A UK scientist has discovered clumps of previously-unreported
callus hairs growing in the flesh of mature apples of Fuji and
closely-related varieties, which may have storage implications for
commercial growers.
Scanning Electron Micrograph of Fuji apples showing extensive branching of callus hairs.
“To find out something new about apples is really
exciting”, says Dr Mary Parker of the Institute of Food
Research. “Apples have been cultivated for about as long as
human history and Fuji apples are particularly prized for their
crispness, sweet flavour and keeping qualities “.
The variety was developed in Japan, but is widely grown in the
Southern Hemisphere, China, Southern Europe and the USA. It is a cross
between Ralls Janet and Red Delicious, and is itself used as a parent
in breeding programmes.
“The reason these hairs have not been spotted before
is probably because the full extent of their growth can only be
appreciated in 3D”, says Dr Parker.
Dr Parker used light microscopy and scanning electron
microscopy to reveal clumps of small, elongated and branched cells in
the air spaces between cells. She named them callus hairs because of
their resemblance to the cells which make up the white velvety tufts
(sometimes mistaken for fungus) which develop around the seeds in some
apple varieties.
The presence of callus hairs filling the airspaces of mature
Fuji could account for the susceptibility of late-harvested apples to
internal browning. Unrestricted gas flow through the fruit is vital for
successful long-term storage particularly in modified atmospheres.
Callus hair growth, with its own oxygen requirement and carbon dioxide
output, may reduce the efficiency of gas transport through the spaces
between cells.
“With this new knowledge, breeders could pick parent
varieties with all the positive traits of Fuji apples but with
less-developed callus hairs”, says Dr Parker. The presence or
absence of callus hairs could also be used to test the authenticity of
dried apples labelled as Fuji.
Preliminary studies have shown that callus hairs are rich in
phytonutrients but may also contain allergens. Further investigations
are needed to establish how growth conditions and orchard management
affect the extent of callus hair development.