Aeginetia indica
(forest ghost flower)

Aeginetia indica is not considered as an invasive species in its native range and it is not known to occur as an introduced species elsewhere. It has a wide distribution in Asia and Oceania (Papua New Guinea), where it is reported as dispersed in scattered locations throughout its range. Although it is listed as common in Thailand, the species is rare and declining elsewhere throughout its native distribution. It has a local IUCN Red List status of “Critically Endangered/Possibly Extinct” in Sri Lanka, with only a small population known after not been recorded for 125 years.

Because A. indica is a holoparasite affecting a number of crops, it is a species of concern for some countries outside of its native range. It is designated as a noxious weed in the USA, even without the species being present in the New World. Possible distribution models for A. indica show that the species has a broad invasive potential in tropical and subtropical areas of all continents where potential host crops are grown. The germination requirements and host-specificity of A. indica could be a deterrent for the species expanding outside its native range.

Aeginetia indica is a parasitic herb native to tropical and subtropical regions of Asia, from India to China and Japan, and throughout southeast Asia into Oceania (Papua New Guinea) (Lemmens, 2003; Flora of China Editorial Committee, 2019; Useful Tropical Plants, 2019; POWO, 2020). According to Ekanayake et al. (2015), A. indica is widely dispersed in scattered locations in its native range.

There are insufficient data to properly assess the risk of introduction of A. indica. The species is a recognised holoparasite of various crops, which is a major concern for its spread (Auttachoat, 2003). Although Mohamed et al. (2006) present a model with the possible areas worldwide where A. indica could grow, the species is not known in the wild outside its native habitat. The germination requirements, including low conditioning temperatures and specific host relations are an apparent constraint to the spread of the species (French and Sherman, 1976). Nevertheless, due to the possible introduction of the seeds as contaminants of various crops, it has been declared as a noxious weed in USA (USDA-ARS, 2019). A. indica is valued for medicinal purposes in various Asian countries which may facilitate its spread into other countries (Darbyshire and Prasad, 2009).

Aginetia indica is a gregarious root parasite that can be found on shaded forest floor covered with leaf litter in India (Flowers of India, 2019). In Thailand, the species occurs in a wide range of habitats including roadsides, hills and evergreen, bamboo, pterocarpus and pine forests, at elevations from sea level to 1,600 m (Parnell, 2012). It is also reported growing in grassy places in lowlands and low mountains, mixed evergreen-deciduous forests, and in mostly alluvial areas beside or near streams, in hummus soils and slopes (Chavan et al., 1961; Auttachoat, 2003; Ekanayake et al., 2015; Flora of China Editorial Committee, 2019; Useful Tropical Plants, 2019; Zheng et al., 2019).

Aginetia indica is reported as a holoparasite of various species, including some crops (Useful Tropical Plants, 2019). Host species include Imperata sp., dryland rice (Oryza sativa), sugarcane (Saccharum officinarum), Miscanthus sp., millet (Panicum miliaceum), Italian millet (Setaria italica), maize (Zea mays), Carex spp., Dioscorea sp., Luzula spp., Japanese ginger (Zingibermioga) and Canna spp. (Chavan et al., 1961; Lemmens, 2003; Ray and Dasgupta, 2010a; Flora of China Editorial Committee, 2019). In Thailand, the species grows under shady areas of bamboo (Auttachoat, 2003).

Nickrent and Musselman (2004) consider the species as only causing minor problems on monocots. It is reported as being able to be a destructive parasite of rice without further details (Lemmens, 2003; EPPO, 2019). The species causes damage to sugarcane plantations by lowering the sucrose content of healthy sugarcane from 13% to 5% (Hunsingi, 2012).

Genetics

The chromosome number reported for A. indica is 2n = 30 (Flora of China Editorial Committee, 2019). The species is not threatened by genetic erosion due to its large area of distribution (Lemmens, 2003). It is morphologically variable throughout its range (Parnell, 2012).

Reproductive Biology

Aginetia indica is a holoparasite native to Asia and Oceania (Useful Tropical Plants, 2019). The species reproduces by seeds. A. indica probably self-pollinates, as the flower’s corolla is bent down with the stigma and anthers situated at the same level (Tiagi, 1952). Although the species produces seeds in abundance, many of the seeds lack an embryo or endosperm. The seeds will not germinate unless they are in contact with root exudates of another plant species. Seedling development only occurs in contact with the roots of the host species, mostly Poaceae (Auttachoat, 2003).

Physiology and Phenology

In India the species appears during the rainy season and grows until October when it set seeds (Tiagi, 1952). It is reported as flowering from April to August and fruiting from August to October in China (Flora of China Editorial Committee, 2019). In Thailand, flowering occurs during the rainy season (September to October) (Auttachoat, 2003).

The seeds are reported as being short lived, although other species in Orobanchaceae have long live seeds (Barnes, 1909; Auttachoat, 2003). The seeds will germinate only under the stimulus of root exudates from some specific vascular plant species. The germination occurs by the development of large globular cells at the radicular end of the embryo. These cells develop into a germ tube which will penetrate the host root to produce a haustorium. The part that remains outside the root forms a tubercule from which the plant body develops (Barnes, 1909; Auttachoat, 2003). Seedling development is host-specific (Auttachoat, 2003).

The isolation of the exudates that stimulate germination in Orobanchaceae has been difficult due t: the amount of stimulatory compound produced per root being very low, the compounds being unstable at high temperatures and the exudates being a mixture of compounds varying among the different host species. Some of the exudates that have been isolated appear to be unsaturated lactones (Auttachoat, 2003).

The seeds germinate slowly and show distinct dormancy (Lemmens, 2003). Treating the seeds with sodium hypochlorite has proven to be successful in breaking dormancy. Stratification of the seeds for about eight days at 3-5°C, or by brief exposures (15 min) to 50°C will break the dormancy. Continuous light, even if it is low, inhibits the germination completely. After breaking dormancy, the seeds have a high germination percentage when incubated at 25-30˚C (French and Sherman, 1976; Auttachoat, 2003).

Longevity

Aginetia indica is an annual (Auttachoat, 2003).

Associations

The seeds of A. indica will not germinate unless they are in contact with the roots of certain vascular plants. Germination has been recorded near the roots of the following species: Corchorus capsularis, Raphanus sativus,Glycine max, Helianthus annuus, Pisum sativum, Sorghum bicolor, Sorghum halepense, Triticum aestivum, Zea mays, Phaseolus vulgaris, Ipomoea purpurea, Oryza sativa and Beta vulgaris (French and Sherman, 1976). The seedlings only grow in contact with the roots of specific species, mostly Poaceae (Wolf, 1912). Host species include Imperata sp., Oryza sativa, Saccharum officinarum, Miscanthus sp., Panicum miliaceum, Setaria italica, Zea mays, Carex spp., Dioscorea sp., Luzula spp., Zingibermioga and Canna spp. (Chavan et al., 1961; Lemmens, 2003; Ray and Dasgupta, 2010a; Flora of China Editorial Committee, 2019).

Environmental Requirements

The Orobanchaceae in general grow in poor soils and the addition of fertilisers is detrimental to the species as they have a low ability to detoxify chemicals. There is very little information on the environmental requirements for A. indica. In Thailand the species is reported as growing in acidic soils (pH 4.49), with low phosphorus, low potassium and high calcium (Auttachoat, 2003).

In the Philippines, Platyptilia moth species have been reported damaging the flower buds of A. indica. Moths in the Daulia genus are also herbivores that affect young stems (Ray and Dasgupta, 2010b). Takano (1934) reports the following insects attacking A. indica in Taiwan: Daulia afralis, Platyptilia sp., Pericallia sp., and Amsacta lactinea.

General

• Botanical garden/zoo
• Ritual uses
• Sociocultural value

Medicinal, pharmaceutical

• Traditional/folklore

Early Warning Systems

Although A. indica is not known to occur outside its native range, the species is listed in USA as a noxious weed due to its possible negative impact to the agriculture (USDA-ARS, 2019).

Aginetia indica is similar to A. flava. This species differs from A. indica by having conspicuous scale leaves near the base of the stems. The flowers of A. flava are yellow with broadly spreading dentate lobes while in A. indica the corolla is purplish, not dentate and slightly to not spreading (Parnell, 2012). The species is also confused with A. pedunculata but the later has shorter pedicels and larger whitish or yellowish flowers with purplish or bluish corolla lobes (Lemmens, 2003).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control and Sanitary Measures

Almost no information is available on the control of A. indica. Elzein and Kroschel (2003) published a technical report on the control of other Orobanchaceae that parasitize various crops. They recommend an integrated control approach with a combination of various methods.

Some cultural methods tried with other Orobanchaceae are: transplanting the host on seeding stages, crop rotating with a “trap crop” species that stimulates the seed germination, and intercropping with species not susceptible to the parasite’s infestation.

Physical/Mechanical Control

Hand Pulling and solarisation are methods recommended as part of an integrated control approach (Elzein and Kroschel, 2003).

Chemical Control

Glyphosate and Dicamba had been used in other Orobanchaceae species to control post emergence stages and control seed production. The application of germination stimulants (e.g. ethylene, ethephon, strigol) to induce suicidal seed germination has also been investigated (Elzein and Kroschel, 2003).

Host resistance

Large scale replacement of sugarcane (Saccharum officinarum) varieties with field resistant cv. NCo 310 had been successful for the control of A. indica in Taiwan (Ray and Dasgupta, 2012).

Various authors discuss the need for more information on A. indica or the Orobanchaceae in general, including: the ecology, morphology, development, host relationships, longevity, pollination and dispersal (Theeret, 1971; Auttachoat, 2003). Although reported as affecting various crops there are no details of the effects and economical losses caused by the species. Also needed is information about the medicinal potential of A. indica (Lemmens, 2003).

30/09/19 Original text by:

Jeanine Vélez-Gavilán, UPR-RUM, Mayagüez, Puerto Rico