Advanced Cereals Specific Content

What is inhibition in the germination process?

The process of water uptake by the seed

What moisture does cereal seed require to start germination?

18%

What is are the main components of a seed?

The embryo is found in the endosperm (granules of starch for energy) surrounded by the bran

What are the two main hormones involved in germination?

ABA = Absicisic Acid

GA = Gibberellic Acid

What does Absicisic Acid do?

It suppresses growth (leads to dormancy) unless broken down by oxygen

What is required to break down absicisic acid?

Oxygen (seed needs oxygen to germinate)

Where is absicisic acid found?

In the aleurone layer

What does Gibberellic acid do?

It promotes growth (germination)

Where is Gibberellic acid found?

In the scutellum

If GA > ABA, what happens?

Germination

If GA < ABA, what happens?

Dormancy

What happens once there is excess GA within the seed once ABA has been degraded by oxygen?

Hydrolactic enzymes (amylace, glucanase, lipase and protease) start to break down starch in the endosperm which releases sugars to allow the embryo to grow

What factors influence seed vigour?

• Variety

• Storage period (longer periods degrade seed)

• Heat during grain drying

• Grain size (smaller = fewer starch reserves)

• Seed treatment

How does low vigour seed vary depending on the conditions it is grown in?

It will still establish well in warm, moist, early drilled conditions (similar level to high vigour seed), however in damp, cold, later drilled conditions it will perform much worse compared to high vigour seed

How does heat have an impact on crop establishment?

Warmer temperatures will increase the speed of chemical reactions (up to a point) and so germination will occur quicker if other conditions are met (moisture and oxygen)

How can rainfall impact inhibition?

Excess water (waterlogging) can reduce oxygen levels and therefore respiration, meaning inhibition takes longer to occur as there is less oxygen to break down the absicisic acid

Why is excess rainfall when temperatures are lower more of a problem for establishment?

Later drilled crops when temperatures are lower are more prone to waterlogging as less water will evaporate and so respiration (oxygen) is limited for a longer period

Which crop is most sensitive to waterlogging and how long will the seed survive before 100% seedling death?

After germination but before establishment, WW seed will survive only 16 days before 100% seedling death (population will be impacted after just 6 days depending on soil type)

What is the optimum temperature for cereal seed germination?

20 to 24 degrees

What is the thermal time (day degrees) from inhibition to emergence in cereals?

150 day degrees

When does soil temperature at 15cm peak during the calendar year?

In August then gradually declines through to February

How long does it take to reach 150 day degrees if a crop is drilled in mid September?

7 days

How long does it take to reach 150 day degrees if a crop is drilled in mid December?

28 days

How does soil temperature impact crop establishment?

Lower soil temperature = lower establishment (25% reduction when drilling from November onwards instead of early September)

Why do sandy soils have a much higher establishment rate than clay soils?

• Friable over a much wider range of soil moisture

• More likely to provide good seed to soil contact

• Smaller amount of water required to stimulate inhibition

• Lower strength allows unrestricted root and shoot growth

Why do clay soils have a much lower establishment rate than sandy soils?

• Poor sed to soil contact as only friable over a very narrow range of soil moisture

• Require a much higher water content to start inhibition

• Not free draining

Which 4 environmental factors influence crop establishment?

• Rainfall

• Waterlogging

• Temperature

• Soil Texture

Why does wheat straw left on the surface after harvest cause an issue in the following cereal crop?

It releases allelopathic chemicals which affect seedling growth (deter germination as chemicals signal there are other plants within that area) - known as autotoxicity

Why is WB and WO less vulnerable to slug damage than WW?

They have an extra seed coat and so are more protected

How many seedlings can each slug kill before emergence?

50

Why does WW following oats have a higher establishment rate than if following potatoes or beans?

The WW is drilled earlier

Why should drilling be avoided from December to February?

The higher seed rate, increased risk and low yield potential dont make it viable

Why does increasing the seed rate with later drilling still result in poor establishment?

The allelopathic chemicals released from the seed deter germination due to competition

What is the seed rate for WW within the optimum period (first half of October)?

300 seeds/m² - aiming for 500 to 600 ears at harvest

What is the risk with increasing the seed rate when drilling later?

It results in plants will less tillers that are more prone to lodging (high risk)

What is the ideal drilling depth for successful establishment?

30mm to 70mm (>70mm and first leaf emerges beneath surface or worse, soil restricts plants from emerging)

How much does establishment decrease with every additional 100 seeds/m²?

It is reduced by 2.6% for every additional 100

What does the rate of photosynthesis depend on?

Higher photon flux density

What is the range of Photosynthetically Active Radiation (PAR)?

400nm to 700nm

Which wavelengths do chlorophyll react with?

Blue and red waves (not green as this is reflected)

How does the endosperm support the seedling before photosynthesis can occur?

It provides enough energy to produce the first few leaves until photosynthesis takes over

How much solar energy on average is captured by a wheat crop in the UK across the season?

47% (can reach 60% if managed right)

What is the yield equation?

Y = QIEH

• Y: Yield of the crop per unit area over a given period (growing season)

• Q: Total quantity of solar radiation received during the period

• I: Fraction of total light (Q) intercepted by the canopy

• E: Photosynthetic efficiency (dry matter per unit of intercepted light)

• H: Harvest index (proportion of plant that goes into yield)

How would a GAI of 2.0 be interpretated?

There is 2m of leaf area for 1m of soil (2 / 1 = 2)

What is the optimum range of GAI for cereals?

4.0 to 7.0

What is the optimum GAI for WW and WB?

• WW = 6.3

• WB = 5.8

Why will crops with a below optimum GAI yield less?

They cannot utilise all of the sunlight falling upon them and therefore have less grain sites

What are the negatives with growing a crop with a higher than optimum GAI?

• They incur greater costs for inputs (seed, nitrogen, PGRs, fungicides etc)

• Greater risk of lodging

• Will potentially yield less

What are the 6 factors that influence canopy size?

• Seed rate

• Variety

• Time of drilling

• Nitrogen supply

• Growth regulators

• Fungicides

What is the relationship between yield and spec weight?

• Varieties bred for a high spec weight can limit the number of grain sites (lower yield)

• Varieties bred for high yield (more grain sites) may cause low spec weights in years when PAR is limited (eg, 6 row barley will have a lower spec weight than 2 row barley if PAR is limited)

• Wheat varieties with good, reliable spec weights tend to be lower yielding

What is the average number of grain sites per m² for WW?

20,000

How are the number of leaves on the main stem set in a WW crop?

They are determined by the time of sowing:

• October drilled = 8.4 leaves on main stem at GS31 and more tillers

• November drilled = 5 leaves on main stem at GS31 and less tillers

How are the number of tillers set in a WW crop?

They are determined by the time of sowing, nitrogen rate and timing of application

How much nitrogen is required in WW and WB to raise the GAI by 1.0?

• WW = 36kg N/ha

• WB = 28kg N/ha

When is the most important fungicide timing in WW?

T2 (flag leaf) - for every day you keep the canopy greener it is worth 0.1t/ha in yield

Why is an early nitrogen application important in winter drilled cereal crops?

It helps the tillers to survive (doesn’t stimulate them to be produced)

What can be done in the spring to stimulate tiller production?

Rolling or grazing

When is the main tillering period for WB?

In the autumn (slower growth in the North due to colder temperatures allows for tilling to occur for longer)

How does the level of photosynthesis from the lower leaves in WB compare to WW?

They perform a greater proportion of photosynthesis (fungicides important from an early stage to keep older leaves clean and maintain GAI)

Why is good establishment vital for spring sown cereals?

There is less opportunity for tillering (N should be applied early or in the seedbed)

What is the impact on yield when growing malting barley?

It has a lower grain N requirement (less N applied) so yield is sacrificed

What are three ways that can be used to measure GAI?

• Image analysis using a phone

• NDVI (NIR - Red / NIR + Red) → green vegetation absorbs red light and reflects NIR

• Ceptometer (measures light above and below the canopy, requires a known value of K)

How does variable rate seeding have an impact on maize and wheat?

• Maize - Higher seed rates on more fertile soil increases yield

• Wheat - Higher seed rates on heavier patches increases yield by 0.3-0.5t/ha on those areas

What is stem lodging?

Where the stem buckles (internode breaks) → less common than root lodging

What is root lodging?

Where the whole plant topples (stem remains straight and unbroken) and the roots rotate in the soil

What is the most common type of lodging?

Root lodging

When will root lodging occur?

When the ears are heavy after rainfall and the soil is weak with high wind force

What does WW have that provide anchorage for the plant?

Crown/nodal roots that are fully developed by GS39

Why is managing seed rate vital to reduce the risk of lodging?

Higher seed rates result in more crowded plants and therefore a lower number of crown roots per plant so each plant is more prone to lodging (150 plants/m² has 4x the anchorage strength than 500 plants/m²)

How do PGRs work?

They reduce the chance of lodging without reducing yield by shortening the height of the plant (lower center of gravity) and increase the natural frequency of the plant to prevent unwanted oscillation with the wind

How much can PGRs decrease the leverage force by?

30%

What equivalent effect does applying a split dose of chlormequat have on a crop?

• 1 to 2 units of varietal straw strength

• 2 to 4 weeks later drilling

• 100 plants/m² fewer

What are the two modes of biochemical action for reducing lodging risk?

• Gibberellin biosynthesis inhibition (Chlormequat)

• Ethylene generation (Terpal)

How does Gibberellin biosynthesis inhibition (Chlormequat) work?

They act on a single point in the Gibberellin biosynthesis pathway to reduce internode expansion (lower internodes only) therefore reducing plant height and leverage. They also increase stem diameter and cell wall thickness so the stem is stronger.

When would Chlormequat have a poorer uptake?

• If applied to the older leaves

• Temperature is below 10 degrees

• In barley (poor translocation from leaf to the growing point)

What is bounce back when applying Gibberellin inhibitor PGRs?

When the PGR is applied too early and the plant metabolises the Gibberellin inhibitor before it can have an effect (leads to increased number of tillers with no PGR effect)

What are three other Gibberellin inhibitors aside from Chlormequat?

• Mepiquat chloride (found in Terpal and Canopy)

• Trinexapac-ethyl (found in Moddus)

• Prohexadione calcium (found in Canopy)

How does Trinexypac-ethyl differ from Chlormequat?

It acts on 5 points in the Gibberellin biosynthesis pathway and so is more effective and persistent than Chlormequat (also greater uptake at lower temperatures)

What are the active ingredients found in Canopy?

Prohexadione calcium and Mepiquat chloride

When should Canopy be applied in cereals (except SW)?

From GS30-39, split dose of 0.3L/ha at T0 and T1

What is an example of an ethylene generator for PGR?

2-chlorethphosphonic acid (found in Terpal)

When will ethylene generators (Terpal) be most effective?

Below 20 degrees (above 25 degrees and it is converted to ethylene gas on the leaf surface and is too active, causing the ears to distort and grain becomes shrivelled)

How do ethylene generators (Terpal) work to reduce plant growth?

They stimulate the production of ethylene which reduces upper stem internode extension and increase lower internode stem wall thickness

What is the basic process of plant breeding?

• Two varieties are crossed to produce F1 plants (half genes from each parent)

• The reproduce to produce F2 plants, with those with desirable traits selected to further reproduce

• This process happens all the way down to F12, with seed multiplication from F6 onwards until a solid variety with stable traits is produced (Recombinant Imbred Line)

Which plant breeding method is now most commonly used?

Marker assisted selection is now more popular than the pedigree method as it is a much faster process (fewer varieties progress at each step)

How have wheat yields changed over the past 70 years due to plant breeding?

Yields increased from 3t/ha to 8t/ha from 1950-1990 and have now plateaued → gene editing is required to further this

What happens once a variety is classed as a Recombinant Imbred Line (RIL)?

It is eligible to qualify for the National List (EU Common Catalogue before Brexit) and can be marketed - regulated by FERA

What must a variety have to be added to the National List?

• Value for Cultivation and Use (VCU)

• Distinct Uniform Stable (DUS)

What can happen once a variety is added to the National List?

• It can be marketed

• Other breeders can use the variety as a parent for further development

• It can be put forward for further testing for the Recommended List

What are the requirements when using certified seed?

• It must be sold from a licensed merchant and not farm-to-farm

• Royalties paid on any farm saved seed

What is the chain of seed quaity?

• Breeders seed (only used with breeders permission)

• Pre-basic seed (only used with breeders permission)

• Basic seed (used by commercial seed growers)

• C1 (ideal if wanting to home save going forwards)

• C2

What is the process of developing hybrid seed?

The F1 cross is made and no further reproduction occurs (half genes from each parent)

How is plant vigour effected with every further generation of hybrid seed after F1?

It declines → F1 generation is highest yielding

What are the advantages of hybrid seed?

• Uniform establishment

• Higher vigour

• Quicker to combine traits in F1 than waiting for further generations

• Farmers cant save the seed (commercial benefit)

How are varieties selected for the Recommended List?

They are selected to be trialed for the RL based on the previous 2 years data from the NL. Following a year of further trials may be submitted to the RL if qualified based on 3 years data in total (if yields 2% higher than current varieties it will be automatically selected)

How is grain hardiness determined and why is “hard” when preferred?

• Determined by friabilin

• Hard wheat has mutated friabilin and so starch granules don’t separate cleanly from the protein matrix when milled and it cracks instead.

• Higher levels of starch damage allows for greater water absorption (preferred)

How is grain protein quality determined by both genetics and agronomic advice (N input)?

• Hard wheat = Elastic gluten

• Soft wheat = Extensible gluten

What is the Hagberg Falling Number (HFN) and how is this calculated?

• Indirect measurement of alpha-amylase (AA) activity (degrades starch into simple sugars) by measuring the proportion of intact starch

• Flour is suspended in water, tube placed in and stirred, stirrer released, time measured to reach bottom

• More active AA = more degraded starch = less viscous = stirrer falls quicker = lower HFN

What will cause the HFN to be lower?

If sprouting occurs post maturity (stored for too long)

What are the properties of Group 1 varieties?

Consistent milling and baking performance (13% protein, 250 HFN, 76kg/hl SpWt)

• Crusoe, Skyfall, KWS Vibe