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Why Do Some Strawberries Turn a Ghostly Shade of White?


Strawberries are not always red. Native to the Himalayas, Fragaria nubicola can produce a vibrant red or ghostly white fruit; another species, F. vesca, can produce a white fruit with bright red seeds alongside the traditional red variety. What gives some strawberries such a ghostly pallor?

An answer has been uncovered by scientists wondering about the genetic material of the humble strawberry. There are numerous types of fruit, and some carry five times more chromosomes than others. Strawberry scientists think this means that as plants evolve, they acquire extra genes that could provide a playground for unusual new traits.

While core genes run the plant’s day-to-day work, the extras can be altered to give them a new shade of pink, new resistance to drought or particularly prickly leaves – whatever the strawberry’s unique environment demands.

Inside An article published Monday in the Proceedings of the National Academy of Sciences, biologists reported that they sequenced the genomes of a handful of strawberry species and identified a set of genes common to all of them that represent the core genome of the strawberry. Along the way, the researchers identified a number of mutations that turn the strawberry white while keeping the taste and aroma the same. The findings open the door to understanding how strawberries manage their cumbersome genetic heritage, as well as revealing the possibility of more targeted breeding.

Patrick Edger, professor of horticulture at Michigan State University and author of the new paper, said strawberries grow wild in a variety of places, such as the Alaskan and Southern California coasts. But they probably originated in Asia. For this study, scientists collected samples from 128 wild strawberry plants in China and sequenced their genes, looking for commonalities between species.

While examining the data, they made a surprising discovery. Dr. “It was very clear that there was another species that no one had detected before,” Edger said.

In addition to a number of strawberries known to science, another new species was found among the samples collected from nature. Genetic analysis showed it to be different from the others, and the plant looked different too, with thicker leaves that were light green on the underside, among other changes. (The new species was named Fragaria emeiensis.)

The scientists found that 45 percent of a strawberry’s genes are shared among the 10 species studied in the paper. This means that the remainder of more than half of a strawberry’s genetic material is used to adapt a species to its particular location and situation. In the future, breeders can help strawberry farmers solve problems such as drought by bringing these genes into existing commercial varieties.

Dr. โ€œThis is something that me and collaborators in the larger strawberry community will begin to dive into this dataset to understand,โ€ Edger said.

The research also pieced together the genetic puzzle that causes some types of strawberries to turn white. The team found that the lighter fruits were linked to mutations in a gene called MYB10, which controls the production of pigments called anthocyanins. Lower anthocyanin levels are expected to result in a paler color.

In this study, each of the strawberry species had two sets of chromosomes. Later, Dr. Edger and colleagues plan to focus on species with eight sets of chromosomes to investigate how the extra genetic material is used and to continue to clarify the composition of the core genome.

As scientists better understand what makes fruits what they are, Dr. Edger expects strawberry cultivation to be more precise, not just in matters of practical importance to farmers.

“Many breeding efforts have focused on yield,” he said. But more and more breeding programs are trying to improve the flavor of strawberries.

Apples are notorious for reaching a low flavor appeal a few decades ago, when the beautiful, tough but tasteless Red Delicious apples were one of the few choices available in grocery stories. These days, thanks to the efforts of plant breeders, it’s not hard to find apples in a wide variety of colors and shapes that are full of flavor.

“I guess so,” said Dr. Edger, “strawberries will be the same in 10 to 20 years.”



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