''Lolium rigidum'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of annual

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns a ...

. Common names by which it is known include annual ryegrass, a name also given to

Italian ryegrass ''Lolium multiflorum'' (Italian rye-grass, annual ryegrass) is a ryegrass native to temperate Europe, though its precise native range is unknown. It is a herbaceous annual, biennial, or perennial grass that is grown for silage, and as a cover ...

(''Lolium multiflorum''), rigid ryegrass, stiff darnel, Swiss ryegrass and Wimmera ryegrass. It is a native of southern Europe, northern Africa, the Middle East and the Indian subcontinent and is grown as a forage crop, particularly in Australia, where it is also a serious and economically damaging crop weed.

Description

''Lolium rigidum'' is an annual grass that grows in open tussocks. It has fibrous roots and can grow up to a metre tall. The plant form is usually erect but may be prostrate. The stems are often geniculate (with a knee-like bend) and are purplish at the base. The leaves are long, and wide; the upper surface is glossy dark green, flat and hairless with longitudinal veins, and the underside is shiny and smooth. Lolium rigidum spikelets5 annotated (7370409964)

Lolium rigidum spikelets5 annotated (7370409964)

The young leaves are rolled when in bud, the auricles are small and the ligule is white and translucent, wider than it is long. The unbranched flower spike is up to long, with the

spikelets A spikelet, in botany, describes the typical arrangement of the flowers of grasses, sedges and some other Monocots. Each spikelet has one or more florets. The spikelets are further grouped into panicles or spikes. The part of the spikelet that ...

on alternating sides and edgeways-on to the

rachis In biology, a rachis (from the grc, ῥάχις [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this c ...

(stem), pressed into recesses in the stem. The spikelets bear up to twelve florets, mostly with a single

glume In botany, a glume is a bract (leaf-like structure) below a spikelet in the inflorescence (flower cluster) of grasses (Poaceae) or the flowers of sedges (Cyperaceae). There are two other types of bracts in the spikelets of grasses: the lemma and ...

, with only the terminal floret having two. The glumes are up to three-quarters the length of the spikelet; their outer surface is finely ribbed with longitudinal veins. There is no awn, the lemma is oblong and has five nerves and the palea is a similar shape with two nerve and a few fine hairs. The three anthers are yellow.

Distribution and habitat

''Lolium rigidum'' is a native of the Mediterranean area. Its natural range includes Western, Southern and Central Europe, northern Africa, the Near East, western Asia and the Indian sub-continent. It has spread to many other parts of the world and is considered invasive in some regions. It is planted in Australia as a forage crop but not usually in Europe. It was introduced as a forage crop in Australia around 1880, but has since proven to be an economically damaging weed that infests other more important crops, such as

canola Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, ...

and

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

Ecology

''Lolium rigidum'' is a diploid grass with a chromosome number of n=7 (2n=14). It exhibits much genetic variability and grows readily in a variety of situations and habitats. It can hybridise with both

perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wid ...

(''L. perenne'') and

(''L. multiflorum''), as well as some species of ''

Festuca ''Festuca'' (fescue) is a genus of flowering plants belonging to the grass family Poaceae (subfamily Pooideae). They are evergreen or herbaceous perennial tufted grasses with a height range of and a cosmopolitan distribution, occurring on ever ...

''. It propagates solely by seed; freshly shed seed displays dormancy. It is sometimes infected by a rust fungus which has an inhibitory effect on the growth of clovers. The flower spike of ''L. rigidum'' may become infected by a certain species of bacteria, which results in the production of corynetoxins which are toxic to livestock; ingestion of infected material causes a disease, known as annual ryegrass toxicity or annual ryegrass staggers, which is known to occur in the west and south of Australia and in South Africa. The infection is caused by the bacterium ''

Rathayibacter toxicus ''Rathayibacter toxicus'' is a phytopathogenic bacterium known for causing annual ryegrass toxicity (ARGT) commonly found in South and Western Australia. Etymology The genus ''Rathayibacter'' is an homage to E. Rathay, the plant pathologist ...

'', which is introduced into the grass by the nematode ''

Anguina funesta ''Anguina funesta''
at ergot (''Claviceps purpurea''), and also by

take-all Take-all is a plant disease affecting the roots of grass and cereal plants in temperate climates caused by the fungus ''Gaeumannomyces tritici'' (previously known as ''Gaeumannomyces graminis ''var. ''tritici''). All varieties of wheat and ba ...

fungus (''Gaeumannomyces graminis'') which can cause serious losses in cereal crops.

Uses

''Lolium rigidum'' is grown as a forage crop in suitable areas. About 80% of the seed germinates in the autumn, soon after the first significant rains, and about 5% may remain dormant for twelve months. The plant has vigorous growth, and flowering is initiated when the day length is at least eight hours. This means that the crop has a relatively uniform flowering period in late winter/early spring.

Damaging effects

Because ''L. rigidum'' has been grown as a forage crop in southern Australia since the nineteenth century and seeds readily, it grows ubiquitously in the region with large, genetically diverse populations. Now that arable crops are increasingly been grown, it has become an important weed of these crops. The main reason for its success in competing with crops is its ability to produce prolific numbers of seeds per plant – up to 45,000 seed per – and also its ability to compete with crops at a very early stage of their life cycle. In addition, it serves as a host for species of the bacteria

Clavibacter ''Clavibacter'' is a genus of aerobic Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories a ...

, which cause annual ryegrass toxicity (ARGT), and it can also and can be infected by the poisonous ergot fungus, which causes ergotism in humans and other mammals. Attempts to control it with herbicide have met with an unexpectedly high level of herbicide resistance. Over 90% of plants in some populations are tolerant to some of the widely used herbicides. Instead of wiping out the ''L. rigidum'', the herbicides have resulted in the selection of resistant genotypes. Possible bioherbicides are being explored, including '' Pyrenophora seminiperda'', a fungus. ''L. rigidum'' has become one of the most serious and economically damaging weeds in southern Australia. A 2021 study listed annual ryegrass as fourth on the list of invasive species which cost Australian farmers the most over a 60-year period, at over a billion Australian dollars.

References

External links

* {{Taxonbar, from=Q3156354 Pooideae Flora of Lebanon