White rust of crucifers:
Causual organism :– Albugo candida / Albugo cruciferum
- White rust is found in number of cruciferous plant like cabbage , turnip, cauliflower, raddish, broccoli, knol khol etc. Albugo candida is an obligate parasite with intercellular mycelium and also produce knob shaped haustoria. Estimated Loss due to floral infection is 23-54%. Mostly Disease is supposed to occurs in association with downy mildew.
Symptoms of White rust of crucifers:
- All parts of plants affected except roots
- Symptoms are divided into Local and systemic on the basis of symptom development on the host.
Local symptom of White Rust
Local symptoms are seen on the particular area where the pathogen attacks on the crop plants. some of the localized symptoms are as:
- white creamy pustules appears on the surface of the leaves, stem and inflorescence which are 1-2mm in diameter.
- Pustules coalesce to form large irregular patches
- Host epidermis rupture and exposed sori reveal a white powdery mass containing a number of spores.
Systemic symptom of White Rust
Systematic symptoms are those which occurs on different part of plants even if the pathogen attacks on certain region or part of the plants. it affects the physiology of the plant and shows symptoms like deformities and physiological disorder may be due to hormonal imbalance or other reasons. some of the systematic symptoms of white rust of crucifers are mentioned below:
- When young stems and inflorescence are infected fungus become systemic and stimulates various types of deformities like hypertrophy and hyperplasia.
- Due to deformities the flower axis and the flower stalks may be enormously thickened up to 12 to 15 times than the normal diameter.
- Petals become sepal like and stamens leaf like or carpel like
- Ovules or pollen grains usually atrophied .
- Affected ovaries remain sterile.
- If systemic infection occurs early, plant remains dwarf and only small leaves are formed
- Axis of the inflorescence and stem are often twisted giving a zigzag appearance known as Staghead.
Disease cycle and epidemiology of white rust of crucifers
Oospore that survives in soil, seed, alternate and collateral host are the primary source of inoculum. Disease is carried from year to year through over wintering oospore. Secondary infection is carried by sporangia and zoospore.
RH more than 70%, 13-15ºc and 4-10 mm of water favors for stag head formation. In general 10-20ºc, RH 65%, moist, cool weather favors disease.
Management of White rust of Crucifers
- First of all we must destroy plant debris, alternate and collateral host from our field.
- Crop rotation should be followed integrating legumes.
- Use of healthy seed is the must for healthy crop plant.
- Use resistant varieties Like radish, china rose winter
- Seed treatment with systematic fungicide like captah, thiram or metalaxyl
- Pre or co-inoculation with avirulent strain of candida provides protection against a virulent strain
- Spraying Ridomil(0.1%), Metalaxyl(0.2%) at 20, 40,60 days after sowing helps to prevent White rust caused by Albugo candida.