title: Effects of 2,4-D on the germination of megaspores and initial development of Regnellidium diphyllum Lindman (Monilophyta, Marsileaceae).
abstract: Regnellidium diphyllum is considered as endangered, occurring in the State of Rio Grande do Sul, Brazil, and a few adjoining localities in Uruguay, Argentina and the State of Santa Catarina. It grows in wetlands frequently altered for agricultural activities. Herbicides based on 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in these fields. The effects of 2,4-D on the germination of megaspores and initial sporophytic development of R. diphyllum were investigated. Six concentrations of 2,4-D (0.32; 0.64; 1.92; 4.80; 9.60 and 19.20 mg.L-1), and the control (0.00 mg.L-1), were tested in vitro, using Meyer's medium. Cultures were maintained in a growth chamber at 24 +/- 1 degrees C, under artificial light with nominal irradiance of 110 micromol.m-2/s and 16 hours photoperiod. Megaspore germination was lower at 9.60 and 19.20 mg.L-1 of 2,4-D (56 and 48%, respectively), compared with the control (68%). Herbicide concentrations of up to 1.92 mg.L-1 did not significantly decrease the number of sporophytes formed. At 19.20 mg.L-1, no sporophytes were formed. The lengths of the primary root, primary and secondary leaves were greater at concentrations of 0.32 and 0.64 mg.L-1 of 2,4-D. Low concentrations of 2,4-D do not affect germination rates and initial development of R. diphyllum in a significant way. However, higher concentrations (9.60 and 19.20 mg.L-1) affect substantially the germination of the megaspores and interfere with the establishment of the species.
authors.affiliation: Universidade do Vale do Rio dos Sinos, São Leopoldo, RS, Brazil.
authors.forename: M B B
authors.initials: MB
authors.lastname: Cassanego
authors.forename: A
authors.initials: A
authors.lastname: Droste
authors.forename: P G
authors.initials: PG
authors.lastname: Windisch
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018525:Germination / Q000187:drug effects*; D006540:Herbicides / Q000494:pharmacology*; D043964:Marsileaceae / Q000187:drug effects* / Q000254:growth & development; D013170:Spores / Q000187:drug effects* / Q000254:growth & development
chemical_list: D006540:Herbicides; D015084:2,4-Dichlorophenoxyacetic Acid