Resumo

CASSANEGO, MBB; DROSTE, A  e  WINDISCH, PG. Effects of 2,4-D on the germination of megaspores and initial development of Regnellidium diphyllum Lindman (Monilophyta, Marsileaceae). Braz. J. Biol. [online]. 2010, vol.70, n.2, pp. 361-366.  Epub 02-Abr-2010. ISSN 1519-6984.  http://dx.doi.org/10.1590/S1519-69842010005000014.

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 °C, under artificial light with nominal irradiance of 110 µmol.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.

Palavras-chave : heterosporous fern; germination; herbicide; ecophysiology; conservation.