VARIABILITY OF VOLATILE ORGANIC COMPOUNDS EMITTED BY SEEDLINGS OF SEVEN AFRICAN MAIZE VARIETIES WHEN INFESTED BY ADULT CICADULINA STOREYI CHINA LEAFHOPPER VECTORS OF MAIZE STREAK VIRUS
2012; African Journals OnLine; Volume: 20; Issue: 2 Linguagem: Inglês
ISSN
2072-6589
AutoresSunday Oluwafemi, MA Birkett, John C. Caulfield, J. A. Pickett,
Tópico(s)Insect and Pesticide Research
ResumoMaize ( Zea mays L.) is an important source of energy for the people in sub-Saharan Africa. Unfortunately, maize production is under the threat of Maize streak virus (MSV) (Geminiviridae: genus Mastrevirus), an endemic pathogen of native African grasses. This virus is acquired and transmitted in a persistent manner, by Cicadulina spp. leafhoppers (Homoptera: Cicadellidae) .One possibility for controlling the virus and the vectors is to exploit volatile semiochemicals released by plants following insect herbivory. A study was conducted on herbivoreinduced volatile organic compounds (VOCs) of seven African maize ( Zea mays L.) varieties in the presence of the leafhopper ( Cicadulina storeyi China, Homoptera: Cicadellidae) an important vector of maize streak virus (MSV) with a view of developing novel leafhopper control strategies in sub-Saharan Africa. VOCs are known to repel herbivory and also serve as cues for parasitoids to locate their hosts. Volatiles were collected from young maize seedlings of 7 varieties after entrainment with or without infestation of leafhoppers in 0 - 24, 24 - 48, 48 - 72 and 72–96 hr periods and combined and subsequently analysed by gas chromatography. Analysis of the VOCs collected from the seven elite African varieties shows high interspecific VOC variability. Gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS) led to the identification of (z)-3-hexen-1-ol, heptanal, (z)-2-pentenyl acetate, MHO, octanal, myrcene, (z)-3-hexen-1-yl acetatate, (E)-3-hexen-1-yl acetatate, nonanal Linalool, DMNT, (E)-2-decen-1-ol, Methyl salicylate, DMNT, Phenethyl acetate, Indole, cis-jasmone, α-copaene, Geranyl acetone, β-caryophyllene, α-bergamotene, (E)-β-farnesens, TMTT, and Humulene from infested seedlings. Of these, methyl salicylate, (E)-caryophyllene, (E)-β-farnesene and TMTT were identified previously as volatile semiochemicals involved in plant defense against other sucking insect pests. TZB-SR seedlings emitted 22 compounds in the presence of leafhoppers, compared with 5 by uninfested seedlings; while BR9943-DMR.SR emitted only seven compound in the presence of leafhoppers compared with 6 by uninfested seedlings. The compounds emitted by the seven maize varieties after herbivory were in the following descending order: TZB-SR > TZBR.ELD3.C3 > AMA.TZBR = 8338-1> GUSAU 81.POOL16-SR = 9021-18.STR > BR9943-DMR.SR. Although these varieties were bred for resistance to MSV and other production constraints like downy mildew and stem borers, the variability being reported would have significant ecological implications in utilising plant induced volatiles as repellents for leafhoppers in controlling MSV and underscores the need to breed for varieties that produce volatiles which are very attractive to biological control agents and repellent to leafhoppers. This is the first report of variability of maize genotypes on herbivores-induced volatiles from an African pest/pathogen complex and is in conformity with previous studies that maize shows relatively high genetic and VOC variability, both intrinsically and in herbivore-induced emissions. Key Words: Herbivores-induced volatile organic compounds, Zea mays Le mais ( Zea mays L.) est une importante source d’energie du peuple d’Afrique sub-saharienne. Malheureusement, sa production est affectee par la striure brune du mais (MSV) (Geminiviridae: genus Mastrevirus), un pathogene endemique originaire d’herbes africaines. Ce virus est acquis et transmis de maniere persistante par la Cicadelle (Homoptera: Cicadellidae). Pour controler ce virus et ses vecteurs, il est possible d’exploiter les produits semiochimiques emis par les plantes infestees par les insects. Une etude etait effectuee sur des composes organiques volatiles emis par sept varietes de mais ( Zea mays L.) losrqu’infectees par la cicadelle ( Cicadulina storeyi China, Homoptera: Cicadellidae), un vecteur important du virus de la striure de mais (MSV) afin de developper des strategies de control de la cicadelle en Afrique sub-saharienne. Les VOCs servent comme signaux pour les parasitoides afin de localiser leurs hotes. Les volatiles etaient collectes des jeunes plants des sept varietes apres introduction ou pas d’infestation de la cicadelle a des periodes de temps allant de 0 - 24, 24 - 48, 48 - 72 and 72–96 heures et combinee, plutard analyses a l’aide du gaz chromatographique. L’analyse des VOCs issus de sept varietes africaines elites montre une variabilite interspecifique des VOCs. Le gaz chromatographique (GC) et la combinaison GC- masse spectrometrie (GC-MS) ont permis l’identification de (z)-3-hexen-1-ol, heptanal, (z)-2-pentenyl acetate, MHO, octanal, myrcene, (z)-3-hexen-1-yl acetatate, (E)-3-hexen-1-yl acetatate, nonanal Linalool, DMNT, (E)-2-decen-1-ol, Methyl salicylate, DMNT, Phenethyl acetate, Indole, cisjasmone, α-copaene, Geranyl acetone, β-caryophyllene, α-bergamotene, (E)-β-farnesens, TMTT, et Humulene dans des plants infestees. De tous ces produits precites, seuls methyl salicylate, (E)-caryophyllene, (E)-β-farnesene et TMTT etaient auparavant identifies comme volatiles semiochemiques impliques dans la defence des plants contre d’autres pestes d’insectes suceurs des plantes. Les plants TZB-SR ont emis 22 composes en presence de la cicadelle en comparaison avec 5 plants non infestes; alors que BR9943-DMR.SR ont emis seulement sept composes en presence de la cicadelle en comparaison de 6 plants non infestes. Les composes emis par les sept varietes de ma?s apres infestation de la cicadelle etaient classes comme suit par ordre descendant: TZB-SR > TZBR.ELD3.C3 > AMA.TZBR = 8338-1> GUSAU 81.POOL16-SR = 9021-18.STR > BR9943-DMR.SR. Bien que ces varietes etaient dotees de resistance au MSV et autres contraintes a la production comme le mildew et le stem borers, la variabilite manifestee pourrait avoir des implications ecologiques significatives dans l’utilisation des composes volatiles emis des plantes comme moyen de repousser les cicadelles dans le control du MSV. Ceci souligne le besoin d’entreprendre des etudes d’amelioration genetique des varietes pouvant emettre des composes volatiles comme agent de control biologique et repulsif de la cicadelle. Ceci constitue le premier rapport sur la variabilite des genotypes de ma?s eu egard aux composes volatiles organiques emis a partir du complexe de peste/pathogene africain. Ceci est en conformite avec des etudes anterieures qui montrent une relative variabilite genetique et des VOCs, tous intrinsequement dans des emissions induites des herbivores. Mots Cles: Composes organiques volatiles emis par des herbivores, Zea mays
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