Plant molecular farming: challenges and opportunities.

Lawsone, (2-hydroxy-1,4-naphthoquinone or HNQ), is known for its antimicrobial activity, corrosion inhibition and metal chelation properties. We describe here a simple methodology to functionalize Fe 3 O 4 nanoparticles with lawsone to produce Fe 3 O 4 -Cysteine-HNQ nanocomplex, using cysteine as a linker. The characterization of the nanocomplex is done using Fourier Transform Infrared (FTIR) spectroscopy, Thermogravimetric Analysis (TGA), Dynamic Light Scattering size measurement, zeta potential and contact angle measurement. The zeta potential of uncoated nanoparticles and Fe 3 O 4 -Cysteine-HNQ nanocomplex is found to be +48 mV and 238 mV respectively. The reversal of surface charge from positive to negative corroborates the presence of lawsone monolayer at particle interface. Further, TGA result shows a weight loss of 32% for these nanocomplexes due to the decomposition of lawsone and cysteine present on the nanoparticles. The FTIR spectrum of the nanocomplex exhibits CLC and CLO stretching bands of lawsone, with a slight shift in their position, which confirms the interaction of lawsone with the cysteine coated nanoparticles. Fe 3 O 4 -Cysteine-HNQ nanocomplexes exhibit interesting properties such as increased wettability (contact angle y20u) on stainless steel substrate and antimicrobial activity against Staphylococcus aureus, with a minimum inhibitory concentration of 700 mg mL 21 . These results show that lawsone functionalized magnetite nanoparticles can be used as response stimulus antimicrobial agents.

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Even though pesticides have greatly contributed to boosting agricultural productivity and farmer income over the years, there have been concerns about the safety of some of these pest control products. Besides, there has been a growing demand for good quality and safe food in the recent past – as reflected in the stringent regulations on pesticide residue levels in produce. Biopesticides in comparison with conventional synthetic chemical pesticides are usually less toxic, generally affect only the target pest and closely related organisms, are often effective in relatively small quantities and decompose faster, resulting in lower exposure. Consequently, over the last few years, biopesticides have attracted global attention as a safer pest control strategy for incorporation into Integrated Pest Management (IPM) programmes. Besides, in the last decade, adoption of IPM programmes has significantly enhanced pest management practices and, in some cases, reduced pesticide use, consequently reducing the rise in demand for synthetic chemical pesticides. Also, the development of new synthetic chemical pesticides has declined considerably in the recent past, as regulations have become tighter, with products being withdrawn from the market, resulting in a more limited choice of chemical solutions such that biopesticides have become a more feasible option. Many countries have also increasingly lowered chemical Maximum Residue Levels for agricultural imports which have made it increasingly necessary to explore pest control options which would ensure reduced reliance on the use of synthetic chemical pesticides. In this paper, avenues of addressing challenges to biopesticide research and development are evaluated by seeking the inputs of a wide range of stakeholders, building on a recent international workshop with biopesticides practitioners from across the globe. Prospects for biopesticide application are detailed using a case study on the fall armyworm (Spodoptera frugiperda) in Africa.