Bush Tomato

24.05.17

Bush tomato (Solanum centrale) belongs to the Solanaceae family, which includes plants such as potato, tomato, eggplant, capsicum and chilli. It grows naturally throughout the central deserts of Australia. There are over 100 species of wild tomatoes in Australia but only six are known to be edible. Bush tomato is also known as desert raisin and kutjera. Several Solanum species have been used by Indigenous Australians for food for possibly thousands of years.

Overview

Bush tomato is a small perennial shrub that spreads by underground suckers and grows to a height of 30–45cm. It has grey-green leaves and mauve-blue frilled flowers, and there may be spines on the stems. The fruit of the bush tomato plant is globular-shaped and usually 10–15mm in size. It turns from green to yellow as it ripens, then dries on the bush until it is a reddish colour and looks like a raisin.

Bush tomato has a strong flavour which has been described as earthy caramel and tomato with a pungent aftertaste. The sun dried fruit may be eaten directly after harvest but are generally further dried and ground to be used as a spice or flavouring. Caution must be exercised when harvesting bush tomato, as the green (unripe) fruits are potentially toxic. Further, the ripe fruit of some related species are toxic, so correct plant identification is critical if wild harvesting.

The demand for bush tomato has outstripped the supply possible from wild harvest. To meet growing demand for the fruit, bush tomato is produced by cultivation in the Northern Territory and South Australia. To support this new industry, research is underway to develop the horticultural, fruit quality and genetic understanding of bush tomato.

Facts and figures

Names for bush tomatoes from indigenous languages include akatyerr, akatjurra, katyerr, kampurarrpa and yakajirri
There are over 100 species of Solanum in Australia but only six are known to produce edible fruit — so correct identification of wild plants before harvest is critical
Demand for bush tomato and its value-added product outstrip supply
Cultivation of bush tomato is a sustainable means of meeting market demand, and by managing irrigation schedules the fruiting cycle can be manipulated to some extent to distribute timing of fruit maturity
Bush tomato can be dried on-farm and stored for extended periods allowing farmers to control the flow of product to market
Most bush tomato growers sell raw product to processors

Production status

The wild harvest of bush tomato is undertaken mainly in South Australia and the Northern Territory as it is highly adapted to arid environments.

Wild harvest can account for up to 80% of supply of product in good seasons, however this source is always variable and unpredictable and in normal years it is estimated that approximately half of production is derived from wild harvest.

Bush tomato is grown commercially by five Indigenous communities in diverse locations across South Australia and two communities in the Northern Territory. All communities have grower contracts to sell their product to one of two major processors. In addition to the involvement of these Indigenous communities and the two major processors of bush tomato, there are a number of smaller enterprises that grow or buy bush tomato and sell it to the food service industry or value-add and sell at farmer’s markets and online.

The volume of bush tomato on the market fluctuates greatly from year to year.

Map of current and potential growing regions

Uses

The fruit of the bush tomato plant is usually harvested when it is sun dried. The mature yellow fruit can be eaten fresh but generally the dried raisin-like fruit is sought for processing to make value-added product.

Bush tomatoes initially have a distinctive raisin or caramel taste, followed by a strong spicy aftertaste. Bush tomato is a good source of vitamin C, selenium and iron. The dried and ground fruit can be used as a savoury spice, and is coarse ground or fine ground according to the end product.

Bush tomato has three key end uses:

as a prime ingredient, supplied as whole dried fruit or ground to powder
value-added into industrial food flavourings and seasonings
value-added into consumer/retail products (such as sauces, chutneys, herbs and herb blends, biscuits, and as an additive for curries, salsas, meat crusts and dukkah).

Production Requirements

Growing regions

Bush tomato is native to the central deserts of Australia, in Western Australia, the Northern Territory and northern South Australia. A significant proportion of fruit reaching the market as bush tomato products is wild-sourced from the deserts of central Australia, over a two-month period of the year.

Bush tomatoes are cultivated in a diverse range of locations in South Australia, from the Eyre Peninsula to the Riverland. An attempt to cultivate bush tomatoes in the south east of the state was not successful. In the Northern Territory, bush tomatoes are cultivated at two sites, approximately 100km south and 200km north west of Alice Springs, respectively. The availability of irrigation at the cultivated sites has expanded the fruiting cycle of the plants from two to eight months of the year by manipulation of water scheduling.

Soil type

Bush tomatoes have similar requirements to other horticultural crops in arid environments: a site with deep sandy soils with good drainage, set on a flat or gently sloping plain. The key soil characteristics when selecting a site for cultivation are high water-holding capacity, ample soil depth and effective infiltration and drainage. All these will increase the soil’s ability to absorb and use any rainfall, and reduce the extent of irrigation required. Bush tomato plants are deep rooted (a survival adaptation to their arid native environment) and they send out extensive laterals in search of water; therefore, deep soils are favoured.

Climate

As a desert plant, the bush tomato can grow in very harsh environments, withstanding extreme temperatures, drought and some frost. It is well adapted to arid and semi-arid areas, and cultivation has been successful in temperate, seasonally dry areas such as the Eyre Peninsular of South Australia. The plant responds very well to managed irrigation, but will not tolerate humid or moist conditions.

Cultivation attempts in the south east of South Australia failed due to cold temperatures and too much rainfall, indicating the climatic limits of the species. The plant may experience some damage from frosts, and severe frosts can kill shoots in the first year of growth. However, the ability of bush tomatoes to sucker and reshoot from the rootstock makes the plant highly productive over time.

Varieties

There are no recognised varieties of bush tomato recommended for cultivation. Research indicates that there is a high degree of genetic diversity in the gene pool of wild bush tomatoes, which bodes well for developing varieties for cultivation.

The seed of Solanum centrale has a very low germination rate (less than 5%) but several methods have been developed to significantly enhance germination. There is considerable variability amongst the resulting seedlings, because it is an outcrossing species. Methods of clonal propagation from stems and roots, and tissue culture are under investigation. The Bush Tomato Handbook provides detailed information on plant selection, seed germination and propagation of bush tomato.

While S. centrale is by far the most used Solanum species in the industry, S. cleistogamum and S. chippendalei have also been harvested and marketed. Although the fruit of S. chippendalei are the largest of the native Solanums, the seeds are inedible.

Planting and crop management

Bush tomatoes have evolved to cope with their harsh natural environment. However, the plant responds well to soil modifications to improve organic content, soil pH and nutrient levels. Detailed information about soil preparation and management is provided in The Bush Tomato Handbook.

Access to good quality irrigation water is essential for commercial production of bush tomatoes. Although bush tomatoes have a natural tolerance to salinity, better growth and yield will be achieved with fresh water. In many seasons, irrigation will be required to ensure the crop produces a reasonable quantity of fruit. Further, the fruiting season of bush tomato can be extended from two to eight months with irrigation. Soil moisture monitoring instruments will enable careful water management to assist getting the best production from water resources.

For bush tomato enterprises in arid regions, irrigation water will most likely be sourced from groundwater, therefore it is critical that the water is tested before the planting is established. Water quality can affect plants, soils, irrigation equipment and general farm activities.

The bush tomato crop can be established from seed, seedlings or root fragments. Seedlings should be planted with 30–50cm between plants within the row, and 1.5m between the rows.

Irrigation is recommended to keep newly planted seedlings well watered until they are established; maintain consistent soil moisture content; and ensure water is available at critical crop development stages, such as flowering. Soil moisture monitoring equipment will help water management to be effective and efficient.

A fertiliser program, as detailed in The Bush Tomato Handbook, can help ensure the crop has adequate nutrition to support good plant growth and yields, and to replenish soil nutrient status.

Weeds, pests, and diseases

Other plant species will enjoy the good conditions provided for bush tomatoes, and can compete for light, moisture and nutrients with the crop. Research has demonstrated a seven-fold increase in fruit yield when weed competition was eliminated from an irrigated block of bush tomato. Weeds can also harbour pests and diseases that infest bush tomatoes; and make hand harvesting difficult. Weeds should be removed manually, chemically or by mowing the inter-row spacing.

There is a range of pests and diseases that may affect the plants and fruits of bush tomato, including aphids, whitefly, mites and nematodes. Details of potential pests and treatments are provided in The Bush Tomato Handbook.

Infrastructure Requirements

A cultivated block of bush tomato may require fencing, depending on potential vertebrate pests. Kangaroos and rabbits appear to do little damage, but cattle, horses, donkeys and camels can cause significant damage.

A source of water at the block will be required, and if the planting is large, an irrigation system will improve labour efficiency. Good quality water will be required for irrigation and for washing and cleaning the fruit. A hot water unit will be required for the washing water.

Depending on the size of the block, equipment and tools will be required for day-to-day maintenance of a block, for example weeding and shaping of the plants. The bush tomato sends out subterranean lateral roots, which abundantly come to the soil surface. This makes the crop appear unruly and poses a challenge for weed control by cultivation as the plants root system can be easily damaged. For this reason, manual weeding and spot spraying is recommended.

Many cultivated blocks of bush tomato are hand harvested several times throughout the season. Mechanical harvesting, with a modified cereal harvester, is under investigation and as at 2010 much improvement in the system was still needed. At present, the quality of hand harvested product is significantly better, but the efficiency of mechanical harvesting means that further refinement is worth pursuing.

Post-harvest facilities are required for washing, cleaning and drying the fruit, and for packaging the final product for transportation and/or sale. If the product is to be value-added, equipment for grinding will be required.

Markets & Marketing

Bush tomato has been described as one of the most marketable products emerging from the Australian native foods industry. A native foods industry stocktake published in 2012 concluded that the demand for bush tomato had increased consistently and now significantly outstrips supply. Cultivation is regarded as the only path to commercial success.

Several market opportunities have been identified for bush tomato. These included extensive use in the native food service and catering industries; online availability from at least fifteen companies as whole, ground or value-added product; shelf product in specialty tourist and food shops (a major market); and an ingredient in supermarket products, e.g. beef and bush tomato flavoured sausages at one major supermarket. The export market was also identified as important with seasonings and flavourings available throughout Europe, the UK and Asia.

While demand for the product suggests there is ample room for increased cultivation of bush tomato, overcoming the production issues seems to be the main limitation to industry development.

Risks & Regulations

Risks/challenges

Being a developing industry, there are two main challenges facing the bush tomato industry and limiting the profitability of the enterprise. First, propagating seedlings is difficult due to the low germination rate of seed, and high variability and low yield of seed-raised plants; and it is costly and difficult to produce plants from cuttings and/or tissue culture for large-scale field plantings. Second, there is not yet an efficient means of harvesting the crop. The lack of a purpose-built harvester increases quality control operations to achieve a quality product; and while manual harvest achieves a quality product, it is costly and difficult to retain a labour force for hand harvest.

A risk to the reputation of bush tomato is contamination of harvested product with the green fruit, which is potentially toxic and imparts bitterness. Mechanically harvested product needs to be adequately cleaned to remove foreign material, including green fruit; and correct plant identification is essential when harvesting wild bush tomato.

As an industry, the development of bush foods has a challenge safeguarding indigenous cultural heritage and intellectual property associated with traditional knowledge about the uses and lore of bush plants.

Regulatory considerations

There are no specific regulatory requirements for the production of bush tomato. Some producers of native foods choose to participate in Freshcare, which is currently the largest Australian on-farm assurance program for fresh produce that addresses on-farm food safety and quality, and environmental responsibility.

When processing raw product and value-adding, consideration should be given to food standards regulations, as administered by Food Standards Australia New Zealand (FSANZ) and set out in Chapter 3 of its Food Standards Code. Information about certification can be found at, but is not limited to, the websites of Freshcare and HACCP.