Effect of polyploidy on the leaf epidermis structure of Cynodon dactylon (L.) Pers. (Poaceae)

Cynodon dactylon has different ploidy levels. The 'gigas effect' in morphoanatomic traits caused by the increase in the genetic material is poorly studied in the species. Thus, the present research aimed at carrying out a quantitative and descriptive study of the leaf epidermis structure in PI291169-04 (2n = 2x = 18); PI477004-26 (2n = 3x = 27); PI291721-22 (2n = 4x = 36); PI289750-10 (2n = 5x = 45) accessions, in order to investigate the consequences of the polyploidy. Adult leaves were fixed in FAA and the paradermal sections obtained through the scraping technique were stained in 5% safranin. The measurements of the stomata characteristics (polar diameters - PD, equatorial diameters - QD, stomatal density - SD, stomatal functionality - SF, and stomatal index - SI) were taken by means of the software ImageJ. For analysis in scanning electron microscopy, leaf fragments were fixed in Karnovsky, dehydrated in an acetone series, subjected to a critical point and covered with gold. Stomata were classified as paracytic, dumbbell-shaped and partially covered by papillae. Tector trichomes were classified as uniseriate with pointed tips. In general, as ploidy level increased, there was an increase in stomata dimension and a decrease in SD. Diploid and triploid accessions were easily differentiated in relation to PD and QD, which makes it an indirect method for determining the variation in ploidy level. The variables SD and SI were not efficient to discriminate the accessions. Leaf epidermis has characteristics that emphasize the effect of polyploidization process and its analysis may be used to screening of genotypes in breeding programs.