diseases of mustard

White rust disease of Mustard
Blister disease of Crucifers

Host: Brassica campestris (L.)
Pathogen: Albugo canida (syn. Cystopus candidus)

Distribution

The disease is of global distribution and reported from more than 50 countries. White rust disease of Crucifers causes more up to 90 % loss in annual yield (Saharan et al. 2014). The disease reduces the total yield as well as quality of nutrient in mustard crop.

Symptoms

Underside of the mustard leaf showing white pustules (blisters)

Early symptoms appear in the form of white raised pustules only at the lower side of the leaves. At maturity, these blisters get ruptured and powdery mass of conidia come out in forms of white rust. In severe infection, pathogen attacks the floral parts and induces hyperplasia and hypertrophy in the floral part. The infected inflorescences are malformed and fruits become abnormal.

Pathogen

Albugo conidia with conidiophore

The disease is caused by oomycetous fungus, Albugo candida (syn. Cystopus candidus). It is an obligate parasite (biotroph). Pathogen produces basipetal chain of sporangia/conidia born on the small club-shape conidiophores inside the pustules. The nature of sporangia or conidia depends upon the temperature and humidity. If adequate moisture is available, it germinate into six zoospores and behave like an sporangium, whereas in low moisture conditions, it germinate directly by producing germ tubes and behave as conidium. The zoospores are naked (lacking cell wall), reniform (kidney-shaped) and bi-flagellate. The flagella are inserted laterally. Towards the end of the host season, fungus become systemic and develops oospores in the infected parts. These oospores are thick walled resistant structures and help in perennation of disease.

Control measures

• According to Saharan et al. (2014), no single method is effective in managing the white rust of crucifers. Therefore, adapting more than one control measures like, cultural, chemical, biological and host resistance are suggested.

References

• Saharan, G.S., Verma, P.R., Meena, P.D. and Kumar, A., 2014.  White rust of crucifers: biology, ecology and management. Springer.

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Leaf-spot disease of Brassica
Blight of Crucifers

Host: Brassica spp. (Mustard, Cabbage, Radish, Sarson, Rai, etc.)
Pathogen: Alternaria brassicae

Distribution

It is one of the common diseases of crop plants in northern India, which decreases the yield significantly. The disease is caused by Alternaria brassicae.

Symptoms

Mustard leaf showing spots

Leaf spot showing concentric rings

The leaf of the infected plant shows round to irregular concentric spots. In severe cases, the symptoms may be seen on leaves, stem and even on pods of sarson (Brassica compestris L.).

Pathogen

Alternaria brassicae (Berk.) Sacc. is causative fungi of this disease. Fungus grows inter or intracellularly in the host. Conidiophores arise form the mycelium after a few days of limited growth. One to several conidia may develop (singly or in chain) at the tip of conidiophores. The conidia are bottle like with long beak and narrow base. The body of the conidia are septate with several cross and vertical septa (see photograph) and also called as muriform conidia.

Conidia of Alternaria brassicae. bar = 20 μm

Nature and recurrence of the disease

The disease is soil born and seed-born. Conidia of the pathogen survive in the soil and in the debris. On getting host in moist weather they germinate and cause primary infection. In foggy weather with high relative humidity conidia germinate and cause secondary infection.

Control measures

• Crop rotation with non-crucifer plants, seed treatment, sanitation and use of resistant varieties  are useful control measures.
• Deep ploughing in summer reduces the disease incidence.
• Early-sown mustard are free from this diseases. In Indian sub-continent, mustard sown before October are free from diseases.
• Seed should be treated in hot water at 50 °C for 20 minute.
• In order to prevent the crop from leaf spot, fungicide (Copper oxychloride or Mancozeb or Zineb @ 2.5 g/l) should be sprayed at 15 days interval from 6 week after sowing.
• Use blight-resistance varieties of mustard.

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Content first created on 14-11-2020
last updated on 22-04-2021