Farah, Abdiqani Ahmed
The development of a commercially-available Neem seed kernel extract as a soil-applied systemic granular plant protection product.
PhD thesis, University of Glasgow.
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Crude extracts of the seed kernels of the neem tree (Azadirachta indica) are widely used as plant protection products. The active ingredient (a.i.) of these extracts is azadirachtin A (aza A). aza A is a phytochemical
(botanical) complex secondary metabolite which, with it is multiple toxic effects on insects, protects the plant against predation. Aza A is present in only low concentration in neem oil, but makes up 20-50% in the NSKEs extracted by polar solvents from the kernels. However, when used as foliar sprays it is rapidly destroyed by sunlight, and might be more effective if it is used systemically. Therefore the aim of the project was to extend previous work and to prepare a pelleted version of the main commercially-available neem-seed kernel extract, NeemAzal®-Technical (NAT) produced by Trifolio GmbH, in preparation for the expected registration of the product in the UK in 2011.
It was first necessary to purify a quantity of aza A for quantification of the a.i. pelleted material and in soil and plants in the rest of the project. In achieving high purity (over 98%) aza A, reverse phase chromatographic methods were used, and mass spectrometery was used to confirm purity and identification. A final quantity of 6.2 mg of azadirachtin A was obtained from 4 gm of NAT, a yield of 0.15%.
If aza A and the other neem terpenoids are to be used to plant protection, they must have a low phytotoxicity. Effect of NAT on the germination and its ensuing seedling development of two commercially important crops, sugar beet and cabbage was examined. NAT did have an inhibitory effect on seedling growth at 10-3 M aza A. In order to explore the inhibitory affect of aza A, the second part of the chapter was to examine effect of aza A on mitosis of onion root tips. The limonoids in concentration of 10-3 M adversely affected the mitotic activity of onion root tip cells. This could be failure of microtubules polymerisation into microtubules, or some other biochemical effect. From the findings in this part of the project, it can be concluded that only at a concentration of 10-3 M is aza A toxic to plant young seedlings, but in practice this is unlikely to be a significant problem.
The first part of Chapter 4 of the project was to lay the foundations for the behaviour of aza A in soil environment in both powder form and in 2 types of granular formulations. The half-life of azadirachtin in soil from this work was found to be 1.6 days which is consistent with the previous reports. This short half-life of aza A may be problematic in use as a PPP. The short persistence might be overcome by formulating neem materials in granules to achieve environmental stability and biological efficacy of application. The granular formulations used in the project showed controlled release characteristics. The release of azadirachtin into the soil water was in fact delayed by encapsulating it in pellets. Systemic uptake of aza A by roots and subsequent presence in the vascular system of plants was assessed. Aza A was transported and was more stable in the leaf areas of cabbage and sugar beet plants than in the soil, as the half-life was found to be 9 days. The concentration of aza A in the leaf-water was less than 10% of the solution bathing the roots.
The final part of the project, the application of the pelleted NSKE to protect cabbage, in both glass house and field conditions, demonstrated that neem products in pelleted formulations could be used as effective, systemically applied PPP to control pests of cabbage. In the field tests, the protective effect of the neem extract could be shown over a period of at least 5 weeks after addition of the pellets to the soil.
In conclusion, the short soil half-life of the neem a.i., aza A, in PPP could be overcome by a pelleted formulation, the composition of which can delay release of the a.i. The technology allows protection of crops from soil-borne, as well as foliar sucking and biting pest damage by controlled release into the soil to allow uptake into plant vascular system.
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