Forage Grass Breeding Research Articles

Genetic variation in an orchardgrass population promises successful direct or indirect selection of superior drought tolerant genotypes

AbstractImprovement in drought tolerance is an important component of forage grass breeding. To assess the potential of selecting drought tolerant genotypes of orchardgrass, a polycross population was created in 2010 and evaluated in the field under normal and drought stress conditions during 2011–2013. Drought stress reduced performance in forage yield, growth characteristics, and most of the physiological traits measured, but increased carotenoid content, proline content, and the chlorophyll a/b ratio. High estimates of narrow‐sense heritability for chlorophyll and carotenoid content, as well as forage yield components, indicated that phenotypic selection would be successful in achieving genetic progress. Indirect selection to improve forage yield under drought stress conditions was efficient through selecting for chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content. These physiological traits were also significantly associated with drought tolerance index. Overall, families 5, 7, 8, 13, 14 and 24 with high stress tolerance index values and high forage yield under both water conditions were identified as suitable families for breeding drought adaptive varieties.

Variation and Correlations among European and North American Orchardgrass Germplasm for Herbage Yield and Nutritive Value

Efforts to improve water-soluble carbohydrate (WSC) concentrations are common in perennial forage grass breeding. Perennial ryegrass (Lolium perenne) breeding has been very successful in developing new cultivars with high WSC and high agronomic performance. Breeding efforts are ongoing to improve the WSC of other perennial forage grasses, such as orchardgrass (Dactylis glomerata). The United States Department of Agriculture Forage and Range and Deutsche Saatveredelung orchardgrass breeding programs cooperated to characterize the expression and genotype by environment interaction (GEI) of water-soluble carbohydrates in a collection of orchardgrass populations from both breeding programs. Additionally, the effort characterized the relationship between water-soluble carbohydrates and other agronomic and nutritive value traits in these populations. Overall, the Deutsche Saatveredelung populations had higher herbage mass (15%), rust resistance (59%), and later maturity. The Forage and Range Research populations had higher water-soluble carbohydrates (4%), nutritive value, and earlier maturity. However, results were highly dependent on GEI. Differences were very pronounced at the French and German field locations, but less pronounced at the two US locations. Combining the germplasm from the Forage and Range Research and Deutsche Saatveredelung programs may be a way to develop an improved base germplasm source that could then be used separately in the EU and US for water-soluble carbohydrate and other trait improvement.

Low-cost automated biochemical phenotyping for optimised nutrient quality components in ryegrass breeding

Quantification of forage quality is essential for the identification of elite genotypes in forage grass breeding. Perennial ryegrass is the most important temperate species for global pastoral agriculture. However, the protein content of ryegrass generally exceeds the requirements of a grazing animal, and the ratio of water soluble carbohydrate (WSC) to protein is too low for efficient protein utilisation. This results in poor nitrogen use efficiency (NUE) in the farming system by livestock, and hence limits optimal animal production. New ryegrass cultivars with optimised WSC and protein content are desirable for farming efficiencies. Several methods are available for quantification of WSC and plant protein (such as near-infrared spectroscopy [NIRS] and high performance liquid chromatography [HPLC]). However, such methods are labour-intensive, low-throughput and cost-prohibitive for commercial breeding programs, which typically need to assess thousands of samples annually. An accurate high-throughput micro-plate-based protocol has been developed and validated, with the ability to simultaneously process and quantify WSC and plant protein with a high level of automation, and an increase in sample processing of ~10-fold compared with commonly-used methods, along with a 3-fold cost reduction. As WSC and protein are extracted simultaneously and quantified within micro-plates, consumable costs are minimised with optimal reagent use efficiency, resulting in a low per sample cost that is suitable for commercial pasture breeding companies. This is the first demonstration of a forage quality phenotyping protocol suitable for broad-scale application, and will allow breeders to select elite genotypes based not only on visual assessment but also on WSC : protein ratios for improved ruminant nutrition.

Genomic structure of androgenic progeny of pentaploid hybrids, Festuca arundinacea × Lolium multiflorum

AbstractTo assess the usefulness of the doubled haploid (DH) method in the breeding of forage grasses, a sample of anther‐derived progeny of pentaploid F1 hybrids of Festuca arundinacea × Lolium multifiorum was karyotyped using genomic in situ hybridization (GISH). The technique allowed scoring of the total number of chromosomes, the number of chromosomes contributed by each parent, and the number and positions of the Festuca‐Lolium translocation breakpoints. Among 27 plants analysed, 13 belonged to three clones, effectively reducing the number of different progeny karyotyped to 17. These included 10 haploids, five doubled haploids and two plants for which the origins could not be explained. In all plants analysed, a mixture of chromosomes of both parents was present, including an average of 1.88 intergeneric translocations per plant. The translocation breakpoints were distributed along almost the entire length of the chromosome arms. Chromosome variation among androgenic progeny appeared much wider than that in the conventional backcross but low vigour and high mortality suggest that this additional variation may be difficult to exploit directly in breeding. However, a change in the pattern of recombination makes the entire genome accessible to manipulation.

Disturbed Mendelian segregations at isozyme marker loci in early backcrosses of Lolium multiflorum × Festuca pratensis hybrids to L. multiflorum

The segregation of interspecific recombinant Festuca pratensis (Fp) alleles, introgressed into the germolasm of Lolium multiflorum (Lm), at four loci (PGI/2, AcP/2, GOT/3 and BAP) is described. Heterozygous (Lm/Fp) plants were backcrossed to L. multiflorum (2n=2×=14) and subsequent BC2 Lm/Fp sibling genotypes intercrossed. In crosses between BC1 heterozygous plants (Lm/Fp) used as males and L. multiflorum, there was a reduced transmission of the F. pratensis (Donor Parent) derived alleles in the populations with PGI/2 and AcP/2 marker loci compared to the reciprocal cross but the reduction was not significantly different in those with GOT/3 and BAP markers. Two PGI/2 marked BC2 half-sib families in particular exhibited a more extreme deficiency of Fp/Fp progeny plants than anticipated from the BC2 segregations indicating possible linkage to zygotic lethals. Deficiencies of F. pratensis alleles were, in most cases, less marked in BC2 half-sib families indicating that a further round of recombination had reduced the size of the introgressed chromosome segment or that deleterious linkages had been broken. A tendency towards heterozygote advantage was found in one BAP marked halfsib family. The significance for forage grass breeding of reduced transmission rates of Donor Parent alleles in early back-cross generations especially through the male gametes is discussed.

Grass Host Preferences of Listronotus bonariensis (Coleoptera: Curculionidae)

Host plant preferences for feeding and oviposition by adult Listronotus bonariensis (Kuschel) were determined in multiple-choice experiments in the field and laboratory using 19 grasses. Feeding intensity was negatively correlated with fiber (cellulose + hemicellulose + lignin) content of foliage, possibly indicating an effect of leaf toughness on feeding. Oviposition preferences were correlated with feeding intensity; 29-86% of the variation in egg numbers per plant was accounted for in numbers of feeding scars on these plants. Numbers of eggs deposited in the plants were negatively correlated with the density of intercostal silica deposits (inclusive of trichomes) in the abaxial surface of the grass sheaths. A causal relationship between silicification and oviposition preference was confirmed in a pot experiment where increased silica uptake and deposition reduced egg-laying on two ryegrass cultivars. The dispersion of eggs in the various grasses also was apparently related to the density and distribution of intercostal silica deposits and trichomes on the sheath. Feeding and oviposition on ‘Grasslands Nui’ ryegrass, Lolium perenne L., were reduced by plant infection by the endophytic fungus Acremonium lolii Latch, Christensen & Samuels. In the absence of A. lolii infection, ryegrass cultivars of L. multifiorum L. parentage were preferred over L. perenne cultivars. These results are briefly discussed in relation to breeding of forage grasses.

Response to Selection for Leaf Area Expansion Rate of Tall Fescue1

Development of effective selection criteria for the improvement of dry matter yield is a desirable goal in forage grass breeding. Leaf area expansion rate (LAER) has been suggested as acceptable selection criterion for improving post‐flowering yield of tall fescue (Festuca arundinacea Schreb.). Our objectives were to evaluate the responses of LAER, and its components leaf elongation rate (LER) and leaf width (WID) to five cycles recurrent phenotypic selection for both high and low LAER. In August 1980, a representative Co population, parents and offspring of the third and fifth cycles of selection for high and low LAER, and the check cultivars Missouri 96 and Kentucky 31 were transplanted into a field experiment. One tiller on 40 plants of each entry was evaluated in the fall of 1980 and 1981 for LER, WID, and LAER. Linear regression of performance on cycle of selection predicted an increase in LER of 0.87 and 0.48 mm/day/cycle of selection for high LAER in 1980 and 1981, respectively, while selection for low LAER resulted in a predicted decrease in LER of 0.77 and 0.84 mm/day/cycle of selection in 1980 and 1981, respectively. Predicted increase of WID was 0.45 and 0.33 mm/cycle in 1980 and 1981, respectively. Response of LAER to selection for high LAER in 1980 and 1981 was an increase of 15.7 and 10.8 mm2/day/cycle of selection, respectively, while selection for low LAER caused LAER to decrease by 11.6 mm2/day/cycle of selection in 1980 and 10.5 mm2/day/cycle in 1981. In both years, the responses of LER, WlD, and LAER to divergent selection for LAER were largely linear and symmetric. Thus, gene action for LAER and its components is additive in large part, and it is likely that continued response to selection would be realized in additional cycles.

Theory and application of half-sib matings in forage grass breeding

Half-sib (HS) matings, including polycross, topcross, and open-pollination, are useful in the breeding of cross-pollinated sexual perennial forage grasses to evaluate general combining ability of parental clones for synthetic cultivar development, recombine selected entries in recurrent selection programs, and obtain quantitative genetic information. The objective of this paper is to review uses of HS matings in breeding of these forage grasses with emphasis on theoretical aspects related to quantitative genetic analysis.Polycross mating with adequate replications and sufficient isolation is recommended over topcross and open-pollinated mating schemes in generating HS families for quantitative genetic studies. For the estimates of many genetic parameters to be valid, the parents must be a random sample from a random mating population in linkage equilibrium. Precision of the estimates depends on adequante sampling of the population of genotypes and environments used for evaluation.Analyses of variance on HS families and parental clones, and analysis of covariance between parent and offspring provide useful information on additivity of genetic effects and on genotype × environment interactions. Classical, narrow-sense heritability on an individual plant basis can be estimated and used to predict genetic gain from individual (mass) selection, providing that within family variance is estimable. If the forage breeder uses family selection, heritability should be estimated according to the proposed unit of selection. The selection unit must be specified in terms of numbers of replications, years, and locations. Polycross HS family selection can be readily adapted to a population improvement program in forage grass breeding.Narrow-sense heritability can also be estimated by doubling the linear regression coefficient of HS prog eny means on parental means. When HS families and parents are evaluated together in replicated experiments under similar environments, covariance analysis is recommended to remove the genotype × environment interaction covariance and environmental error covariance between parent and offspring, since these nongenetic covariances may result in inflated heritability estimates and misleading expected genetic gains from selection.

Field Measurement of Photosynthesis in a Forage Grass Breeding Program1

A system for rapid measurement of net carbon exchange (NCE) by leaves of clonal lines of forage grasses growing in the fidd has been developed. Air‐sealed leaf chambers of laminated construction connected to a manifold permit the determination of the average NCE of several leaves measured simultaneously. With 4 replications and more than 10 genotypes, the average NCE from 6 individual leaf measurements per plot was adequate to detect statistical differences of 2.0 mg dm−2 hour−1 between 2 genotypes with 83% power. Two units of six leaf chambers, each operating simultaneously, are monitored by one infrared CO2 analyzer, allowing the average NCE rates of 20 plots/hour to be accurately measured. The system is reliable, rapid, relatively simple, and uses intact leaves for field measurement. The technique is being used to determine genetic variability, heritability, and potential use of NCEin a tall fescue (Festuca arundinacea Schreb.) breeding program.