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This study also identified the increased expression of many interesting genes, including M. Forage NUE is a target for breeding, particularly as protein content of crops is so valuable. Protein accumulation is linked to N status and when the supply is supra-optimal greater storage occurs. When compared with grain crops that have been bred for high seed starch, forage crops often require N in greater amounts due to their increased growth, storage capacity and higher fiber content Parsons et al.

Principally NUE for forage crops can be based on N utilization efficiency NUtE as we are interested in the highest achievable biomass of the shoot which will form the content to be dried for feed production Xu et al. Not only does this include biomass, but also the relative N levels in this tissue; it is not enough to only have a high yield of biomass in the shoots, it must also yield optimal amounts of N. Moreover, when looking at the effect of fertilizer use we are also interested in how both the biomass and N status change on application and thus also N uptake efficiency NUpE.

Forage crops offer challenges for NUE as there is a requirement for optimal yield of shoot biomass with a high N content NUtE while also optimizing N fertilizer acquisition NUpE throughout the growth season. As NUE is an important criterion for biomass improvements, many genes relating to N acquisition or metabolism have been the subject of study in model systems. Additionally, genes important in carbon metabolism have also been the focus, due to the links between C:N ratios for plant growth Jaradat et al.

Despite the long evolutionary divergence between grasses and legumes, many key candidate genes have high genetic similarity, meaning one can use known genes which effect a trait in a forage crop from one species and investigate it within another. For example, a range of vegetative N storage proteins have been identified and the reviewed for leaves Muntz, and roots Bewley, To illustrate this further, the phylogeny in Figure 4 is the known and predicted coding sequences for rbcS including the model species Arabidopsis thaliana , many significant grass and legume crops.

Many of the forage crops have high similarity in their coding sequence to more well-studied crop species. For example, Medicago and Trifolium rbcS sit closely to the legume species which have their genomes sequenced [ Cajanus cajan , Cicer arietinum , Glycine max , Lotus japonicus , Medicago truncatula , and Phaseolus vulgaris Jacob et al. For example, investigation of Heat Shock Protein in M. The phylogeny was built using Newick format in iTOL v3. The tree was color coded to show model species, human food crops and forage crops for both legumes and grasses, although it should be noted that many can overlap in their uses.

In forage crop vegetative biomass, the most important nutrients for livestock are proteins and water-soluble carbohydrates WSCs , and ideally the post-harvest quality of these should be maintained. There has been considerable interest in developing organ specific proteome reference maps for stems and leaves. As the D -value of forage is mostly linked to cell wall concentration and a reduction of this can aid digestibility Jung and Allen, ; Jung et al.

Some research has focussed on transgenic approaches to increase and enhance amino acids and proteins. As many forages have low concentrations of the sulfur-containing amino acids of methionine and cysteine, both important in animal and human nutrition Ball et al. These have included using lupins Lupinus albus Molvig et al. Consequently, stress proteomes have also been used for vegetative tissue; lupin stem proteins have been analyzed under water stress to show increases in serine protease and cysteine protease required for remobilization of proteins Pinheiro et al.

Moreover, through harvesting regimes, forage crops undergo extreme stress which has shown to cause the remobilization of vegetative storage proteins VSPs to boost new shoot regrowth in both Medicago and Trifolium as well as being important for cultivars with better cold tolerance Avice et al. Finally, the N consumed by livestock is recycled and increasing ruminant productivity is a major target for as the conversion of plant to microbial protein is inefficient.

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Furthermore, the process of rumen fermentation is important for the generation of greenhouse gasses like methane Bannink et al. The impact of genomics extends beyond the crop plants to their environmental interface. For example, the rhizosphere microbiome is likely to be a future target for improving the nutritional quality of crops.

Epiphytic bacteria living on and in the plant, may be important for crop health and nutrition, and some microorganisms can fix atmospheric N within legume root systems. Bacteria living with plants may be able to assist in digestion and absorption of forage eaten by livestock. In the soil, the rhizosphere microbiome is important for nutrient cycling and uptake, particularly in low input systems like those grown in the tropics.


The inoculation of new forage crops with beneficial microorganisms is likely to be a target for research and use in future crops, coupled with rhizosphere microbiome research of root exudate composition. The root is known to directly modify the rhizosphere population by altering the chemical constituents of root exudates.

For example, the roots of the tropical grass Brachiaria specifically produce a chemical shown to inhibit nitrifying bacteria and to specifically block ammonia-oxidizing pathways in soil bacteria, the first step in the process of converting ammonium to nitrate Byrnes et al. Nitrification inhibitors have been identified in root exudates from several legumes and grasses including sorghum and rice, but by far the largest activity was detected in the tropical grass Brachiaria humidicola Subbarao et al.

The biological nitrification inhibitor BNI activity of root exudates has been assayed using a recombinant luminescent reporter ammonia-oxidizing bacteria Nitrosomonas europaea Subbarao et al. This exciting example offers the potential for transferring this trait to other forage crops to improve NUE. In the future synthetic pathways to produce plant nitrification inhibitors will be fully elucidated, providing the opportunity to capture this trait in forages and transfer to other crops to improve yield and nitrogen acquisition.


As protein digestion and uptake in livestock is directly related to energy availability ME Nocek and Russell, ; McCarthy et al. In Lolium WSCs include fructans which are the most important storage polysaccharide and thus improved metabolism of fructan from sucrose can help improve the D -value Chalmers et al. Use of distinct Fructan:Fructan 6G-fructosyltransferase sequence variants has shown to increase fructan levels at warmer temperatures in Lolium , thus hoping to aid development of high sugar-content grasses even at changing climates Rasmussen et al.

Such work provides a platform for future studies to identify promotors important in other nutritional traits. The amounts of resistant starch are important for the digestibility and nutritional content of forage crops. Resistant starch RS generally has lower digestibility until it reaches the large intestine Englyst et al.

Research studies have shown that M. One major difference between dietary RS is that it is seen to have advantages in the human diet by providing more fiber, but disadvantages in livestock feed for non-ruminants as it remains undigested. In general, lower RS will improve the digestibility of forage crops for both ruminant and non-ruminant livestock.

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As a crops D -value is closely linked with its starch, protein and lignin content, genomic studies have begun large-scale genome-wide association studies GWAS to confirm correlations across a range of traits, such as using three distinct alfalfa cultivars with a high-throughput genotyping-by-sequencing approach Biazzi et al. However, this study did highlight that differences in SNPs associated in different tissue types shoots and leaves can vary in correlation with traits such as protein content, and so care must be taken when using GWAS to aid crop improvements.

Plant breeding using genotypic markers, marker assisted selection

Another substantial nutrient in forage crops is that of proanthocyanidins or condensed tannins CTs. CTs bind to protein making it unavailable to digestion for ruminants until it reaches the rumen, and thusly an important trait in increasing the D -value of a crop Min et al. Whilst some species of legumes have optimum levels of CTs such as Lotus corniculatus , others such as Onobrychis viciifolia and Trifolium ambiguum are often poor choices for forage in many climates Min et al.

Such knowledge can be used to manipulate forage crops. A similar study showed that expression of the TaMYB14 transcription factor from a low-yielding forage activates CT biosynthesis in both Trifolium and Medicago Hancock et al. Other approaches have involved characterizing early steps of CT biosynthesis in M.

Molecular breeding for the genetic improvement of forage crops and turf

There has been an effort to engineer better digestibility in some forage cultivars Wang and Brummer, and microbial pre-digestion after cutting and before feeding, including microbial supplements Boyd et al. As biomass yield is the main target for forage crop improvement, more rapidly growing cultivars can be targeted for breeding. Studies have consequently focussed on heading date Fe et al. Manipulating genes involved in delayed senescence has been targeted for increasing biomass yields.

A final example is the expression of the Panicum virgatum NAC1 and NAC2 transcription factors in Arabidopsis atnap lines mutants with defective senescence to restore wild-type phenotype, predominantly measured using total chlorophyll concentrations Yang et al. However, fast growth must also be coupled with the ability of the plants to respond to cutting by providing rapid regrowth. Growth rates and recovery from cutting are traits that are relatively easy to select for in breeding trials, and have been of regular interest to researchers for many decades in both Lolium and Medicago Wilman et al.

In addition, cutting experiments using 13C and 15N in both Lolium and Medicago have shown how the soil is affected both for dissolved organic C and N, and microbial biomass, demonstrating that management schemes can be critical to subsequent soil health Schmitt et al.

Future directions in the molecular breeding of forage and turf

An ability to rapidly regrow may increase the susceptibility of the plant to insect and pathogens and this is worthy of further investigation. The relationship between tissue wounding and plant immunity is a topic that is quickly developing and there is now good evidence that tissue growth rate is closely linked with immunity Huot et al. Thusly, management schemes for forage crops are very important for yield. For example, choosing when to cut or graze a crop is crucial for subsequent regrowth of the plant Karn et al.

To assist in this choice there is scope for the use of molecular markers, with the future possibility of a PCR test for the optimal time harvest based on the expression of candidate genes like storage proteins. Such tissue testing of crops can also be used for decisions on the timing of fertilizer applications as the two evaluations are made at around the same time. There is scope to identify a suite of marker genes that can be used to help decide when these key decisions are made.

Mixed cropping schemes are already widely used for forage crops and there are clear advantages in growing legumes and grasses together. Legumes increase soil N through their N fixation symbiosis with Rhizobium , with their biological nitrogen fixation ranging from 32 to kg ha -1 Iannetta et al.