Abstract
Parasitic plants belonging to the Orobanchaceae family include species that cause heavy damage to crops in Mediterranean climate regions. Phelipanche aegyptiaca is the most common of the Orobanchaceae species in Israel inflicting heavy damage to a wide range of broadleaf crops, including processing tomatoes. P. aegyptiaca is extremely difficult to control due to its minute and vast number of seeds and its underground association with host plant roots. The highly efficient attachment of the parasite haustoria into the host phloem and xylem enables the diversion of water, assimilates and minerals from the host into the parasite. Drip irrigation is the most common method of irrigation in processing tomatoes in Israel, but the delivery of herbicides via drip irrigation systems (herbigation) has not been thoroughly studied. The aim of these studies was to test, under laboratory and greenhouse conditions, the factors involved in the behavior of soil-herbigated imazapic, and the consequential influence of imazapic on P. aegyptiaca and tomato plants. Dose-response Petri dish studies showed that imazapic does not impede P. aegyptiaca seed germination and non-attached seedlings, even at the high rate of 5000 ppb. Imazapic applied to tomato roots inoculated with P. aegyptiaca seeds in a PE bag system revealed that the parasite is killed only after its attachment to the tomato roots, at concentrations as low as 2.5 ppb. Imazapic sorption curves and calculated Kd and Koc values indicated that the herbicide Kd is similar in all soils excluding a two-fold higher coefficient in the Gadash farm soil, while the Koc was similar in all soils except the Eden farm soil, in which it was more than twofold lower. In greenhouse studies, control of P. aegyptiaca was achieved at >2.5 ppb imazapic, but adequate control requires repeated applications due to the 7-day half-life (t1/2) of the herbicide in the soil. Tracking of imazapic in soil and tomato roots revealed that the herbicide accumulates in the tomato host plant roots, but its movement to newly formed roots is limited. The data obtained in the laboratory and greenhouse studies provide invaluable knowledge for devising field imazapic application strategies via drip irrigation systems for efficient and selective broomrape control.
Highlights
Parasitic plants account for approximately one percent of angiosperm species and are present in 275 genera belonging to 28 botanical families [1]
Broomrape species are extremely difficult to control during the cultivation of agricultural crops due to the intimate hidden underground association of the parasite haustoria with the roots of the host plant
Numerous methods have been attempted for field broomrape control including hand weeding, chemical herbicides, bioherbicides and biological agents, and naturally and genetically engineered crop resistance [5,6,9,10,11], most of them resulting in limited success under field-application conditions
Summary
Parasitic plants account for approximately one percent of angiosperm species and are present in 275 genera belonging to 28 botanical families [1]. Some of the parasitic plants are important agricultural weeds, infest a varied range of crops worldwide, and pose a threat to the food security of many communities [2,3,4]. The parasitic plant family Orobanchaceae includes 270 species in 20 genera of root holoparasites of which the two Orobanchaceae genera, Orobanche and Phelipanche (common name broomrape), include more than 100 species, a few of which are major agricultural weeds in regions with Mediterranean climates. Phelipanche aegyptiaca is a major obstacle to the production of many broadleaf crops, most of them belonging to the Solanaceae, Fabaceae, Cruciferae and Umbelliferae plant families [5,6]. Broomrape species are extremely difficult to control during the cultivation of agricultural crops due to the intimate hidden underground association of the parasite haustoria with the roots of the host plant. The use of chemical control as reported in this study requires a highly effective and selective herbicide to control the parasite without harming the crop
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