Glossary of terms

Alternate host: second host species required by some rusts and other organisms to complete their life cycle.

Anthesis: developmental main stage when yellow anthers are clearly visible. Also known as 'flowering'. Each floret's lemma and palea are forced by swelling of their lodicules, which allows the anthers to protrude.

Auricle: pale-colored papery extension of a leaf blade at its junction with its leaf sheath. Also called a collar.

Auxin: compound regulating the growth of plants.

Awns: coarse, hair-like protrusions on a spike, which extend from the tip of the lemmas and sometimes to a small extent on the sterile glumes.

Boot: as the young spike expands inside the leaf sheaths it can eventually be felt and finally seen after the flag leaf stage as a sheath swelling or boot.

Chlorophyll: green pigment in plants required for photosynthesis.

Chloroplast: plant structure where photosynthesis occurs.

Chlorosis: abnormal yellowing (or whitening) of normally green leaves.

Collar: another word for the ligule and auricle grouped together.

Conidiophore: threadlike stalk upon which conidia (spores) are produced.

Conidium (pl. conidia): any asexual spore formed on a condiophore.

Conventional tillage: inverting the soil surface layer, incorporating crop residues and vegetation, and breaking up the suface to a fine tilth.

Crusting: sealing of the soil surface by fine soil particles. These block the larger pores, reducing the movement of gases into and from the soil and reducing the penetration of water.

Diapause: a period of dormancy.

Double ridges: a developmental stage of the growing apex (growing point) when it is approximately 0.5 mm long; the new leaf primordia are rounded ridges and associated with each one is a bud in its axil.

Enzyme: an organic compound catalyzing a specific reaction in the cell.

Exudate: gel-like accumulation of spores or bacterial ooze.

Floret: each spikelet has between 2 and 6 florets where the grains form; each floret is made up of a papery lemma with its long awn and and an opposing palea, which together form a cup for the grain. The number of grains in a spike is equal to the number of fertiles florets produced by the spike.

Foot rot: disease symptoms, such as discoloration, necrosis and decay, affecting the roots and basal portions of the plant or culm.

Gall: a localized proliferation of plant or parasite tissue that produces an abnormal growth or swelling, usually caused by pathogenic organisms, nematodes, or insects.

Green leaf area index (GLAI or LAI): the area of all green leaves on a square meter of ground; when each 1 square meter of ground has more than 4 square meters of leaf growing on it, the crop is intercepting about 90% of the solar radiation falling on it. GLAI is well linked to yield.

Heading: developmental stage when the head, spike or ear emerges from its enclosing sheath.

Honeydew: sticky exudate (containing conidia) produced during one stage of the life cycle of Claviceps purpurea.

Hypha (pl. hyphae): a tubular, threadlike filament of fungal mycelium.

Immune: not affected by pathogens.

Inoculum: spores or other diseased material that may cause infection.

Jointing stage: period when the stem elongates by extending the regions between the stem nodes. The first nodes (joints) become visible and progressively larger after the terminal spikelet has formed on the microscopic spike.

Lesion: a visible area of diseased tissue on an infected plant.

Ligule: papery structure 1 mm or so which marks the junction between a leaf sheath and its blade and is in the same plane as the sheath; together with the auricle is it called the leaf collar.

Meristem: tissue of rapidly dividing cells, generally at the apex of shoot and root.

Metabolite: compound undergoing chemical transformations within the plant.

Micronutrient: nutrient required in trace amounts.

Minimum tillage: with a limited number of passes of machinery, it aims to achieve some soil disturbance and physical weed control but to leave much of the crop residues on the surface of the soil or in the surface layers.

Mosaic: a pattern of disease symptoms displaying mixed green and lighter colored patches.

Mycelium (pl. mycelia): a mass of hyphae that form the body of a fungus.

Necrosis: abnormal death of leaves, usually accompanied by discoloration.