Nature has beaten the scientists at their own game by bestowing durable pest and disease resistance to several apple
types. The challenge for the scientists is to breed commercial varieties from these.
Resistance for commercial apples is the objective for a determined scientist Vincent Bus, working at HortResearch's
Hawke's Bay site. Mr Bus is searching for genes conferring resistance to several apple pests and diseases. Many
thousands of seeds from old apple varieties and crab apples, including wild apples from Kazakhstan, have been grown and
tested for resistance, mainly to black spot, but also for other nasties like fire blight, powdery mildew and woolly
apple aphid.
Crab apples carry genes that confer immunity, and because there usually is only one gene involved, it is easy to use
them for breeding. Some were imported via France and some via the USA, but most actually have their origins in Russia,
China or Japan.
Eating apples are believed to have originated in Kazakhstan and HortResearch has material gathered from there during
expeditions in 1993, 1995 and 1996, lead by Dr Phil Forsline of the USDA. Plants grown from seeds collected in 1993 are
starting to fruit now and have already provided a number of new sources for resistance.
Of the 2500 seed from the 1995 and 1996 Kazakhstan expeditions, about 25 percent have shown resistance to black spot.
Using the Kazakhstan material has major advantages. The fruit is already large and has a fair eating quality. And it
appears that nature has beaten the scientists to durable resistance and has already "pyramided" resistance genes into
some of the germplasm (genetic material). Preliminary information coming from the USA shows that some of these
accessions already have three or four resistance genes to black spot alone.
"The whole theme of my breeding programme is to bring different types of resistances together. There are eight or nine
known major resistance genes to black spot to date, and the idea is to put different types together and make a more
durable resistance," said Mr Bus.
"It would then be a lot harder for black spot to overcome that resistance. By bringing different types of resistance
together into one variety, we effectively have several weapons in one to fight disease," he said.
But the next stage is to put that resistance into popular commercial varieties. Mr Bus said that using crabs it has
taken three to five generations to get to the stage of gene pyramiding, with the Kazakhstan material it might only take
two generations to the final product, new cultivars with durable resistances.
ENDS