DISEASES OF WHEAT
| DISEASES | CAUSAL ORGANISM |
| Black / Stem rust | Puccinia graminis tritici |
| Leaf / brown / orange rust | Puccinia recondita |
| Yellow / stripe rust | Puccinia striiformis |
| Loose smut | Ustilago nuda tritici |
| Flag smut | Urocystis agropyri |
| Rough spore bunt / stinking bunt | Tilletia caries |
| Smooth spored bunt | Tilletia foetida |
| Kernal bunt | Neovassia indica |
| Powdery mildew | Erysiphe graminis var tritici |
| Tundu / Yellow ear rot / ear cockle disease | Anguina tritici and corynebacterium tritici |
1. Black / Stem rust- Puccinia graminis tritici
Symptoms
Symptoms are noticed mainly on stem than leaf sheath and leaves. Reddish brown pustules [uredia] appear on stems and leaves at early stage of crop and at maturity. Also, a mixture of brown and black lesions [telia] can be seen
Causal organism – Puccinia graminis tritici
The fungus is a biotrophic (obligate) parasite and its survival and growth in the host tissue depends upon the living condition of the host. It’s a polymorphic species, producing a succession of different types of spores. The fungus has the following stages,
Stage 0 : Pycnia and pycniospores
Stage 1 : Aecia and aeciospores
Stage 2 : Uredia and urediospores
Stage 3 : Telia and teleutospores
Stage 4 : Basidia and basidiospores (produced on inactive substrate on which teleutospores are present)
Mode of spread
The primary infection takes place through the air borne uredospores from hills and early season crops. The secondary spread is through air borne uredospores.
Survival
The pathogen survives in alternate hosts (Barberry), crop debris and weed hosts
Epidemiology
Warm temperature (20 to 300 C) and heavy rain favour the disease development.
Management
- Mixed cropping with suitable crops.
- Avoid excess dose of nitrogenous fertilizers
- Sulphur dusting at 25 kg/ha
- Seed dressing with oxycarboxin or spray zineb at 2.5 kg/ha
- Grow resistant varieties like Lerma rojo and Sonalika
2. Leaf/ brown / orange rust – Puccinia recondita
Symptoms
The symptoms are mainly noticed on leaves, rarely on leaf sheath and stem. The spots are orange in colour. The irregular arrangement of the sori and their colour are the most distinguishing characters. The sori are bigger than yellow rust and severe attack results in drying of leaves.
Mode of spread
The pathogen spreads through air borne uredospores
Survival
The pathogen survives in alternate host (Thallictrum Spp.) and crop debris.
Epidemiology
Warm temperature (20 to 300 C), heavy rain favour the disease development
Management
- Mixed cropping with suitable crops.
- Avoid excess dose of nitrogenous fertilizers
- Sulphur dusting at 25 kg/ha
- Spray zineb at 2.5 kg/ha
- Grow resistant varieties like CPAN 1796, HB 208, Shailya, Lerma rojo and Sonalika
3. Yellow / stripe rust – Puccinia striiformis
Symptoms
The symptoms are mainly noticed on leaves than leaf sheath and stem. Bright yellow pustules [uredia] appear on leaves at early stage and turns to dull black lesions [telia] at maturity. Each row consists of a series of oval, lemon yellow pustules arranged end to end, and each row is distinct from below and above. In severe attacks the serial arrangement seems to be lost, large patches become covered with crowded pustules
Mode of spread
The pathogen spreads through wind borne uredospores
Survival
The fungus survives in crop debris and weed hosts.
Epidemiology
Optimum temperature ideal for the disease development is 8 to 130 C and no infection occurs above 230 C and below 20 C and during heavy rains.
Management
- Mixed cropping with suitable crops.
- Avoid excess dose of nitrogenous fertilizers
- Sulphur dusting @ 25 kg/ha
- Spray zineb @ 2.5 kg/ha
- Grow resistant varieties like DWL 5023, HD 2281, UP 262, WH 47, Lerma rojo and Sonalika
DIFFERENCES BETWEEN WHEAT RUSTS
| Character | Black / Stem rust | Brown/leaf/orange rust | Yellow / Stripe rust |
| Pathogen | Puccinia graminis tritici | Puccinia recondita | Puccinia striiformis |
| Location of uredosori | Mostly on stem and Leaf sheath | Mostly on leaves, rarely on leaf sheath | Mostly on the leaf blade |
| Uredosori / uredia | Large, elongated,epidermis broken early | Small, arranged irregularly on the upper surface of leaves | Uredosori small, oval, arranged in lines between veins |
| Reddish brown | Bright orange | Lemon yellow | |
| Uredospores | Oval with 4 equatorial Germ pores | Spherical with 7 to 10Scattered germ pores | Round with 6 to16Scattered germ pores |
| Echinulated | Minutely echinulated | Minutely Echinulated | |
| Brown | Brown | Yellow | |
| Teliosori / Telia | Black | Dull black | Dull black |
| Large and elongatedScattered on the stems as streaks | Scattered on the undersurface of leaves | Small, oval but more flattened and arranged in rows on the under surface of leaves | |
| Telia burst soon | Telia covered by epidermis | Telia covered by epidermis | |
| Teliospores | Dark brown – chestnut brown | Brown | Dark brown |
| Two celled | Two celled | Two celled | |
| Thick walled and smooth | Thick walled and smooth | Thick walled and smooth | |
| Elongated or rounded with pointed apex. | Broader and rounded apex | Flattened apex | |
| Paraphyses in telia | Teleutosorus is not divided in to compartment, paraphyses absent | Teleutosorus divided in two more compartments by sterile paraphyses | Teliosorusis divided in to fewer compartments by sterile paraphyses. |
| Mode of spread | Air borne uredospores | Air borne uredospores | Air borne uredospores |
| Mode of survival –Alternate host | Barbery (Berberis vulgaris), Mahonia | Thallictrum flavum, Isopyron sp. | Not known |
| Uredospores and teliospores survive on stubbles and straws and self-sown wheat plants | Uredospores and dormant mycelium persist on stubbles and straw and weed hosts | Uredospores and dormant mycelium survive on stubbles and straw and weed hosts and in self-sown wheat plants | |
| Favourable conditions | Temperature 17-180 C | Temperature 150 C | Temperature 110 C |
4. Loose smut – Ustilago nuda tritici
Symptoms
Symptoms appear only after emergence of ear heads. Affected ear heads produce dark powdery mass of smut spores. The smutted spikelets are covered by a silvery membrane which contains black, dry powdery mass of spores.
Mode of spread
Internally seed borne and remains viable in stored seeds for long period (more than 15 years)
Survival
The pathogen survives in the infected seeds as dormant mycelium.
Epidemiology
Temperature of 18 to 200 C and high humidity (60 – 80 %) during flowering stage favour the disease development. Flowers of cultivars with loose spikelets are more susceptible than those with compact spikelets.
Management
- Hot water treatment:
- The seeds are soaked in cold water for 4 h. [to activate the mycelium] followed by dipping in hot water at 520 C for 10 min.
- Solar heat treatment (Luthra 1953).
- Seeds are soaked in cold water for 4 h, followed by spreading and drying of seeds in bright sun in the afternoon for 4 h
- Seed treatment with carboxin or carbendazim at 2 g/kg of seed
- Grow resistant varieties like kalyansona, C-302, WG-307 and PV18.
5. Flag smut – Urocystis agropyri
Symptoms
The symptoms appear from late seedling stage to maturity of the crop and seen on stem, culm and leaves. Grey to grayish black sori occurs on leaf blade and sheath. The sorus contains black powdery mass of spores.
Mode of spread and Survival
The fungus is transmitted as seed contaminant and survives in the infected seeds
Epidemiology
Temperature of 18-240 C and soil pH of 5.1 to 5.7 favour the spore germination.
Management
- Treat the seeds with carboxin or benomyl @ 2g/kg.
- Burning of stubbles, long rotation of the crop.
- Grow resistant varieties like CI –13596, 13751, 13755, HP –1102, HS – 86 and WG 377.
6. Rough spore bunt / stinking bunt and smooth spored bunt – Tilletia caries
Symptoms
The diseased plants mature earlier and all the spikelets are affected. Spikelets are transformed in to smut sorus of dark green colour with masses of chlamydospores
Mode of spread and Survival
The pathogen is externally seed – borne and survives in the infected seeds and also present in the soil for longer period even for 10 years.
Epidemiology
Temperature of 18-240 C and soil temperature of 9-120 C favour the disease development
Management
- Seed treatment with carboxin or carbendazim at 2g/kg
- Adopt shallow sowing.
- Grow resistant varieties like kalyansona, HD 2021, 4513, 4519, PV – 18 and S 227.
7. Kernal bunt – Neovassia indica
Symptoms
The disease was first identified in Karnal and hence the name. The infection occurs only at the flowering stage. The infected spikelets are converted in to dark coloured sori.
Mode of spread and Survival
The pathogen survives in infected grains and young spike lets and is soil borne and air borne.
Epidemiology
Temperature of 20-250 C, high humidity, cloudy weather during flowering stage favour the disease development. In India high incidence of the disease was recorded in the varieties which flowers during last week of February to first week of March.
Management
- Deep summer ploughing.
- Avoid continuous cropping of wheat in the same field.
- Grow resistant varieties like HD 2281, 2283 2285, DWL-1562, 5023 and HD 2329.
DIFFERENCES BETWEEN BUNTS
| CHARACTER | ROUGH SPORED BUNT | SMOOTH SPORED BUNT | KARNAL BUNT |
| Pathogen | Tilletia caries | Tilletia foetida | Neovassia indica |
| Damage / stage infection | All spikelets in the earhead are infected. | All spikelets are infected | Few spikelets in an earhead are infected. |
| Seedling stage (8-10 days old plant) | Seedling stage ( 8-10 days old plant) | At flowering stage. | |
| Spore wall | Reticulate, rough walled | Smooth walled | Reticulate, smooth walled |
| Spores | Round and 15-23 um in dia. | Irregular and 17-22 um in dia. | Spherical to oval 22-49 um in dia. |
| Resting period of spores | No resting period | No resting period | Requires a long resting period |
| Sporidia | Produce filiform, hyaline primary sporida which unite to form H-shaped structures | Produce filiform, hyalineprimary sporida which unite to form H-shaped structures | Produce 60-185 long sickle shaped primary sporidia on short stout basidium; do not fuse |
| Mode of spread | Externally seed – borne | Externally seed – borne | Soil borne and air borne |
| Favourable conditions | Temperature of 18-200 C, high soil moisture | Temperature of 18-200 C, high soil moisture | Temperature of 15-200 C high humidity, cloudy weather during flowering |
8. Powdery mildew – Erysiphe graminis var tritici
Symptoms
Grayish white powdery growth appears on the leaf sheath, stem and floral parts. Powdery growth later becomes as black lesions and cause drying of leaves and other affected parts.
Mode of spread and Survival
The pathogen spreads through air borne conidia and survives in the infected plant debris.
Epidemiology
Temperature of 20 – 210 C is ideal for the disease development
Management
- Dusting sulphur at 40 kg/ha
- Growing resistant varieties like C 591, E 750, HD 2189, 2278, NP710, UP 1109 and VL 421
9. Tundu/Yellow ear rot/Ear cockle disease –
Anguina tritici (nematode) and corynebacterium tritici (Bacteria)
Yellow ear rot is also known as Bacterial spike blight and Yellow slime disease.
Ear-cockle and Tundu are two distinct phase of the same disease complex which is determined by the environmental conditions. Under high humidity and low temperature tundu phase is more conspicuous in which both the pathogens (Anguinea tritici and Corynebacterium tritici) are involved. Under low humidity and high temperature the Ear cockle phase appears which is due to the nematode component of the disease.
Symptoms
Infected leaves may be rolled / twisted. Spikelet infection is accompanied by a yellowish exudation. The infected spikes are smaller than the normal spikes and the glumes protrude outward.
Mode of spread and Survival
The pathogens spread through infected seeds and the galls can survive in soil for more than 20 years.
Epidemiology
Temperature of 20 –22.50 C is optimum for the disease development.
Management
- Floatation of contaminated seed-lot in brine solution (18 kg salt in 110 litres of water)
- Grow resistant varieties like Sharbati, Sonora, E 9176
- Summer ploughing and crop rotation
- Affected plants should be located, uprooted carefully and burnt.
