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 72–96 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 tha