Diseases of Vegetable, Ornamental and Spice Crops

DISEASES OF CINNAMON AND FENUGREEK

DISEASES OF CINNAMON

Cinnamon (Cinnamomum zeylanicum Blume) popularly known as Darchini belongs to family Lauraceae is an important tree species of India. Cinnamon consists of layers of dried pieces of the inner bark of branches and young shoots from the evergreen tree. It is obtained when the cork and the cortical parenchyma are removed from the whole bark. The thickness of the bark ranges from 0.2 to 1.0 mm. In India it is grown on the west coast and western Ghats. During cultivation the trees are affected by several diseases which cause significant yield reductions. In this lecture, important diseases along with their management practices are described.

1. LEAF SPOT AND DIE-BACK

A severe leaf spot and die-back disease of this crop has been observed in many parts of Kerala which is serious both in nurseries and grownup trees.

Symptoms:

• Small spots develop on leaf lamina which gradually enlarge and coalesce to form irregular patches. Ultimately the leaves dry up and the pathogen spreads to the stem resulting in die-back symptoms. Young seedlings are killed. In mature trees, small specks appear which increase in size resulting in necrotic blotches. Light to deep brown concentric zones develop on the spots during alternate dry and wet conditions. Shot hole symptoms are rarely noticed.

Pathogen:

• The disease is caused by fungus Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.
• Pathogen, disease cycle and epidemiology have been described under clove diseases

Management:

i) Collect and destroy the infected plant debris.
ii) With the initiation of the disease, spray the crop with Bordeaux mixture (5:5:50) or copper oxychloride (0.3%) or combination of mancozeb (0.25%) and carbendazim (0.1%) and repeat at 14 days interval.

2. CANKER

The bark canker of this crop occurs in the west coast of sumatara and indonesia. The pathogen has also been reported from india.

Symptoms:

• irregular and vertical necrotic stripes (1-5 cm) appear on affected plants. The cankers are sunken with zonations and separated from the healthy tissue by a black line.

Pathogen:

• The disease is caused by phytophthora cinnamomi Rands.
• The hyphae are broad, hyphal swellings typically spherical (42 µm). Sporangiophore are thin (3 µm) and occasionally branched. Sporangia are broadly ellipsoidal or ovoid (33 x 57 µm), papilla absent.
• Oogonia (40 µm) have smooth walls and become yellow or golden with age. Antheredia amphigenous, long and measure 21-23 x 17 µm. Oospores hyaline, nearly filling the oogonium and thick.

Disease cycle and epidemiology

• The optimum temperature for growth of the fungus is 24-28^o C.

Management:

i) Soil application of sulphur has been recommended for the control of this disease.

DISEASES OF FENUGREEK

1. Powdery mildew:
Symptoms:

• The symptoms of the disease appear as white, floury patches on both sides of the leaves as well as on other green parts of the plant (Plate-1).
• The floury patches consist of the mycelium, conidiophore and conidia of the fungus.

Pathogen:

• The disease is caused by Erysiphe polygoni DC.
• Fungus Oidiopsis taurica (imperfect stage of Leveillula taurica) has also been reported to be associated with this disease.
• The mycelium of Erysiphe is generally fine and persistent ,rarely thick.
• The haustoria develop as outgrowths from lobed swellings. The haustorium penetrates the cell wall and forms a sac in the epidermal cell.
• Conidiophores arise vertically and each bears several spores in chain.
• In dry temperate zone, perithecia appear as sharp black specks, scattered on the surface of the white mycelium.
• During following season, they disintegrate and liberate ascospores which germinate and infect the new crop.

Disease cycle and epidemiology:

• Wherever the perithecia are formed they explain the mode of perrenation.
• In other areas the pathogen survives as mycelium and conidia on the host and on other annual and perennial hosts.
• The disease is more prevalent in dry weather and moderate temperatures.

Management:

• Sow the crop by the end of the October.
• Use resistant variety like Prabha. Lines GC-39UM-32, GC-7, GC-20 and UM-34 have also been reported as resistant and can be utilized in breeding programme.
• With the initiation of the disease spray the crop with wettable sulphur (0.2%), or hexaconazole (0.05%) or dinocap (0.06%) or difenoconazole (0.04%) and repeat at 10-14 days interval.

2. Root rot
Symptoms:

• The symptoms of the disease appear in 30-45 days old plants as rotting of roots leading to yellowing of foliage.
• The affected plants wither and dry up.

Pathogen:

• The disease is caused by Rhizoctonia solani Kuhn.
• The pathogen is described under French bean diseases.

Disease cycle and epidemiology:

• The fungus is soil borne and survives in the form of sclerotia.
• Disease cycle and epidemiology is described under French bean diseases.

Management:

• Follow 3-4 years crop rotation.
• Soil amendment with neem cake (1 t/ha) alone and in combination with Trichoderma reduces root rot.
• Seed treatment with carbendazim (0.2%) followed by drenching @ 0.1 per cent effectively controls this disease.