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|Stalk rot of
Rhizome rot of red ginger
Rhizome rot of Heliconia
TYPE: Kingdom: Fungus
Order: Agaricales (mushrooms)
Family: Tricholomataceae( over 140 genera)
Species: the species for the red ginger and heliconia pathogen, has not been identified
Stalk rot of red ginger
Rhizome rot of red ginger
Rhizome rot of Heliconia
Marasmius species have been observed on red ginger (Alpinia purpurata) and Heliconia species. Mushrooms which are the fruiting structures of these species have also been observed on taro corms and banana clumps. Marasmius is a pathogen of red ginger and heliconia but pathogenicity to taro and banana are unknown. It is not known whether the same species of Marasmius attacks red ginger and heliconia. Many species of Marasmius are saprophytic (non-pathogenic) and grow on dead plant tissue. In the continental U. S., Marasmius is common on fallen leaves, pine needles, and logs of oak, maple, birch, pine and many other types of trees.
In Hawaii, a few species of Marasmius have been found in forests. Sugarcane root rot has been attributed to Marasmius sacchari but the fungus associated with sugarcane root rot may be several species of Marasmiellus instead.
Marasmius species are distributed worldwide. The distribution of the heliconia and red ginger pathogens is unknown as these are new diseases.
HELICONIA: Marasmius causes a brown, dry rot of the underground stems or rhizomes of heliconia. Rots of the older part of the rhizomes are fibrous (Fig. 1) and the diseased rhizomes fall apart easily. Younger sections of the rhizome that are producing shoots with leaves and flowers have soft brown rots. These are best observed when the rhizomes are sliced open.
Brown sheath rots also occur and young shoots can be killed by this pathogen. Plants infected with Marasmius grow poorly and fail to thrive. Sections of the plant may wilt, die, or appear to suffer from nutritional deficiency.
Evidence of the fungus can be found on rotted plants, in which white threadlike growth and/or small mushrooms are sometimes present.
RED GINGER: The ginger plant produces stalks of leaves and flowers from the growing point on the underground stem or rhizome. The stalk of the flower is composed of many leaf sheaths that surround the true stem leading to the flower.
The fungus attacks the rhizome and causes a brown rot. This pathogenic fungus feeds on the infected rhizome and grows between the sheaths forming the leaf and flower stalks. When flowers are harvested, the fungus is already present between the leaf sheaths. A white to brownish mat of fungal growth is visible when sheaths are removed. During the shipment period, the fungus grows and emerges from beneath the leaf sheath covering the stem and forming thick layers of white mycelium or fungal growth. The active growth of Marasmius, causes sheath rots of cut flowers.
White mats of fungal growth are a good indication that Marasmius is present (Fig. 2).
Fungi that produce mushrooms, such as Marasmius (Fig. 3) belong to a group called the Agaricales. Mushrooms are also often called toadstools. The fungi of the Agaricales include species of mushrooms which are edible, but also those that are hallucinogenic or poisonous.
Among Marasmius species however, only a few are worth eating. Most are too small or have little flavor. Marasmius copelandii (the garlic mushroom) is very tiny, with an odor true to its name. Marasmius oreades is reported to be the only one that is delicious. It grows in lawns in the Pacific Northwest. In Hawaii however, Chlorophyllum molybdites is a common lawn mushroom. It is poisonous!!
Mushrooms produce sexual spores of the fungus. Under the right conditions the spores will blow to new locations, germinate, and establish a new colony. Only a few species of Marasmius are plant pathogens and more research is needed on these pathogens, especially in the tropics.
A unique feature of the threads or mycelium produced by Marasmius is the production of clamp connections. These are specialized branching structures that are useful for the recognition of basidiomycetes. All fungi that produce clamp connections are basidiomycetes, however some basidiomycetes do not produce clamp connections.
Marasmius spreads by growing from diseased plants to healthy plants. The range and effectiveness of pathogen distribution from basidiospores needs to be investigated.
The common practice of cutting old ginger and heliconia stalks and piling them in the field as compost is good, only if pathogens are absent. With pathogens present, the host tissue provides the best nutrient source for pathogen growth and tremendous amounts of inoculum are produced. The heavy, thick mycelial growth emerging from infected tissue readily penetrates healthy stalks and rhizomes. The fungus needs a continuous source of nutrients to grow vigorously and infect healthy host tissue. Without this nutrient source, the fungus dies.
Production of spores (mushrooms) follows active growth of the fungus. The number and size of the mushrooms are related to the amount and quality of mycelium produced in the growth phase of this fungus.
Red ginger: It is uncertain whether severely diseased ginger fields can be economically salvaged. Several practices will reduce disease levels and these should be implemented. Diseased fields should be cleaned and all old leaves and stalks should be removed from the nursery. Plants that are wilted or dying, and rhizomes that are infected should be removed also. If bare ground (soil) is unacceptable, use new cinders on the walkway.
Provide the best air movement possible. Trim old sections of the plant and remove shrubs, weeds, etc. surrounding the field. High moisture favors the growth of the fungus.
In limited studies, heat treatment of heliconia rhizomes infected with Marasmius did not kill the fungus. Research is needed to determine if effective control options are available for this new pathogen. These would include: modification of heat treatments to establish clean rhizomes; screening for effective fungicides; and biocontrol inhibitors.
At present the best option for growers with severely infested fields is the establishment of new clean fields. New fields should be at a separate location. For new fields, carefully check all new plants. If possible, obtain rhizomes from fields without this disease. If clean fields are not available, growers should take small sections of healthy plants, remove all soil and old leaves, wash rhizome and roots in running water and check for any sign of disease. Trim diseased sections and remove all roots. Place in 20% household bleach for 3-5 mins and plant in pots using new potting mix (Sunshine Blend 4, ProMix, etc.). Repeat with more plants . After plants have grown, check the roots and rhizomes carefully for disease and use only clean plants for the new field.
Do not transport soil, cinders, plants, etc. from the old field to the new field. The mycelium can survive in soil on infected host debris. Be sure to wash and dry all tools and equipment that have been used in diseased fields. If possible, keep a separate set of tools for the new location.
If tractors or other field equipment are needed to prepare the new field, be sure that tires and lower sections of the equipment are clean and free of soil and plant debris before starting. When herbicide applicators and tanks are used in large fields, trucks must not travel from old diseased fields to new fields. Use clean trucks to treat the new field, then go to older fields. Completely abandon old fields as soon as possible otherwise a continuous source of the pathogen will be maintained. If possible remove all plants from abandoned fields and bury in a deep pit or take to the county dump.
1. Arora, D. 1986. Mushrooms Demystified. Ten Speed Press, Berkeley, CA. 959 pp.
2. 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, Minnesota. 1252 pp.
3. Hawksworth, D. L., P. M. Kirk, B. C. Sutton, and D. N. Pegler. 1995. Ainsworth and Bisbys Dictionary of the Fungi. CAB International. University Press, Cambridge, Oxon, U.K.
COPYRIGHT: Janice Y. Uchida
Depatment of Plant Pathology
University of Hawaii