Diseases of Fruit Plantation Medicinal and Aromatic Crops

Trunk and Root rot

Causal organism: Ganoderma lucidum

• Trunk/root rot is caused by a root infecting fungus called Ganoderma lucidum which usually remains within the tissues. This pathogen also causes root rot in areca and stem decay in oil palm. Its occurrence is restricted to sandy and sandy-loam soils.
• This malady was first noticed in Thanjavur district at Tamil Nadu after the cyclones of 1952 and 1955 and hence called 'Thanjavur wilt'. Now it is widespread in other districts, viz; Kanyakumari, Tiruchirapally, South Arcot , North Arcot and also the border areas of Kerala. Ganoderma- wilt is prevalent in Tamil Nadu, Andhra Pradesh, and Karnataka mainly; and minor incidences reported in Maharashtra, Gujarat and Orissa. The infected palms die within 2 or 3 years after infection. In dead palms, brackets of Ganoderma lucidum and G. applanatum are also found.
Symptoms

• Although the seat of infection is the base of the trunk/root, yet the characteristic symptom is visible on the crown followed by withering and drooping of the older leaves which remain hanging around the trunk for several months.
• The new leaves are reduced in size and yellowish in colour, the inflorescences become suppressed and palms remain barren.
• Bleeding patches occur at the base of the trunk which slowly extend to the stem and ultimately kill the plant.
The major symptoms are:

• Palms show wilting due to internal rotting and crown topples.
• Withering and browning of outer leaves followed by yellowing, leaf drooping and flaccidity of' spindle leaves.
• Reduction in spindle size arresting the crown and fruit-set.
• Decay of finer roots extends to bole region and slowly moves upwards to stem base.
 


Etiology

• Ganoderma is a heterothallic fungus.
• Mycelia- Septate
• Vegetative spores- Chlamydospores.
• Sexual spores-Basidiospors
• Mode of spread-Air
• Source of inoculum
• Primary source of inoculums- Chlamydospores
• Secondary source of inoculums- Basidiospores
Epidemiology

• Disease spreads in conditions like
• Neutral pH,
• Sandy loam soil,
• High density plantation.
Management

• Ploughing in affected areas may be minimized, close planting avoided, good drainage to be provided, adequate irrigations needed. Application of mulches or green manuring at the basin of the palm etc are some of the cultural methods of control.
• Diseased palms should be removed and burnt.
• Bleeding patches should be chiseled completely followed by hot coal tar application; (Plate 15). Stem bleeding' (Courtesy: CPCRl). Isolation trenches (1 cm x 30 cm) may be dug up around diseased palms to prevent root contact.
• Application of 5 kg neem cake along with sufficient organic matter and 500 gm phosphate + 1200 gm potassic fertilizer per palm per year is necessary so as to keep proper nutrients in the soil.
• Drenching with 40 L of 1% Bordeaux mixture and stem injection or root feeding with solution containing 2 gm Aureofungin + 1 gm copper sulphate in 100 litre water thrice a year, for only one year may reduce intensity of this malady.