Diseases of fruit plantation medicinal and aromatic crops (2+1)

Leaf rot

Causal Organism: Phytophthora parasitica var.piperrina, P. nicotianae var. parasitica f. piperina (Dastur)
Symptoms

• Symptoms appear only during rainy season when both the temperature and atmospheric humidity are high and favorable.
On leaves

• Initially brown to black spots appear which and then it becomes soft & deliquescent in appearance under the continuous humid conditions.
• When disease advances spots rapidly increase in diameter under moist condition and extends to the major part of the leaf causing soft rot.
• The rot may extend to the petiole and in some cases to the stem also.
• In wet conditions, a white cottony growth appears on the lower side of the infected leaf at the light colored margins of the spots is due to the presence of sporangia & sporangiophores of the fungus coming out through the stomata by disintegrating the lower epidermis.
• With intervening dry warm periods, the diseased areas develop concentric zones of development.
• One or more than one spots may be found on a leaf within the plant part 2-3 feet of the ground level are more commonly affected than others leaves.
• It also infects root system and causes root rot or wilt.
Etiology

• Mycelia is aseptate, zoospores are borne in sporangia.
• oospores are sexual spores borne in Oogonium.
• Primary source of inoculum: Oospores
• Secondary source of inoculum: Zoospores
Epidemiology

• The Sporangia develops only at 20-31⁰C and 100% relative humidity.
Life cycle
Management

• Cuttings for plantation purposes should be obtained from healthy orchards. All the infected parts of the plant should be carefully cut and destroyed.
• Spraying the foliage with fungicides before and during rains gives effective protection. Leaves should be harvested only ten days after the spray.
• Infected vines are dipped in 1% Bordeaux mixture, sprayed twice a month. Spraying of 1.5% concentration of Azadirachta indica (Neem) extracts is also recommended.