Insect specific viruses like nucleopolyhedrosisvirus (NPV) can provide an alternative and effective insect pest control compared to conventional chemicals; however, on certain crops like chickpea efficacy of the virus is limited. Previous studies have demonstrated that inactivation on chickpea was leaf surface based and rapid, however, the compound identified (isoflavonoid, sissotrin) could not account for the total inactivation that was recorded on chickpea leaves. The present study investigated further the legume-NPV insect interaction, with aim of identifying conclusively the compound(s) responsible for NPV inactivation on chickpea, and also to determine if the same plant chemistry also occurs on two other major African and Asian legumes, cowpea and pigeonpea, and to understand the mechanism involved. Laboratory results showed that chickpea leaf surface was more inactivating to NPV than cowpea or pigeonpea. Although both cowpea and pigeon also reduced the efficacy of NPV the effect was relatively small. Bioassays with the isoflavonoids (biochanin A and formononetin), identified to be present or induced at higher levels after spraying with HearNPV, showed that although both compounds significantly reduced NPV efficacy, the effect was modest compared to that recorded on chickpea leaves. When the most abundant chickpea acids (malic and oxalic) were mixed with different concentrations of the isoflavonoids and tested on NPV, significant inactivation was observed which was comparable to that obtained on chickpea leaves. The inactivation of NPV by the combination of chickpea acids plus isoflavonoids was not dependent on high concentrations of isoflavonoid tested, suggesting that chickpea acids alone could be responsible. Therefore, further tests were carried out to determine the role of the acids alone on NPV. The most abundant chickpea acids were prepared at different concentrations and tested with the virus at high lethal concentration. The results showed that chickpea acids alone were responsible for the inactivation of NPV, and among the two acids tested, oxalic was found to be more active against the virus. Although the inactivation was shown to correlate negatively with pH of the acids, the results suggest that oxalic acid was exerting its effect independently of the pH. This is the first study to demonstrate that organic acids of chickpea were responsible for inactivation of NPV. The findings from this study will be helpful in identifying suitable formulation additives to improve the field persistence of NPV on chickpea and other crops.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:732839 |
| Date | January 2015 |
| Creators | Aminu, Aliyu |
| Contributors | Stevenson, Philip ; Grzywacz, David |
| Publisher | University of Greenwich |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://gala.gre.ac.uk/18204/ |
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