Monographella nivalis

Names

Scientific Name

Monographella nivalis (Schaffnit) E. Müll. [teleom.]
Microdochium majus (Wollenw.) Glynn & S.G. Edwards [anam.]
Microdochium nivale (Fr.) Samuels & I.C. Hallett [anam.]

Synonyms

Micronectriella nivalis (Schaffnit) C. Booth [syn.]
Calonectria nivalis Schaffnit [obs.]
Griphosphaeria nivalis (Schaffnit) E. Müller & Arx [obs.]
Microdochium nivale var. majus (Wollenw.) Samuels & I.C. Hallett
Microdochium nivale (Fr.) Samuels & I.C. Hallett var. nivale
Gerlachia nivalis (Ces. ex Berl. & Voglino) W. Gams & E. Müll. [obs.]
Lanosa nivalis Fr. [obs.]
Fusarium nivale (Fr.) Sorauer [obs.]

Common Names

English: Foot rot of cereals, snow mold, snow mold, pink snow mould, Fusarium leaf blotch, head blight, ear blight, scab, whiteheads; French: Fonte des semis des céréales, Pourriture nivale des céréales; German: Schneeschimmel; Spanish: Moho de la nieve

Biology

Description

Monographella nivalis is an ascomycetous fungus belonging to the order Xylariales. Oval to globose, papillate perithecia (100 - 260 x 300 µm) may develop in cereal leaf sheaths or the stem base. They have gold to dark-brown plectenchymatous walls (10 - 30 µm thick). Asci are clavate (60 - 70 x 6 - 9 µm), thin-walled, and contain 6 - 8 hyaline ascospores (10 - 17 x 3.5 - 4.5 µm).

Damage

M. nivalis can attack cereals during all stages causing various diseases:
Seedling blight: Infection of seedlings can cause pre- and post-emergence damage; death early after germination, discoloration of coleoptiles, superficial lesions on plants. Sometimes lens-shaped, pale-brown lesions appear on the first and second leaves.
Snow mold: Bleached patches covered with abundant white mycelium, which may mat together the leaf blades, appear after prolonged snow cover of crops. Patches gradually turn pink due to color changes in the mycelium and the development of sporodochia.
Foot rot: At tillering stage, brown decay of the lowest leaf sheaths is visible, sometimes a shredded first leaf blade lies on the soil surface. The oldest two leaves may bear red/brown spots. Following stem elongation, dark perithecia may appear in the brown areas of the lowest leaf sheaths. Later on a grayish-brown discoloration, frequently girdling the first internode above crown roots, sometimes vertically as dark brown stripes appear as first foot rot symptoms. After milk ripening, brown to black streaks or blotches may occur on higher internodes and nodes are discolored dark-brown. Severely infected stems may break at ground level and may bear orange fungal mycelium. Premature death of tillers causes whiteheads.
Ear blight: Early symptoms consist of small, brown, water-soaked lesions on the outer glumes of florets. Under humid / wet conditions, florets or whole spikelets become infected associated with premature bleaching of ears. Orange sporodochia become visible on the rachis at the base of infected spikelets under humid conditions. Purplish-brown perithecia may also develop on the bracts.

Cause

M. nivalis is active over a wide range of temperature conditions favoring its wide geographical distribution on the Gramineae. With an optimum between 18 - 20 °C (64.4 - 68 °F) for most isolates, some isolates are able to grow at temperatures as low as -6 °C (21.2 °F) and as high as 32 °C (89.6 °F). Infections of roots, coleorhizas and coleoptiles generally occur under cold (0 - 5 °C; 32 - 41 °F)), dry soil conditions. The pathogen spreads to the ears via splash dispersal of conidia or wind dispersal of ascospores. Infection of ears occurs during anthesis at 12 - 18 °C (53.6 - 64.4 °F) and is promoted by prolonged periods of wetness.

Lifecycle

Conidia are curved, broadly falcate with a pointed apex and a flattened, wedge shaped foot-cell. Depending on the number of septae (0 to >5) conidial size varies from 8 - 18 x 2 - 3 µm to 19 - 30 x 2.5 - 4 µm with M. majus producing larger conidia. As M. nivalis does not produce chlamydospores, soil-borne saprophytic mycelium on infected straw is central to the life cycle for seedling blight, foot rot and ear blight. Later in the growing season, air-borne inoculum (conidia or ascospores) can infect ears and results in ear blight and the development of seed-borne inoculum. Although M. nivalis colonizes all tissues of cereal grain - epidermis, pericarp, testa, endosperm and embryo- the fungus has been isolated preferentially from the epidermis, pericarp and testa. Seed-borne inoculum is the predominant source of M. nivalis inoculum. Seed severely infected by M. nivalis may be small and shrivelled and is associated with reduced germination and reduced emergence of seedlings. However, heavy infected seed results in more severe symptoms of seedling blight than light seed.

Occurrence

Crops

Additional Crop Information

Diseases due to M. nivalis are confined to members of the Poaceae including cereals as well as forage and turf grasses.

Control

Integrated Crop Management

As M. nivalis may survive saprophytically on crop debris, cultivation techniques which remove or reduce the presence of debris significantly reduce disease incidence and severity.
Cereal varieties vary in their resistance to M. nivalis. However, only ear blight is considered during breeding programmes where genotypes are selected for the Fusarium head blight complex involving also M. nivalis.

Chemical Control

Modern fungicidal seed treatments effectively control early disease phases caused by M. nivalis such as seedling blight and snow mold and improve therefore significantly seedling emergence and overwintering capacity of young cereal plants.
Beside direct fungicidal effects the reduced seed born transmission of the pathogen helps also to minimize the inoculum density which may cause damages in later growth stages.
Seed treatment products being effective against M. nivalis are mostly based on fungicides including azoles (e.g. triadimenol, bitertanol, prothioconazole) or strobilurins (e.g. fluoxastobin). Other fungicides used in seed treatment product for control of M. nivalis are fuberidazole, and iprodione.

For the control of head blight via spray application several fungicides are available.
DMI (azole) fungicides such as tebuconazole and prothioconazole and / or strobilurins (QoIs) such as fluoxastrobin and trifloxystrobin show a good effectiveness against ear blight caused by M. nivalis. Control is most effective when fungicides are applied around flowering (anthesis).

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