Many investigations have been carried out with the purpose of investigating the possibility of using alkaloids in plant protection617'618'619'620'621. Organic farming requires new possibilities to protect plants without strong synthetic pesticides. Natural botanicals and natural compounds extracted from plants are considered as possibilities. Alkaloids are considered useful for this purpose.
Quinolizidine alkaloids, pure or in mixtures of plant extract, can be used to protect plants against noxious insects. Scientific data has shown that quino-lizidine alkaloids play a role in the resistance of some lupine varieties to the pea
• N in the Soil 1 ON in the Soil 2 T N in the Soil 3 v N in the Soil 4
Figure 94. Nitrogen content in different soils after 1 year from sample preparations. (Notes: Soil 1 = control soil after lupine cropping, no canopy addition, stored as a large sample in a laboratory with a constant temperature of -15°C; Soil 2 = soil identical to control with the lupine canopy and water addition (5 kg canopy, 13.5 kg standard soil, 201 water), stored as a large sample in the experimental area; Soil 3 = soil identical to control 1 with lawn plant canopy (dominant species Poa, Festuca, Lolium) addition (5 kg canopy, 13.5 kg control soil and 20 l of water), stored as a large sample in the experimental area; Soil 4 = control soil after lupine cropping stored in natural conditions in the experimental area, stored as a part of natural soil; Bars indicate standard deviations (SD)). (Sources: Refs [615, 616])
aphid (Acyrthosiphon pisum Harris) due to their ability to inhibit the development of this pest population617. Evidence also points out that alkaloidal extracts have an important influence on the feeding and development of larvae and on potato beetle mortality. Researchers concluded that the toxicity and restricted larval development was correlated with alkaloid content618. In this research, the strongest action of the extract contained 1.6-3.3% alkaloids. Spraying potatoes with lupine extract seems to be effective and hence a very promising possible application for alkaloids as natural plant-protecting agents. Other alkaloids toxic to insects can also be tested and used for this purpose. Kahnt and Hijazi332 have suggested that Lupinex, a natural product which contains 5% quinolizidine alkaloids, is not only a fertilizer but also a protector against insects.
An extract taken from the composted straw of the alkaloid-rich lupin plants has produced very promising results in the development of biological control agents622. The fungistatic activity of straw compost extracts increased markedly when the lupin straw used for composting was enriched with alkaloid extract.
Alkaloids are botanicals. Their use in plant control is a very promising technological challenge in today's world, wrought with ecological problems connected to production and farming. The alkaloids are one group of compounds that seem
to play a role in the natural resistance mechanism of some plant species. The possibilities of using natural resistance in plant protection and in the development of resistance cultivars are both considered relatively large in number623. This is of importance when considering molecular biology possibilities in plant breeding. It is theoretically feasible that in the future alkaloid-immune and alkaloid-resistance models will be mimicked in new cultivars without decreasing the quality of food and feed. Toxic compounds will be replaced by non-toxic ones, which will have selective toxicity only to the noxious plant insect species.
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