Native citrus brings hardiness to exotics

Native citrus hardiness giving strength to exotics

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Horticulturalist Darren Williams is 10 years into an experiment that could soon see new citrus varieties on the Australian market.

Horticulturalist Darren Williams is 10 years into an experiment that could soon see new citrus varieties on the Australian market.

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An Austraian citrus breeder is introducing disease, frost and drought resistance to commercial varieties thanks to the native finger lime's toughness.

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WHAT began as long-standing interest in native Australian bush foods has taken Darren Williams on a long journey of breeding native citrus disease resistance into mandarins, yuzu and blood oranges.

Horticulturalist Darren Williams has been breeding native citrus, such as the Australian fingerlime (Citrus australasica), desert lime (Citrus glauca) and Dooja (Citrus australis), with exotic varieties of mandarins, yuzu and blood oranges since 2010.

It is just now that he is beginning to see the fruits of his labours.

Read also: First edition citrus growers' guide now out

Australia has six species of native citrus, growing from the rainforest (Citrus australasica), to the desert (Citrus glauca).

"The desert lime is frost and drought hardy; it's the only xerophytic (desert) citrus in the world," said Mr Williams.

"What we're doing, by crossing them with regular citrus like mandarins or oranges, is to bring a lot of that hardiness to new varieties with novel looks and tastes.

"You can also screen the seedlings for diseases such as Alternaria brown spot, which can be a problem for coastal growers in Queensland," said Mr Williams.

It's not a short-term program.

Citrus breeding programs take a notoriously long time to bring a new variety to market, generally 10 to 15 years.

"We are trying to reduce this by using native citrus that fruit earlier and can be cutting grown because they are naturally drought and disease resistant," he said.

"Each hybrid is seed grown and can take from three to seven years for their first fruit.

A reddish-coloured hybrid fringer lime that fruited this year.

A reddish-coloured hybrid fringer lime that fruited this year.

"The 2010 trees are fruiting now and we've got two excellent looking trees with yellow and red fruit; both are Alternaria-resistant hybrids that are undergoing evaluation with a local company.

"We are actively seeking new collaborations with growers, the horticultural industry and also the Queensland government, as we believe it can be a boon for in coming decades."

He said similar but much larger research work was being done in the US in California to combat the disease citrus greening using Australian natives.

"They seem to do more research work in the US, it may be similar to what happened with macadamias yet, where we end up importing US cultivars back here to be grown commercially," said Mr Williams.

He said likely US breeders would breed the Australian native's traits into mandarins and then breed them back again to gain the classic mandarin shape.

A finger lime hybrid next to a native form of the fruit (on the right).

A finger lime hybrid next to a native form of the fruit (on the right).

Governments have wound back many regional research centres that used to focus on plant breeding for new varieties.

"But with diseases such as citrus canker and HLB (citrus greening) on our doorstep, we should be using our native genetics as breeding stock; researchers have shown four native citrus have excellent resistance to HLB.

"Our first hybrid to fruit was a large yellow fruit with a more subtle lemon flavour than the traditional sharp finger lime taste, also with hints of mandarin from one of the parents.

"It can be peeled like a mandarin and has vesicles inside like a fingerlime.

"Another one is red/orange skinned and is very juicy, way more than a finger lime," he said.

"This gives it the ability to be used in versatile ways; I think chefs will love it."

In Australia the finger lime is becoming popular in high-end restaurants and the Chinese have now discovered the delights of the caviar-like pockets of citrus the fruit offer, making them popular in both cooking and cocktails.

"We've also found a variegated mutation (sport) on a seedling and grafted that up," said Mr Williams.

"It looks fantastic but we'll have to wait until it fruits to see whether it will be headed for commercial applications."

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