''Backhousia myrtifolia'' (commonly referred to as ''carrol, neverbreak, iron wood, grey myrtle'' or ''cinnamon myrtle'') is a small
rainforest
Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainfores ...
tree species which grows in
subtropical
The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
rainforests of Eastern
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
.
First discovered and subsequently used by the indigenous communities of Australia, this plant produces oils that have a cinnamon-like aroma, and display both
anti-bacterial and
anti-fungal properties.
Therefore, it has potential applications as not only a
spice
A spice is a seed, fruit, root, bark, or other plant substance primarily used for flavoring or coloring food. Spices are distinguished from herbs, which are the leaves, flowers, or stems of plants used for flavoring or as a garnish. Spices a ...
in food preparation, but also in the medical field as a treatment option for
microbial
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
infection.
''Backhousia myrtifolia'' can grow up to 30 metres. The leaves are ovate or elliptic, 4–7 cm long, and the flowers star-shaped in appearance.
''Backhousia Myrtifolia'' is renowned for the snow-white colour of its flowers, a characteristic that makes it suitable not only as a domestic/commercial crop but also as an internationally exported product.
[Firrel, C. (2006). To intervene or Not to intervene? An Evaluation of Strategic Intervention and its Usefulness in the Development of a Value Chain Alliance for the Native Flower Industry. MPhil Thesis, School of Natural and Rural Systems Management, University of Queensland.] However, the susceptibility of this plant to "post-harvest browning syndrome" (a disease resulting in leaf discolouration and wilting), threatens its potential as a crop plant.
Characteristics
''B. myrtifolia'' is a native Australian species that belongs to the Myrtaceae family.
''B. myrtifolia'' is a
canopy species of plant (occupying high light environments) that form coppiced thick trunks, and tend to grow in warmer,
temperate rainforest
Temperate rainforests are coniferous or broadleaf forests that occur in the temperate zone and receive heavy rain.
Temperate rain forests occur in oceanic moist regions around the world: the Pacific temperate rain forests of North American Paci ...
conditions.
They are most often found in regions close to watering bodies, such as the Eastern coastal edges of Queensland, New South Wales and Victoria.
Its most common locations include the South Coast of NSW in Bega, and off Fraser Island in Queensland. ''B.myrtifolia'' is an
evergreen
In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, which ...
and has an average life-expectancy of between 80 and 100 years.
These plants tend to bloom between late spring and early summer, producing ivory white starfish-shaped flowers with 5 individual sepals and capsule like fruiting bodies.
Lastly, oil glands are visible as fine white dots throughout the leaf's structure and are responsible for the release of four major organic compounds:
methyl eugenol, (E)-methyl isoeugenol,
elemicin
Elemicin is a phenylpropene, a natural organic compound, and is a constituent of several plant species' essential oils.
Natural occurrence
Elemicin is a constituent of the oleoresin and the essential oil of ''Canarium luzonicum'' (also referred ...
and (E)-isoelemicin which collectively produce the plant's distinct cinnamon-like aroma.
Discovery and early uses
''Backhousia myrtifolia'' was first documented and subsequently named after an English
botanist
Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek wo ...
James Backhouse (1794–1869), in his report on Australian landscape and wildlife titled ''A narrative of a visit to the Australian colonies''.
James Backhouse was renowned not only for his publications in the field of botany, but also the friendships he formed with the
indigenous Australians
Indigenous Australians or Australian First Nations are people with familial heritage from, and membership in, the ethnic groups that lived in Australia before British colonisation. They consist of two distinct groups: the Aboriginal peoples ...
, whose land he was conducting research on.
However, prior to this ''B. myrtifolia'' was used extensively by indigenous Australians as a spice in cooking, due to its unique aroma and widespread accessibility.
Common diseases and cultivation options
B. myrtifolia species is fast-growing (as measured by
plant biomass,
leaf area and
leaf biomass per plant) under ideal conditions, which includes fertile soil, high
irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
levels and sufficient water supplies.
Maximum growth is achieved in the presence of oxygen-rich air (minimal carbon or
nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
pollutants) as well as nutrient-abundant soil, rich in micro-organism and mineral diversity. In addition to this ''B.myrtifolia'' tolerates drought, periods of inundation and repeated root disturbance, meaning that they are capable of flourishing in areas that experience constant temperature, and weather fluctuations.
Therefore, this plant is suitable for cultivation in both domestic and commercial Australian environments (gardens or on footpaths) in both
tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
(higher rainfall) and
coastal climates. In these urban settings ''Backhousia myrtifolia'' has an average life expectancy of 60 years, requiring very little maintenance, presuming it receives consistently high sunlight levels.
This is ideal for domestic governments and councils, since it minimises the costs associated with plant watering, trimming and root clearance.
Post-harvest browning syndrome
However, despite these seemingly ideal properties for domestic cultivation, the species is particularly susceptible to a condition termed "post-harvest browning syndrome", which involves the discolouration, browning and
wilting of the plant's stereotypically dark green leaves.
[Sommano, S., Joyce, D.C., Dinh, S.Q., D’Arcy, B. (2012). Infection by Alternaria alternata causes discoloration of Backhousia Myrtifolia foliage and flowers. The journal of Horticultural Science and Biotechnology, 87(1), 41-46. ] This browning syndrome was first documented between July to September 2008, on a 4-year stock of ''B. myrtifolia'' plants located at the University of Queensland. The discolouration was visible initially as small black dots on the surface of the leaves, progressing later into larger brown stained regions.
[Sommano, S. (2011). Browning mechanism in Backhousia Mmrtifolia. PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland.] This condition affected, approximately 30% of the harvested plants, signifying it infects populations of {''B. myrtifolia'' randomly, in non-specific quantities.
[Ekman, J., Eyre, J., Joyce, D. (2008). Flowers by Sea: Improving market access for Australian wildflowers. Australian government: Rural Industries Research and Development Corporation.]
Although research is still being conducted into its causes, "post-harvest browning syndrome" has been attributed to two primary factors:
* Fungal and/or bacterial infection
* Prolonged heat exposure and lack of temperature control
Infection of ''B. myrtifolia'' by the fungus
Alternaria alternata was analysed and confirmed via
Koch's postulates (a series of tests used to analyse the pathogenicity of certain bacteria and fungi).
Alternaria alternata was found to release certain low-
molecular weight
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
host-specific
toxin
A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849– ...
s (HSTs) such as
tenuazonic acid,
tentoxin
Tentoxin is a natural cyclic tetrapeptide produced by phytopathogenic fungus ''Alternaria alternata''. It selectively induces chlorosis in several germinating seedling plants. Therefore, tentoxin may be used as a potential natural herbicide.
Ten ...
and zinniol .
These toxins not only damage plant
cell membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
s but also cause permeability changes in the
cell wall
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...
, that may contribute to plant browning and death .
In addition to this, these HST toxins may also cause disruptions in the oil gland structure of the plant's leaves, resulting in oil leakage.
The leakage of the plant's 4 oil
chemotype A chemotype (sometimes chemovar) is a chemically distinct entity in a plant or microorganism, with differences in the composition of the secondary metabolites. Minor genetic and epigenetic changes with little or no effect on morphology or anatomy m ...
s damages the efficiency of sunlight capture by
chlorophyll
Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...
s (decreased
chlorophyll fluorescence) resulting ultimately in the development of black and brown spots along the leaves' surface.
On the other hand, prolonged exposure to heat stress, was also found to produce
free radicals
In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron.
With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spont ...
in the leaves of ''B. myrtifolia'' plants.
These radicals oxidise the
lipoprotein
A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, sur ...
membranes surrounding cells, resulting in a loss of cellular
compartmentalisation and structure, once again damaging chlorophyll content and chlorophyll fluorescence.
This is thought to be another significant contributing factor to the high rates of browning observed for this particular plant.
Therefore, it is recommended that ''B. myrtifolia'' be kept at temperatures above in the presence of above 20mL of water, to prevent the development of post-harvest browning syndrome.
This browning of leaves not only damages the visual appearance of ''B. myrtifolia'' leaves, but also eliminates the recognisable cinnamon aroma produced by the oils of the plant.
Therefore, since no treatment options currently exist for "post-harvest browning syndrome" (despite its high frequency), the viability of ''B. myrtifolia'' as a domestic product is decreased considerably.
Possible uses of ''Backhousia myrtifolia''
Food additives
''Backhousia myrtifolia'' is used extensively as an aromatic/spice, due to the unique properties of its natural oils; methyl eugenol and elemicin. These oils combine to produce a natural cinnamon-like fragrance, and as a result ''B. myrtifolia'' can be used as a
flavouring agent
A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of the gustat ...
in biscuits, stews and deserts.
In addition to this the ''B. myrtifolia'' plant is rich in
fibres,
vitamin
A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an Nutrient#Essential nutrients, essential micronutrient that an organism needs in small quantities for the proper functioning of its ...
s (Vitamin A, C, E, K and
pyridoxine
Pyridoxine, is a form of vitamin B6 found commonly in food and used as a dietary supplement. As a supplement it is used to treat and prevent pyridoxine deficiency, sideroblastic anaemia, pyridoxine-dependent epilepsy, certain metabolic disorde ...
) and
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s (potassium, calcium and copper) which are important in maintaining
homeostatic
In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and i ...
body function.
Vitamins function as
co-enzymes
A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's role as a catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can be considered "helper molecules" that ass ...
in the body, accelerating the rate of biological reactions, whilst minerals such as potassium are useful in preserving cellular
electrochemical gradients, and thus maintaining
musculoskeletal function.
Medicinal applications
Despite this, research is also being conducted into ''B. myrtifolia's'' application as an anti-bacterial or anti-fungal agent, due to the
bactericidal
A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics.
However, material surfaces can also have bactericidal properties based solely on their ...
properties of its oils. The methyl eugenol and elemicin components of ''B. myrtifolia's'' natural oils are very potent
anti-septic
An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...
agents, capable of inhibiting the growth of over 100 species of
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
cumulatively. The methyl eugenol oil of ''B. myrtifolia'' is capable of breaking down the thick peptidoglycan wall of gram positive bacteria whilst, elemicin creates small pores in the outer lipopolysaccharide layer of gram negative bacteria. Through both these mechanisms, ''B. myrtifolia'' is capable of exposing the interior of bacterial cells, to the external environment, therefore killing them. Consequently, the
Aqueous and
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
ic leaf extracts of ''B. Myrtifolia'' were found to inhibit the growth of both ''
Proteus mirabilis
''Proteus mirabilis'' is a Gram-negative, facultatively anaerobic, rod-shaped bacterium. It shows swarming motility and urease activity. ''P. mirabilis'' causes 90% of all ''Proteus'' infections in humans. It is widely distributed in soil and ...
'' and ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' bacteria. Infection by the P. mirabilis bacterium is responsible for between 1-10% of
urinary tract infections and has also been linked as a causative agent of
rheumatoid arthritis
Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involv ...
, whilst ''E. coli'' is generally responsible for
gastro-intestinal
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
infections such as food poisoning.
In addition to this, the oils produced by the ''B. myrtifolia'' plants are non-toxic (as determined by an Artemia franciscana nauplii bioassay) further supporting their use as either an internal or
topical treatment for bacterial/fungal infections.
Insect repellents
In this same vein of thought, the anti-septic properties of Backhousia myrtifolia's oils also make it suitable for use as an
insect repellent against common disease-carrying
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
s such as mosquitoes, flies and beetles.
Elemicin, a compound derived from the oils of ''B. myrtifolia'' leaves can replace substances such as
citronella oil, which is the common active ingredient in candle and torch insect repellents.
The resultant naturally sourced insect repellents, would be especially useful to individuals who suffer allergic reactions to the chemicals present in conventional repellents (
diethyl phthalate
Diethyl phthalate (DEP) is a phthalate ester. It occurs as a colourless liquid without significant odour but has a bitter, disagreeable taste. It is more dense than water and insoluble in water; hence, it sinks in water.
Synthesis and application ...
,
dimethyl carbate
Dimethyl carbate is an insect repellent. It can be prepared by the Diels–Alder reaction of dimethyl maleate and cyclopentadiene
Cyclopentadiene is an organic compound with the chemical formula, formula C5H6.LeRoy H. Scharpen and Victor W. L ...
etc.).
In countries such as Indonesia and Papua New Guinea, where the rates of mosquito spread malaria and West Nile virus are high, ''B. myrtifolia'' based repellents would be especially useful.
''Backhousia myrtifolia'' as an exported product
''B. myrtifolia'' is a desired product for international
export
An export in international trade is a good produced in one country that is sold into another country or a service provided in one country for a national or resident of another country. The seller of such goods or the service provider is an ...
ation (particularly to Asian regions such as Japan) due to the unique ivory-white colour of its flowers. Initially, between 1995 and 2000 the profits made through exportation, specifically around the holiday season were high, since the flower was labelled “the Christmas Carol” by Australian farmers.
Therefore, the plant was exported mainly due to its aesthetic qualities rather than its medicinal or food-related uses. To match the slowly increasing demand for the plant in various countries including Asia and Western Europe, Australians in southern NSW began to develop farms dedicated to its production.
However, through mismanagement, ineffective sales tactics, and the increasing prevalence of “post-harvest browning syndrome” the popularity of the plant decreased by over 40% in 2004.
The browning syndrome was reported to infect up to 20% of all exported plants causing a drop in the average exported plant quality from a rating of 2.75 (classified as ideal quality and freshness) to 1.75 (acceptable quality).
The ''B. Myrtifoli'' market was dependent entirely on plant quality and appearance, and therefore as this began to decrease so did the profits generated by the industry.
In response to this Australian growers and exporters in 2004, congregated to form the Backhousia Group, an organisation determined to improve sales, through more efficient farming techniques and aggressive sales campaigns.
The development of this value chain alliance in 2004, helped restore the Backhousia botanical industry, to a profitable margin within a period of two years.
Furthermore, with the uses of the plant now expanded, its potential as an exported product for antibacterial, cooking or repellent purposes may grow.
References
Further reading
*Floyd, A.G., ''Rainforest Trees of Mainland South-eastern Australia'', .
External links
Plant profile, including cultivation requirements APNI Australian Plant Name Index
{{Taxonbar, from=Q4839673
Bushfood
Myrtales of Australia
myrtifolia
Australian cuisine
Crops originating from Australia
Flora of Queensland
Flora of New South Wales
Spices