The findings, the result of a five-year long research project at CSIRO, could help the fresh produce industry attract new consumers with more brightly coloured apples, and also market an even healthier apple, richer in anthocyanins.
Anthocyanins are compounds that give plants their red colour but they have also been shown to boost human health through their antioxidant activity.
The research, reported in the November issue of Plant Physiology 142:1216-1232 (www.plantphysiol.org/), used the latest molecular technology to measure how much particular genes were activated, or expressed, in apple skin as the fruit ripened and coloured.
The scientists at the CSIRO Plant Industry team focused on master genes that were activated by light. Apple growers have always known that apple colour is dependant on light as apples grown in darkness or even heavy shade do not turn red when they ripen.
"That made it very likely that the gene we were looking for requires light to be activated," said Dr Mandy Walker, leader of the team.
By identifying master genes that were activated by light, post-doctoral fellow Dr Adam Takos was able to pinpoint the gene that controls the formation of anthocyanins in apples.
"We found that in green apples this gene is not expressed as much as in red apples," said Dr Walker.
Working with apple breeders at the Department of Agriculture and Food in Western Australia (DAFWA), the scientists were able to show that fruit colour can be predicted even in seedling apple plants by measuring the form of this gene that is present.
"We now want to work out if there are other versions of this gene, which are more stable and less controlled by the environment. We know that some apple varieties are not so sensitive to light, like Fujis for example," Dr Walker told AP-Foodtechnology.com.
If the team finds another version of this colour gene that is less sensitive to light, it could enable breeders to select varieties and start a breeding programme to produce a more evenly coloured apple.
For growers, even colour is one of the important factors in success on the market. Dr Walker noted however that it would take between 15 and 20 years before a new variety reaches the marketplace. But new varieties have been shown to boost sales. For example, the Pink Lady variety, recently developed in Australia, is now one of the most popular varieties.
And industry needs to introduce new varieties if it wants to boost stagnant sales. Research by apple and pear growers in Australia in 2005 found three in five female grocery buyers had not changed their apple consumption.
Researchers in New Zealand's Hortresearch have also been working to identify a gene for colour and are expected to publish their findings in coming months.
Research institutes are getting government and industry funding to develop new apple varieties in the wake of rising competition from markets like China. The country surpassed the US a few years ago as the world's leading apple producer.
