Browsing by Author "Khan, Zeyaur R."

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    Combined control of Striga hermonthica and stemborers by maize–Desmodium spp. intercrops
    (ScienceDirect, 2006-09) Hassanali, Ahmed; Midega, C. A.O.; Wadhams, Lester J.; Pickett, John A.; Khan, Zeyaur R.
    The African witchweed (Striga spp.) and lepidopteran stemborers are two major biotic constraints to the efficient production of maize in sub-Saharan Africa. Previous studies had shown the value of intercropping maize with Desmodium uncinatum in the control of both pests. The current study was conducted to assess the potential role of other Desmodium spp., adapted to different agro-ecologies, in combined control of both pests in Kenya. Treatments consisted of intercropped plots of a Striga hermonthica- and stemborer-susceptible maize variety and one Desmodium sp. or cowpea, with a maize monocrop plot included as a control. S. hermonthica counts and stemborer damage to maize plants were significantly reduced in maize–desmodium intercrops (by up to 99.2% and 74.7%, respectively) than in a maize monocrop and a maize–cowpea intercrop. Similarly, maize plant height and grain yields were significantly higher (by up to 103.2% and 511.1%, respectively) in maize–desmodium intercrops than in maize monocrops or maize–cowpea intercrops. These results confirmed earlier findings that intercropping maize with D. uncinatum effectively suppressed S. hermonthica and stemborer infestations in maize resulting in higher crop yields. They also demonstrate that the other Desmodium spp. assessed in the current study have similar effects as D. uncinatum, indicating comparable phytochemical and other relevant attributes in these species. Overall results indicate the suitability of the Desmodium spp. for the control of both S. hermonthica and stemborers in maize.
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    Desmodium species and associated biochemical traits for controlling Striga species: present and future prospects
    (2008-01-07) Hassanali, Ahmed; Hooper, A. M.; Midega, C. A.O.; Khan, Zeyaur R.
    We discovered serendipitously a new and highly effective intervention against Striga spp., including Striga hermonthica (African witchweed), in cereals, which involves intercropping with cattle fodder legumes, Desmodium spp., including D. uncinatum. Although soil shading and additional nitrogen made some contribution to the reduction of S. hermonthica infestation, an allelopathic mechanism associated with the intercrop was a major factor. Root exudates of D. uncinatum contain novel flavonoid compounds, some of which stimulate germination of S. hermonthica and others dramatically inhibit its subsequent development, including radicle growth. Desmodium spp. have been developed as intercrops for both maize and sorghum and are now being evaluated for millet. From the experience with Desmodium spp., there is now the possibility for producing edible legumes suitable for intercropping with maize and other cereals to respond to a broader profile of farmer practices. These legumes would incorporate the powerful S. hermonthica controlling properties of D. uncinatum through feasible breeding programmes, with appropriate contributions from analytical chemistry to plant molecular genetics and biotechnology. In the longer term, it may also be possible to transfer genes associated with the allelopathic attributes to cereals themselves by heterologous gene expression, creating a new generation of parasitic weed-free cereals.
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    Integrated pest management: the push–pull approach for controlling insect pests and weeds of cereals, and its potential for other agricultural systems including animal husbandry
    (Philosophical Transaction of the Royal Society, 2008-02) Hassanali, Ahmed; Herren, Hans; Khan, Zeyaur R.; Pickett, John A.; Woodcock, Christine M.
    This paper describes the ‘push–pull’ or ‘stimulo-deterrent diversionary’ strategy in relation to current and potential examples from our own experiences. The push–pull effect is established by exploiting semiochemicals to repel insect pests from the crop (‘push’) and to attract them into trap crops (‘pull’). The systems exemplified here have been developed for subsistence farming in Africa and delivery of the semiochemicals is entirely by companion cropping, i.e. intercropping for the push and trap cropping for the pull. The main target was a series of lepidopterous pests attacking maize and other cereals. Although the area given to the cereal crop itself is reduced under the push–pull system, higher yields are produced per unit area. An important spin-off from the project is that the companion crops are valuable forage for farm animals. Leguminous intercrops also provide advantages with regard to plant nutrition and some of the trap crops help with water retention and in reducing land erosion. A major benefit is that certain intercrop plants provide dramatic control of the African witchweed (striga). Animal husbandry forms an essential part of intensive subsistence agriculture in Africa and developments using analogous push–pull control strategies for insect pests of cattle are exemplified.
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    Responses of the blister beetle Hycleus apicicornis to visual stimuli
    (Wiley Online Library, 2011) Lebesa, Lefulesele N.; Khan, Zeyaur R.; Hassanali, Ahmed; Pickett, John; Bruce, Toby A.; Skellern, Matthew; Uger, Kerskink
    Insect attraction to host plants may be partly mediated by visual stimuli. In the present study, the responses of adult Hycleus apicicornis (Gu´er.) (Coleoptera: Meloidae) to plant models of different colours, different combinations of two colours, or three hues of blue of different shapes are compared. Single-colour models comprised the colours sky blue, bright green, yellow, red, white and black. Sky blue (reflecting light in the 440–500 nm region) is the most attractive, followed by white, which reflects light over a broader range (400–700 nm). On landing on sky blue targets, beetles exhibit feeding behaviour immediately. When different hues of blue (of different shapes) are compared, sky blue is preferred over turquoise, followed by dark blue, indicating that H. apicicornis is more attracted to lighter hues of blue than to darker ones. No significant differences are found between the three shapes (circle, square and triangle) tested, suggesting that reflectance associated with colour could be a more important visual cue than shape for host location by H. apicicornis. The preference of H. apicicornis for sky blue can be exploited in designing an attractive trap for its management.