IMPROVED LEMON AND LIME VARIETIES
SCIENTIFIC NAME: Citrus species
FAMILY: Rutaceae
The lemon was introduced into Australia in 1788 by Captain Cook and thrived in the coastal climate where it was widely planted as the colony expanded.
Principal uses of lemons and limes include the making of lemonade, cordials, soft drinks, frozen lemon concentrate, as a garnish for fish and meats. It is also used for a wide variety of culinary preparations and as a flavouring for jams, jellies, marmalades and preserves. Principle by-products are citric acid from the juice and pectin, and oil from the rind. Unless new uses can be found for lemons including export markets, their acreage will not greatly increase, because they cannot be eaten as fresh fruit. Its main constituent, citric acid, can be produced synthetically at a low cost, and returns from its by-products seldom equal the production costs of the raw material.
On a world-wide basis, the United States, Italy, Spain and Argentina are large producers of lemons while Mexico and Brazil are the two big lime producers.
PRESENT AND FUTURE IMPORTANCE OF LEMONS AND LIMES IN AUSTRALIA
In Australia, the lime is comparatively new as a commercial fruit, with a small but growing acreage. Statistics for lemons and limes are therefore grouped together. The total Australian production in 1986 was 46.4 kt from 581 thousand trees worth $A11.7 million, of which $A2.1 was exported. Both in production and value, lemons and limes constitute 7 to 8 percent of the Australian citrus crop. The 1985-86 production included using 13.8 kt as fresh fruit, 28.4 kt for processing and 3.8 kt exported. Imports as fresh and dried fruit in the same period amounted to $A1.87 million and the juice $A0.54 million.
New South Wales is the largest producing State with 719 ha of lemons in December 1985, of which 88 percent was Eureka and 10 percent Lisbon. Total area planted to limes was 62 ha, of which 50 ha was non-bearing (Forsyth, 1986). Since 1974, lemon production in NSW has declined by 607 ha or 48 percent due to oversupply and low prices for processed juice. The poor demand for lemon juice is causing South Australian growers to decide on the fate of some of the 232 ha of Eureka and 12 ha Lisbon grown in that State (Gallasch, pers. comm.).
In Victoria, the important lemon-growing districts are Sunraysia which grows Lisbon and Eureka (3:1) and the mid-Murray including Swan Hill, Cobram and the Hills area around Melbourne where Eureka and Lisbon are grown in 3: 1 ratio (Thornton, pers. comm.). In Queensland, the most important lemon-growing district is North Moreton which has three quarters of the State's acreage with Meyer lemon accounting for half the lemons grown, with the other half comprising Villafranca, Eureka and Lisbon. The latter three varieties are also grown in Central Burnett, another important district. Only 7000 lime trees are grown in Coastal Queensland. (Chapman, pers. comm.).
ADVANTAGES AND DISADVANTAGES OF PRESENT VARIETIES
Due to the current downturn in processing lemons there is a glut in the fresh market.
Fruit must be attractive, of good internal quality, medium-sized (smaller counts for some export markets) and a larger proportion of fruit produced in summer when returns are high. Ilkin (1974) listed the lemon and lime varieties grown in the country shown in (Table 1).
Some of the important commercial ones are considered below:
Eureka Lemon:
A major world variety originating in 1877 in California, which is thornless and precocious. In coastal areas it bears a number of crops annually, while inland it produces a main winter crops followed by a small summer crop. Fruit cures and keeps well after harvesting. Trees are usually smaller than Lisbon and not as cold-hardy.
A number of clones have been selected overseas and in Australia, including nucellar budlines which have greater vigour and are normally free of viruses. Taylor and Lambert are two promising nucellar selections made in New South Wales. At present, Eureka is grown on rough lemon rootstock and produces heavy crops. The disadvantages of using rough lemon rootstock are its susceptibility to phytophthora root and collar rot especially in replant soils. Trees also become very big and produce large, somewhat rough fruit. Favoured rootstocks like Poncirus trifoliata, troyer and carrizo citranage and Swingle citrumelo are incompatible with Eureka, producing a yellow ring condition which can kill trees in a few years. On the coast, Eureka is also susceptible to citrus scab because sprays which control the disease in the main crop are easily missed on subsequent flowerings.
Lisbon Lemon:
A major world variety that originated in Portugal and is hardier and better-adapted to the cold and heat of southern inland Australia. Trees are vigorous, large, thorny and productive. Fruit is somewhat smaller, smoother and less ribbed than Eureka. The main crop is produced in winter with a very light summer crop, if any. The Frost Lisbon is an important nucellar clone grown around Sunraysia. It has fewer thorns but carries exocortis virus which is also present in Munroe Lisbon. Prior and Doncaster are other important clones. Lisbon is compatible with P. trifoliata and the citranges. Its main disadvantages are the thorny trees which make it difficult to harvest and the production of a negligible summer crop.
Meyer Lemon (C.meyeri):
A natural hybrid between a lemon and most probably an orange, Meyer lemon is popular in coastal Queensland and backyards around Sydney. It is less susceptible than the lemon to frost damage. Its advantages are production of off-season crops and attractive fine-textured fruit with high juice content. Its disadvantages are tender, juicy fruit which cannot withstand handling, transport and storage without serious losses. It also does not cure well, and because of its somewhat low-acid content is not acceptable to some consumers when lemons are available. It is also a symptomless carrier of tristeza and should be tested free from virus.
Villafranca Lemon:
Originated in Sicily and looks similar to Eureka. Villafranca is favoured in Queensland because of its summer cropping. At Gosford, Sarooshi (unpublished data) found its main and summer crop yields were better than those of Lisbon and Eureka, but juice yield and quality was not as good and it had a thicker rind. In Queensland it is susceptible to a rind breakdown during prolonged wet weather in March-April.
Tahiti Lime (C. latifolia):
Also called persian or bearass lime is a hybrid of lime x lemon or citron. This large-fruited lime is the main variety grown in coastal Australia due to its resistance to tristeza virus, cold tolerance which equals that of the lemon and a more robust tree. Fruit is used fresh but is unsuitable for lime cordial product in Australia.
It is susceptible to lemon scab and if left on the tree past maturity, breaks down at the stylar end. Wood pocket disorder was reported by Nauer et al (1984) to be a genetic problem in most large-fruited limes, leading to tree decline in 12 to 14 years or sooner in desert areas. This disorder has not been recorded in Tahiti limes in Australia.
West Indian Lime (C. aurantifolia):
This small-fruited lime has excellent fruit quality and is the main processing variety throughout the world. At present it is not cultivated because its small size makes harvesting costly. It is very cold-sensitive and is also very susceptible to tristeza virus. Currently it is used as an indicator plant for this virus.
Buds of lemons and limes which were supplied in the last two years to nurserymen and growers in various States from the mother tree block at Dareton, give a good indication of varietal demand (Table 2). Demand for Eureka is twice that of Lisbon and stable, while demand for Meyer lemon and Tahiti lime is increasing. Most of the Meyers are used for backyard plantings.
RESEARCH INTO OVERCOMING SOME VARIETAL PROBLEMS
• In a rootstock trial using Taylor Eureka, Sarooshi (unpublished data) found Benton citrange, citremon and red rough lemon 502 were promising rootstocks. Trees on both Benton and citremon were considerably smaller than on rough lemon, producing high-cropping efficiencies, juice content, citric acid/t and thinner rind.
• Summer production of lemon and persian limes by the "Verdelli" process has been reported by various workers (Maranto and Hake, 1985; Barbera et al, 1981; Goodall and Silveira, 1981). Research into summer production of Eureka is being undertaken at Vanco (Hutton, 1986). Similar work should also be undertaken for the Lisbon.
• The Frost nucellar Lisbon which has small thorns is being shoot-tip grafted at Rydalmere to free it of exocortis virus.
• Sarooshi (unpublished data) found the canopy area of mature Prior Lisbon on P. trifoliata was reduced by a third when trees were inoculated in the nursery with mild strain dwarfing factor 3538. Cropping efficiency was slightly increased.
• Paclobutrazol (PP333) may have an application in reducing or preventing large tree sizes in Eureka or Lisbon on rough lemon rootstock. Aron et al (1985) found that sprays of this chemical markedly reduced total growth, shoot number and internodal length of Minneola tangelos.
• Barkely (pers. comm.) is attempting to cross-protect West Indian limes by inoculating them with mild strains of tristeza. If successful, this may lead to commercial plantings of this variety in coastal areas.
• The Eustis, a hybrid between a West Indian lime and Marumi kumquat bred by Swingle, may be worthy of introducing into Australia for testing. Hume (1954) reported it to be a high grade lime able to withstand as much cold as the sweet orange.
BREEDING REQUIREMENTS
• There is a need to breed scab resistance into the Eureka variety. The Perrine lemonlime, a hybrid of West Indian lime and Genoa lemon which is reported to be resistant to lemon scab (Elsinoe fawcetti), Reuther et al (1967) could be introduced as a gene source for breeding purposes.
• Lisbon needs to be bred free of thorns.
• Though not as important as the first two requirements, breed better keeping and handling qualities into the Meyer lemon while maintaining its attractive appearance.
There is a limited genetic variability within Australia for the breeder to achieve some of the desired characteristics. It may therefore be necessary to import material from some of the countries listed by Gulick and Van Sloten (1984) in "Directory of germplasm collections - Tropical and Sub-tropical fruits and tree nuts".
TABLE 1: LEMON AND LIME VARIETIES IN AUSTRALIA, 1974 (R. Ilkin)
| LEMONS | LIMES |
|---|---|
| Esmond Seedless | Djeruk Keprok |
| Eureka (various) | East Indian |
| Genoa | Imperial |
| Hoolong Long | Kaffir |
| Ideal | Linau Lankau |
| Lambert Nucellar Eureka | Limau Paruit |
| Lisbon | Palestine Sweet |
| Lisbon-Frost, Doncaster, Prior etc. | Persian Sweet |
| Lorama | Sepora |
| Meyer | Selanga |
| Messina | Tahitian |
| Rosenberger | West Indian (syn. Mexican) |
| Related to Lemons | Sweet Lime (C. limettoides) |
| Citrus acida | Related to Limes |
| Rangpur | |
| Columbia Sweet Lime |
TABLE 2: NUMBER OF BUDS SUPPLIED TO NURSERYMEN AND GROWERS BY NEW SOUTH WALES - HORTICULTURAL PROPAGATION CO-OP. SOC. LTD. FROM MOTHER TREE BLOCK, DARETON
| 1985-86 | 1986-87 | ||
|---|---|---|---|
| Eureka Lemon A | 38,335 | 35,630 | Stable |
| Lisbon Lemon A | 19,035 | 17,230 | Stable |
| Meyer Lemon S | 14,945 | 17,300 | Increasing |
| Tahiti Lime S | 17,360 | 23,605 | Increasing |
| A - Approved source S - Selected Source | |||
DATE: May 1993
* * * * * * * * * * * * * * *
