First report of Maize chlorotic mottle virus and maize (corn) lethal necrosis in Kenya

Authors: WANGAI, ANNE - Kenya Agricultural Research Institute; Redinbaugh, Margaret; KINYUA, Z - Kenya Agricultural Research Institute; MIANO, D - Kenya Agricultural Research Institute; LELEY, P - Kenya Agricultural Research Institute; MAHUKU, G - International Maize & Wheat Improvement Center (CIMMYT); SCHEETS, KAY - Oklahoma State University; JEFFERS, DANIEL - International Maize & Wheat Improvement Center (CIMMYT)

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2012
Publication Date: 10/1/2012
Citation: Wangai, A., Redinbaugh, M.G., Kinyua, Z., Miano, D., Leley, P., Mahuku, G., Scheets, K., Jeffers, D. 2012. First report of Maize chlorotic mottle virus and maize (corn) lethal necrosis in Kenya. Plant Disease. 96:1582-1583.

Interpretive Summary: In 2011, many corn (Zea mays L.) fields in the Southern Rift Valley of Kenya became diseased. By 2012, the disease had spread to several districts in southwestern Kenya and at up to 7000 feet above sea level. Diseased plants develop symptoms characteristic of virus diseases including yellowing and mottling on the leaves, usually starting from the base of the young leaves in the whorl and extending upwards toward the leaf tips. The edges of leaves turn brown and die. This necrosis of young leaves leads to a ‘dead heart’ symptom, and plant death. The disease severely reduced cob size, and little or no yield is obtained from diseased plants. All of the corn hybrids and varieties grown in the affected areas had similar symptoms. Since most virus diseases are transmitted by insects, insect populations were noted. Very high populations of thrips, but not of other insects known to transmit viruses to corn were found. We tested infected leaf samples for a virus called Maize chlorotic mottle virus (MCMV) that is transmitted by thrips, and found it to be present in most leaf samples. When MCMV is present together with a second virus called Sugarcane mosaic virus (SCMV), the two viruses can work together to cause corn lethal necrosis. As the name implies, plants infected with both viruses die fairly rapidly. SCMV was found in most samples, and 23 our of 34 plants tested were infected with both viruses. This is the first report of MCMV and corn lethal necrosis in Kenya and in Africa. The disease is a serious threat to farmers in the affected areas, who are suffering complete crop losses.

Technical Abstract: In September 2011, high incidence of a new maize (Zea mays L.) disease was reported at lower elevations (1900 masl) in the Longisa division of Bomet County, Southern Rift Valley of Kenya. Later the disease was noted in Bomet Central division, spreading into the neighboring Chepalungu and Narok South & North Districts and Naivasha. By March 2012, disease was reported in areas up to 2100 masl. Diseased plants develop symptoms characteristic of virus diseases including chlorotic mottle on the leaves, usually starting from the base of the young leaves in the whorl and extending upwards toward the leaf tips; mild to severe leaf mottling; and, necrosis of leaf margins that progresses to the mid-rib. Necrosis of young leaves before expansion often leads to a ‘dead heart’ symptom, and plant death. Severely affected plants form small cobs with little or no grain set. The entire crop was frequently killed before tasseling. All maize varieties grown in the affected areas had similar symptoms. In these regions, maize is grown continuously throughout the year, with the main planting season starting in November. Streaking associated with Maize streak virus was also present, but MSV incidence was low (data not shown). Infected plants were distributed throughout the fields, with heavy infection along the field edges. High thrips (Frankliniella williamsi (Hood)) populations were present in sampled fields, but populations of other potential disease vectors such as aphids, leafhoppers, planthoppers and beetles were low. Due to the high incidence of thrips and foliar symptoms, symptomatic plants were tested for the presence of Maize chlorotic mottle virus (MCMV) using tissue blot immunoassay (TBIA; 1). Symptomatic leaves were collected from five fields each in Bomet and Naivasha, and 9 of 16 from Bomet and all samples from Naivasha were positive for MCMV. As symptoms were more severe than commonly associated with MCMV, samples were also tested for the presence of Sugarcane mosaic virus (SCMV), which is known in Kenya (2) and which causes corn lethal necrosis (CLN) when present together with MCMV (3). Twenty-six samples were positive for SCMV by TBIA, and 23 of 34 samples were infected with both viruses. The identity of the viruses was verified using RT-PCR. MCMV sequences corresponding to nt 2681-3226 of MCMV (GenBank Accession NC 333627) were amplifed from three leaf samples. Sequences of the resulting amplicons were identical, and had 95-98% identity with MCMV sequences in GenBank. Sequences corresponding to nt 8679-9595 of SCMV (NC 003398) amplified from four leaf samples had 96-98% identity, and were 88-96% identical with SCMV sequences in GenBank. This is the first report of MCMV and CLN in Kenya and in Africa. CLN is a serious threat to farmers in the affected areas, who are experiencing extensive to complete crop loss.