Castor leaf blight is caused by the fungus Alternaria ricini. It affects the aerial parts of castor plants, causing brown spots on leaves and stems that later coalesce and cause defoliation. The fungus produces olive-colored spores in chains on conidiophores. The disease favors high humidity and low temperatures. It can be controlled through seed treatment with fungicides, spraying mancozeb or copper oxychloride, and using healthy seed.

1. Castor Leaf blight
Course teacher : Submitted by :
Dr.S.Parthasarathy, Rohith .A. K
(Asst. Prof. Plant Pathology) 2015021109
COLLEGE OF AGRICULTURAL TECHNOLOGY
(Affiliated to Tamil Nadu Agricultural University, Coimbatore-3)
Kullapuram (Po),ViaVaigai Dam, Theni-625 562

2. Contents
 Introduction
 Distribution
 Symptoms
 Etiology
 Favourable conditions
 Systemic Classification
 Disesase Cycle
 Control
 References

3. Introduction
 Other name : Macrosporium ricini
 Alternaria ricini is a fungus species first described by Yoshii,
and became known as Clifford George Hansford in 1943.
 Alternaria ricini the genus Alternaria and the Pleosporaceae
family. No subspecies are listed in the Catalog of Life .

4. Distribution
 Occurs in E. & W. Africa, S. Asia and S. & E. USA.,
Host Plant: Ricinus communis

5. Symptoms
 All the aerial parts of the plant, i.e., stem, leaves, inflorescence and capsules are liable
to be attacked.
 The disease first makes its appearance on the cotyledons in the form of spots and if the
infection is extensive, the plants become stunted and ultimately die.
 The spots on the leaves are seen throughout the year and become more extensive
during rainy season.
 These may appear on any portion of the leaf and are irregular, scattered, and have
concentric rings.

6.  These are brown and later become covered with bluish-green or sooty growth.
 When the attack is severe the spots coalesce and form big patches resulting in
premature defoliation of the plant which gradually wilts away.
 The inflorescence and the capsules are also attacked and get covered partially or
fully with a similar sooty growth.
 In one case the capsules, when half mature, wilt suddenly, turn brown and due to
collapse of the pedicel the capsules fall or hand down.

7.  The germination of the affected seeds is also adversely affected.
 In other case, the attack is generally on the fully developed capsules resulting in
the appearance of sunken spots on one side of the capsule which gradually enlarge
to cover the whole pod with characteristic growth of the fungus.
 The pathogen may infect the seed if the capsule cracks.
 Stem of the castor plant has also been reported to show symptoms of the disease
in some of the exotic varieties.

8. Etiology
 The disease is caused by Alternaria ricini. The conidia are produced abundantly on
the diseased portion under moist conditions and borne in chains on the conidiophores.
 The conidiophores are straight, erect or irregularly bent, sollitary, sometime in
fascicles and are olivaceous in colour.
 The conidia are obclavate, light olive in colour but become darker in mass.

9.  They are segmented into 5-16 cells with transverse and longitudinal septa with and
without beak.
 The beak is narrow, colourless, long and unbranched.
 The conidia formed in culture are usually smaller in size than those formed on the
host.
 The disease is carried over through the seed both externally and internally.

10.  It is reported that the disease causes pre and post-emergence damping off and a
seedling and foliage blight when the diseased seeds are sown.
Favourable Conditions
 High atmospheric humidity (85-90 %).
 Low temperature (16-20˚C)

11. Pictures
© vikaspedia
© Ikisan © Silks

12. Systemic classification
Domain Eukaryotes
Kingdom Fungi
Division Ascomycota
Class Dothideomycetes
Order Pleosporales
Family Pleosporaceae
Genus Alternaria
Species Alternaria ricini

13. Disease Cycle
The pathogen survives on hosts like Jatropha pandurifolia and Bridelia
hamiltoniana. The pathogen is externally and internally seed-borne and
causes primary infection. The secondary infection is through air-borne
conidia

15. Control
 Seed treatment may be useful in combating the initial phase of the disease.
 Use of healthy seed and treat the seed with Captan or Thiram @ 3g/kg seed.
 Spray Mancozab at 2.5g/lit concentration at an interval of 15days commencing
from 90days of crop growth.
 Spray copper oxychoride @ 3 g/L.

16. References
 http://eagri.org/eagri50/PATH272/lecture10/003.html
 http://www.ikisan.com/tg-castor-disease-management.html#Alternaria
%20Blight
 http://agritech.tnau.ac.in/crop_protection/castor_diseases/castor_d2.html