Johnson grass

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Code: g10
Latin name: Sorghum halepense
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Panicoideae
Tribe: Andropogoneae
Common names: Johnson grass, Johnsongrass, Sorghum grass

Synonyms: S. controversum, S. miliaceum, Holcus halapensis, Holcus halepensis

Do not confuse this plant with its close relation, S. bicolour (Common Wild Sorghum), or S. vulgare (Jowar). S. bicolor (Sorghum) is one of the world's leading cereal crops.


A grass species producing pollen, which often induces hay fever, asthma and conjunctivitis in sensitised individuals.

Allergen Exposure

Geographical distribution

Panicoideae are found mostly in the more humid and tropical environments of the savannas of Indonesia and Africa, and in north-eastern South America. This family includes Bahia grass and Johnson grass and accounts for more than 75% of the grasses in the Panama Canal Zone, 50% in the southern United States, but only 5% in the north-western United States (1).

Johnson grass is a robust perennial native to North Africa, South Asia, and southern Europe, in a range from 55°N to 45°S. It has been reported as a weed when found among 30 crops in 53 countries, and in all major agricultural areas in the world. Introduced to South Carolina into the United States as a foliage crop around 1830 from Turkey, it occurs in most states, and as far north as Ontario (2).

Johnson grass – although regarded as a warm-season grass – has adapted well to colder climates. It differs from other Sorghum species in being a perennial that spreads by vigorous, extensive rhizomes, which can be as much as 1cm in diameter and 2m long. Stems (stalks) are typically 0.5 to 1.75m high, occasionally reaching heights of 3 to 3.5m. Its purplish, open panicles are 10 to 50cm long, with sessile red to purple spikelets 4.5 to 5.5mm long, and the numerous bright green slender leaves are 10 to 50cm long and 2cm wide. Some mature spikelets are awns that are bent and needle-like. The awned, ovoid seeds are brown.

Growth is very vigorous, and two or three crops of hay may be harvested in a season. The flowering times are highly variable and may be lengthy, as they depend crucially on temperature. In the Mediterranean area, Johnson grass flowers between June and August. In other parts of Europe the season is from July to September. In the US, it usually flowers from May to July or, in the extreme south, from December to January. The flowers are hermaphrodite (have both male and female organs) and are pollinated by wind. Johnson grass re-colonises by its large quantity of seed, as well as by its creeping rhizomes.


Johnson grass grows in sandy and rugged soils. It is cultivated for livestock feeding around the Mediterranean. It can be found in cultivated beds, but more often invades open or scrubby places such as irrigation ditches, waste areas and disturbed areas, roadsides, and crop fields; especially places subjected to unnatural frequent flooding. It easily escapes cultivation and is difficult to eradicate, since it reproduces both by seed and by thick underground rhizomes that may be 2m long. It has become a common weed through much of its range (1). It often becomes a troublesome weed, difficult to eradicate.

Though Johnson grass is primarily a hay and pasture grass, humans eat the seed, raw or cooked. The seed may be used whole, in a similar manner to that of rice or millet, or it can be ground into a flour and used as a cereal in making bread, cakes, etc. In some places the root is used as a substitute for sarsaparilla. Johnson grass is also used as a folk remedy.

The leaves may contain hydrocyanic acid (1). Any factor interrupting the normal growth may release HCN within the plant: most common causes are rapid growth of new leaves, and wilting from drought, freezing, cutting, or trampling (1,3).

Allergen Description

Sor h 1, a 28-35 kDa protein, a Group 1 grass allergen (4-8).

Sor h 7, a calcium-binding protein (CBP), (polcalcin) (9, 10).

Sor h 12, a profilin (6, 11).

Potential Cross-reactivity

Extensive cross-reactivity among the different individual species of the genus may be expected, as well as to a certain degree among members of the family Poaceae. Cross-reactivity between Bahia grass (g17), Johnson grass (g10) and Maize pollen (g202), which are related through the sub-species Panicoideae, is likely (12, 13).

Although S. halepense and S. bicolour are members of the same genus, and would therefore be expected to be closely related, studies have demonstrated that although the genomes of Johnson grass and Sorghum are homologous to a certain extent, there are great genetic differences between these two species (14).

This grass contains one of the Group 1 allergens, which are glycoprotein isoallergens shared by many species of grass (15). Group 1 allergens are highly homologous, but not all of the antigenic epitopes are cross-reactive (16). For example, Group 1 allergens from eight different clinically important grass pollens of the Pooideae (Rye grass, Canary grass, Meadow grass, Cocksfoot and Timothy), Chloridoideae (Bermuda grass) and Panicoideae (Johnson grass, Maize) were isolated, and IgE binding to an allergic human serum pool was conducted to determine the degree of antigenic and IgE-binding similarities. The highest IgE-binding similarity was observed between Cocksfoot and Rye grass (53%) and between Rye grass and Canary grass (43%). No IgE-binding similarity was observed between Maize and other grasses. The highest antigenic similarity was also observed between Rye grass and Cocksfoot grass (76%), and the lowest similarity between Maize (23%) and Bermuda (10%) (5). As a result of the presence of the Group 1 allergen, similar cross-reactive patterns are possible with Johnson grass.

A study was conducted in India to explore the common antigenic/allergenic components of five important grass pollens of India (a tropical country). To explore cross-reactivity, intradermal tests and specific sera IgE tests were performed with pollen extracts of Cenchrus (English Bunch grass), Cynodon (Bermuda grass), Imperata (Cottonwool grass), Pennisetum (Kikuyu), and Sorghum (Johnson grass), in patients with nasobronchial allergy. Among 133 patients, Cynodon extract elicited markedly positive skin reactivity in most patients, followed by Pennisetum, Imperata, Cenchrus, and Sorghum. ELISA inhibition experiments showed different degrees of cross-reactivity among the grass pollens studied (17).

On the basis of RAST inhibition tests, Johnson grass appeared to share allergenicity with both Northern grasses (Timothy, Meadow, Rye, Redtop, Meadow Fescue, and Sweet Vernal) and Bermuda grass (18).

Clinical Experience

IgE-mediated reactions

Johnson grass pollen often induces asthma, allergic rhinitis and allergic conjunctivitis in sensitised individuals (7, 8, 19-22).

Farmers exposed to grain Sorghum and grain Sorghum dust were more likely to experience respiratory symptoms such as cough or chest tightness, as well as an acute febrile illness, than were farmers exposed to other types of grain (23).

In a study in Texas that examined aeroallergen sensitisation rates in children of military personnel undergoing skin testing for rhinitis, of 209 patients, 35.4% had at least one skin-test-positive result. The most common allergens were mould mix (16.3%), cat (13.2%), dust mite mix (11.4%), tree mix (9.4%), and grass mix (9.4%). A total of 345 children underwent testing against a 51-allergen panel. A total of 80.3% had at least one positive test result, and the average number of positive test results was 11.4. Johnson grass skin-prick test was positive in 30.7% (24).

In Thailand, specific IgE tests with 14 selected local aeroallergens on 100 asthmatic children aged 0-16 years demonstrated Johnson grass to be a common aeroallergen, with 14% of the study group sensitised to it (25). In 100 older patients with allergic rhinitis, Johnson grass was shown to be the most prevalent aeroallergen, with 21% of this group positive on specific IgE determination (26).

Johnson grass is also a common aeroallergen in Turkey, as was demonstrated by specific IgE testing of 614 respiratory-allergic patients (27).

In Cape Town, South Africa, pollen from Johnson grass was reported to be a clinically important allergen (28).

In an Indian study in Hyderabad, 84% of 500 patients with asthma, allergic rhinitis and/or urticaria were reported to have perennial symptoms. The most predominant pollen allergens in asthma and urticaria patients were to a closely related species of Johnson grass (S. halepense), Sorghum vulgare (Jowar) (54.9% and 64.7%) followed by Pennisetum typhoides (Pearl millet) (53.1% and 56.7%) and Artemisia scoparia (Scoparia Wormwood) (48.1% & 51.9%). The high sensitivity to Sorghum (59% (average)) was not reported from other parts of India (29).

A study conducted in Mashhad City, a city with a semiarid climate and the second largest city in Iran, evaluated the prevalence of positive skin tests to various common aeroallergens among allergic rhinitis patients. It reported that of 311 patients with allergic rhinitis, the overall rate of sensitisation to any allergen of a panel of allergens was 81%. Of these patients, 76% were poly-sensitised, and weed and grass were the most prevalent allergens (77% and 62% respectively). Salsola Kali was the most prevalent individual allergen (72.5%). Of the 311 patients, 33.8% were sensitised to Johnson grass (30).

A Thai study of patients with allergic rhinitis reported that of 434 patients, 277 (63.8%) were skin-prick test positive, and that 39 (14.1%) were sensitised, to Johnson grass (31).

Other reactions

RAST of sera from subjects sensitised to Wheat and Rye flour indicates that significant cross-reactions occur between seed extracts of 12 cereals (Wheat, Durum Wheat, Triticale, Cereal Rye, Barley, Rye grass, Oats, Canary grass, Rice, Maize, Sorghum and Johnson grass) (32). A common allergen between Johnson grass pollen and Johnson grass seed has not been demonstrated to date.

Compiled by Dr Harris Steinman, developer of Allergy Advisor,


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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.