Evaluation of bioactivity of phytotoxins from pathogenic fungi of orobanche sp

Abstract

Weeds and Orobanche species in particular cause great loss to crop farmers worldwide. The devastating effect that Orobanche crenata attack has on legumes forces many farmers to delay or abandon their cultivation. Many efforts have been devoted to control this parasitic weed, but to date there are no completely satisfactory control measures. When comparing the control of Orobanche with non-parasitic weeds, it is realised that the control of Orobanche is exceptionally difficult. The ability of the parasite to produce a tremendously high number of seeds, which can remain viable in the soil for more several years, and the intimate physiological interaction that exists with their host plants, are the main difficulties that limit the development of successful control measures that can be accepted and used by all farmers. However, several control methods have been tried and recommended for the control of Orobanche. These include cultural and mechanical (crop rotation, trap and catch cropping, fallowing, hand-pulling, nitrogen fertilization, time and method of planting, intercropping and mixed cropping), physical (solarisation), chemical (herbicides, artificial seed germination stimulants), use of resistant varieties, and biological. At the field level, the management of Orobanche is still unsatisfactory since - with the exception of the use of glyphosate in faba bean to control Orobanche crenata, present control methods are not efficient enough to control the underground development stages of the parasite. Considering the increasing awareness of herbicide resistance, and the restriction of the use of chemical pesticides in agriculture, novel compounds from micro-organisms and plants may provide new alternatives for the control of weeds that may otherwise be difficult to control, e.g. parasitic weeds. Pathogenic fungi and bacteria often damage their host plants by producing toxins, which cause various symptoms including necrosis, chlorosis, wilting, water soaking and eventually the death of plants. Since it is known that toxins produced by Fusarium spp. are also phytotoxic to several plants, this provided an impetus to investigate firstly whether potential Fusarium isolates from infected Orobanche crenata plants obtained in Greece are pathogenic to Orobanche crenata itself and other related species. Secondly, this study aimed at investigating if isolated Fusarium oxysporum is able to produce phytotoxic metabolites that have bioherbicidal effects against different developmental stages of Orobanche sp and selective effects on various Orobanche spp and other plants. To attain the objective of the work, green house and laboratory studies were conducted to determine the pathogenicity and phytotoxicity of Fusarium oxysporum on Orobanche crenata and related Orobanche species. When the results obtained proved that the Fusarium specie is pathogenic and phytotoxic to Orobanche crenata, identification of the possible metabolites were done using TLC, HPLC, MPLC, GCMS and NMR techniques. The following metabolites were identified: 1H-indole-3-carboxaldehyde, oleic acid methylester, oleic acid, glycerol, tyrosol and P-hydroxybenzoic acid. Preliminary phytotoxicity tests conducted with the identified metabolites proved that only 1H-indole-3-carboxaldehyde and tyrosol were of interest to this research and so bioassays were conducted to ascertain their effectiveness as phytotoxins.

Στην μελέτη αυτή: 1. Απομονώθηκαν στελέχη του Fusarium oxysporum παθογόνα στην Orobanche crenata από καλλιέργεια κουκιάς. 2. Αξιολογήθηκε η in planta επίδραση των στελεχών του Fusarium oxysporum στην παρεμπόδιση παρασιτισμού ειδών οροβάγχης στους ξενιστές τους. 3. Μελετήθηκε η επίδραση φυτορρυθμιστικών ουσιών και διεγερτών βλάστησης σπόρων οροβάγχης στην in vitro ανάπτυξη των Orobanche crenata, Orobanche cumana και Orobanche aegyptiaca. 4. Μελετήθηκε η βιοδραστικότητα παρασκευασμάτων από καλλιέργειες των παθογόνων στελεχών του Fusarium oxysporum σε είδη οροβάγχης και σε ιστούς κουκιάς. 5. Απομονώθηκαν οι μεταβολίτες glycerol, 1H-indole-3-carboxaldehyde, oleic acid methylester, oleic acid, tyrosol, parahydroxybenzoic acid υτοτοξικά παρασκευάσματα καλλιεργειών του από Fusarium oxysporum 6. Αξιολογήθηκε η φυτοτοξικότητα των ουσιών αυτών και η εκλεκτική φυτοτοξικότητα των 1H-indole-3-carboxaldehyde.