Phenotypic variation in somaclones of Paspalum dilatatum and their seedling offspring

Abstract

Embryogenic callus cultures were initiated from immature embryos of the apomictic Paspalum dilatatum cultivar ’Grasslands Raki’. Embryogenic callus was transferred to a regeneration medium at four different times from 121 to 206 d after culture initiation and a total of 231 somaclones were obtained. Phenotypic variation in the somaclones increased as the length of the callus phase and the length of the regeneration period were increased. Phenotypic changes ranged from floral abnormalities, reduced vigour (including dwarfism) and smaller tillers (narrow leaves) to loss of cold tolerance (leaf chlorosis). There was no useful variation in leaf dry matter digestibility and none of the plants showed any resistance to ergot. Seed was collected from 60 somaclones but viability was very low. Sufficient seedlings (SC2 generation) for progeny studies were obtained from only 18 somaclones. Fifteen of these somaclones produced offspring which showed variations including dwarfism, reversion to a coarser plant type and changes in anther colour. Seed germinability was restored in some offspring to a level approaching Raki. A second seedling generation (SC3) was obtained in which dwarfism reappeared, although most plants showed maternal characteristics. None of the somaclones, nor the SC2 and SC3 seedlings, was agronomically superior to Raki seedlings. However, the production of variable offspring by the somaclones suggested a breakdown of apomixis and some sexual reproduction. In a second experiment, callus cultures were initiated from Raki and a sexual P. dilatatum accession Bo211 (2n = 40) using both immature embryos and immature inflorescence sections as explants. In this experiment the callus phase was reduced to 34–84 d. The somaclones obtained exhibited very little variation and appeared identical to their respective donor lines.Key words: Paspalum dilatatum, somaclonal variation, apomixis, plant improvement, dallisgrass