Maize lethal necrosis disease (MLN disease, MLND, corn lethal necrosis) is a viral disease affecting

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...

(corn) predominantly in East Africa, Southeast Asia and South America, which was recognised in 2010. It is caused by simultaneous infection with two viruses, MCMoV and any of several ''

Potyviridae ''Potyviridae'' is a family of positive-strand RNA viruses that encompasses more than 30% of known plant viruses, many of which are of great agricultural significance. The family has 12 genera and 235 species, three of which are unassigned to ...

''.

Etiology

MLND is caused by simultaneous infection with two viruses, maize chlorotic mottle virus (MCMoV) of the ''

Tombusviridae ''Tombusviridae'' is a family of single-stranded positive sense RNA plant viruses. There are three subfamilies, 17 genera, and 95 species in this family. The name is derived from '' Tomato bushy stunt virus'' (TBSV). Genome All viruses in the ...

'' family and any of several viruses from the ''

'' group: the Potyviruses

maize dwarf mosaic virus ''Maize dwarf mosaic virus'' (MDMV) is a pathogenic plant virus of the family ''Potyviridae''. Depending on the corn plant’s growth stage, the virus can have severe implications to the corn plant’s development which can also result in economi ...

(MDMV),

sugarcane mosaic virus ''Sugarcane mosaic virus'' (SCMV) is a plant pathogenic virus of the family ''Potyviridae''. The virus was first noticed in Puerto Rico in 1916 and spread rapidly throughout the southern United States in the early 1920s. SCMV is of great concern ...

(SCMV), Johnsongrass mosaic virus (JGMV), or the Tritimovirus wheat streak mosaic virus (WSMV). JGMV is found to be a contributor - and the other viruses are briefly reviewed and bibliography provided - by Stewart et al. 2017.

Transmission

Spread of the disease is driven by expansion in the range of maize chlorotic mottle virus, which is thought to be transmitted by species of

thrips Thrips (order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...

including maize thrips (''Frankliniella williamsi'') and possibly

western flower thrips The western flower thrips 'Frankliniella occidentalis'' (Pergande)is an invasive pest insect in agriculture. This species of thrips is native to the Southwestern United States but has spread to other continents, including Europe, Australia (wher ...

(''Frankliniella occidentalis''). The potyviruses involved in MLND are transmitted by several species of

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

s and, in the case of wheat streak mosaic virus, wheat curl mite. MLN is associated with the presence of maize thrips and the growth of several crops of maize annually.

Epidemiology

SCMV is the most common second contributor in East Africa, but also JGMV and MDMV. This is the location of Stewart et al. 2017's discovery that JGMV contributes they also review and provide a bibliography as to SCMV and MDMV.

Economic impact

In late 2014, it was reported that MLND could cut

Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi ...

's maize production by as much as 30%. In early March 2015, the middle of the rainy season, losses were estimated at 10%.

Symptoms

Leaves of infected plants become yellow from the tip and margins to the centre. Older leaves (bottom of plant) remain green. Ears and leaves dry up and sometimes look like a mature plant. The whole plant dies and maize cobs remain without kernels. MLND symptoms can be confused with symptoms of nutrient deficiency but plants affected by MLND appear only in some areas and are scattered or clumped in a field while nutrient deficiency appears on many plants over large areas of a field. In the early stages, MLND causes long yellow stripes on leaves. Unlike maize streak virus disease though, the streaks of MLND are wider. As the disease advances, the maize leaves become yellow and dry out from the outside edges towards the midrib. MLND can also cause dwarfing and premature aging of the plants. Finally, the entire plant dries out and dies. Dead plants can then be seen scattered across the field among healthy looking plants. Late infected plants don't tassel and tend to produce poor grain filled cobs. MLND presence in a field is also found by Parsons and Munkvold 2010 to increase susceptibility to ear rot conditions. This may be due to earlier stages of thrips feeding on earlier stages of kernels.

Management

Partners of the CABI-led programme,

Plantwise CABI (legally CAB International, formerly Commonwealth Agricultural Bureaux) is a nonprofit intergovernmental development and information organisation focusing primarily on agricultural and environmental issues in the developing world, and the c ...

recommend where possible using certified, disease-free seed. They also recommend not moving infected maize plants and seeds to disease-free areas. Plantwise and partners also recommend rotating with non-cereal crops (e.g. beans, faba bean, chickpea etc.) for at least 2–3 years/seasons and removing alternate hosts including, sorghum, grasses, millet, wheat, oats, sudan grass. The Ministry of Agriculture and Natural Resources of Ethiopia recommend uprooting and burning of diseased plants. Another method of prevention is to leave land fallow for 2 months especially where maize is produced using irrigation. It is also recommended to plough and expose soil to sunlight for at least 2 months. MLN resistance is an important trait to maize

breeders A breeder is a person who selectively breeds carefully selected mates, normally of the same breed to sexually reproduce offspring with specific, consistently replicable qualities and characteristics. This might be as a farmer, agriculturalist, ...

Forward genetics Forward genetics is a molecular genetics approach of determining the genetic basis responsible for a phenotype. Forward genetics provides an unbiased approach because it relies heavily on identifying the genes or genetic factors that cause a partic ...

is increasingly being used.

Sources

References

External links

* {{cite web , last=Dahm , first=Madeline , title=MLN Diseases portal , website= CIMMYT , date=2021-10-27 , url=http://mln.cimmyt.org/ , access-date=2021-11-26 Viral plant pathogens and diseases Maize chlorotic mottle virus *