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Into Horticulture

Issue 5   November 2011

Plant & Garden News

Cycads not so ancient
Our perception of cycads as ancient plants will have to altered a little in the light of recent research results. While cycads did exist in the time of the dinosaurs, molecular analysis of two-thirds of the world's living species indicates that contemporary cycads have evolved more recently. Read more at the University of California Berkeley website: Cycads are not "living fossils" from Dinosaur Age

2012 Carnival a great success
Toowoomba Regional Council reports that a record number of people attended this year's Carnival of Flowers. In addition to the garden competition and displays, and the great spring weather, the food and wine component of the modern Carnival is credited with contributing to it's success. More information at the Council's website: Record visitor numbers add to 2011 Carnival lustre

Caution advised with "non invasive" cultivars
U.S. researchers warn that some plant cultivars being promoted as "non-invasive" could still spread if they retain the ability to produce some viable seed. Apart from the total number of seed that could be produced over the life of a long-lived species, the offspring could be more prolific, especially if they result from crossing with other cultivars or relatives. They suggest that population growth rate and the likelihood of the plant breeding true from seed be considered when assessing invasiveness, unless it can be proven to be completely sterile. Media release: "Non-invasive" cultivar? Buyer beware.

Urban trees' filtering effects examined
Research estimates that urban trees in the Greater London Authority area remove between 850 and 2000 tonnes of particulate pollution from the air every year. There are plans to increase tree planting in London and the rest of the country, and the methodology used in the study could with help with species selection and location of planting with respect to this form of pollution and its associated human health effects. Source: New study shows how trees clean the air in London

Pitcher plant could revolutionise housework
Inspired by the slippery surface of a pitcher plant's trap, scientists have developed a material that repels a wide range of liquids and solids, even under harsh conditions. It has potential in a wide range of medical and industrial applications, including self-cleaning windows and anti-graffiti coatings. Source: Slippery slope: Researchers take advice from a carnivorous plant

Roots' modification of soil moisture a surprise
Plant roots and associated microorganisms alter the soil environment in a variety of ways, but it has recently been discovered that there is actually more water within a few millimetres of roots than the rest of the soil. This runs counter to previous assumptions. The mechanism may be water-holding gels exuded from roots, which can then act as a temporary water supply and help maintain plants for a few hours if soil moisture becomes inadequate. The future breeding of drought-tolerant plants or development of more efficient irrigation systems could be influenced by these findings. More information from Helmholtz Centre for Environmental Research, Germany: Plants create a water reserve in the soil

Saving nuts is far from nutty
The Macadamia Conservation Trust and Bundaberg Regional Council are working together to help preserve endangered Macadamia with a planting of rainforest trees at Bundaberg Botanic Gardens. Four species will be planted: Macadamia integrifolia and Macadamia tetraphylla, which are quite well known, plus the rare Macadamia ternifolia and Macadamia jansenii. This will not only help preserve their gene pools, but educate the public about the threat to native macadamia populations. Source: Endangered macadamia species to be planted at Bundaberg Botanic Gardens

Hidden menace could lurk in veggies
Research has demonstrated that it is possible for Salmonella and E. coli to develop inside plant tissues grown from contaminated seeds. If they were to occur in vegetables in this manner, they could not be removed with simple washing. Source: E. coli, Salmonella may lurk in unwashable places in produce

A new class of fungi discovered in soil
Although its existence has been known about for some time from the DNA analysis of soils, a fungus that represents an entirely new class - Archaeorhizomycetes - has been now cultured in the laboratory. It does not appear to be pathogenic, but there appears to be an association with mycorrhizal fungi. The ability to use cellulose suggests it might be involved in the recycling of plant residues. Its role in the soil ecosystem and the identification of other species in this class will be the subject of further research. Source: Hidden soil fungus, now revealed, is in a class all its own and Visiting researcher at IU leads international team in formal identification of new fungi class

Plant poison a rat protector
Acokanthera poison, which is used by African hunters for their arrows, is used in a somewhat similar way by the African crested rat. According to a recent study, it chews the tree's bark and applies the toxin to sponge-like hairs on its body. This is the only known example of a mammal employing a plant toxin for defense. How the rat itself survives the poison, is still unknown. Source: African rodent uses 'poison arrow' toxin to deter predators

Better timber preservation a Qld innovation
Queensland scientists have developed a new timber preservation technology that is both environmentally friendly, efficient and gives better penetration of difficult timbers. Read more at the DEEDI website: Breakthrough for better timber and eco preservation

Pruning could affect DNA
Endoreduplication is the process of chromosome duplication without cell division and a new study has shown that a plant's ability to do this after damage may contribute to its chances of survival. Of two cultivars of Arabidopsis, the one which exhibited endoreduplication was able to to this actually able to quickly regrow and increase its seed production after clipping. (source: Some plants duplicate their DNA to overcome adversity).

CSIRO unzips plant virus mystery
Insight into how plant viruses can target their hosts so specifically has been gained in Australian research. It has been found that certain genes must match genes in the plant for Cucumber Mosaic Virus (CMV) for infection to occur. Complimentary sections "zip" together, interrupting the normal functioning of the plant. CMV interferes with a gene involved in chlorophyll synthesis, hence the symptoms of yellowing. Searching for matching DNA sequences may help scientists pinpoint the mechanism of other plant virus diseases and lead to ways to engineer resistance into plants. Source: Major breakthrough on how viruses infect plants

Leaves that speak to bats
If you're a plant that exploits bats for pollination, how do you attract them? Marcgravia evenia, a rainforest vine from Cuba has evolved a special concave leaf next to its flowers. Researchers have found that it's acoustic properties make it an effective aid to echolocating bats. Source: Rainforest plant developed sonar dish to attract pollinating bats

Editorial - Challenges ahead

Between the wet weather of the past year and predictions of more to come, Queenslanders have undoubtedly been thinking they could forget their drought worries for a while. Yet here we find ourselves in an extraordinarily dry November. As lawns turn brown and crispy and veggies droop, many will be asking - is it worth the bother?

Gardening in Australia has been practised for relatively short time in historical terms, and is still largely based on a culture imported from Britain and Europe. Mediterranean and temperate-climate plants and techniques are even less appropriate for our northern regions than they are for southern Australia. In the years ahead, we have much to learn from gardeners in other subtropical and tropical climates, as well as developing our own home-grown methods.

Hopefully, this will make it easier to cope with the conditions that the Australian climate throws at us in future. An added bonus is that new and better garden plants bred from Australian native species, and new equipment and other products invented here have the potential to be exported to other parts of the world. Unique gardens can be tourist drawcards, too.

Even if the world doesn't come to an end in 2012, we still have to make it through the summer! Here's hoping for season free of more weather extremes, and safe and happy holidays for all readers!

Queensland Garden Events 2012

A reminder to Queensland residents who might be organising a public garden-related event next year: If you have dates confirmed, be sure to send them in for free inclusion at Additional details such as guest speakers and other attractions can be added closer to the event if these have yet to be finalised. Meanwhile, it gives potential visitors a chance to mark their calenders and plan their trips. Don't forget a link to your website can be included, if you have one.

The Science of Horticulture

Seed Dormancy (Part 2)

In the previous newsletter, the concept of seed dormancy was introduced, and some of the major mechanisms briefly covered. Here in part two, some more specific examples which are likely to be encountered by gardeners at some time or another, are discussed in a little more detail.

Legumes and scarification

The imposition of dormancy by a hard impermeable seed coat is not widespread in the plant kingdom, but is very familiar to gardeners because it's common in the legume family, including ornamental species like Acacia, Bauhinia and Delonix (Poinciana). This form of dormancy may also be encountered in the hibiscus, geranium, lily and canna families.

Seeds possessing such dormancy generally have a specialised pore or plug that regulates water transfer. In nature, exposure to traumas such as fire or passage through an animal's digestive system cause sufficient disruption to permit entry of water. In a commercial or laboratory setting, abrasive, temperature or chemical treatments can be applied (scarification) to make the seed coat permeable enough to allow water entry and initiate germination.

For the home gardener requiring a relatively few plants, nicking or sandpapering the seed coat is the most straightforward method, taking care not to damage the seed excessively. A simple hot water treatment can also be used and is popular for Acacia (see bibliography below).

Smoke and Australian natives

Smoke has been found to enable or enhance germination in a diverse array of Australian species, although the phenomenon is not restricted to plants from this continent. The discovery means that a wide variety of Australian native species can now be considered for horticultural production, and could even have implications for gardening and farming more generally.

The smoke effect is distinct from any heat effect of fire. In the nursery, seeds can be exposed to smoke in a special tent or soaked with water through which smoke has been passed. The latter is very convenient for the home gardener because smoke water is now available commercially. Note that additional dormancy factors may also be in play when attempting germination of a given species.

The biochemical basis of smoke stimulation is the subject of ongoing research. One group of plant-active molecules from smoke called karrikins has been recently discovered. The finding that many species not normally associated with fire-prone habitats, even some garden vegetables, are response indicates that there is still much to be learned and may even lead to development of new agricultural chemicals.


One of the most common backyard crops with dormancy issues is lettuce. It's response to light has been well-studied. Red wavelengths (predominant in direct sunlight) stimulate germination and far-red light (typical of light filtered through leaves) inhibit it. This has an obvious evolutionary advantage, as seeds germinating under established plants are unlikely to be successful.

Lack of light can also induce dormancy in weed seeds. If buried, they can remain viable for years, waiting for exposure to spring into action. The gardener can exploit this knowledge to reduce weed problems with appropriate cultural techniques such as no-dig/low-till methods and mulching.

An additional problem with lettuce is thermoinhibition. High soil temperatures will inhibit germination, and if they last long enough, may cause the seed to enter secondary dormancy.

In the garden, the actual response will depend on the cultivar of lettuce as these responses have a genetic basis. Like other forms of dormancy, conditions under which the seeds were produced and stored can also potentially affect subsequent dormancy behaviour.

In Conclusion

Dormancy problems can be eliminated by breeding, or minimised via production methods in the case of commercially produced seed. They can nevertheless provide hurdles for the home gardener, especially as they are likely to be propagating plants that have received relatively little scientific study, (compared to the most important crops), or home-produced seed.

The precise mechanism(s) employed by a particular species will be greatly influenced by the habitat in which it has evolved. Undoubtedly there is much still to be discovered on the subject of seed dormancy in the plant world.

Besides the economic advantages to the farmer or production nursery of faster or more uniform germination, unlocking the secrets of dormancy could make a difference to the survival of endangered species. If the dormancy-release mechanism (e.g. fire, animal) is removed from a habitat, the plant too may eventually disappear. While vegetative propagation may be one way of rescuing plants from the brink, greater numbers can be propagated and distributed, and greater genetic diversity preserved, more cheaply and easily with seeds.

Bibliography and further reading:

8.1.2 Seed dormancy Plants in Action, a plant physiology textbook available online at the UQ website
Seed Conservation and Biology Royal Tasmanian Botanical Gardens
Seed Germination and Dormancy Article from journal "The Plant Cell" (PDF)
Overcoming Seed Dormancy: Trees and Shrubs N.C. State University, North Carolina
The Seed Biology Place Gerhard Leubner Lab. University Freiburg, Germany
Cultivation of Acacias World Wide Wattle
Smoke Germination of Australian Plants Rural Industries Research and Development Corporation, Australia

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