Cereal growth guide: a glossary of terms

From anthesis to xylem, cereal growth is described with a wide array of terms. Some of the most commonly used are outlined in this glossary.

Anthesis

Anthesis (flowering) is normally recognised by appearance of pollen sacs (anthers) from florets within the ear.

Anthers

Pollen-containing units located in the stamens.

Assimilate

The product of the crop’s synthetic processes, mainly photosynthesis.

Benchmark

A quantitative reference point against which a crop’s performance can be compared.

Biomass

Biomass growth represents the net effect of photosynthesis after losses from respiration and leaf fall. It can be assessed by measuring changes in above-ground dry matter over time.

Canopy

The above-ground parts of plants capable of photosynthesising.

Carbohydrates

Synthesised entirely from carbon dioxide and water, these are mainly starch and cellulose, which are not ‘soluble’ or mobile, and sugars (e.g. fructan), which are ‘soluble’ as they dissolve in water and are mobile in the plant.

Chondrometer

A machine used to measure specific weight.

Coleoptile

The first leaf structure to emerge from the seed at germination. It protects the first true leaves during emergence of the seedling. It has little chlorophyll but may give rise to tillers.

Culm

An alternative term for stem.

Day degrees

See ‘thermal time’.

Development

Changes in crop form/structure, as defined by the decimal growth stage (GS) code.

Dormancy

A condition in which grains do not germinate in the presence of adequate moisture, temperature and air.

Dry matter

Crop constituents other than water, left after tissue has been dried. Often, ‘total dry matter’ refers to just the above-ground parts of the crop.

Ear (spike)

The grain-bearing tip located at the top of a cereal stem.

Floret

The primary sub-component of a spikelet. Each fertile floret bears one grain.

Frost heave

Lifting of the soil surface, caused by freezing of moisture in the topsoil and expansion, often leading to stretching and breaking of roots and other sub-surface structures.

Fructan

A form of sugar, a polymer of fructose (the main component of soluble carbohydrate), used by wheat and other grass species as storage assimilate in stem tissues.

Glume

A bract (leaf-like structure) below a spikelet in the inflorescence (flower cluster).

Green Area Index (GAI)

The ratio between the total area of all green tissues, one side only, and the area of ground from which they came.

Growth

The increase in crop size or weight, which results from photosynthesis.

Growth phase

Period during which a specific crop structure is produced.

Growth stage (GS)

A finite point in a crop’s development.

Hagberg Falling Number (HFN)

A measure of the hot-paste viscosity of a wholemeal suspension in water. In the laboratory, a suspension of flour is heated in water for a fixed period. The time in seconds taken for a plunger to fall through the resultant gel is recorded as the ‘Hagberg Falling Number’.

Harvest Index

The ratio between grain yield on a dry basis and the total crop dry weight at harvest.

Imbibition

Initial uptake of water by dry seed.

Internode

The section of stem between two adjacent nodes.

Leaf blade

The upper portion of a leaf, from the tip to the ligule (junction with the sheath).

Leaf sheath

The basal portion of a leaf that encloses the stem and sheaths of younger leaves.

Ligule

A small structure at the junction of leaf sheath and leaf blade.

Lodging

Permanent displacement of a stem or stems from a vertical posture.

Main shoot

The primary axis of the plant on which the primary tillers are borne.

Mean

The average. The sum of all the values divided by the number of values.

Median

The middle value when all values are ranked by size. Medians may provide more robust summaries than means because they are not influenced by exceptional values.

Node

The point at which a leaf sheath is attached to a stem.

Ovary

Part of the female sex organ of flowering plants, which comprises the ovary, as well as the style and stigma. The ovary contains ovules that develop into seeds upon fertilisation.

Partitioning

The division of dry matter between organs.

Peduncle

The topmost internode, between the flag leaf node and the base of the ear (the collar).

PGR (plant growth regulator)

Applied substances to slow down or speed up plant growth/development.

Photosynthesis

Formation of carbohydrates by green tissues from absorbed carbon dioxide and water, driven by energy from sunlight.

Phloem

Moves the products of photosynthesis to where they are needed in the plant.

Phyllochron

The interval in thermal time from emergence of one leaf tip on a shoot to emergence of the next. Phyllochron is the reciprocal of leaf emergence rate.

Pith

The (usually) continuous central strand of spongy tissue located in stems.

Pollination

Reception by the stigma of pollen, leading to fertilisation of the ovum. Fertilisation of wheat normally occurs within one floret, rather than between florets.

Rachis

The central portion of the stem within the ear (above the collar) bearing the spikelets.

Radicle

The first organ to appear when a seed germinates (primary root).

Respiration

Degradation of sugars and the associated absorption of oxygen and emission of carbon dioxide (and water) to yield energy for crop metabolism.

Ripening

The changes that occur in the grain between completion of growth and maturity. These include drying, development and loss of dormancy.

Senescence

Loss of greenness in photosynthetic tissues, normally brought about by ageing, but also by diseases or drought.

Shoots (stems)

All the axes of a plant with the potential to bear an ear. The main shoot and all tillers are included. Shoots retaining the potential to form grain are termed ‘fertile shoots’.

Sink capacity

The number of grains set and the potential size of each grain determine a crop’s ‘sink capacity’ for assimilates. Sometimes the capacity is less than the assimilates available (sink limitation – more common in barley). Sink-limited grains may appear plump. Sometimes the capacity is greater than the assimilates available (source limitation). Source-limited grains may appear pinched.

Specific weight

The weight of grain (corrected for variation in moisture content) when packed into a standard container. It is expressed in kilograms per hectolitre (100 litres).

Spikelet

The primary sub-component of the ear.

Stamen

The pollen-producing reproductive organ of a flower.

Stem reserves

Soluble carbohydrate stored in the stem that can translocate and contribute to yield.

Stigma

Part of the female sex organ of flowering plants, which comprises the stigma, as well as the style and ovary.

Thermal time

The sum of all daily temperatures (mean of maximum and minimum) above a base temperature below which the process in question stops. In the case of leaf development, this is 0ºC. Results are expressed in ‘day degrees’ (ºC days).

Thousand grain weight (TGW)

The thousand grain weight (TGW) is a commonly used metric measurement for grain weight.

Tiller

A side shoot (does not include the main or primary shoot).

Transpiration

Loss of water vapour from a crop’s green surfaces, mainly through leaf pores (stomata).

Vernalisation

A change in the physiological state of a plant from vegetative to reproductive brought about by a period of cold – can be applied to seeds or (in the case of wheat) to the young plant.

Waterlogging

Filling of soil pores with water to the extent that there is insufficient oxygen for normal root function.

Xylem

Transports water and minerals from the roots up the plant stem and into the leaves.