Cytology of 2n Pollen Formation in Diploid Crested Wheatgrass, Agropyron cristatum

Abstract

Hybrids between induced tetraploids of diploid crested wheatgrass, Agropyron cristatum (L.) Gaertn. (2n = 2x = 14), and tetraploid crested wheatgrass, A. desertorum (Fisch. ex Link) Schult. (2n = 4x = 28), have provided improved germplasm with unique agronomic traits. Introgression from diploids to tetraploids would be simplified if diploids that produce 2n gametes (gametes with the sporophytic chromosome number) could be identified. This study was initiated to determine if 2n pollen is produced in diploid crested wheatgrass and to determine the cytological mechanisms of 2n pollen formation. Pollen diameters were investigated by measuring 60 pollen grains from each of 600 diploid and 100 tetraploid genotypes. Pollen diameters averaged 37.9 μm (SE = 0.17) and 41.1 μm (SE = 0.33) for diploid and tetraploid genotypes, respectively, with a range of 35.3 to 41.3 μm among the diploids, and 39.7 to 46.8 μm among the tetraploids. Approximately 16% of the diploid genotypes produced some pollen grains with twice the mean volume of n pollen. Cytological analyses of 17 individuals that produced variable‐sized pollen indicated that 2n pollen was produced via restitution at the second meiotic division. Meiotic abnormalities that could give rise to 2n microspores include i) arrest at metaphase II, ii) lack of sister chromatid movement in anaphase II, iii) movement of all or most sister chromatids to a single pole in anaphase II, and iv) abnormal cytokinesis after telophase II. The formation of 2n pollen in diploid crested wheatgrass should facilitate efficient transfer of germplasm from diploids to tetraploids within the genus Agropyon.