LINDELL BEACH, B.C. – Scientists have published a draft sequence of the apple genome.
“The genome sequencing has revealed the total number of potential genes related to disease resistance, fruit development and organoleptic (sensory) properties that are important for the apple as a commodity,” says Amit Dhingra, assistant professor and horticultural genomicist from Washington State University.
“Now apple researchers worldwide can draw from this information and find gene-based solutions to the unique issues that face their geographical areas.”
Dhingra is part of a team of scientists from Italy, France, New Zealand, Belgium and the United States that recently published its findings inNature Genetics.
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Some of the sequence information came from a genetically simpler derivative of the Golden Delicious apple.
Dhinga’s team sequenced and analyzed this unique genome, in which all duplicated chromosomes are genetically identical. The information was used to validate the sequence of the more complicated heterozygous Golden Delicious apple.
“The heterozygous Golden Delicious apple is the apple you find in the store,” Dhingra said.
“When the tree flowers, it produces male (pollen) and female gametes. The chromosome number is reduced to half in the resulting gametes, which is termed the haploid state. In a normal situation, the pollen from one variety combines with female gamete of another apple variety after pollination, restoring the original chromosome number in the resulting seed.”
He said it is also possible to generate a new plant with just the male or the female gamete. The doubling of the chromosomes can be induced chemically or can happen naturally. The resulting plant is called a double haploid.
“The strain we are using for sequencing is a naturally derived double haploid, which was developed by our collaborators in France.”
Dhingra said the breeding of perennial crops has relied on breeders’ ability to follow traits through generations using their sensory perceptions.
“While we have great varieties (more than 7,500 known cultivars) as a result of that, the consumer and the market needs defined product suited to different geographical regions, economies and demographics,” he said.
“The availability of a genome provides an opportunity now to cater to such needs.”
He said genetic research had previously identified regions of the genome that were termed molecular markers with which a breeder could track a desirable trait that would be present in the fruit even at the seedling stage.
“Now that we have all the gene information in a genome, gene-linked markers can be used to track the inheritance of traits,” he said.
“One prerequisite for utilizing this information is to have the knowledge of each gene’s function. Earlier the breeder had to grow thousands of seedlings all the way to a tree to wait and observe fruit related traits. Now, with the gene-based information, a breeder can weed out the undesirable seedlings and only keep the selected few that possess the desirable genes. It increases the efficiency of breeding. A breeder can focus on multiple traits using function guided gene-based markers.”
Canada was not directly involved in the sequencing research, but Dhingra said he is working with researchers at the University of Guelph in Ontario on the post-harvest biology of apples, which integrates biochemistry approaches with genomic sequence information.
The research team also compared the apple genome with that of pear, peach and grape.
“Apple and pear belong to the same sub-family and share a 96.35 percent similarity. Grapes were found to be the most distant from members of the Rosaceae (apple, pear and peach).”
ALL ABOUT APPLES
•The domestic apple is one of the most important fruit crops in the world’s temperate regions
•It is a member of the Rosaceae plant family, which includes other commercially important fruit species such as cherry, pear, peach, apricot and strawberry
•At least 55 million tonnes of apples were grown worldwide in 2005 with a value of about $10 billion
•According to Statistics Canada, in 2009 Canadian farms produced 413,096 tonnes of apples for a farmgate value of $176 million
