10. Evaluation of the biological activity of flax as a trap crop against orobanche parasitism of vicia faba.
Trop. Agric. (Trinidad), 69, 1, 1992, pp. 35-38
The objective of the present work was to study the efficiency of flax as a trap crop in reducing Orobanche infestation on Vicia faba and the growth stages at which the stimulating germination factor was found in flax.
Crop species which stimulate germination in the seeds of parasitic plants, but are not themselves parasitized, are known as trap crops. In this respect, many investigations have reported that flax, a non-host, is regarded as a crop well suited for the control of Orobanche parasitism under field conditions because it is capable of including the seeds of Orobanche spp. to germinate, without itself being parasitized.
Three Orobanche species, O. crenata, O. ramosa and O. aegytiaca, failed to infect flax roots (Linum usitatissimum) at 30, 45 and 60 days from sowing, but heavy infection was observed with O. crenata on faba bean roots (Vicia faba) at 45 and 60 days from sowing. Flax seed exudates markedly induced the germination of O. crenata and O. ramosa in vitro; germination in O. crenata was much higher (75%) than in O. ramosa (16.6%).
The present work indicates that a stimulant exists in the flax crop non-host at the germination stage only (the first eight days after sowing). Flax roots free of infection by the three Orobanche spp. (O. crenata, O. ramosa and O. aegyptiaca) might be associated with the absence of the active material during the later course of the plant development, or with its fibre root anatomy.
The important views emerging from the present study are that the flax germination stimulus is formed during metabolic seed germination, and is characterized by possessing a broad spectrum of germination activity on numerous parasitic weeds and/or the flax exudates might contain more than one stimulant which differed in their biological response.
Ultimately, such response might support the view that although the flax plants showed a substantial influence in stimulating different parasitic seeds (Orobanche spp. and Striga spp.) in vitro, the flax plants have limited influence in reducing these parasitic weeds under field conditions, since the flax plants secrete the active material in a very limited period (germination stage).
Concluding, flax plants being used as a trap crop for controlling
Orobanche parasitism on faba bean and other hosts must be considered impractical to a large extent under field conditions, since the flax plant exudate the active material only during the germination period.
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