Maize streak, maize stripe and maize mosaic virus diseases QJ in the tropics (Africa and islands ■ h in the Indian Ocean) Dossier prepared by f C. JOURDAN-RUF, J.-L. MARCHAND, M. PETERSCHMITT ■ Impact of maize virus @®CA, BP 5035, 1 • 34032 Montpellier Cedex 1,iranee diseases and current research B. REYNAUD, J. DINTINGER I C tR i0 € A , station, de Ligne Pqljdis, ■ Vectors ■ 97410 Saint-Pierre, Réunion, Fw ce The main research scientists that and epidemiology collaborated in these studies are: G. KONATE, O. TRAORE and S. TRAORE ■ Maize virus diagnosis and (Burkina Faso); #> f r; M. ESSEH-YOVO ¡Togo); C. THE (Cameroon): maize streak virus variability H. PHAM ¡Zimbabwe); P. MARKHAM (UK); C. BUDUCA, B. CLERGET and A. RODIER ■ Maize resistance [Réurtion, France) = } M i ' and breeding Photos D. Debert: Bagging maize inflorescenles. p /Vaize fields in Burkina Fasfx Photo B. Reynaud: Peregrínuâmaidts. Impact of maize virus diseases and current research Regions Madagascar, Réunion, and central in East Africa, Tanzania, Kenya, Africa. The disease is also sometimes Mauritius and Réunion, but MStpV found in West Africa, particularly has caused very little damage. The The three main tropical maize in Mali, Togo, Côte d'Ivoire virus was recently identified viruses are: maize streak virus (MSV), and Senegal. In West Africa, in West Africa (Côte d'Ivoire, maize stripe virus (MStpV) and maize there was a widespread outbreak Togo, Nigeria, Burkina Faso and mosaic virus (MMV). Their impacts of MSV in 1983-1984, sometimes Cameroon). However, it seems to vary markedly between countries completely destroying all maize have had a greater impact in Latin (Figures 1 & 2). crops. This disease also occurs in America, particularly Venezuela and MSV was first detected in South India in wheat and millet, but it has the West Indies. It also occurs in the Africa at the beginning of the not been detected in the South Philippines and Australia. century, and similar virus diseases American tropics. have been described in sugarcane MMV, first discovered in 1921 and in many wild Poaceae species. It MStpV is not as common. Peregrinus in Hawaii, is also transmitted by is transmitted by homopteran insects maidis Ashmead (Homoptera, P. maidis. It was later detected of the genus Cicadulina (Homoptera, Delphacidae), the insect vector, is in Cuba, Guadeloupe, Surinam, Cicadellidae). MSV infections have present in many African countries Venezuela, Guyana, Puerto Rico, been noted in many different (Côte d'Ivoire, Zaire, Nigeria, Burkina Faso, Côte d'Ivoire, Nigeria, countries, with varied incidence. It is Burkina Faso and Cameroon). Since Mozambique, Tanzania, Kenya, endemic to all East African countries, 1936, this insect has been reported Réunion, Mauritius and India. Evolution of host plant/vector/virus complexes P. maidis and the viruses it transmits evolved together in a few plant species. Maize is the favoured host of this vector/virus complex; the original host was teosinte or sorghum. The close host plant/vector relationship perpetuates the complex with the virus, despite the narrow range of host plants and susceptible species. The evolution of MSV, transmitted to maize by Cicadulina mbila Naude, is different: the virus was revealed in maize crops, but also infects wild grasses through the leafhopper vector, which is common in Africa and has a wide host range. 5 6 Agriculture et développement ■ Special issue - December 1995 and more regular maize yields could in resistance transfers to create maize Organizations be obtained with such varieties. varieties that will be more efficient under cropping conditions found in Maize breeding studies began in the involved Africa and throughout the Indian 1930s in East and South Africa with Ocean region. The developed the aim of obtaining MSV resistance. CIMMYT, Centro Internacional de diagnostic techniques can be applied Moreover, the 1972 MSV epidemic Mejoramiento de Maíz y Trigo, Mexico at a variety of sites, without special that occurred in West Africa promp­ CIRAD, Centre de coopération equipment, to identify viruses and ted certain research organizations internationale en recherche assess varietal susceptibility. (IITA and CIMMYT) to conduct agronomique pour le développement, similar studies. France CORAF, during the general assembly meeting of its maize network in CORAF, Conférence des responsables During the 1 970s, CIRAD (in Yaoundé (Cameroon) in 1987, deci­ de la recherche agronomique africains collaboration with African and European partners) focused research ded to launch an MSV research pro­ IRA, Institut de la recherche ject because of the urgency of the agronomique, Cameroon on this topic in order to deal with the serious maize virus epidemic situation. For resistance transfers, INCV, Institut national des cultures problems — the three mairi maize national CORAF correspondents vivrières, Togo viruses and their vectors are present chose a number of varieties from INERA, Institut national d'études rurales including local resistant varieties. among already (or soon to be) et agricoles, Burkina Faso widely grown maize varieties. IITA, International Institute of Tropical The research This multidisciplinary project brings Agriculture, Nigeria together virologists, entomologists John Innés Institute, Norwich, UK and who is involved and geneticist/breeders: Since the 1980s, CIRAD and partners - virus studies by John Innes Institute, The incidence of MMV is generally have been focusing on the following Norwich (UK) and CIRAD, Montpellier (France); low in all of these countries. topics: Nevertheless, serious MMV - insect vectors and their - interactions between viral isolates epidemics have been reported in epidemiology; and resistant genotypes in Réunion some regions of maize growing - maize virus diagnosis; (CIRAD) and Burkina Faso (INERA); countries such as USA (Hawaii, - breeding and investigating - insect vectors in Réunion (CIRAD), Florida), Brazil and Mexico. the genetic factors determining Burkina Faso (INERA) and Cameroon resistances, and transferring them (IRA); Control into susceptible maize genotypes. - maize virus dynamics in host Virus-resistant varieties of maize are These investigations revealed the plants in the tropical phytovirology laboratory (CIRAD); of considerable economic interest vectors and factors involved in due to the extent of damage caused triggering and spreading viral - resistance genetics in Réunion by maize viruses in the tropics epidemics in maize crops and led to (MSV, MStpV, MMV) (CIRAD) and in (Africa, South America) and the the development of specific maize Togo (MSV) (INCV); lack of efficient agronomical and virus diagnosis techniques. Resistant - creation of resistant varieties in chemical control techniques. Higher ecotypes in Réunion have been used Réunion, Togo and Cameroon. ■ Agriculture et développement ■ Special issue - December 1995 5 7 Symptoms Maize streak disease Maize streak is characterized by chlorotic spots along the leaf veins, forming discontinuous streaks of varying thickness. Dwarfism is very marked in young infected plants. Dwarfed young plant. MSV leaf symptoms. Maize mosaic disease Maize mosaic is characterized by regular continuous chlorotic lines running along the whole length of the leaf, parallel to the veins. The symptoms vary according to the thickness of these lines, their spacing and discontinuous appearance. Limited growth of infected plants. Continuous chlorotic stripes caused by MMV. Maize stripe disease Maize stripe occurs in two forms. The first, simply called stripe, is characterized by chlorotic stripes of various widths along the leaves, and the apex is typically curved. The second form, called chlorotic stripe, is characterized by the formation of chlorotic stripes, and the leaves eventually become totally chlorotic, with the reappearance of thick green discontinuous stripes. Young infected plants present severe dwarfism, and then dry up and die. Chlorotic stripes on maize leaves due to MStpV. Photos P. Baudin and B. Reynaud Infected plants are dwarfed and dry up. 5 8 Agriculture et développement ■ Special issue - December 1 995 S t # * * Virus reservoir plants Vectors and A 3-year (1988-1990) wide ranging survey of herbaceous plants was conducted in Burkina Faso, resulting in the detection of 41 Poaceae epidemiology species with MSV symptoms. ELISA tests revealed the presence of the virus in 25 species. Analysis of the spatiotemporal distribution of virus reservoirs (host As early as 1973, Insect vectors plants) highlighted three main points: severe epidemics of several reservoirs were greater in maize crop In Réunion, Cicadulina mbila is the zones; the incidence of MSV in maize viruses were noted main MSV vector even though this maize fields was proportional to the insect occurs in relatively small in Réunion. In 1985, three number of reservoirs; and there were quantities on maize, the final host of very few infectious reservoirs in May, viruses were identified the disease. It is a very active and with an increase 3-4 weeks after the efficient Poaceae-specific vector. by serological techniques: onset of the rains to reach a peak C. storeyi is the next important MSV in August. In Burkina Faso, the MSV, MStpV and MMV. vector in Réunion. Insect vectors are required incidence of MSV is generally 6% or In Burkina Faso, five Cicadulina less in maize plants presenting virus for their transmission. species have been identified in symptoms; it increases to 30-40% MSV is transmitted all ecological zones: C. mbila, during severe epidemics.