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News archive 1997-2008

First report of maize chlorotic mottle virus in Spain

A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>

Date: November 2016
Source: Plant Disease [edited]
<http://apsjournals.apsnet.org/doi/full/10.1094/PDIS-09-16-1261-PDN>

[ref: MA Achon, et al (2016). First report of _Maize chlorotic mottle virus_ on a perennial host, _Sorghum halepense_, and maize in Spain.

Plant Disease 100, posted online; DOI: 10.1094/PDIS-09-16-1261-PDN]

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Maize lethal necrosis disease (MLND) is caused by the synergistic interaction between _Maize chlorotic mottle virus_ (MCMV) and _Maize dwarf mosaic virus_ (MDMV), _Sugarcane mosaic virus_ (SCMV) and _Wheat streak mosaic virus_ (WSMV). MLND is an economically devastating disease in the New World and an emerging disease in Africa and Asia.

The rapid spread of MLND in these continents generated increasing concern in Spain. MLND has not been formally observed in Spain because _Maize rough dwarf virus_ in single or mixed infections with MDMV and SCMV is the major threat, and these viruses cause diseases that are able to mask the symptoms of MLND.

To assess the presence of MCMV in Spain, 198 samples of weed grasses including 102 of _Sorghum halepense_, 34 of _Setaria_ sp., 22 of _Cynodon dactylon_, 14 of _Phragmites australis_, 8 of _Brachypodium phoenicoides_, 6 of _Echinochloa crus-galli_ and 12 of other _Gramineae_ species were collected in northeastern Spain during 2014 and 2015. _S. halepense_ was the unique grass showing symptoms consisting of mosaic, yellowing, and in some plants, necrotic lesions.

Moreover, 10 maize (_Zea mays_) samples with mosaic symptoms and yellowing longitudinal bands along leaves were collected in the same area.

All these samples were analyzed by DAS-ELISA using commercial antisera against MCMV, MDMV and SCMV. 48 samples of _S. halepense_ tested positive to both MDMV and MCMV, 13 to MDMV, and 3 to MCMV. Out of 10 maize samples, 9 were positive to MDMV and MCMV, the remaining one to MCMV only. None of the other grass species tested positive to any of the viruses.

To confirm results, 12 _S. halepense_ and 6 maize leaves including mixed MCMV-MDMV and single MCMV infected samples [were] analyzed for MCMV by reverse transcription (RT)-PCR. The 18 samples gave the expected PCR product. One product from _S. halepense_ was sequenced.

Comparisons of the 519 bp segment showed 96 to 99 per cent identity with MCMV sequences in GenBank. 6 _S. halepense_ and 4 maize samples were also analyzed with primers designed to amplify a 950 bp [segment] of MCMV. The sequence from _S. halepense_ shared identities from 96 to 100 per cent with MCMV sequences in GenBank.

To our knowledge, this is the 1st report of the occurrence of MCMV in Spain and in Europe. Furthermore, this is the 1st report of MCMV in a perennial host such as _S. halepense_. The role that this grass could play in the epidemiology of this virus needs further investigation.

communicated by: ProMED-mail <promed@promedmail.org>

[Maize lethal necrosis (MLN) is caused by co-infection of _Maize chlorotic mottle virus_ (MCMV, genus _Machlomovirus_, transmitted by chrysomelid beetles) with one of several species in the family _Potyviridae_. As synergistic partners of MCMV in MLN, _Wheat streak mosaic virus_ (WSMV, genus _Tritimovirus_) or _Maize dwarf mosaic virus_ (MDMV, genus _Potyvirus_) have been reported previously from the Americas and Europe. MLN as well as MCMV were reported for the 1st time in Africa from Kenya in 2012 (ProMED-mail post http://promedmail.org/post/20130123.1510727). The disease is spreading in the region where millets have recently also been identified as an additional crop host being affected by MLN (ProMED-mail post http://promedmail.org/post/20150820.3590521). _Sugarcane mosaic virus_

(SCMV) has been reported as the co-infecting virus in Sub-Saharan Africa, but MDMV and SCMV belong to a complex of closely related potyviruses infecting tropical grasses. Based on serology, some strains (for example, MDMV-B) varying in host range and ability to be seed transmitted have been reassigned between the species which has resulted in some confusion in taxonomy.

Symptoms of the individual viruses are synergistically enhanced in MLN and may include leaf mottling and necrosis, distortion of ears, absence of kernels, failure to produce tassels, as well as stunting, premature aging and death of plants. Symptoms may disappear during the growing season leaving plants with latent infections but reduced yield and as virus reservoirs, making disease monitoring difficult. While MCMV is not seed transmitted, the synergistic partner viruses WSMV and MDMV (including some reassigned strains previously included in SCMV) are. Thus, losses from MLN are both due to yield reductions and trade implications resulting from the risk of virus infected seed.

Infectious vector insects may be carried by wind over long distances.

Disease management may include crop rotation, certified clean seeds, control of vector species and weedy reservoir hosts, as well as use of crop cultivars or hybrids with reduced sensitivity to the viruses.

The report above confirms the presence of a perennial reservoir host for MCMV and this needs to be taken into account for MLN disease management in all affected areas. It also shows the importance of molecular diagnosis since symptoms may be influenced or masked by multiple other factors like environment, host and pathogen strains, and, as this case illustrates, presence of other pathogens.

_Maize rough dwarf virus_ (MRDV; genus _Fijivirus_) may result in yield losses of up to 30 per cent. Besides maize, it can also affect oats, rye, barley, wheat, rice and several grassy weeds. It is spreading in parts of Europe, Africa and South America.

Maps

Spain:

<http://www.map-of-spain.co.uk/large-map-of-spain.htm>

Provinces of Spain:

<http://www.venamicasa.com/wp-content/uploads/2012/03/spain_map3.gif>

Europe, overview:

<http://www.edinphoto.org.uk/0_MAPS/0_map_europe_political_2001_enlarged.jpg>

Pictures

Maize lethal necrosis:

<http://cabiplantwise.files.wordpress.com/2013/04/maize-lethal-necrosis.jpg>

and

<http://1.bp.blogspot.com/-8DVgQ8JnqQw/UBv0MFhAGQI/AAAAAAAAAAc/QrawWiKF06o/s1600/Maize.JPG>