<b>HRAC Group 12</b> <font size='2'> (Legacy F1) </font> resistant Hydrilla verticillata from United States, Florida

International Survey of Herbicide-Resistant Weeds

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Thursday, October 31, 2024

HRAC GROUP 12 (LEGACY F1) RESISTANT HYDRILLA
(Hydrilla verticillata)

Phytoene Desaturase inhibitorsHRAC Group 12 (Legacy F1)

United States, Florida

INTRODUCTION		HYDRILLA
Hydrilla (Hydrilla verticillata) is a monocot weed in the Hydrocharitaceae family. In Florida this weed first evolved resistance to Group 12 (Legacy F1) herbicides in 2002 and infests Aquatic. Group 12 (Legacy F1) herbicides are known as Phytoene Desaturase inhibitors (Inhibition of Phytoene Desaturase ). Research has shown that these particular biotypes are resistant to fluridone and they may be cross-resistant to other Group 12 (Legacy F1) herbicides. The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

QUIK STATS (last updated Apr 29, 2009 )
Common Name	Hydrilla
Species	Hydrilla verticillata
Group	Phytoene Desaturase inhibitors HRAC Group 12 (Legacy F1)
Herbicides	fluridone
Location	United States, Florida
Year	2002
Situation(s)	Aquatic
Contributors - (Alphabetically)	Franck Dayan
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ACADEMIC ASPECTS

Confirmation Tests

Field, Greenhouse, and Laboratory trials comparing a known susceptible Hydrilla biotype with this Hydrilla biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on HRAC Group 12 resistant Hydrilla indicate that the inheritance is determined by a one gene, nuclear trait. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

Studies on the mechanism of resistance of Group 12 (Legacy F1) resistant Hydrilla from Florida indicate that resistance is due to an altered target site. There may be a note below or an article discussing the mechanism of resistance in the Fact Sheets and Other Literature

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of Group 12 (Legacy F1) resistant Hydrilla from Florida please update the database.

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CONTRIBUTING WEED SCIENTISTS

FRANCK DAYAN

Plant Physiologist USDA-ARS Natural Products Utilization Research Unit P.O. Box 8048 University, 38677-8048, Mississippi United States Email Franck Dayan Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Florida have been instrumental in providing you this information. Particular thanks is given to Franck Dayan for providing detailed information.

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Herbicide Resistant Hydrilla Globally
(Hydrilla verticillata)

Country

FirstYear

Situation

Active Ingredients

Site of Action

United States (Florida)

2002

Aquatic

fluridone

Phytoene Desaturase inhibitors ( HRAC Group 12 (Legacy F1)

Literature about Similar Cases

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Benoit, L. K. ; Les, D. H.. 2013. Rapid identification and molecular characterization of phytoene desaturase mutations in fluridone-resistant hydrilla (Hydrilla verticillata). Weed Science 61 : 32 - 40.

Florida hydrilla populations have shown an alarming increase in resistance to fluridone, an herbicide used extensively for controlling invasive US hydrilla populations. A rapid PCR and sequencing method was developed to identify and screen hydrilla genomic DNA for three previously identified phytoene desaturase (pds) gene mutations that confer resistance to fluridone. Ninety hydrilla accessions were screened for fluridone resistant genotypes including 46 accessions from the US and 44 accessions from 15 other countries. In Florida, hydrilla from five of nine sites tested was heterozygous for wild-type and herbicide-resistant alleles. Additionally, a new resistant population was identified from Lake Seminole in Georgia, the first genetically confirmed strain of resistant hydrilla outside of Florida. All resistance-conferring mutations were located on the same homologous haplotype of US dioecious hydrilla. All other hydrilla samples tested possessed only wild type alleles, including monoecious strains that had been exposed to fluridone. Management implications are discussed..

Schmid, T. A. ; Cuda, J. P. ; MacDonald, G. E. ; Gillmore, J. L.. 2010. Performance of two established biological control agents on hydrilla genotypes susceptible and resistant to fluridone herbicide. Journal of Aquatic Plant Management 48 : 102 - 105.

Hydrilla (Hydrilla verticillata [L.f.] Royle: Hydrocharitaceae) is a submersed aquatic plant widely distributed in most tropical and temperate zones worldwide. A dioecious female strain of hydrilla was introduced into Florida from Sri Lanka in the early 1950s through the aquarium trade. This aggressive submersed plant spread rapidly and now occurs in all states bordering the U.S. coastline except New Mexico and Oregon. The recent development of fluridone herbicide resistance in Florida hydrilla populations has resulted in the inability to economically control large infestations of this invasive aquatic weed. The objective of this study was to compare the performance of two established insect biological control agents, a stem-mining midge (Cricotopus lebetis Sublette: Chironomidae) and a leaf-mining fly (Hydrellia pakistanae Deonier: Ephydridae), on a fluridone susceptible and two fluridone-resistant genotypes. Terminal shoots of susceptible, moderately resistant, and highly resistant hydrilla genotypes were obtained and placed in individual culture tubes. Two neonate larvae of each biocontrol agent were transferred to culture tubes containing the three hydrilla genotypes. Survival and sex of the emerged adults were recorded. Results showed that the two biocontrol agents differed in their acceptance of the hydrilla genotypes. Survival of the leaf-mining fly was similar on all three Florida genotypes tested. In contrast, the stem-mining midge exhibited significantly lower emergence when reared on the medium and highly resistant genotypes compared to the fluridone susceptible hydrilla genotype. These findings highlight the importance of examining insect performance on all plant genotypes present in the invaded range when selecting effective biological control agents..

Puri, A. ; MacDonald, G. E. ; Haller, W. T.. 2007. Ploidy variations in floridone-susceptible and -resistant hydrilla (Hydrilla verticillata) biotypes. Weed Science 55 : 578 - 583.

Hydrilla is one of the most serious aquatic weed problems in the USA, and fluridone is the only U.S. Environment Protection Agency (USEPA)-approved herbicide that provides relatively long-term systemic control. Recently, hydrilla biotypes with varying levels of fluridone resistance have been documented in Florida. Fluridone-susceptible (S) and several fluridone-resistant (R1 to R5) hydrilla biotypes varying in resistance levels were maintained in 950 litre tanks under ambient sunlight and daylength conditions. To correlate varying levels of fluridone resistance to ploidy in hydrilla, flow cytometric analysis was performed. Differential ploidy levels (diploid, 2n=2x=16; triploid, 2n=3x=24; and tetraploid, 2n=4x=32) were reported among different hydrilla biotypes, plants within each biotype, and within shoot tissues of the same plant. Triploid plants were predominant in all biotypes. Diploid plants were observed in all hydrilla biotypes except the susceptible hydrilla (S). Plants with tetraploidy were rare within biotypes. The diploid, triploid, and tetraploid plants had nuclear DNA contents of 2.43 to 2.73 pg, 3.44 to 3.71 pg, and 4.64 to 4.90 pg, respectively, and there were no differences observed among plants with same ploidy for nuclear DNA content in different hydrilla biotypes. Endoreduplication patterns were observed in diploid plants of R1 and R3 biotypes. However, no plant with higher ploidy levels (triploid or tetraploid) in any hydrilla biotypes showed endoreduplication..

Puri, A. ; MacDonald, G. E. ; Altpeter, F. ; Haller, W. T.. 2007. Mutations in phytoene desaturase gene in fluridone-resistant hydrilla (Hydrilla verticillata) biotypes in Florida. Weed Science 55 : 412 - 420.

Hydrilla is one of the most serious aquatic weed problems in the United States, and fluridone is the only U.S. Environment Protection Agency (USEPA) - approved herbicide that provides relatively long-term systemic control. Recently, hydrilla biotypes with varying levels of fluridone resistance have been documented in Florida. One susceptible and 5 fluridone-resistant biotypes of hydrilla varying in resistance levels were maintained in 950-litre tanks under ambient sunlight and day-length conditions from September 2004 to September 2005 in the absence of fluridone. Because fluridone is an inhibitor of the enzyme phytoene desaturase (PDS), the gene for PDS (pds) was cloned from fluridone-susceptible and -resistant hydrilla biotypes. Somatic mutations in amino acid 304 of hydrilla PDS are known to confer herbicide resistance. We determined pds sequence from these hydrilla biotypes during planting and at 12 months after planting. Two independent mutations at the arginine 304 codon of pds were found in the resistant hydrilla plants. The codon usage for arginine 304 was CGT, and a single point mutation yielding either serine (AGT) or histidine (CAT) was identified in different resistant hydrilla biotypes. There were no differences at codon 304 in the PDS protein of any hydrilla biotype at 12 months after planting. Several other mutations were also found in the resistant pds alleles, although their possible role in herbicide resistance is unclear..

Puri, A. ; MacDonald, G. E. ; Haller, W. T. ; Megh Singh. 2007. Growth and reproductive physiology of fluridone-susceptible and -resistant hydrilla (Hydrilla verticillata) biotypes. Weed Science 55 : 441 - 445.

Hydrilla biotypes with varying levels of fluridone resistance have been documented in Florida. Several biotypes of hydrilla varying in resistance levels were maintained in 950-litre tanks under ambient sunlight and day-length conditions from September 2004 to September 2005 in the absence of fluridone. Phenotypic measurements were performed during this one-year period to monitor differences in growth and reproductive physiology. All fluridone-resistant biotypes (except R3) were growing at the same rate or greater than the susceptible hydrilla. These data suggested that there are no deleterious effects on growth and reproductive physiology because of the development of fluridone resistance. The aggressive spread of fluridone-resistant dioecious hydrilla in aquatic ecosystems can severely affect hydrilla management and, consequently, cause substantial and long-lasting ecological and economic problems throughout the southern United States..

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