Abstract
In Yanqi County of Xinjiang Uygur Autonomous Region, China, broomrape species (Orobanche cumana Wallr and Phelipanche aegyptiaca Pers.) contribute to significant losses of processing tomato and sunflower. During the past decades, a significant infestation pattern was observed between these broomrape species with no scientific peer-reviewed explanation. A two-year pot experiment simulating the crop rotation and an independent hydroponic experiment were performed to address the problem and indicate the main reason behind the differential infestation pattern. Different varieties of three crops (sugar beet, pepper, and wheat) were grown in rotation with tomato and sunflower to identify a crop-rotation induced control mechanism on these two broomrape species. Germination bioassays were performed in vitro to identify stimulation of plant biochemicals collected as methanolic shoots/roots extracts and root exudates on the germination patterns of broomrape seeds. Results indicated that sunflower broomrape soil seed banks reduced during the two-year crop rotation; however, Egyptian broomrape seed banks did not alter and the resulting parasitism significantly reduced tomato growth. Seed germination bioassays confirmed that the methanolic shoot/root extracts successfully stimulate sunflower broomrape seeds germination but fail to stimulate Egyptian broomrape seeds germination. Root exudates collected from hydroponically grown crops also confirmed differential germination patterns in both broomrape species. Current results are of vital importance to explain the control effect of a crop rotation system and moreover, lay the foundation to study the genetic evolution of broomrape species that results in their differential germination responses to natural stimuli.
Highlights
Broomrapes (Orobanche spp.) are holoparasitic weeds which significantly impair agricultural crops in many regions of the world [1]
At the outcome of the study, it is thoughtfully concluded that the cropping system practiced in Xinjiang Uygur Autonomous Region of China is responsible for the differential infestation of sunflower and Egyptian broomrape
The root exudates from these crops are able to successfully germinate the sunflower broomrape seeds and reduce the seed bank considerably such that the area does not exhibit infestation of sunflower broomrape
Summary
Broomrapes (Orobanche spp.) are holoparasitic weeds which significantly impair agricultural crops in many regions of the world [1]. Agronomy 2020, 10, 18; doi:10.3390/agronomy10010018 www.mdpi.com/journal/agronomy (Pers.) Pomel; synonym: Orobanche aegyptiaca Pers.) which attack and severely damage sunflower and processing tomato production in the Shaanxi Province and Xinjiang Uygur Autonomous Region [1,3,4] These broomrape species are holoparasites and due to their lack of chlorophyll, entirely depend on the host plant for nutrition, thereby considerably reducing the growth and development of the host plants [5]. Seed germination of broomrape is a highly specialized process comprised of two prominent steps: the first is a conditioning period which is the provision of optimum temperature and humidity to the seeds and the second is the perception of a germination stimulant usually obtained from the host plant [7] All these processes occur underground; it is extremely difficult to control these notorious weeds. Due to their long dormancy span, achlorophyllous nature, and capability to survive harsh environmental conditions, these weeds arise as highly notorious to the crops and require considerable attention
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