Lime a zesty key to drought tolerant crops

You might think a lime is simply a zestyaddition to your favourite drink.

But Griffith researcher Dr Sarah Ashmore knows for a fact it holds the key to so much more.

Citrus is one of the most significant fruit crops in the world, yet seeds from many of the wild species of Citrus have not been systematically collected nor are they represented in national or international seed banks.

Dr Sarah Ashmore, from Griffith’s Environmental Futures Research Institute, is determined to see this changed.

A Citrus australis round lime

She said that, of the 31 Citrus species worldwide, 10-11 are found in Oceania. Six of these are found in Australia, with the remainder located in PNG and New Caledonia. Seeds from none of these species have been collected and secured in seed banks.

“It is vital to store Australia’s six native citrus species, as they are not found anywhere else in the world. These are the wild relatives of the citrus fruit we buy in our grocery stores,” she said.

The six wild citrus species in Australia – Citrus australasica (Finger Lime), Citrus australis (Round Lime), Citrus garrawayi ( Mount White Lime), Citrus glauca (Desert Lime or Lime Bush), Citrus gracilis (Humpty Doo lime) and Citrus inodora (Russel River Lime) — are only found in restricted locations in the wild.

“Getting these fruits into our seed banks is important to secure this untapped genetic diversity which is vital to our future global food security,” Dr Ashmore said.

“The crops upon which we currently depend may not be adapted for changes in climate or new pests and diseases.

“Scientists can draw on the genetic traits of the wild ancestors of our crops for continuing development of new and robust crops. This relies on a comprehensive collection of seed from these ancestors being available.”

Identifying the gaps

Currently a Global Conservation Strategy for Citrus Genetic Resources is being developed. Dr Ashmore hopes her research will help identify the gaps in current global collections of Citrus, as well as their crop wild relatives in Oceania, and lead to the conservation of all citrus before they disappear.

“The Citrus taxa from Oceania are recognised locally as valuable and are produced on a small scale as local crops and sold in processed foods and cosmetics. A very limited amount of work has also shown the value of these for the development of hybrid varieties and improved rootstocks for the citrus industry,” Dr Ashmore said.

“The identified characteristics in these taxa that are useful for future crop improvement include drought tolerance, salt tolerance, boron tolerance, and red flesh. Red flesh is used in the production of niche market preserves and sauces.

“Long term collections of these crop wild relatives will ideally be stored in the form of seed but for some tropical species of citrus it will be necessary to use cryopreservation to store the seeds or extracted embryos.”

Cryopreservation involves freezing the seed or embryo in liquid nitrogen at -196oC

Cryopreservation involves freezing the seed or embryo in liquid nitrogen at -196^oC, well below the -20^oC traditionally used in seed banks such as the Global Seed Vault at Svalbard in Norway. When stored as embryos, the plants can only be regenerated through tissue culture methods in controlled environment growth rooms.

Dr Ashmore’s research is being undertaken in close association with the Australian Seed Bank Partnership, the International Society for Horticultural Science and the Global Crop Diversity Trust.