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Effects of bush mint(Hyptis spicigera L.) On maize (Zea mays L.)seeds germination and the control of maize weevil sitophilus zeamais motschulsky(Coleoptera:Curculionidae)

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dc.contributor.author Wekesa, Ingrid
dc.date.issued 2012-03
dc.date.accessioned 2022-09-28T09:28:57Z
dc.date.available 2022-09-28T09:28:57Z
dc.description.abstract Striga hermonthica is a noxious obligate root parasite that is a threat to cereals, especially maize and sorghum production, in sub-Saharan Africa. Bush mint. (Hyptis spicigera), has been identified as trap crop that stimulates ‘suicidal’ germination of S. hermonthica preconditioned seeds. This study focused on evaluating the mode of release of allelochemicals from H. spicigera that interfere with germination and growth of maize seedlings. Fresh and dried plant extracts, root exudates. essential oils and leaf debri treatments were used in radicle length and growth bioassays. Further work involved determining the toxicity and repellent potencies of H. spicigera against the maize weevil. Silophilus zeumais. Essential oils. methanol extracts and hexane extracts were tested against the maize weevil in fumigation. contact and repellency laboratory bioassays. All treatments were arranged in a completely randomized design (CRD) and replicated appropriately. Results revealed that H. spicigera extracts exerted typical allelopathic effects on radicle lengths of maize seedlings. Aqueous fresh inflorescence, leaves and stems plants extracts significantly inhibited radicle length by 1.55 i 0.06°. 1.77 i 0.04°and 257$ 0.07b respectively compared to dried leaves and stem plant extracts by 3.30 1 0.l7a and 4.54 1 0.32“ at 50% treatment and control 3.21 i 0.09“. Root exudates inhibited radicle length by 2.24 :i: 0.02b compared to the control 2.35 i 0.03“. while plant volatiles and leaf debri did not exert inhibitory effects on radicle growth and growth of maize seedlings respectively. H. spicigera aqueous extracts are therefore allelopathic to maize under laboratory conditions and could be responsible for the interference observed in field conditions. Notably, essential oils possessed potent dose- dependent fumigant toxicity against S. zeamais. Total mortality was observed within 48h of exposure in >20 pl essential oil treatments. LC50 value was 48.1 lpl. Contact assays revealed significant mortality of the insects. over 50% after 72h and 48h of exposure. for hexane and methanol extracts respectively. applied at 50 mg, with significantly lower progeny emergence. Essential oils and solvent extracts caused over 50% repellency. with l00pl evoking 84% repellency (RD5@44.32ul). Analysis of essential oils by GC-MS revealed abundance of mono- and sesquiterpenoids, with constituents identified as 0.-pinene. [5-pinene. (1-phellandrene, isocaryophyllene, limonene-co-eluting with phellandrene and L-phellandrene co-eluting with ot- thujene. The plant may be exploited for the development of botanical insecticides to be used in weevil management. en_US
dc.language.iso en en_US
dc.publisher Egerton University en_US
dc.subject Bush mint en_US
dc.subject Control of maize weevil en_US
dc.title Effects of bush mint(Hyptis spicigera L.) On maize (Zea mays L.)seeds germination and the control of maize weevil sitophilus zeamais motschulsky(Coleoptera:Curculionidae) en_US
dc.type Thesis en_US

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