symptoms, pathogen, epidemiology and management

1. DISEASES OF CROSSANDRA
COURSE TEACHER
Dr. PARTHASARATHY S
Asst. Professor (Plant Pathology)
STUDENT
Miss. SRIMATHI P
ID. NO. 2015021124
COLLEGE OF AGRICULTURAL TECHNOLOGY
(Affiliated to Tamil Nadu Agricultural University, Coimbatore-3)
Kullapuram (Po),ViaVaigai Dam, Theni-625 562

2. 1. Wilt : Fusarium solani
2. Stem rot : Rhizoctonia solani
3. Leaf blight : Colletotrichum crossandrae
4. Alternaria leaf spot : Alternaria amaranthi var.
crossandrae
MAJOR DISEASES

3. 1. Wilt : Fusarium solani
SYMPTOMS
 Wilt is observed in batches. In the field the disease is
observed one month after transplanting.
 Leaves of infected plants become pale and droop.
 Margin of the leaves show pinkish brown
discolouration.

4.  The discoloration spreads to the midrib in a period of
7 to 10 days.
 Stem portion gets shriveled. Dark lesions are noticed
on the roots extending upto collar region which result
in sloughing off the cortical tissue.
 Favoured by nematodes.

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6. PATHOGEN
F. oxysporum produces three types
of asexual spores:
(a) microconidia
(b) macroconidia and
(c) chlamydospores

7. PATHOGEN
 Micro-conidia are ellipsoidal, straight to curved, one
to two celled and hyaline.
 Macro-conidia are hyaline, 3-5 septate, falcate having
gradually pointed and curved ends.
 Chlamydospores are characterised by thick walls are
terminal or intercalary.

8. EPIDEMIOLOGY
 These fungi survive in the infected plant debris as
well as in soil as chlamydospores.
 Moderate to high temperature with fair amount of
moisture is conducive for disease development.
 The infection is more severe when the nematode
(Pratylenchus sp.) predisposes the plant for the attack
of the pathogens.

9. MANAGEMENT
Affected plants should be pulled out and
destroyed to reduce the disease.
The nematode can be controlled by soil
application of Phorate at the rate of 1 g/plant on
10th day of transplanting.

10. MANAGEMENT
 Soil drenching with Carbendazim 0.1 per cent or
Copper oxychloride 0.25 per cent on 30 days interval
controls the disease.
 The treatment may be repeated after 3 to 4 weeks if
needed.

11. 2. Stem rot: Rhizoctonia solani
SYMPTOMS
• The pathogen also causes pre-emergence damping off,
Brown to black lesions develop on stem just above
soil level and result in girdling of the stem.
• The lesions extend to the upper part of the stem and
result in collapse of seedlings. The roots are also
rotted.

12. PATHOGEN
 Rhizoctonia solani is a basidiomycete fungus that does
not produce any asexual spores (called conidia) and
only occasionally will the fungus produce sexual spores
(basidiospores).
 In nature, R. solani reproduces asexually and exists
primarily as vegetative mycelium and/or sclerotia.

13. PATHOGEN

14. EPIDEMIOLOGY
 R. solani can survive in the soil for many years in the
form of sclerotia.
 Sclerotia of Rhizoctonia have thick outer layers to
allow for survival.
 The fungus is attracted to the plant by chemical
stimuli released by a growing plant.

15.  Suitable conditions are:
• soil pH above 5.8
• soil temperature of the order of 15°C to 35°C, dry
soil.

16. MANAGEMENT
• Drenching with Fosesty1-A1 has been found effective
in the control of the disease.
• Spraying with Carbendazim (1g/l), Contaf (2ml/l),
Tilt (1ml/l), Benomyl and Iprodione.

17. 3. Leaf blight : Colletotrichum crossandrae
SYMPTOMS
• The symptoms of leaves consist of the development
of brownish, depressed necrotic areas surrounded by
reddish and slightly raised margins.
• Initially the spots appear as brownish specks but
become darker as they expand.

18. SYMPTOMS
• The lesions are more prominent on lower leaves and
confined to the margins.
• Infected leaves roll up, shrivel and drop off, leaving a
barren stem with a whorl of young leaves at the top.

19. PATHOGEN
 Mycelium is septate,
intercellular as well as
intracellular.
 Acervuli are round and
elongated in shape.

20. PATHOGEN
 Conidiophores are short, hyaline, cylindrical, septate
or aseptate.
 Conidia hyaline, one celled, uninucleate, fusiform
with acute apices.

21. EPIDEMIOLOGY
 The pathogen survives in infected plant debris.
 Secondary infection takes place through wind borne
conidia.
 Temperature of 26°C and presence of RH 100% is
optimum for disease development.

22. MANAGEMENT
 Collect and burn the infected plant debris.
 Spraying with benomyl 0.1% (or) Mancozeb 0.2%
(or) Carbendazim 0.1%.

23. 4. Alternaria leaf spot : Alternaria amaranthi var.
crossandrae
SYMPTOMS
• This disease was first reported from Tamil Nadu during
1972.
• Infected leaves show small, circular or irregular yellow
spots on the upper surface.

24. SYMPTOMS
• They soon enlarge turn brown and develop dark
brown concentric rings.
• Infected leaves become yellow and drop off
prematurely.

25. PATHOGEN
 Mycelium septate, branched,
light brown hyphae.
 Conidia are muriform, 5 to 10
transverse and a few
longitudinal septa are present
in each conidium.

26. EPIDEMIOLOGY
 Alternaria species survive in the debris of diseased
plants and can persist for 1to 2 years in the soil.
 Primarily seed borne pathogen.
 Secondary infection through wind and water.

27. MANAGEMENT
 Collect and destroy the infected plant debris.
 Follow atleast 2 years crop rotation.
 Use healthy seed and treat them with captan (0.3%).
 Avoid moisture and stagnant conditions.
 Spraying with Benomyl 0.1% (or) Mancozeb 0.2% (or)
Carbendazim 0.1% (or) Chlorothalonil (0.2%).

28. REFERENCES
 Gupta.S.K, R.C. Sharma and Monica Sharma, 2017,
Diseases of Vegetable, Ornamental and Spice Crops,
Scientific Publisher. Pg No:120-122
 Saha.L.R,2009,Handbook of Plant Diseases, Kalyani
publisher, New Delhi. Pg No:407
 www.agritech.tnau.ac.in
 https://www.researchgate.net