Investigation on the control of Egyptian broomrape (Orobanche aegyptiaca)

In the summer of 2006, 18 isolates of Fusarium spp. were obtained from Egyptian broomrape (Orobanche aegyptiaca) in tomato fields in Karaj, Varamin and Golpayegan areas (Iran). In pathogenicity test of the isolates on Egyptian broomrape with stem puncture method, local symptoms were occurred after 3-4 days which finally resulted in wilting of the host plants 10-12 days after inoculation. The pathogens were re-isolated from infected tissues and each one was compared with its original culture. The isolates which were recognized as the pathogen of Egyptian broomrape and produced no symptom on important crops were selected for the effect of the role of nutrition on their sporolation and washing the spores with carbohydrates on spore germination. To investigate the application of an isolate of Fusarium oxysporum for biocontrol of Egyptian broomrape (Orobanche aegyptiaca), the biological agent was formulated with Aluminum Silicate and white flour as wettable powder. Then, the efficacy of this biological product was investigated in 2008 at two Agricultural Research Stations in Varamin and Zanjan, and in 2009 only in Zangan. In experiments of first year, the methods of application of this product at 1x106 or 1x107 spores L-1 in water were studied. But, in the experiment of the second year, the efficacy of this product was compared with chemical herbicide sulfosulfuron. Among the pathogenic isolates, one of them was recognized F. equesiti and five other F. oxysporum. To evaluate the virulence of pathogenic isolates with soil inoculating method, three isolates reduced the number of Egyptian broomrape plants from 82.7 to 89.7 percent which were significantly more virulent than the other isolates. Host range test showed no symptom on tomato, soybean, red bean, chick pea, canola, sugar beet, sunflower, tobacco, cucumber, cucurbit, maize, wheat, barley, cotton, rape seed, alfalfa and clover when they were soil-inoculated with the selected isolates at 5×106 spores ml-1. The highly virulent isolates were selected for further investigation on microbial control of the parasitic weed. Sporulation of the isolate in the liquid cultures with the C:N ratios of 5:1 or 15:1 was significantly higher than that of C:N ratio of 40:1. In the pH range 5 to 8 of liquid culture at the time of inoculation, the highestspore yield was obtained at pH 6.5, but there was no significant difference between pH 6.5 and 7. The pH had no significant effect on spore germination. Adding glycerol at 2 to 7 percent into liquid culture showed no significant influence on sporulation and spore germination. Increasing the amount of vitamins of liquid culture vigorously enhanced spore yield, but had no effect on spore germination and germ-tube elongation. Washing the spores with Tween20 or coconut oil, compared with distilled water, increased their tolerance to desiccation during 7- to 28-day drought periods. After longer drought period (21-28 days), the effect of coconut oil was more pronounced than that of Tween20. But, washing the spores with 6- or 12-C sugars, compared with distilled water, had no significant effect on enhancing spore germination or germ-tube elongation after desiccation periods. In Varamin experiment, the biological product used at 1x107 spores L-1 was significantly more effective in reducing number of stems, number of plants and dry weight of broomrape and enhancing of tomato fruit yield than that used at 1x106 spores L-1. In Zanjan experiment in 2008, submerging the roots of tomato in solution of biological product in water at 1x107 spores L-1, was more effective in reducing the number of broomrape plants than the other application methods. But, non of application methods, compared with control, had significant effect on dry weight of broomrape. In this experiment, just the putting the biological product at 1x107 spores L-1 in the soil around the tomato plants immediately after transplanting resulted to significant increase of crop yield. In Zanjan experiment in 2009, application of sulfosulfuron, compared with control, in most causes, significantly reduced number and dry weight of broomrape, but this chemical herbicide had no significant different with the biological control. In this experiment, only twice application of sulfosulfuron, each time 50 g ha-1, compared with control, significantly increased the crop yield. In all experiments, no wilting or phytotoxicity due to application of the biological product or the chemical herbicide was observed. To determine the response of broomrape seeds to different plants, the results indicated that soybean, mangbean and vicia induduced the seed germination of this parasitic plant but no hostorial attachment to the root of the relevant hosts was occurred.