Chapters authored
Gene Flow from Herbicide-Resistant Crops to Wild Relatives
Development of herbicide-resistant (HR) crops is way to overcome problems in weed control due to weed resistance to herbicides and absence of new herbicides with a new mode of action for their control. Three types of HR crops were developed: nontransgenic, transgenic, and multiple HR crops. Cultivation of HR crops is associated not only with many benefits (simplification of weed control, more effective and efficient weed control, higher yields, etc.) but also with various risks (development of HR weeds, development of HR volunteer crops, gene flow from HR crops to susceptible relatives, etc.). The greatest risk is gene flow from HR crops to related weed species, wild relatives or conventional crops of the same species. Unwanted gene flow could be prevented or reduced using different barriers such as isolation in space or time, protective vegetation barriers, male sterility, etc. Sunflower hybrids resistant to herbicides (imidazolinones and sulfonilureas) was developed by conventional breeding methods, and their introduction in Serbian fields has enabled a more efficient control of harmful weed species, but the presence of huge populations of weedy sunflower is the main concern associated with their cultivation, because numerous studies have confirmed gene flow from sunflower to its relatives.
Part of the book: Herbicide Resistance in Weeds and Crops
Weed Resistance to Herbicides
Unfortunately, herbicide resistance developed shortly after the introduction of the herbicides 2,4‐D in 1957. According the herbicide resistance mechanisms, all processes can be grouped as follows: target‐site resistance, non‐target‐site resistance, cross‐resistance and multiple‐resistance. Target‐site resistance is generally due to a single or several mutations in the gene encoding the herbicide‐target enzyme, which, in turn, decreases the affinity for herbicide binding to that enzyme. Non‐target‐site resistance is caused by mechanisms that reduce the amount of herbicidal active compound before it can attack the plant through the reduced absorption or altered translocation, increased herbicide sequestration or enhanced herbicide metabolism. Cross‐resistance means that a single‐resistance mechanism causes resistance to several herbicides with some mode of action. Multiple‐resistance is a situation where two or more resistance mechanisms are present within the same plant, often due to sequential selection by herbicides with different modes of action. Currently, herbicide resistance has been reported in 478 weed biotypes (252 weed species) in 67 countries. Many of those biotypes are resistant to acetolactate synthase (ALS) inhibitors, PS II inhibitors, ACC‐ase inhibitors and EPSPS inhibitors. Strategy for herbicide‐resistance weed management must involve all the available preventive, cultural, mechanical and chemical measures for effective, safe and cost‐effective weed control.
Part of the book: Herbicide Resistance in Weeds and Crops