Aromatic Plants as Sources of Photoactive Biological Products Useful to Crop Protection

Aromatic plants are economically important due their flavouring, pharmacological or industrial utilities. The bioactivity of several substances synthesized by plants is triggered by absorption of solar light. Studies have been developed aiming to protect crops against pests and diseases by using this new type of natural substances whose activity is enhanced or started by the absorption of light. Natural photo-pesticides can act as potent herbicides and can control viruses, bacteria, algae, nematodes, yeasts and fungi. Present work relates to a large number of aromatic plants subjected to extraction procedures in the search of their potential as source for new natural photoactive plant products. The species Althaea officinalis, Calamintha baetica, Coriandrum sativum, Cuminum cyminum, Chelidonium majus, Ephedra fragilis, Juniperus comunnis, Laurus nobilis, Mentha pulegium, Origanum vulgare, Picris spinifera, Sambucus nigra, Satureja montana, Syzygium aromaticum and Thymus sp., traditionally used as spices or for medicinal purposes, were analysed for their photoactive potential. Plants were extracted in water or organic solvents, while essential oils were obtained by hydrodistillation. Both essential oils and extracts prepared were tested against the phytopathogenic fungi Aspergillus flavus, A. niger, Botrytis cinerea, Cladosporium cucumerinum, Fusarium culmorum; plant extracts were also tested on the bacteria Erwinia carotovora and Pseudomonas aeruginosa. For irradiation a sun light simulator was used. Effects of plants oil and extracts were detected, by comparing the microorganisms growth inhibition on the plates irradiated to those kept under dark. Strong photoactivity was observed to C. majus and C. cyminum both against fungi and bacteria; C. baetica, O. vulgare, P. spinifera and S. montana were very active, while L. nobilis was only slightly active. Good results observed for this set of plants enhances their antimicrobial properties and their photoactive potential.