Identification and monitoring of Palmer amaranth occurrence and spread in South Africa
A key part of the program is to identify new populations of Palmer amaranth in South Africa. This is done by following up on reports from the public, farmers and agricultural agents across South Africa. Reports are confirmed with the aid morphological and molecular identification. Once a new population is identified it is important to regularly monitor these populations and prevent the spread by providing farmers with appropriate management strategies. In order to help identify Palmer amaranth an Identification guide has been compiled and is distributed to farmers and agricultural agents across the country.
Currently the SAHRI have confirmed populations of Palmer amaranth in the Northern Cape, North West, Kwa-Zulu Natal and Limpopo provinces. Cases of herbicide resistant Amaranthus hybridus have also been confirmed in the Eastern Cape and the Free state.
Figure 1: Spread of Amaranthus palmeri and Amaranthus hybridus populations with known herbicide resistance.
Herbicide resistance profiling of Amaranthus palmeri and Amaranthus hybridus
Once new populations of Palmer amaranth are confirmed, or in cases where we receive reports of Amaranthus species not controlled by herbicides, it is important to develop a sensitivity/resistance profile of these populations against various herbicides. Resistance profiling is done by glasshouse screenings as well as by sequencing the genes of various herbicide target enzymes in order to identify possible mutations that can confer resistance.
Developing a comprehensive herbicide sensitive/resistance profile is important not only to know which herbicides to avoid but also to develop comprehensive management strategies that include alternative herbicides in combination with non-chemical management options.
Figure 2: Herbicide dose responce of Palmer amaranth
Molecular characterization of Amaranthus populations from South Africa
In order to understand the population structures, development of herbicide resistance and the specific resistance mechanisms in Amaranthus species, we use molecular characterization to develop DNA profiles of different populations. This allow us to link specific populations in order to understand their spread and distribution. Molecular characterization also allows us to identify possible cases of hybridization between Amaranthus species which can contribute to the horizontal spread of herbicide resistance characteristics between species. A detailed understanding of the specific resistance mechanisms also help us in the development of better resistance management strategies.
Figure 3: DNA sequence of Palmer amaranth target genes