RESUMEN
The efficient preservation of protein in silage for livestock feed is dependent on the rate and extent of proteolysis. Previous research on fresh forage indicated enhanced protein stability in certain Festulolium (ryegrass × fescue hybrids) cultivars compared to ryegrass. This is the first report of an experiment to test the hypothesis that a Lolium perenne × Festuca arundinacea var glaucescens cultivar had reduced proteolysis compared to perennial ryegrass (L. perenne) during the ensiling process. Forages were harvested in May (Cut 2) and August (Cut 4), wilted for 24 h and ensiled in laboratory-scale silos. Silage was destructively sampled at 0 h, 9 h, 24 h, 48 h, 72 h, 14 days and 90 days post-ensiling, and dry matter (DM), pH and chemical composition were determined. At Cut 2, there was no difference in crude protein between treatments but ryegrass had higher soluble nitrogen (SN) (P < 0.001) and grass × time interactions (p = 0.03) indicated higher rates of proteolysis. By Cut 4, Festulolium had (5.5% units) higher CP than ryegrass (p < 0.001) but SN did not differ. Ammonia-N did not differ between silages in either cut. DM differences (11.8% units) between treatments in Cut 4 (v.2.2% in Cut 2) may have masked effects on proteolysis, highlighting the importance of management on silage quality. This was despite higher WSC in ryegrass in both cuts (p < 0.001), with grass × time interactions (Cut 2; p = 0.03) showing slower WSC decline in ryegrass in Cut 4 (p < 0.001). Silage pH values did not differ between grasses in either cut, but grass × time interactions (p < 0.001) showed a slower decline in both ryegrass cuts, resulting in higher (p < 0.05) pH at 24 h and 72 h for Cuts 2 and 4, respectively. Overall, the hypothesis for an enhanced protein stability in Festulolium when ensiled as ruminant feed was evidenced by lower SN but not ammonia-N in an early-cut silage with a comparable DM to ryegrass.
RESUMEN
Quantitative trait loci (QTLs) for frost and drought tolerance, and winter survival in the field, were mapped in meadow fescue (Festuca pratensis Huds.) and compared with corresponding traits in Triticeae and rice to study co-location with putatively orthologous QTLs and known abiotic stress tolerance genes. The genomes of grass species are highly macrosyntenic; however, the Festuca/Lolium and Triticeae homoeologous chromosomes 4 and 5 show major structural differences that is especially interesting in comparative genomics of frost tolerance. The locations of two frost tolerance/winter survival QTLs on Festuca chromosome 5F correspond most likely to the Fr-A1 and Fr-A2 loci on wheat homoeologous group 5A chromosomes. A QTL for long-term drought tolerance on chromosome 3F (syntenic with rice 1) support evidence from introgression of Festuca genome segments onto homoeologous Lolium chromosomes (3L) that this genome region is an excellent source of tolerance towards drought stress. The coincident location of several stress tolerance QTL in Festuca with QTL and genes in Triticeae species, notably dehydrins, CBF transcription factors and vernalisation response genes indicate the action of structural or regulatory genes conserved across evolutionarily distant species.
Asunto(s)
Mapeo Cromosómico , Frío , Sequías , Festuca/genética , Sitios de Carácter Cuantitativo , Cromosomas de las Plantas , Clonación Molecular , Evolución Molecular , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Lolium/genética , Oryza/genética , Estaciones del Año , Factores de Transcripción/genética , Triticum/genéticaRESUMEN
At present, breeding programmes aimed at combining advantageous traits within the Lolium-Festuca complex, are mainly focused on introgression procedures. One principal objective, is the transfer of genes conferring resistance to abiotic stresses from Festuca species (F. pratensis, F. arundinacea and F. glaucescens) into Lolium multiflorum and L. perenne germplasm. In our experiments, two different hybrids: triploid - L. multiflorum (4x) x F. pratensis (2x) and pentaploid - F. arundinacea (6x) x L. multiflorum (4x) were backcrossed twice onto L. multiflorum cultivars, and numerous BC2 progeny generated. BC2 plants from both combinations were tested in field and/or simulated conditions for winter hardiness and drought resistance. GISH (genomic in situ hybridisation) analyses were then performed on the most winter hardy and drought resistant plants to locate putative genes for stress resistance. Using resistant L. multiflorum genotypes with a single Festuca chromatin segment, it was possible to allocate AFLP (amplified fragment length polymorphism) markers specific to that segment. Markers associated with genes conferring stress resistance facilitate marker-assisted selection programmes to obtain new, more persistent grass cultivars. Preliminary results of GISH analysis, to identify Festuca chromosome segments in L. multiflorum introgression lines and to find segment-specific AFLP markers, are presented