Ingress, internal spread and some factors affecting pathogenicity of Diplodia tubericolar (E. E.) Taub. in sweet potato [Ipomoea batatas] (Philippines)
1984
Sarsud, V. | Divinagracia, G.G.
Inoculation by placing the fungus in a 5-mm diameter and 8-mm deep hole was suscessfully employed in these studies. Mycelial discs induced disease development faster than spores suspension. The mycelia could not penetrate through the well-formed periderm of sweet potato storage roots inoculated 12 days after harvest. On newly harvested storage roots with loosely formed periderm, the mycelia invaded intercellularly and were restricted in the cork layer. A periderm was formed in response to penetration which separated the healthy tissues from the penetrated cells. Inter- and intracellular penetration through wound made on the storage roots were observed 6 h after inoculation and pycnidial formation was noted at the cork cambium layer 4 days after. Incubation for 48 h in moist chamber and exposure under room condition was recommended for disease initiation. Disease development was favored at 30 deg C. Six-day old storage roots were more susceptible than the newly harvested or 3-day old roots when inoculated with the fungus. Injured surfaces of newly harvested roots inoculated with the fungus was observed to form a wound periderm which protected the healthy tissues from mycelial penetration
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