Thursday, June 29, 2017

Origins of the Stone Fruit Species

As global competition for fresh and processed fruit increases, breeders and producers also have to deal with the effects of climate change and more pathogens, especially sharka disease, appearing in their orchards. EU-funded research traced the origins of stone fruits to discover genetic clues for better disease resistance.

In an effort to learn more about stone fruits, European scientists have traced the origins of the beloved apricot all the way back to wild Asian species. Their investigations reveal several significant evolutionary events and identify natural gene pools for higher resistance to the most serious threat to apricot and plum harvests in Europe today – sharka disease.

Studying the genetic make-up of domesticated plant and animal species, and comparing them to their wild relatives helps scientists understand how populations diverge and adapt over time and in different climates and conditions.

Credit: © M.studio - fotolia.com

Apricots are an important fruit in the Northern hemisphere. In France, for example, it is the third-largest fruit crop with some 12 800 hectares under cultivation. Italy, France and Spain are the principle apricot-producing countries by weight in Europe. But pathogens like the Plum pox virus (PPV), which causes sharka, pose a huge threat to production everywhere.

Yet very little is known about the history of how the apricot tree was domesticated for farming and its resistance to sharka over time. Veronique Decroocq, a scientist at INRA in Bordeaux, took up the challenge with colleagues in the EU-funded STONE project to map the genetic landscape of domestic and wild apricot trees worldwide.

“We used 18 specific markers to genotype a collection of 230 wild trees from Central Asia and 142 cultivated ones, a representative sample of the cultivated apricot landscape around the world,” says Decroocq. She received a Marie Sklodowska-Curie research staff exchange grant to study the genetic diversity of stone fruit trees, such as apricots, peaches and cherries in Europe, the Caucasus and Central Asia.

The search for sharka resistance

Natural forests of wild apricot trees are expected to carry a higher level of resilience to pathogen attacks and climate changes thanks to their richer genetic diversity. A series of PPV inoculation tests was carried out on the apricot trees, as part of the four-year STONE project, to test this assumption.

Genetic markers during the testing revealed the highest levels of diversity in Central Asian and Chinese wild and cultivated apricots, which confirmed Decroocq’s suspicion that the original species can be traced back to this region. “There was a clear branching out of cultivated apricots between Chinese and Western varieties or ‘accessions’. We also noted distinct differences between cultivated and wild apricots.”

After some analysis, the STONE team now believes apricots underwent two independent ‘domestication events’ stemming from the same wild, ancestral gene pool. A genetic subdivision was also noted in apricots native to Central Asia, which showed higher resistance to sharka.

“These findings help us understand the domestication history of cultivated apricots and provide valuable evidence that a rich and exploitable source of genetic diversity and disease-resistance lies hidden in wild apricot varieties from Central Asia,” says Decroocq.

That is also potentially good news for producers in the € 260 billion (US$274 billion) a year global fruit and vegetable processing market.

These and other key outputs of the project’s research, such as a phytosanitary survey of fruit tree species in the Caucasian region, and the identification of key genes involved in peach fruit quality, would not have been possible without the EU staff exchange grant. “It has provided a chance to advance this little-known field and one day develop more effective disease-resistant stone fruit production,” concludes Decroocq.


Contacts and sources:
EC Research and Innovation

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