To develop simple sequence repeat (SSR) markers for the hexaploid forage grass timothy (Phleum pratense L.), we used four SSR-enriched genomic libraries to isolate 1,331 SSR-containing clones. All four libraries contained a high percentage of perfect clones, ranging from 78.1% to 91.6%. From these clones, we developed 355 SSR markers when tested from 502 SSR primer pairs. Using all 355 SSR markers we tested one screening panel consisting of eight timothy clones to detect the level of polymorphism and identify a set of loci suitable for framework mapping. The SSR markers detected 90.4% polymorphism between the parents of a pseudo-testcross F1 population. These SSR markers will provide an ideal marker system to assist with gene targeting, QTL (quantitative trait locus) mapping, and marker-assisted selection in timothy.

Isolation and characterization of simple sequence repeat markers in the hexaploid forage grass timothy (Phleum pratense L.).

In vitro studies were performed to quantify the putative allelopathic effect of pollen from Phleum pratense (Aveneae: Poaceae). Extract from ground pollen was partitioned, using ion-exchange chromatography. Acidic, basic, and neutral fractions were isolated. These fractions, along with extract from intact pollen, were applied in increasing concentrations of the equivalent of 0 (control), 0.1, 1, 3, 5, 10, and 25 pollen grains of P. pratense/μL. Pollen from five sympatric, wind-pollinated species of Poaceae and P. pratense was germinated on agar medium that contained different extract concentrations. In response to increasing extract concentrations, from intact pollen or from acidic fractions, mean percentage of germination of pollen of Agropyron repens, Bromus inermis, Danthonia compressa, and Poa compressa decreased in a nonlinear manner. Basic, neutral, and solvent fractions did not show any allelopathic activity; hence, the allelochemicals may be acidic in nature. An extract concentration equivalent to...

Allelopathic Pollen Extract from Phleum pratense L. (Poaceae) Reduces Germination, In vitro, of Pollen of Sympatric Species

Three taxa are distinguished in the sectionPhleum
Griseb. in Poland:P. nodosum (2n = 14),P. pratense (2n = 42), and the third one unformally named hereP. “commutatum” (2n = 14). It corresponds morphologically toP. commutatum
Gaud. reported as a tetraploid taxon (2n = 28) from other geographic regions. Giemsa C-banded karyotypes of these three taxa help clarify the taxonomic status ofP. “commutatum” and the origin of the hexaploidP. pratense. It is suggested that changes in the amount of telomeric heterochromatin played an important role in the evolution ofPhleum karyotypes.

Cytotaxonomy and karyotype evolution in Phleum sect. Phleum (Poaceae) in Poland

Cultivated timothy (Phleum pratense L.) is an important grass for hay production in temperate North America. It is under utilized in management-intensive rotational grazing systems because of its poor persistence when frequently defoliated. The objective of this study was to evaluate the USDA-NPGS collection of timothy accessions for agronomic traits, including persistence under frequent defoliation. Unlike previous reports for infrequent harvest systems, diploid and tetraploid species of Phleum were similar in forage yield to hexaploid P. pratense, suggesting their potential value in livestock agriculture. Cultivated accessions tended to have fewer, but larger leaves; longer and narrower panicles with a greater number of smaller seeds; lower survival under frequent defoliation; and higher forage yield than natural accessions. A considerable amount of phenotypic variation among accessions was explained by geographic source of the accessions. Twenty-one unique phenotypic clusters were formed to account for 50% of the phenotypic variability among accessions, providing the basis for development of a core collection for P. pratense. Clusters were highly differentiated on the basis of geographic origin of the accessions, underscoring the potential importance of the relationship between phenotype and geography in hexaploid timothy.

Patterns of Variation in a Collection of Timothy Accessions

Cytogeography of the Phleum pratense group (Poaceae) in the Carpathians and Pannonia

Two polyploid and one diploid timothy species are found in North America: L. (2n = 42), var. (Gaud.) Koch (2n = 28), and DC. (2n = 14). Karyotypes and photomicrographs of and Gaud. and a photomicrograph of are presented.Chromosome arm-length measurements, arm-length ratios, and other detailed observations showed that has three pairs of short acrocentric chromosomes, three pairs of long submetacentric chromosomes, and three pairs of equisized chromosomes with satellites. has two pairs of small acrocentric chromosomes, and one pair of long metacentrics, a slightly shorter pair of submetacentrics, and a pair of satellited chromosomes. This and other data obtained from photomicrographs of cells of plants from Alaska and Wyoming suggest that has one genome in common with . All indications are that is an autohexaploid, and is an allotetraploid. The genome is karyotypically similar to the genome.

L. J. Klebesadel

Papers

Karyology and Phylogenetic Relationships of Phleum pratense, P. commutatum, and P. bertolonii 1