Briza

Abstract: Summary 1 We investigated patterns of allozyme variation in demes of the grass Briza media in semi-natural grassland fragments within a mosaic agricultural landscape on the Baltic island of Oland. In the study area, Briza is both a characteristic species of old pastures and an early colonizer of young grasslands developing on previously forested or arable sites. 2 Generalized linear models revealed that descriptors of both present landscape structure and past grassland history are significant determinants of genetic variation in the Briza demes. Genetic structure and levels of within-deme diversity are influenced by the size of grassland fragments, the type of habitat surrounding the grasslands, the size/ spatial extent of the demes, the geographic position of the demes and the historical continuity of the grassland fragments. 3 Gene diversity ( H ) was higher in demes from grassland polygons with a high proportion of adjacent grassland, higher in the more extensive demes, and decreased northwards within the study area. 4 The negative association between the inbreeding coefficient ( F IS ) and grassland continuity is interpreted in terms of a two-stage colonization process: recruitment into young grasslands leads initially to spatial patchiness, but subsequent selection in maturing pastures occurs within an increasingly uniform and dense sward. 5 Despite a weak overall genetic structure (as indicated by Bayesian cluster analysis) the between-deme F ST was significant. Linear discriminant analysis of within-deme allele frequencies grouped the demes according to the age and previous land-use history of their grassland polygons. The convergence of the allele frequency profiles in the younger grasslands towards those of the old grasslands is consistent with convergence of selective regimes as pastures mature towards an increasingly uniform, dense sward and characteristic species assemblage. 6 The genetic composition of demes of a grassland species appears to be influenced by the process of plant community convergence during grassland development ‐ complementing the recent finding that convergence of species composition in experimental assemblages of grassland plants is dependent on the genotypic composition of the component species.

Abstract: Floral morphology is shown to be closely correlated with the type of breeding system in the genus Briza L. (Gramineae). The outbreeding species have large anthers and stigmas that are well exerted at anthesis whereas in the inbreeding species anthers and stigmas are small and the flowers are frequently cleistogamous. Self-incompatibility in B. media is controlled by two genes, both with multiple alleles. Identity at both loci is necessary for pollen inhibition. Pollen control is gametophytic, incompatible pollen tubes are inhibited on the stigmatic surface. Unilateral incompatibility occurs in crosses between self-incompatible and self-compatible species. Self-compatible pollen is inhibited on self-incompatible stigmas but the reciprocal shows no inhibition.

Abstract: Chromosome numbers are reported for 94 collections of grasses representing 61 species and 27 genera. Meiosis was analyzed and irregularities were noted. The probable reproductive method is discussed for some species with irregular meiosis. First chromosome counts are given for the following species: Luziola bahiensis, Aristida implexa, Briza rotundata, Gouinia guatemalensis, Bouteloua alamosana, Pentarrhapis scabra, Panicum cyanescens, P. incumbens, P. olivaceum, P. pantrichum, P. tenerum, Paspalum adoperiens, P. plenum, P. serpentinum, Thrasya campylostachya. Counts different from previous counts for the same taxon are reported for Axonopus capillaris, A. compressus, A. poiophyllus, Leptocoryphium lanatum, Paspalum centrale, P. pectinatum, Pennisetum setosum, and Hemarthria altissima.

Abstract: Chromosome numbers have been determined and karyotypes studied in several species of the genus Briza L. Nuclear DNA amounts have also been determined for some of the species and show a considerable variation between the species. The evolution of the karyotypes, particularly that of B. minor, is discussed and an attempt made to relate nuclear DNA content to karyotypes, breeding systems and habit in the different species.