|Crop Knowledge Master|
|Foliar blight of Leea coccinea; common name, West Indian holly|
TYPE: Kingdom: Chromista
In addition to red and green cultivars of Leea, this pathogen also attacks Catharanthus roseus (rose periwinkle or Vinca rosea) in Hawaii. Elsewhere in the world it causes serious leaf loss of rubber (Hevea) and is also reported on cacao, cardamom, Ficus, Piper, and pineapple.
This pathogen is known from Oahu in Hawaii on Leea and Catharanthus. Both are new diseases for Phytophthora meadii. It is present in Asia and Australia on other hosts.
Leaf spots on Leea begin as small, irregularly shaped, dark water-soaked flecks. These expand to distinct dark spots (Fig. 1). Within a few days, spots expand to large rots or blights of the leaf and stem. Young plants are killed in 2 weeks. The color of leaf spots varies with plant cultivar and age of the leaves. On young leaves of the green cultivar, leaf spots are gray-green to brownish while those on red cultivars were olive-green to purplish brown on red cultivars. In dry environments, lesions are dry, brown, shriveled, and appear scorched, resembling phytotoxicity damage from contact with granular fertilizer.
On mature plants, leaf spots expand more slowly and plants are not killed. On red leea cultivars, the leaf blight color sometimes closely matches leaf color and blights are difficult to detect (Fig 2). Drooping leaves or leaflets are a sign of this disease (Fig. 3). Leaves or small branches are killed. If diseased sections are removed, new healthy shoots are produced.
Phytophthora meadii produces microscopic (42-55 X 25-32 um) oval, papillate to semipapillate, hyaline asexual spores or sporangia. Sporangia are deciduous and fall from the colony with a short stalk attached to the base of the sporangia. In water, sporangia release numerous swimming zoospores. Without sufficient water, sporangia germinate by producing germ tubes that penetrate the host. Zoospores are able to swim for many hours and are attracted to organic matter or host tissue. These zoospores encyst, germinate by forming a small germ tube, and penetrate the host.
This pathogen is heterothallic and produces sexual spores, called oospores, when two mating types (A1 and A2) are grown together. Oospores are thick walled and can serve as survival structures in the absence of the host. Both mating types were found in Hawaii although more isolates were of the A1 mating type.
Phytophthora meadii grows well from 68 to 86 F. Fungal growth, reproduction (sporulation), spread, and infection are all favored by moisture.
This pathogen produces sporangia on the surface of large leaf rots or blights.
Advanced stem rots also have sporangia on the surface on the diseased tissue. These sporangia are splashed onto other parts of the plant or to other plants. Rain and overhead irrigation favors diseased spread in nurseries.
Fruit or seed infections have not been found but are likely since several commercial nurseries have lost many young seedling to this pathogen.
The pathogen survives in diseased plant tissue in the absence of the host. Oospores can also survive many months in soil or potting medium.
To begin a new crop, growers should carefully select seeds that are clean and firm. Avoid any seeds that are dented, soft or have dark blemishes. Before planting, surface disinfest seeds by placing in a solution of 10% household bleach with a small amount of detergent for 2-5 mins. Plant seeds in new potting mix and produce the crop away from mature plants. A separate, clean greenhouse for new seedlings is highly recommended.
Since moisture favors the pathogen life cycle and drives the disease cycle, moisture control is important. Without this pathogen Leea crops can be produced in saran covered greenhouses. However, with this pathogen present, solid covered greenhouses are strongly recommended. During periods of prolonged moisture the fungal multiplication and spread will be unchecked in a typical saran house.
If disease is present, collect all diseased plant parts or dying plants and remove from the nursery. Clean all walkways, benches, and pots. Do not reuse potting media. Wash and surface-disinfest pots, tags and trays if they are reused. Handling diseased plants will also contaminate nursery workers (hands, gloves, clothing, etc.).
Metalaxyl and other fungicides such as Dithane M45 can be used to reduce losses from this disease. Follow label directions carefully. Rotate metalaxyl with other fungicides such as Dithane M45 to avoid the selection of resistant fungal pathogens.
1. Aragaki, M., J. Y. Uchida, P. S. Yahata, and C.Y. Kadooka. 1990. Foliar Blight of Leea caused by a Phytophthora species. HITAHR Brief No. 93. CTAHR Publication, University of Hawaii.
2. Aragaki, M. and J. Y. Uchida. 1994. Phytophthora blight of West Indian holly. Plant Disease 78:523-525.
3. Farr, D. F., G. F. Bills, G. P. Chamuris, and A. Y. Rossman. 1989. Fungi on Plants and Plant Products in the United States. APS Press. St. Paul, 1252 pp.
3. Stamps, D. J. l985. Phytophthora meadii. C.M.I. Descriptions of Pathogenic Fungi and Bacteria. No. 834. CAB England.
4. Uchida, J. Y. and M. Aragaki. 1991. Leaf blight of Leea coccinea caused by Phytophthora meadii in Hawaii. Phytopathology 81:1203.
Copyright: Janice Y. Uchida