Pasture Species Selection and Breeding

Core Concepts of Pasture Species and Environmental Adaptation

Lecture Overview: This session focuses on matching pasture species to their environment (climate, soils, and purpose) and the processes of selection and breeding for improved varieties.
System Goal: The objective is to build a feed base from the ground up that is both productive and persistent over time.
Native Pasture Definition: Pastures containing mostly species that existed in Australia before European settlement.
- Examples: Wallaby grass, Kangaroo grass, Black spear grass, and Mitchell grass.
- Characteristics: These species have not been subject to formal selection or breeding; they remain in their natural state.
Naturalized Pasture Definition: Introduced species that have become naturally adapted to a system without active management.
- Examples: Phalaris, Subclover, Medic, and Buffel grass (in Queensland).
Dominance of Native Pastures: The majority of the Australian grazing landscape consists of native vegetation. This is particularly true in rangelands, which are more extensive systems containing shrubs and small trees alongside grasses.
The Adaptation Advantage: Native species are highly adapted to the Australian environment, characterized by:
- Perennial Lifecycle: Most are long-lived.
- Resource Efficiency: They survive by growing less biomass ( $2-3 \times 10^0 \text{ tons}$ ) compared to improved species ( $6 \times 10^0$ to $10 \times 10^0 \text{ tons}$ ), thus requiring fewer resources.
- Tolerance: High tolerance for low soil fertility, low/variable soil moisture, hostile pH, and fire management.
- Morphology: Narrow leaves and deep roots to cope with stress.

Limitations and Management of Native Pastures

Productivity Barriers:
- Leaf-to-Stem Ratio: Native species often have a low ratio, meaning more structural carbohydrates and lower digestibility.
- Palatability: Low palatability can be a persistence trait but limits livestock intake and utilization.
- Short Growing Season: Native grasses may only grow for $2$ to $3 \text{ months}$ of the potential growing season.
- Phenology: Rapid deterioration of quality as the plant moves quickly from vegetative to reproductive stages.
- Flowering: Often long and sporadic, making seed harvesting or grazing management difficult.
Management Strategies for Natives:
- Residual Biomass: Managers must maintain higher residual levels compared to improved pastures; native growing points are often more exposed and easily damaged.
- Stocking Rates: Historically evolved under low grazing pressure from soft-footed animals (kangaroos); hard-hoofed livestock require careful management of trampling effects.
- Recovery Periods: Long recovery periods are needed to allow carbohydrate reserves to replenish in roots and shoots.
- Improvement via "Legume Incorporation": Adding annual temperate legumes (e.g., Subclover) paired with fertilizer (e.g., Single Superphosphate providing Phosphorus and Sulfur) can increase production tenfold by fixing Nitrogen ( $N$ ).
- Fire Management: Used strategically to control woody regrowth and maintain the balance between grasses and shrubs.

Selection Hierarchy for Improved Pasture Species

Definition of Improved Pastures: Introduced or "exotic" species selected for high biomass production, high quality, and grazing tolerance.
The Selection Process: Matching species to environmental conditions follows a specific hierarchy:
1. Climate ( $1^{st}$ Priority):
  - Annual Average Rainfall: Eliminating species that require higher moisture than the site provides (e.g., choosing species for an area with an average of $770 \text{ mm}$ to $780 \text{ mm}$ ).
  - Rainfall Variability: Awareness of extreme dry years (e.g., Armidale in $2019$ at $280 \text{ mm}$ to $290 \text{ mm}$ ).
  - Temperature Extremes: Specifically the risk of frost on Tablelands, which dictates the choice between temperate and tropical species.
2. Soil Type ( $2^{nd}$ Priority):
  - Texture: Light/sandy soils have low water holding capacity; heavy clays have high capacity but may suffer from waterlogging.
  - pH: Critical for determining species suitability.
  - Example: Bambatsi is adapted to waterlogging/heavy soils, while Rhodes grass or Love grass prefer lighter, sandy soils.
3. Intended Purpose ( $3^{rd}$ Priority):
  - Livestock Class: Cattle have higher bloat risks than sheep.
  - Duration: Determining if the pasture is permanent ( $10$ to $20 \text{ years}$ ), short-term ( $2$ to $3 \text{ years}$ ), or a forage crop ( $5$ to $6 \text{ months}$ ).
Cultivar Selection: Refining the choice within a species.
- Flowering Date: In Subclover, this determines the minimum growing season required. Dalkeith requires only $97 \text{ days}$ to flower, while Denmark requires a much longer period.

Pasture Diversity and Landscape Management

Diverse Mixes:
- Benefits: Increased likelihood of green leaf production year-round, utilizing different root depths and water resources.
- Cons: High management complexity (different species reaching reproductive stages at different times) and competition issues (e.g., Rhodes grass can dominate and suppress other seeds during emergence).
Simple Mixes:
- Benefits: Easier to manage and monitor; usually one main grass paired with a few legumes.
- Application: Suggested for intensive systems where fencing matches specific soil types.
Landscape Positioning: Fencing and planting according to site characteristics:
- Crest/Slope: Dries out quickly; requires early-season species.
- Valley/Flat: Retains moisture; supports mid-to-late season species with longer production potential.
- Example: Using Tall Fescue on flats (September to November grazing) and Cocksfoot on ridges (December to February grazing).

Forage Crops and Pasture Cropping

Forage Crop Purpose: Provide high-quality feed quickly to fill seasonal gaps and facilitate weed management.
Types of Forage Crops:
- Brassicas: Leafy turnip, kale (high Crude Protein and Metabolizable Energy).
- Cereals: Oats, rye corn, wheat.
Weed Management Synergy: Brassicas allow for grass-selective sprays to remove perennial weeds; cereals allow for broad-leaf weed control.
Pasture Cropping (Coast Specific): Sowing temperate species (Ryegrass, Oats) directly into summer-active tropical pastures (Kikuyu, Paspalum) in autumn to balance the feed year.

Genetic Selection and Breeding Strategies

Selection: Choosing superior genotypes from existing available germplasm (Gene Banks).
Breeding: Creating new genotypes through progeny crossing to combine traits like productivity, quality, and persistence.
Origins of Germplasm:
- Mediterranean: Source of temperate grasses and legumes.
- Central/South America: Source of tropical legumes.
- Eastern/Southern Africa: Source of tropical grasses.
Gene Banks: The Australian Pastures Gene Bank contains thousands of unique entries, including over $29,000$ for Medicago, $22,000$ for Trifolium, and nearly $3,000$ for Panicum.
Modern Breeding Techniques:
1. Marker-Assisted Breeding: Using Quantitative Trait Loci (QTLs) to track markers associated with specific traits, speeding up the process and reducing costs.
2. Hybridization: Crossing species within the same genus (e.g., Trifolium genus) to combine productivity with hardiness.
3. Ploidy: Adjusting chromosome counts. Tetraploid Ryegrass ( $4 \times \text{chromosomes}$ ) has higher growth rates and quality than Diploid ( $2 \times \text{chromosomes}$ ), though persistence may vary.
4. Genetic Engineering: A potential future pathway for specific pasture needs.

Evaluation and Commercialization

Evaluation Process: Comparing new varieties against a known standard. It takes $12$ to $15 \text{ years}$ and costs between $\$10 \times 10^6$ and $\$20 \times 10^6$ .
Stages of Evaluation: Germplasm assembly → individual plant assessment → single rows → small plots → grazing plots.
Plant Breeders’ Rights (PBR): Provides a commercial monopoly for typically $20 \text{ years}$ to incentivize seed company investment.
Pasture Trials Network (PTN): Independent testing across environments to provide data on autumn, winter, and spring production for commercial cultivars like Fortune, Pastoral, and Hummer Max P.

The Role of Endophytes in Grass Systems

Definition: A symbiotic fungus living within plant cells of Ryegrass and Tall Fescue.
Symbiosis: The fungus receives resources; the plant receives protection via chemical alkaloids.
Life Cycle: The endophyte exists in the seed → grows into the emerging shoot → remains at the plant base during vegetative growth → shifts up the stem into the seed during reproduction.
Types of Endophytes:
- Wild Type: Naturally occurring; produces alkaloids like Lolitrem B, which causes "Ryegrass Staggers" or "Fescue Foot" but provides excellent pest protection.
- Novel/Selected: Strategically selected to provide pest protection (via alkaloids like Peramine) without the toxic effects on livestock.
Management Options:
- Establish new pastures with No Endophyte (leads to lower persistence).
- Use Novel Endophyte lines (best balance of persistence and animal performance).
- Strictly remove all old Wild Type plants before sowing novel lines to prevent contamination.

Seed Technology: Storage and Coatings

Storage: Endophyte survival decreases faster than seed viability. Storage must be cool and dry (ideally < 5 \text{ Celcius} and < 11 \times 10^0 \text{ percent} moisture).
Seed Coatings: Used primarily to improve ballistics and "flowability" of small, light seeds (like tropical grasses).
Coating Components: Often a lime coat including Phosphorus ( $P$ ), Molybdenum ( $Mo$ ), and Rhizobia (for temperate legumes).
The Weight Penalty: Coatings can add $100 \times 10^0 \text{ percent}$ to $500 \times 10^0 \text{ percent}$ to the seed weight. This means sowing $2 \text{ kg}$ of coated seed results in significantly fewer plants per square meter than $2 \text{ kg}$ of bare seed.

Questions & Discussion

Audience Question: What is the average rainfall for Armidale?
- Response: Observations of $900 \text{ mm}$ to $1000 \text{ mm}$ are recent anomalies; the long-term average is approx. $770 \text{ mm}$ to $780 \text{ mm}$ .
Audience Question: Regarding the Subclover cultivar slide, are the ranges in days or months?
- Response: The slide refers to days to flowering; the growing season requirements for those cultivars range from $4 \text{ months}$ up to $8$ or $9 \text{ months}$ .
Audience Question: What happens to leftover seed or culled lines in the evaluation process?
- Response: Lines that fail are simply dropped. If a line is released and later found problematic (e.g., Barnaby Tall Fescue with a toxic endophyte), the seed stock must be destroyed to prevent further planting.

Matching Pasture Species to Environment: Focus on climate, soils, and purpose for optimal selection and breeding.
System Goal: Build a productive and persistent feed base over time.
Native Pasture: Species existing in Australia before European settlement, not formally bred or selected (e.g., Wallaby grass, Mitchell grass).
Naturalized Pasture: Introduced species adapted to a system without management (e.g., Phalaris, Subclover).
Adaptation Advantage of Native Species:
- Perennial lifecycle, resource efficiency, high tolerance to harsh conditions, and specialized morphology.
Productivity Barriers of Native Pastures: Low leaf-to-stem ratio, low palatability, short growing season, and rapid quality deterioration.
Management Strategies: Focus on maintaining residual biomass, careful stocking rates, and long recovery periods.
Improvement via Legume Incorporation: Adding legumes to increase productivity by fixing nitrogen.
Selection Hierarchy for Pasture Species: Prioritize climate, soil type, and intended purpose in choosing species.
Pasture Diversity and Landscape Management: Diverse mixes increase resilience, while simple mixes ease management.
Forage Crops: Used for high-quality feed and weed management.
Genetic Selection and Breeding: Selecting superior genotypes and employing modern techniques to enhance pasture quality and resilience.