Diseases of Fruit Plantation Medicinal and Aromatic Crops

Seedling blight, Black stripe and Stem canker

Causal organism: Phytophthora palmivora Butler
Symptoms

• Seedling blight caused by Phytophthora palmivora is noticeable especially during rainy season in nursery.
• Typical symptom of seedling blight shows leaf blades with few blotches that soon enlarge and coalesce.
• In severe cases, yellowing with defoliation occurs and eventually dieback takes place.
• Phytophthora leaf blight is initiated by the chlorosis at leaf margin which eventually advances until a brown colored lesion develops that becomes water soaked. It is more commonly observed in field plantations.
• Black stripes, stem canker and bark splitting are also frequently observed in rubber plantations.
• The typical symptoms of black stripe are sunken with slightly discolored areas on the tapping panel.
• Later, vertical fissures appear in the renewing bark and when these are removed, dark vertical lines are visible; presence of discolored or black lines in the tapping cut; clogging of the latex flow resulting to massive spilling of latex; cause uneven renewal resulting to burns and depressions on the tapping panel. In case of stem canker, sunken canker is the best diagnostic symptom.
• As the cankers become older, they become brown with a shredded appearance.
• In bark splitting or cracking, there is massive spilling of latex and if scraped, pinkish to reddish discoloration observed.
• Reddish discoloration is also observed which becomes black at a later stage.
• In mature trees, the pathogen causes dropping of premature leaves resulting defoliation and hence the disease is also called as ’Phytophthora leaf fall’.
Etiology

• The fungus belongs to the Phylum Oomycota, Family Pythiaceae and grows abundantly on V-8 agar.
• The colonies are white, aerial, and cottony in culture.
• The sporangia are characterized by lemon-shaped and doubled papillate structures which measure 34.5 – 57.5 x27.5 -49.0 mm in size under 100x and oospores with 22 - 28 mm.
Management

• Prophylactic spray with Bordeaux mixture( 1%) and Zinc sulphate (0.2%) at cropping stage