The genome constitution and phylogeny of hexaploid timothy (Phleum pratense L., 2n = 42) have been studied with C-banding and genome-specific DNA techniques. The cultivated species and two diploid wild relatives P. alpinum (2n = 14) and P. bertolonii (2n = 14) were karyotyped. In P. pratense, two sets of seven chromosomes could not be distinguished from each other either in gross morphology or in C-banding patterns and the third set was found to be differentiated from them. Two genomes, A and B, were established in this species presumably with the genome formula of AAAABB. The banded karyotype in P. alpinum was close to the A genome and that of P. bertolonii was analogous to the B genome, which suggests these wild species were the genome donors of P. pratense. To reinforce this, a molecular assay was performed with genome-specific probes. Eight clones specific to the genome of P. alpinum and thirteen specific to the genome of P. bertolonii were respectively isolated from the genomic DNA libraries of P. alpinum and P. bertolonii. Three P. alpinum-specific sequences and three P. bertolonii-specific sequences were used as probes to hybridize the DNA of P. pratense on slot blot and Southern blot. All the three P. bertolonii-specific probes and two of the three P. alpinum specific probes exhibited cross-hybridization to P. pratense DNA. This has confirmed the allopolyploid origin of hexaploid P. pratense. In addition, phenotypic variations of seed storage proteins were investigated within the cultivated P. pratense with SDS-PAGE analysis. A total of 44 protein monomers were detected in mature seed extracts from 19 cultivars of timothy. The protein banding patterns were differentiated among all the examined cultivars except for two pairs. Such differentiation makes it possible to identify the timothy cultivars.

No description available.

Genetic improvement of timothy digestibility by breeding requires an effective and reliable selection procedure. The general objective of this study was to evaluate the concentrations of four fiber components (neutral detergent fiber, acid detergent fiber, acid detergent lignin, hemicellulose, and cellulose) and four ratios involving these concentrations (acid detergent lignin over hemicellulose, acid detergent lignin over cellulose, acid detergent lignin over the sum of hemicellulose and cellulose and hemicellulose over cellulose) as selection criteria to improve timothy digestibility without affecting plant biomass. Selected genotypes and populations derived from them were evaluated in a field experiment. Significant variability was observed among genotypes for all nine traits. Divergent phenotypic selection for seven of the traits (all except hemicellulose and hemicellulose over cellulose) produced groups of genotypes that consistently differed for the trait used as the selection criterion. Selection criteria that involved acid detergent lignin were the most effective in identifying genotypes with consistent differences in in vitro true digestibility. Genotypes selected for high or low values of each criterion were intercrossed to produce progeny populations. Five of the nine pairs of divergent populations were consistently different for the trait used as the selection criterion. Selection for acid detergent lignin over cellulose was the most effective in producing populations with consistent differences (22 to 32 g kg-1 DM) in in vitro true digestibility, with reduced values of this ratio associated with increased digestibility. This was mainly due to a reduction of the concentrations of lignin and neutral detergent fiber, particularly in the stem fraction, resulting in greater stem digestibility. Among the criteria examined here, the ratio of acid detergent lignin over cellulose therefore seems to be the most promising for phenotypic

No description available.