The document details various fungal diseases affecting crops such as onions, carrots, and ber plants, with a focus on their causal organisms, symptoms, and management strategies. Key diseases discussed include purple blotch of onion caused by Alternaria porri, alternaria blight of carrot from Alternaria dauci, and powdery mildew of ber instigated by Oidium erysiphoides. Management practices such as using disease-free seeds, chemical treatments, and maintaining optimal environmental conditions are emphasized to control these diseases.

1. Diseases of Onion

2. Purple blotch of Onion
Causal organism: Alternaria porri

3. ➢ This disease occurs mainly at the top of the leaves, the infection starts
with whitish minute dots on the leaves with irregular chlorotic areas on
tip portion of the leaves.
➢ Circular to oblong concentric black velvety rings appear in the chlorotic
area.
➢ The lesions develop towards the base of the leaf.
➢ The spots join together and spread quickly to the entire leaf area.
➢ The leaves gradually die from the tip downwards.
Symptoms

5. Causal organism: Alternaria porri
Kingdom Fungi
Phylum Ascomycota
Class Dothideomycetes
Order Pleosprales
Family Pleosproaceae
Genus Alternaria
Species A. porri

6. ❖ This fungus mycelium is branched, coloured and
septate (both horizontal and vertical conidia with
long beak).
❖ Conidiophores arise singly or in groups. They are
straight or flexuous, sometimes geniculate.
❖ Conidia – Dictyospore, brown, obclavate with a
beak, 3-8 transversely septate and 1-2 longitudinally
or obliquely septate, conidia are produced
acropetally in chains through the pores formed at
the apex of the beak of conidia.
Characteristics

7. Disease cycle
➢ Primary infection throw plant debris and seed bulb and spread through air borne
conidia.
➢ It survives as dormant mycelium in the infected debris.
➢ Favourable conditions are warm humid weather with rains or heavy dew and optimum
temperature 23-27°C.
Survival and spread
➢ Primary: Conidia in infected plant debris or seed bulbs,
➢ Secondary: wind borne conidia
Favourable conditions
➢ Thrips infestation. Carried through seed bulbs collected from infected area.
➢ Spreads through air borne spores.
➢ Warm humid weather, rain and dew favours disease development.

8. • Disease free bulb should be selected for planting.
• Seeds should be treated with Thiram @ 4 g/kg seed.
• The field should be well drained.
• Three foliar sprayings with Copper oxychloride 0.25 % or Chlorothalonil 0.2 % or Zineb 0.2
% or Mancozeb 0.2 %.
Management

9. Alternaria blight of Carrot
Causal organism: Alternaria dauci

10. ➢ It is first appear at the margin of the leaflets and are dark brown to black and
irregular in shape.
➢ Lesions produced on the petioles and stems are dark brown and often coalesce
and girdle the stems.
➢ As the disease progresses entire leaflets may shrivel and die, appearing
scorched.
➢ Alternaria leaf lesions are generally more prevalent on older foliage and plants
than on young foliage.
➢ This is due in part to poor air circulation among the older lower leaves in the
canopy and to the moisture-holding capacity of the dense foliage.
Symptoms

12. Causal organism: Alternaria dauci
Kingdom Fungi
Phylum Ascomycota
Class Dothideomycetes
Order Pleosprales
Family Pleosproaceae
Genus Alternaria
Species A. dauci

13. ❖The Mycelium is septate, branched, light
brown hyphae later become dark.
❖Conidia is dark brown in color, born singly or
in chains (1-4 conidia) and muriform with
long beak.
Characteristics

14. Disease cycle
➢ The Pathogen survives in the form of conidia and mycelium with seed
and in infected plant debris in soil.
➢ Prime infection caused by these conidia and mycelium on the leaves
and secondary infection caused by conidia produced on primary
infected plants during the same growing season carried out by
winds healthy plants.
➢ It can persist in soil for up to 8 years.
➢ Fungal spores are often dispersed by air, splashing water, or
machinery and then initiate new infections.
➢ Relative humidity of more than 70% coupled with warm weather (22-
25°C) and intermittent rains favor disease development.

16. • Removal and destruction of infected plant debris
• Use disease free or Seed treatment with hot water (50°C) for 20 minutes, or soaking
seed in a 0.2% suspension of thiram for 24 hours at 30°C.
• Avoid overhead irrigation.
• Deep ploughing, timely weeding and maintenance of optimum plant population.
• Spraying soil isolates of Trichoderma viride at 45 and 75 days after sowing.
• Spray with mancozeb (@0.25%), or Propiconazole (0.1%), or Iprodione (0.2%) at 10
days intervals.
Management

17. Powdery Mildew of Ber
Causal organism: Oidium erysiphoides f. sp. ziziphi

18. ➢ The symptoms of the disease are noticed on flowers and newly set fruits.
➢ The disease may appear earlier if conditions are favorable.
➢ The developing young leaves show a whitish powdery mass, which causes them to
shrink and defoliate.
➢ The disease also appears in the form of white powdery spots on the surface of the
fruits and later covers the whole fruit surface.
➢ The spots turn into light brown to dark brown discoloration.
➢ The infected area becomes slightly raised and rough.
➢ Affected fruits either drop off prematurely or become corky, cracked, misshapen and
remain underdeveloped. Sometimes the whole crop is rendered unmarketable.
Symptoms

20. Causal organism: Oidium erysiphoides f. sp. ziziphi
Kingdom Fungi
Phylum Ascomycota
Class Leotiomycetes
Order Erysiphales
Family Erysiphaceae
Genus Oidium
Species O. erysiphoides f. sp. ziziphi

21. Disease cycle

22. ❖ The powdery mildew fungus overwinters in dormant buds.
❖ When conditions are favorable for growth of the fungus in spring, spores are produced,
released, and cause new infections.
❖ Secondary spread of the disease can occur if spores are produced in these new
infections
Survival and spread
❖ The development of powdery mildew is favour by relative humidity around 80-85% and temperature
range of 24-26°C.
Favorable conditions

23. • Spraying of dinocap 0.05 per cent or wettable sulphur 0.25 per cent or tebuconazole
50% + trifloxystrobin 25% WG should be done during first and third weeks of
November or when the fruit attains pea size.
Management