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
Maize ( 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\u201396 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, \u3b1- copaene, Geranyl
acetone, \u3b2-caryophyllene, \u3b1-bergamotene,
(E)-\u3b2-farnesens, TMTT, and Humulene from infested seedlings. Of
these, methyl salicylate, (E)-caryophyllene, (E)-\u3b2-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.Le ma\uefs ( Zea mays L.) est une importante source
d\u2019\ue9nergie du peuple d\u2019Afrique sub-saharienne.
Malheureusement, sa production est affect\ue9e par la striure brune
du ma\uefs (MSV) (Geminiviridae: genus Mastrevirus), un
pathog\ue8ne end\ue9mique originaire d\u2019herbes africaines. Ce
virus est acquis et transmis de mani\ue8re persistante par la
Cicadelle (Homoptera: Cicadellidae). Pour contr\uf4ler ce virus et
ses vecteurs, il est possible d\u2019exploiter les produits
semiochimiques \ue9mis par les plantes infest\ue9es par les
insects. Une \ue9tude \ue9tait effectu\ue9e sur des compos\ue9s
organiques volatiles \ue9mis par sept vari\ue9t\ue9s de ma\uefs
(Zea mays L.) losrqu\u2019infect\ue9es par la cicadelle ( Cicadulina
storeyi China, Homoptera: Cicadellidae), un vecteur important du
virus de la striure de ma\uefs (MSV) afin de d\ue9velopper des
strat\ue9gies de contr\uf4l de la cicadelle en Afrique
sub-saharienne. Les VOCs servent comme signaux pour les
parasito\uefdes afin de localiser leurs h\uf4tes. Les volatiles
\ue9taient collect\ue9s des jeunes plants des sept
vari\ue9t\ue9s apr\ue8s introduction ou pas d\u2019infestation
de la cicadelle \ue0 des p\ue9riodes de temps allant de 0 - 24, 24
- 48, 48 - 72 and 72\u201396 heures et combin\ue9e, plutard
analys\ue9s \ue0 l\u2019aide du gaz chromatographique.
L\u2019analyse des VOCs issus de sept vari\ue9t\ue9s africaines
\ue9lites montre une variabilit\ue9 intersp\ue9cifique des VOCs.
Le gaz chromatographique (GC) et la combinaison GC- masse
sp\ue9ctrom\ue9trie (GC-MS) ont permis l\u2019identification 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, \u3b1-copaene, Geranyl acetone,
\u3b2-caryophyllene, \u3b1-bergamotene, (E)-\u3b2-farnesens, TMTT,
et Humulene dans des plants infest\ue9es. De tous ces produits
pr\ue9cit\ue9s, seuls methyl salicylate, (E)-caryophyllene,
(E)-\u3b2- farnesene et TMTT \ue9taient auparavant identifi\ue9s
comme volatiles semiochemiques impliqu\ue9s dans la d\ue9fence des
plants contre d\u2019autres pestes d\u2019insectes suceurs des
plantes. Les plants TZB-SR ont \ue9mis 22 compos\ue9s en
pr\ue9sence de la cicadelle en comparaison avec 5 plants non
infest\ue9s; alors que BR9943-DMR.SR ont \ue9mis seulement sept
compos\ue9s en pr\ue9sence de la cicadelle en comparaison de 6
plants non infest\ue9s. Les compos\ue9s \ue9mis par les sept
vari\ue9t\ue9s de ma\ubfs apr\ue8s infestation de la cicadelle
\ue9taient 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 vari\ue9t\ue9s \ue9taient
dot\ue9es de r\ue9sistance au MSV et autres contraintes \ue0 la
production comme le mildew et le stem borers, la variabilit\ue9
manifest\ue9e pourrait avoir des implications \ue9cologiques
significatives dans l\u2019utilisation des compos\ue9s volatiles
\ue9mis des plantes comme moyen de repousser les cicadelles dans le
contr\uf4l du MSV. Ceci souligne le besoin d\u2019entreprendre des
\ue9tudes d\u2019am\ue9lioration g\ue9n\ue9tique des
vari\ue9t\ue9s pouvant \ue9mettre des compos\ue9s volatiles
comme agent de contr\uf4l biologique et repulsif de la cicadelle.
Ceci constitue le premier rapport sur la variabilit\ue9 des
g\ue9notypes de ma\ubfs eu \ue9gard aux compos\ue9s volatiles
organiques \ue9mis \ue0 partir du complexe de peste/pathog\ue8ne
africain. Ceci est en conformit\ue9 avec des \ue9tudes
ant\ue9rieures qui montrent une relative variabilit\ue9
g\ue9n\ue9tique et des VOCs, tous intrins\ue9quement dans des
\ue9missions induites des herbivores