Introduction to Resistance Genetics: Traits

Amy Hauver Author

07/19/2022 Added

30 Plays

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You'll learn the genetic basis for resistance genetics through the example of herbicide resistant Palmer amaranth. This video describes genes, trait expression, and traits.

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[00:00:07.800]This video will act as an introduction
[00:00:10.110]to pesticide resistance genetics.
[00:00:17.310]Palmer amaranth is a common weed in agriculture
[00:00:20.070]and an important weed when discussing herbicide resistance.
[00:00:24.150]Glyphosate resistance in Palmer was first reported
[00:00:27.000]in the United States in the state of Georgia in 2014
[00:00:31.260]and has since emerged in different states
[00:00:33.300]throughout the Midwest.
[00:00:36.120]So how does resistance to pesticides
[00:00:38.610]like Palmer amaranth's resistance to glyphosate develop?
[00:00:43.050]Organisms have different traits
[00:00:44.820]like the height of the Palmer plant in this image.
[00:00:47.790]And they are expressed and can be selected for
[00:00:49.650]in suitable environments.
[00:00:52.050]To begin to understand development of herbicide resistance,
[00:00:55.050]we need to understand traits
[00:00:56.490]and how they express themselves in plants.
[00:01:00.720]Traits are characteristics or features controlled
[00:01:04.170]by genes that can be passed from one generation to another.
[00:01:08.130]Some examples are the height of individual plants,
[00:01:11.820]the flower colors of soybeans, or the ability of a plant
[00:01:15.210]to tolerate herbicides, like Palmer's resistance
[00:01:18.150]to glyphosate being controlled
[00:01:20.010]by the EPS synthase expression.
[00:01:23.190]Traits are genetic factors
[00:01:24.840]that predetermine certain characteristics about a plant,
[00:01:29.520]but there are outside factors
[00:01:31.080]that influence that plant as well,
[00:01:32.790]like the amount of nutrients or water it receives.
[00:01:36.540]The genes controlling
[00:01:37.560]the genetic factor of traits are encoded in DNA,
[00:01:41.700]or deoxyribose nucleic acid.
[00:01:44.190]So let's take a closer look.
[00:01:46.800]Continuing with our example,
[00:01:48.390]let's look at this Palmer plant.
[00:01:50.070]In order to look at its DNA
[00:01:51.750]we need to take an even closer look
[00:01:53.310]at its leaf and its cellular makeup.
[00:01:57.660]Palmer leaves are made up of millions of cells,
[00:02:00.180]each holding a nucleus which contains the chromosomes.
[00:02:03.840]Chromosomes are made up of DNA,
[00:02:06.360]the genetic material in all living things.
[00:02:09.510]Genes are segments of DNA that encode for specific proteins.
[00:02:13.950]Following the polymer example, on this chromosome
[00:02:16.890]the EPSP synthase gene is shown.
[00:02:19.710]Typically one gene is present,
[00:02:21.690]so when glyphosate is applied
[00:02:23.550]it renders the EPSP synthase inoperable.
[00:02:27.810]This paper details the molecular process
[00:02:30.030]by which Palmer amaranth is able
[00:02:31.740]to tolerate applications of glyphosate.
[00:02:34.710]The authors attribute glyphosate resistance
[00:02:36.870]in Palmer amaranth to gene amplification.
[00:02:40.200]Since there is originally only one EPSP synthase gene,
[00:02:44.220]Palmer was controlled easily by glyphosate applications.
[00:02:47.640]Over time and through selection,
[00:02:49.620]Palmer plants with more than one copy
[00:02:51.510]of the EPSP synthase gene became more prevalent
[00:02:54.390]in the population.
[00:02:56.880]The amplification of EPSP synthase genes is responsible
[00:03:00.780]for the glyphosate resistance trait.
[00:03:03.210]Massive overproduction of EPSP synthase
[00:03:06.030]produced by the additional EPSPS gene
[00:03:10.470]allows the plant to cope despite the presence of glyphosate,
[00:03:14.040]essentially acting as a molecular sponge
[00:03:16.170]to soak up the herbicide and allow the plant to survive.
[00:03:20.400]Having different traits means
[00:03:21.720]that there are some individuals that will thrive better
[00:03:23.910]to different environments.
[00:03:25.770]Like Palmer amaranth with glyphosate,
[00:03:27.720]some plants have traits that allow them
[00:03:29.370]to tolerate certain herbicides.
[00:03:31.590]Palmer's high reproductive rates
[00:03:33.210]and its ability to build a large population
[00:03:35.670]makes it difficult to manage and contributes
[00:03:37.710]to the development of resistance.
[00:03:40.860]Traits may only be visible
[00:03:42.390]if they're influenced by the environment.
[00:03:44.580]In the case of this Palmer amaranth,
[00:03:46.260]you can't see that it's a glyphosate-resistant plant
[00:03:48.870]because you cannot see its genes.
[00:03:51.090]But if you take a close look,
[00:03:52.560]you will see that this individual plant carries
[00:03:54.690]extra copies of the EPSP synthase genes
[00:03:57.870]that will make it glyphosate resistance.
[00:04:00.810]Once the environment changes,
[00:04:02.610]like glyphosate being applied by a farmer,
[00:04:05.040]you would be able to see the herbicide resistance trait.
[00:04:08.220]If the Palmer carries the amplified EPSPS genes,
[00:04:12.240]then it is fully resistant
[00:04:14.040]to the herbicide and will survive.
[00:04:16.410]If it only carries half of that amplified amount,
[00:04:18.870]it may be injured, but could still survive an application.
[00:04:22.680]If it carries the single EPSP synthase gene,
[00:04:25.830]then it is fully susceptible and will likely die.
[00:04:29.700]Under certain circumstances, traits like Palmer resistance
[00:04:33.210]to glyphosate can be selected for within a population.
[00:04:36.540]In this case, it would be herbicide applications.
[00:04:39.900]In the case of Palmer,
[00:04:41.220]large populations have a diverse gene pool
[00:04:43.590]with different traits that may be selected for,
[00:04:46.050]which can lead to a higher chance of resistance developing.
[00:04:49.950]Individuals that have these traits survive
[00:04:52.140]and become more prevalent in the population.
[00:04:54.810]As Palmer plants with resistance traits are selected,
[00:04:57.900]they're able to survive
[00:04:59.040]glyphosate application and reproduce.
[00:05:01.560]This increases the frequency
[00:05:02.880]of the resistance traits in the population.
[00:05:07.230]Weed biologists are utilizing tools
[00:05:09.750]of molecular genetics to uncover the genetic basis
[00:05:12.540]for the herbicide resistance traits observed in the field,
[00:05:16.020]like Palmer amaranth resistance to glyphosate
[00:05:18.360]being influenced by gene amplification.
[00:05:21.720]In summary, resistance to pesticides comes
[00:05:24.300]from traits in individuals that are expressed.
[00:05:27.180]These traits allow them to tolerate certain herbicides,
[00:05:29.730]like Palmer with glyphosate.
[00:05:31.680]Under certain environments these traits can be selected for
[00:05:34.170]in the population, like a herbicide application
[00:05:37.020]killing all glyphosate-susceptible Palmer plants
[00:05:40.050]and leaving the resistant plants to reproduce.
[00:05:42.870]These individuals with resistance traits
[00:05:45.180]become more prevalent in the population
[00:05:46.980]as they reproduce, leading to a resistance population.

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Introduction to Resistance Genetics: Traits

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