The finger lime is a citrus relative, scientifically named Microcitrus australasica. Finger limes are native to Australia and are so named because the fruits are long and fingerlike in shape (see figures 1 and 2). Finger limes belong to a group of similar citrus relatives, all originating from Australia with common names such as Round lime, Mount White lime, Kakadu lime and Russell River lime.
In Australia, finger limes have become popular as “bush tucker,” a category of foods that come from the wild and command high prices as a specialty crop. In addition to domestic consumption, a significant amount is also exported to Asia and Europe. In the United States, finger limes have remained rare, only occasionally found as a citrus curiosity and cultivated to a limited extent in California and Florida. But perhaps these funny, little fruits have more than meets the eye.
The finger lime tree is characteristically very thorny. It usually has shorter internodes than conventional citrus cultivars with thorns as long as the leaves at every node (see Figure 1).
The fruit is oval in size and, depending on the cultivar, can range from 1.5 to 4 inches in length. In spite of finger limes being native, there are only a handful of named finger lime varieties from Australia.
Upon cutting open a finger lime fruit, out will spill little round balls. These are the fruit’s juice vesicles. Finger lime vesicles are spherical, unlike the long and narrow juice vesicles from typical citrus (see Figure 2). Also, unlike conventional citrus, finger lime juice vesicles are easy to separate. Because of their appearance, they have been marketed as “citrus caviar.” Chefs at high-end restaurants are using this citrus caviar, which is said to accompany seafood very well, as a plate garnish and as a component of cocktails. Like limes and lemons, the finger lime is an acid fruit. The citrus caviar produces crunchy, tart little bursts of flavor when consumed.
Horticulturally, finger limes are both graft and sexually compatible with citrus. To retain the characteristics that deter psyllid feeding and HLB tolerance or resistance, new genetic combinations are being created at the Citrus Research and Education Center (CREC) by hybridizing finger limes and their close relatives with conventional citrus. Using both conventional and somatic cell fusion techniques, a large population of diploid, triploid and tetraploid hybrids have been produced. Hybrid status is confirmed using molecular markers.
Diploid and triploid progeny were created using conventional breeding between selected monoembryonic citrus cultivars with pollen obtained from finger lime accessions at the USDA-Agricultural Research Service National Germplasm Repository for Citrus and Dates in Riverside, California. Tetraploid progeny were created using the process of somatic fusion, which is an additive process that combines the DNA of two parents. It is hoped that this process will be able to create new citrus cultivars that combine the best attributes from each parent: the spherical juice vesicle trait from the finger lime coupled with lower acidity, larger size and sweetness from the other sweet orange/mandarin parent (see Figure 3).
- By Manjul Dutt, Ethan Nielsen and Jude Grosser, citrusindustry.net
- Photo from shanleyfarms.com