of the persistent nature of the CMD viruses. "Aphids carrying them remain infectious throughout their lives. Aphid control programmes will have to be modified to control both CMD and PYFV. The period of vigilance will need to be extended, with more monitoring of aphid activity. Aphid activity can pick up again in a warm September and continue to the end of October, creating a late season CMD risk period."
[Byline: Rachel Sixsmith]
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Communicated by:
ProMED-mail
[Carrot motley dwarf disease (CMDD) is due to a mixed infection of _Carrot red leaf virus_ (CtRLV, family _Luteoviridae_, not assigned to a genus) with _Carrot mottle mimic virus_ (CMoMV, genus _Umbravirus_) or Carrot mottle virus (CMoV; genus _Umbravirus_), and a satellite RNA associated with CtRLV (CtRLVaRNA) may also be present. The disease can affect carrot, parsley, dill and other species in the family _Apiaceae_. It has been reported from Europe, Australia, New Zealand, and a number of locations in the Americas and Asia. Until the findings of the study above, CMDD symptoms were said to include leaf discolouration (red or yellow) as well as stunting of shoots and roots. Symptoms can vary with environmental factors; for example, in warmer conditions, carrots may be symptomless. CMDD leads to loss of plant vigour, which can cause substantial yield reductions.
The viruses are transmitted by the carrot-willow aphid (_Cavariella
aegopodii_) in a persistent manner (insects remain infectious for life). CtRLV is transmitted independently, but vector transmission of CMoMV, CMoV and the satellite are dependent on the presence of CtRLV as a helper virus. Volunteer crop plants and apiaceous weeds may serve as virus and/or vector reservoirs, and carrots left behind from the previous crop often serve as a primary pathogen source. Disease management may include cultural methods and phytosanitation to minimise inoculum, as well as vector control. It is thought that due to the tendency towards reduced use of insecticides in agriculture, CMDD may become more frequent and important in the future.
_Parsnip yellow fleck virus_ (PYFV; genus _Sequivirus_) also causes yellowing of leaves as well as internal necrosis and browning in carrot roots. It is also transmitted by aphid vectors, but the virus is lost during moulting.
Map of UK:
Pictures
CMD symptoms:
(leaves) and
(whole plants, comparison with healthy)
PYFV symptoms in carrot roots:
Carrot-willow aphid:
Links
Additional news story:
Information on carrot motley dwarf disease and associated viruses:
Taxonomy and description of all viruses via:
Information on aphids, including _C. aegopodii_:
Horticultural Development Council:
- Mod.DHA]
Topics
Species
