5. MYROTHECIUM LEAF SPOT
Symptoms:
On leaves, symptoms appear as circular to irregular, brown to dark brown spots surrounded by yellowish halo but no sporulation is observed on these spots.
Pathogen:
- Myrothecium roridium Tode ex Fr.
- Conidia are aseptate, pigmented, black in mass, wet when young, drying to become hard, shiny black, convex with a white halo of mycelium, 7.2 x 1.8 µm in size.
Disease cycle and epidemiology
- The pathogen survives in infected plant debris
- Moderate temperature and high relative humidity favours the disease.
Management: Spraying the crop with carbendazim (0.1%) or zineb (0.25%) at 10-14 days interval is advocated for the control of this disease.
6. ANTHRACNOSE
Symptoms: Two different pathogens results in different types of symptoms:
a) Elsinoe jasminae:
- Circular to angular, raised spots with slight depressions on the lower surface of the leaves which are pinkish buff in colour and 1-5mm in diameter.
- Similar spots appear on tender shoots also.
- Later these spots coalesce to form large patches.
b) Colletotrichum jasminicola:
- Large, circular, distinct and brownish to grayish spots outlined with brown to yellowish halo appear on the upper surface of the leaf.
- The infected tissues turn grayish in due course, become papery and fall off.
- Spots are studded with numerous acervuli.
Pathogen: Two different fungi Elsinoe jasminae Bitanc. & Jenkins and Colletotrichum jasminicola Tilak are associated with the disease.
- In E. jasminae, the ascomata is composed of pseudoparenchymatous epithecium and measured 45-110x 20-45?m in size.
- Acervuli are intra-epidermal, erumpent, elongated to elliptical, light brown with the basal stroma giving rise to compactly grouped yellow conidiophores measuring 12-27x 32-75?m in size.
- In Colletotrichum jasminicola, acervuli are numerous, epiphyllous, erumpent, globose to cushion-shaped, 80-140 x 64-120?m in size, setae are numerous, long, dark, thick and septate with pointed tips.
- Conidia are numerous, one celled, hyaline, oblong with rounded ends, guttulate, 8-15 x 4 - 4.5?m in size.
Disease cycle and epidemiology
- The disease incitants overwinter in infected plant debris.
- High humidity and moderate temperatures are favourable for the initiation and spread of the disease.
Management:
- Collect and destroy the infected plant debris.
- Spray the crop either with zineb (0.25%) or copper oxychloride (0.3%) and repeat at 10-14 days interval.
7. LEAF SPOT AND STEM BLEMISH
Different leaf spotting fungi have been found infecting this crop which are described below:
Symptoms: Three different types of fungi cause various types of symptoms:
a) Cylindrosporium sp.:
- Spots on leaves and stems are distinct, irregular and smoky-grey in colour which later turn blackish grey. The diseased tissues fall off prematurely.
b) Phyllosticta jasminina:
- Infectious spots are usually circular, pale fulvous to brownish with smooth margins. Adjacent spots become large by coalescing together.
c) Cladosporium spp.:
- On leaf lamina and on the margins, the symptoms appear as light yellow areas which later turn light brown and coalesce forming large patches and eventually result in blight symptoms.
- Effuse velvety olive brown colonies appear on the lower surface of the leaf.
Pathogen: The fungi responsible for these spots are described below:
Cylindrosporium sp. Grev.
- Acervuli are few, subepidermal, subhyaline, cushion to cup-shaped, 200-280 x 200-250 ?m in size.
- Conidia are numerous, hyaline, filiform, straight to curved with 2-5 cells, transversely septate and 35-44 x 4-4.5?m in size.
Phyllosticta jasminina Rao.
- Pycnidia are epiphylous, ampuliform to subglobse, later erumpent, ostiole, 90-170?m in diameter.Spores are hyaline, 1-celled, ovoid to oblong, 5.5-8.5 x 3.3-4.5 ?m in size.
Cladosporium spp.:
- The hyphae are branched, septate, subhyaline 2-3?m wide.
- Conidiophores are macronematous, septate, simple, rarely branched, pale brown or olive brown and 96-160 x 4-9?m in size.
- Conidia are simple or in chains produced terminally or subterminally, ellipsoidal or cylindrical with rounded ends, subhyaline to olive brown, 10-58 x 4-11?m in size and with upto 2 septa.
Disease cycle and epidemiology
- These pathogens overwinter in infected plant debris.
- The disease spread is favoured by temperatures ranges between 20 - 25oC along with high humidity.
Management:
- Collect and destroy the infected plant debris.
- Avoid dense planting, shading of plants, and excessive watering of the beds and fields.
- Spray the crop with carbendazim (0.1%) or mancozeb (0.25%) and repeat at 14 days interval.
8. MOSAIC
Symptoms:
- The diseased plants show stunted growth and yellowish green appearance with small leaves.
- Yellowish green to chlorotic flecks of 1-2 mm in diameter appear irregularly on the leaf.
- The streaks later form ring like structure which are more conspicuous on the older leaves.
Pathogen:
- The virus responsible for this disease is Jasmine Mosaic Virus.
Transmission: The virus is graft transmitted on Jasminium simplicifolium, J. sambac and J. pubescens.
Management:
- Destruction of the infected material and use of healthy stock is recommended.
- J. auriculatum is found relatively tolerant to the mosaic virus.
9. Phyllody
Symptoms:
- The disease is supposed to be caused by Phytoplasma
- The affected plants produce malformed, reduced greenish flowers like structure instead of fragrant white flowers or panicle, which are reduced and become ovate in shape.
- The greenish corolla lobes become reduced and ovate in shapes.
- Flower parts are transformed into leaf like structures.
Management:
- Use disease free cuttings for planting and spray tetracycline hydrochloride (250ppm) for effective checking of the disease.
Other diseases:
i. Crown gall : Agrobacterium tumefaciens (Smith & Townsend) Conn,
ii. Blossom blight : Phoma sp. and Phomopsis pavgii Shukla, Pathak & Rao
iii. Root rot : Armillaria tabescens (Scop.)
iv. Leaf spot : Colletotricum gloeosporiodes(Penz.) Penz. & Sacc.
v. Alternaria leaf spot : Alternaria alternata (Fr.) Keissler
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