Variability of breeding system, caryopsis microstructure and germination in annual and perennial species of the genus Brachypodium P. Beauv.

Abstract

The basis of any patterns of variation in plant populations is the breeding system they express. In the genus Brachypodium, the breeding system ranges from autogamy in facultatively chasmogamic Brachypodium distachyon to allogamy in obligatory chasmogamic B. pinnatum. B. distachyon and B. sylvaticum appeared to be extremes with respect to dormancy and germination behaviour. Winter and facultatively biennial forms of the annual B. distachyon expressed an intermediate dormancy behaviour towards perennial species. Perennial species such as B. pinnatum, B. phoenicoides, B. rupestre and B. sylvaticum demonstrated allogamic behaviour and were highly dormant. The storage potential of hemicelluloses in endosperm cell walls and suberin-phenolic synthesis in testa and pigment strand differ distinctly between annuals and perennials. The suberized glumellae base and caryopsis attachment restrict the growth of coleorhiza and can change growth relationships between root and coleoptile. Coleorhizal hairs facilitating water capillary adhesion to an embryo are developed in both types of Brachypodium species, but in perennial types they are less efficient. The pattern of development of coleorhizal hairs distinguishes Brachypodium species from members of the tribe Triticeae. The coleorhizal hairs are less developed in Triticeae. This trait is variable at the populational level, especially in heterozygous populations (B. phoenicoides). Both extremes in terms of dormancy, i.e. B. distachyon and B. sylvaticum, revealed inter- and intrapopulational variability of germination.