Seed germination and in vitro regeneration of the African medicinal and pesticidal plant, Bobgunnia madagascariensis

Propagation of the medicinal and pesticidal tree, Bobgunnia madagascarensis is difficult due to poor and erratic germination of its seeds and slow growth of its seedlings. This study involved two separate experiments. The first evaluated the effect of pre-sowing treatments and growing medium on ex vitro seed germination and early seedling development. The second experiment involved in vitro germination, shoot initiation and rooting of shoots. Pre-sowing seed treatments involved soaking seeds in cold and hot water for 12 and 24 h and soaking in different concentrations (0, 100, 200, 400 and 800 mg/l) of gibberellic acid for 24 h. Soaking of seeds in cold or hot water for up to 24 h did not achieve more than 45% germination, while seeds treated with gibberellic acid achieved <20% germination rates. On the other hand, in vitro procedures achieved 30 to 70% germination of seeds. Seedling survival of ex-vitro germinated seeds was higher (>76%) when seeds were sown in a growing medium without compost compared with a medium with compost (<43%). All shoot-tips isolated from the in vitro germinated seedlings on B5 media without plant growth regulators continued to grow as a single shoot, while shoot-tips cultured on B5 supplemented with 0.1 mg/l of naphthaleneacetic acid (NAA) and thidiazuron (TDZ) produced two shoots each after four weeks. It was concluded that B. madagascariensis seeds had very low ex vitro germination percentages. Although, in vitro cultures improved seed germination, axillary shoot multiplication and rooting were not satisfactory. Therefore, further studies are needed to develop an optimal in vitro multiplication protocol for B. madagascariensis.Key words: Axillary shoot multiplication, gibberellic acid, in vitro regeneration, seed germination, Swartzia

Pesticidal plants for stored product pests on small-holder farms in Africa

Despite the near elimination of pests from food stores in industrialised nations, insects are still the most important challenge to food security for small-holder farmers in less developed nations. Losses are frequently as high as 20 %. Synthetic products provide effective control when used correctly but are not sustainable or universally appropriate and present many challenges for farmers, not least of all their cost. Pesticidal plants offer an economic, effective and often the only alternative. Much published research, however, overlooks critical knowledge gaps providing outputs that are unlikely to improve pesticidal plant use or improve food security. This chapter identifies opportunities for better targeted research and improvements for uptake and use of pesticidal plants. We also highlight how a deeper understanding of different morphs, gender and age of insect can influence experimental results and should be considered more carefully. To be effective plant materials need to show low animal and environmental toxicity at typical application levels but at the same time be effective against a wide range of target species, at low doses and with longevity. They must also be low cost, safe, compatible with other pest management technologies and stable and have no consequences for the stored products such as impairing flavour. Research should be targeted at optimising the efficacy of the pesticidal plants already known to have potential, and this should be supported by chemistry to fully understand spatial, temporal and phenotypic variability and nontarget impacts. Availability of plants is a limiting factor to uptake so propagation and cultivation of elite provenances would alleviate pressure on natural ecosystems and improve reliability of efficacy and supply when supported by improved harvesting techniques. The large-scale commercialisation of plants may not compete with synthetic products globally but local production may foster a mechanism to support and encourage uptake through local markets and value chains