 Conference
1999
New Zealand Plants and their Story
Elite
Native Plants for Contemporary Gardens
Jack
Hobbs
Curator Manager
Auckland Regional Botanic gardens
Hill Road, Manurewa, South Auckland
Gardening, at least in
my view, is one of the great art forms.
To achieve the ultimate
expression of this art, it is of course necessary to utilise plants
with some aesthetic appeal.
Put simply, the more attractive
the plants are, the more beautiful the completed garden or landscape
can potentially become.
Trying to define beauty
is fraught with difficulties, but there are aspects of the appearance
of plants that can usually be agreed upon.
It seems to me that in
recent years gardeners have increasingly been demanding plants that
are attractive in all their characteristics.
Previously, it often
seemed that the appearance of flowers alone determined a plants
popularity. Two hundred years of dahlia breeding, for example, produced
numerous tall straggly cultivars of unsightly appearance, which
were esteemed for the few perfect prize winning blooms they produced
with great cosseting.
Although flowers are
still an important consideration, it is not uncommon today to see
beautiful gardens dominated by foliage with barely a bloom in sight.
As a plant breeder I
consider my job is to produce plants capable of contributing to
the overall quality of contemporary gardens.
Sometimes this is achieved
by producing plants of particularly attractive appearance. On other
occasions it is performance characteristics that contribute most
to a new plants appeal.
Ultimately any new hybrid
must be successful in the market if it is to be commercially viable,
and therefore ultimately support the breeding programme from which
it came.
In Europe it is vital
that new cultivars must be suitable for mass production, a trend
that is becoming more apparent in this country.
Growers want plants that
propagate readily, are not too prone to disease, and that most importantly
look great at point of sale.
Home gardeners are also
increasingly buying those plants that look great in garden centres
(i.e., usually in flower at point of sale).
The days when gardeners
were prepared to wait for a plant to mature into something impressive
at a future time seem to have largely disappeared.
My own plant breeding
objectives have modified considerably over the years simply to meet
the commercial requirements of the market.
For any new hybrid to
be successful it must exhibit numerous worthwhile characteristics
and very few faults.
Often a single fault,
such as an open leggy habit, is enough to see a promising new seedling
discarded to the compost bin.
Sometimes a batch of
several hundred Hebe seedlings will not produce even one
worthwhile seedling.
The golden rule of plant
breeding, I have found, is to use genetically superior clones as
parent stock.
I have worked mainly
with native plants, many of which exhibit considerable variation
even within species.
Many Hebe species,
for example, are remarkably variable. A population of about twenty
clones of H. obtusata that I collected from a single location
in west Auckland exhibited enormous variation in leaf size, plant
habit, flower size and colour, and even susceptibility to disease.
Every plant was a distinctive
individual.
When a parent plant contains
worthwhile characteristics, such as resistance to disease, these
qualities have a reasonably high chance of being passed on to any
offspring.
Realisation of this saw
me putting considerable emphasis upon the selection of elite plant
material for inclusion in our breeding programmes.
The qualities that these
foundation parents imparted to early generations of hybrid seedlings
were still being expressed in the relatively complex hybrids produced
several generations later.
Another key aspect of
breeding programmes is to develop clear objectives from the outset.
My perfect Hebe
would go something like this: a prolonged and appealing floral display,
handsome healthy foliage, fully hardy, and all of this on a compact
shrub that does not require pruning or spraying. It may not seem
much to ask, but it has proven remarkably difficult to achieve.
To capture the imagination
of the market, any new hybrid must also be distinctively different
in appearance from anything currently available.
'Wiri Mist' is probably
the closest I have come to achieving my ideal, although 'First Light'
is a recent release that is even more distinct and that may eventually
prove to be just as useful.
The simple hybrids (e.g.,
F1 hybrids between two species) that emerged early in
our breeding programme proved to be extremely uniform, with most
individuals being of good quality but few being outstanding.
As the programme progressed,
and complex hybrids containing numerous species in their pedigree
were produced, the appearance and quality of the individual hybrid
seedlings became considerably more variable.
A batch of say 100 of
these complex hybrid seedlings could often contain so many unappealing
'rogues' that some 95 could be discarded at the first cull.
The payoff was that the
remaining handful of seedlings could contain some remarkably new
and different characteristics.
Various techniques were
applied to increase this variability further, in the hope that some
great change could be affected.
Irradiation was discarded
as being too unpredictable after a few trials.
Crosses were attempted
between distantly related species, but although these produced some
interesting offspring, in most cases they produced little or no
viable seed.
Breeding of Leptospermum
produced results in stark contrast to those from parallel programmes
on Hebe.
The programme concentrated
on just one species, L. scoparium, albeit one that exhibits
enormous variation.
Even the earliest Leptospermum
crosses produced extremely variable populations of seedlings.
Once again, the success
of the programme depended largely on the use of exceptional parent
material selected from the wild. Notable parents included the Graeme
Platt selections 'Karekare' (White single) and 'Sherryl Lee' (pink
single).
Probably the best hybrids
to yet emerge, from the programme have been 'Wiri Sandra' (pink
single) and 'Wiri Susan' (white single), although these have not
necessarily proven to be the most successful commercially.
I believe that many other
native plants can be transformed through a combination of selection
and breeding into subjects more suitable for both commercial production
and use in ornamental situations.
Metrosideros excelsa,
our beloved Pohutukawa, is a remarkably variable tree.
At one extreme are trees
with dull flowers of relative insignificance, and at the other end
of the scale are individuals producing spectacular clusters of brilliantly
coloured stamens.
Other characteristics
such as the size, shape and habit of individual trees fluctuate
wildly, as does foliage size and hue.
Even a relatively unattractive
pohutukawa is a good tree, but the very best of them are superb
and must rate amongst the most desirable of all the world's flowering
trees.
To date the best pohutukawa
selection available is 'Vibrance', a relatively small upright tree
with large clusters of brilliant scarlet/red stamens sometimes smothering
the entire tree.
Kowhai (Sophora microphylla)
would benefit greatly from the selection and introduction of superior
forms from the wild.
In fact, the potential
for increasing the use, and ultimately the economic worth, of our
native flora is immense.
Breeding programmes undertaken
to date have been rudimentary at best.
A properly funded breeding
initiative with clear goals that utilised our best plant breeding
talents could lift the status and popularity of native plants to
even greater heights.
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