Taming Wild Limes
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spectrum The three new citrus fruits, the Outback, Sunrise and Blood limes, introduce an appealing range of colour, size and shape to the market. valuable genetic characteristics for improving existing citrus varieties,’ Sykes says. ‘We have used them as an additional germplasm resource in our citrus breeding program. ‘But more recently, encouraged by the expansion of the Australian native foods industry, and working in partnership with people involved in that industry, we have been taking a different tack. ‘For the past decade or so, we have been investigating the potential for developing new crop plants from these wonderful native limes, and their hybrids, using traditional breeding methods of cross- pollination and selection. ‘At Merbein, starting with native trees from our arboretum, we have now bred lime varieties that can be considered distinct citrus fruits in their own right. It is an exciting development, and very timely, Taming wild limes given the unprecedented consumer interest in native Australian foods.’ ost Australians would be surprised to species that is xerophytic, or naturally Well-bred limes M learn that we have six native tree adapted to withstand drought. species that are true citrus, closely related to Seedlings develop an extensive root Three of these varieties – the Blood Lime, conventional oranges, lemons, limes and system before making vigorous above the Sunrise Lime and the Outback Lime – mandarins. ground shoot growth. During extreme are being evaluated in commercial orchards These native limes, long collected in the drought, the plant’s leaves simply fall off (to in Australia by Australian Native Produce wild by Aboriginal people, early settlers and, avoid water loss) while it is thought that the Industries (ANPI). Andrew Beal of ANPI was one of the first people to recognise the more recently, by a burgeoning native food leafless twigs carry on some photosynthesis. potential of Sykes’s research into native industry, have given rise to colourful new The desert lime can tolerate temperature limes, some 10 years ago. citrus varieties, and their commercial extremes of 45 to –24ºC, without injury, ‘Using the CSIRO-bred varieties, we have, production is on the horizon. and is also salt and boron tolerant. It seems over several years, established more than How did this transformation – from to be highly resistant to Phytophthora root 16 000 lime trees throughout the citrus- untamed desert and rainforest denizens to rot. Its yellow-green lime-like fruit matures neatly aligned commercial orchard trees – growing areas of Australia,’ Beal says. in just 10-12 weeks, the shortest flowering come about? And what taste sensations and These trees will supply the fruit for ANPI’s to fruiting period of any citrus species. Little culinary delights can we anticipate? manufactured food products which are wonder the desert lime has attracted the Horticultural scientist and plant breeder at proving popular both here and overseas. attention of citrus breeders worldwide. CSIRO Plant Industry, Dr Steve Sykes, says Growers, under contract, made their first Five other citrus species, previously CSIRO researchers first took an interest in commercial harvest last year and the classified as Microcitrus species, occur in native limes to see if their special company intends to treble the number of Australian rainforests, from Cape York to characteristics, such as salt tolerance, trees under cultivation to meet the expected northern New South Wales, and they disease resistance and novel colours, could demand. produce a range of fruit types with a be bred into conventional citrus fruits. Sykes says that despite the three new pleasant but acidic juice. The small fruits can limes having a lemon-like acidity, each has Desert and rainforest origins be round or finger-shaped and vary in its own unique flavour. They make good Sykes, who is based at Merbein in north- colour, one variant being a striking sauces, preserves, marmalades, chutneys, western Victoria , says the desert lime (Citrus burgundy hue. The dwarf, shrubby habits of syrups, garnishes, confectioneries and glauca) is a good example. It grows mostly these species suggest they could be a useful beverages. in the semi-arid inland regions of source of genes for breeding dwarf varieties. The Outback Lime is an improved variety Queensland, New South Wales and South ‘We were initially drawn to these native of desert lime that Sykes selected for its Australia and is the only known citrus limes because we saw them as a source of large fruit (for a desert lime), high yield, lack 6 Ecos 107 April–June 2001 spectrum of thorns, upright habitat and uniform ripening time. Its natural tendency to drop ripe fruit suggests it may also be suitable for What’s happening mechanical harvesting. The green spherical fruits, each up to 20 mm across, have a thin to India’s skin and turn yellow as they ripen in early summer. vultures? The Sunrise Lime arose from a seedling selected from a hybrid of the native finger A DRAMATIC decline in India’s vulture lime and a calamondin (which is itself a populations has sparked an international mandarin-cumquat hybrid). It boasts dark investigation into its cause. glossy-green leaves, short spines and According to the Bombay Natural golden pear-shaped fruit. Initial investigations suggest a pathogen, History Society (BNHS), a recent survey The Blood Lime also has its ancestral such as a virus, could be the cause of found that more than 90% of Indian origins in coastal rainforest, being selected declining vulture populations in India. white-backed and long-billed vultures from a cross between a sour-mandarin have been wiped out in at least 17 key hybrid and a seedling of the pigmented locations. In some areas none remain. While investigations continue, human variant of the finger lime (C. australasica). Dr Andrew Cunningham, a veterinary and animal carcasses in India are As the name implies, it has eye-catching pathologist at the Zoological Society of creating a new problem. blood-red fruit, which are oval-shaped. London, is working with the BNHS, the ‘The decline of vultures is worrying They ripen in winter. UK Royal Society for the Protection of from a biodiversity viewpoint, but also Sykes and Beal are confident that these Birds, and the Poultry Diagnostic and because a great number of carcasses are Australian newcomers to the citrus industry Research Centre, Pune, to help being left uneaten,’ Cunningham says. will fill an important niche, catering for the coordinate the investigation. Vultures play an important role in growing interest in so-called bush foods. By Cunningham says that in areas where scavenging human and animal domesticating the native limes they believe declines are marked, abnormally high carcasses. For example, India’s 76 000- harvesting pressure on wild trees will be rates of nesting failure and adult, strong Parsees community does not eased and patchiness in the quality and juvenile and nestling mortality have bury its dead; bodies are placed in availability of fruit for processing will be been observed. ‘towers of silence’, for the bones to be smoothed out as the area of native lime ‘Also, vultures with obvious signs of picked clean by vultures. orchards expands. clinical illness – lethargy and ‘Another concern is the increase in intermittent, but often prolonged Contact: Dr Steve Sykes, (03) 5051 3100, number of feral dogs indulging in the periods of neck drooping – have been [email protected]. now abundant food supply. These seen,’ he says. ‘It has been reported by animals can carry diseases such as Steve Davidson the BNHS that birds exhibiting these rabies, which further threaten public clinical signs invariably die after a period health,’ Cunningham says. of 30–32 days of illness.’ Researchers are also concerned that While there may be several reasons for any infectious pathogen in the vultures localised declines, the BNHS has shown has the potential to spread. that normal ecological factors such as ‘The ranges of species in the genus food supply and habitat availability are Gyps overlap from India through central not constraining the vulture Asia and the Middle East to South Africa populations. and Western Europe, and birds travel Initial investigations suggest a widely,’ says Dr Debbie Pain, head of pathogen, such as a virus, could be the international research at the Royal cause. To find out, Cunningham and Society for the Protection of Birds. Indian authorities have turned to ‘Should an infectious pathogen spread, CSIRO’s Australian Animal Health the ecological impacts could be even Laboratory at Geelong in Victoria. more devastating.’ ‘The laboratory has a proven track record in detecting new and emerging This work is supported by the Royal diseases, particularly those with the Society for the Protection of Birds. potential to infect livestock,’ laboratory Contact: Andrew Cunningham, director, Dr Mike Rickard, says. [email protected], or Judith ‘And it is one a handful of facilities Maunders (03) 5227 5426, Plant breeder, Dr Steve Sykes, with one of the anywhere in the world where research [email protected] new citrus varieties, the Outback Lime, a tree can be safely carried out on foreign with upright growth habit, no thorns at animal diseases and pathogens.’ Judith Maunders maturity, and berry-like fruit. Ecos 107 April–June 2001 7.