The Rose and the Avocado
by Laurie Meadows
August 31, 2019
Today I learned famous rose breeder Sam McGredy had recently died.
I met Sam when he brought some rose scions into the New Zealand
Government MAF office I was working at. He came to arrange the
International Phytosanitary Certificate necessary for shipping
them overseas. Sam was a genial man, and naturally the
conversation turned to his work as a plant breeder.
He was a great storyteller, and he told me a story relating to the
nitty-gritty of the life of a working plant breeder. He was
working in the heat of his greenhouse, sweat dripping from his
brow, engrossed in transferring pollen from the chosen paternal
variety onto the stigmas of the maternal parent, when he became
aware he had an unexpected visitor.
A polite and very earnest young Japanese man introduced himself as
a beginning rose breeder interested in picking up practical tips
from the master. Noticing Sam was using a finger to transfer
pollen, he asked Sam if he used alcohol to sterilise his finger
between crosses. Sam had to explain that he simply wiped his
finger clean on his profusely sweating brow!
At one point his operation was generating 60,000
seedlings per year, so speed in physically making the
crosses is essential.
The results of his methods speaks for itself.
Sam was instrumental in setting up plant breeders rights in New
Zealand, and his floribunda rose ‘Matangi’ was the first plant
ever licenced under the new legislation.
According to Sam, some of his creations were so popular that some
nurseries overseas illegally propagated them – or understated the
numbers they were propagating – so avoiding the breeders rightful
Sam was familiar with the major nurseries, of course, and he told
me he would hire a light aircraft to fly over the nurseries he
suspected of cheating on him. It was relatively easy to spot
blocks of his cultivars in flower from the air, and assess the
size of the stock!
On the same day I read of Sam’s passing, I also learned the avocado
genome has been sequenced.
The work was a collaboration between workers in Mexico, Sweden,
USA, Canada, Belgium, Singapore, Australia, Spain, Denmark and
This achievement is the key to the door to finding and naming
avocado genes that express traits of interest, from flower bud
initiation to fruit skin color.
The effort to bring this project to reality is impressive.
Multiple institutions across countries, complex models,
sophisticated software, highly technical biochemical processes.
Why is it so important for avocado breeding?
Because conventional breeding of the sort that Sam McGredy did is
all but impossible for avocado. Breeding for multiple traits –
moderate tree size, self fertility, good production, high quality
taste, no discernible fiber in the flesh, moderate seed size, skin
that peels easily, skin that is not too thick and not too thin,
fruit that ripens evenly from base to neck, fruit of ‘the right
size’, fruit that cool stores well – requires high populations to
select seedlings from, and it probably requires multiple unrelated
families under selection at the same time.
Worst of all, it is prohibitively difficult to succeed in
deliberate hand pollinations – which means difficult to produce
seedlings whose parentage is known with certainty.
The bottom line is that very large hectareages need to be locked
up in slow-to-flower trees for a long time, even while there is
uncertainty of the genetic worth of one parent. And even when
there is almost no information on the mode of inheritance of the
characters of interest the parent (s) display.
Someone has to provide the land, the running costs, and the highly
trained expertise. But not just the expertise, but the experience
and insights that can only build up through years of interaction
and observation with the test subjects. Given the difficulties in
breeding, that’s not an easy situation to sell to anyone!
But now that the genome has been sequenced, it opens the way to
use the genetic code for traits of interest that has been
identified in other species (from tomatoes to poplar trees) to be
compared to the raw code of the avocado genome. If it matches,
even partially, some part of the avocado genome, then that section
of the avocado genome may be coding for that trait.
Once a match is found and confirmed as being the gene controlling
the trait of interest, genetic ‘probes’ based on these snippets of
code can be artificially constructed (and presumably patented).
These probes can be run on tissue samples from avocado seedlings
to see if that particular seedling carries the desired quality.
Any that don’t can be thrown out – saving very large amounts of
time, space, and money.
The same check can be run over and over on the same seedlings, but
using different traits of interest as the screen. For example, in
principle, a probe could be developed for every trait of interest
mentioned above. Of course, it’s not as simple as that. Someone,
sometime, has to find and describe the gene of interest in another
species and deposit that information in the communal database. But
traits may be controlled by more than one gene. Or other, unknown
genes may act as on/off switches to expression of the genes of
All this takes time, effort, and money. And access to money always
has competing interests.
For simple single-gene mediated traits it may be simpler to copy
that gene from an avocado tree with a gene expressing that trait,
and simply paste it into a seedling that is perfect in all
respects – except one. Perhaps the seedling has everything the
industry wishes for, but has green skin, and the industry
considers a color change to indicate ripening is desirable from
the consumer viewpoint. If purple skin color was controlled by a
single gene (and no other gene interfered with its expression),
than a copy (or copies) of the ‘purple skin’ gene could be
inserted via gene editing technology.
So this is a significant advance. But it also signifies a shift. A
shift of resources to those with the necessary institutional money
and technical sophistication. It raises some very interesting
questions about cooperation, patents, funder oversight,
collaborator rights across international borders, affect of
domestic foreign policy on projects (the domain of science
diplomacy), and more.
The difference between the methods of Sam McGredy and these
methods is obviously very great. But no-one should imagine that,
in general, conventional methods have been made obsolete. Very far
from it. But in the specific case of avocado, the door to a slow
acceleration in progress is creaking open.
But nothing changes the question – what exactly are you hoping to
achieve, and what facts and projections have you considered in
deciding on your goal?