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Summary of full report
Grevillea: Breeding and
Development of Cut Flowers
by P.M. Martin and G.N. Brown
July 2007
RIRDC Publication No 07/101 RIRDC Project No US-105A
This project is focussed on the development of improved forms for cut flower use. However, given the unpredictability of the output from a hybridisation program, any forms suitable for general garden use will also be assessed and released if of sufficient merit.
Target Readership
The report is intended to
inform current and potential growers of Grevillea as a cut flower, of progress
towards the goal of providing industry with superior material and will
also be of interest to commercial propagators who would need to be involved
to supply the industry with the very large number of plants required whether
for cut-flower use or garden use.
Objectives
The objectives of the project
as originally laid down were as follows:
Redefining of the objectives
became necessary as the project progressed became there was insufficient
funding available to undertake significant work in all four areas. A decision
was made to place the main emphasis on the development of advanced lines
(2nd objective) that would after appropriate assessment lead to the release
of one or more PBR protected cultivars, suitable for the cut flower trade
(4th objective).
Methods Used
Breeding Strategy
Since the most promising
material currently available for cut flower work has been derived primarily
from crosses involving Grevillea banksii and allied species, it was considered
appropriate from a commercial breeding perspective to undertake an extensive
crossing program between various commercial hybrids of this parentage.
The underlying concept in this method is that by making a large number
of crosses and applying strict selection criteria to the progeny it is
likely that variants on the existing commercial types possessing one or
more of the desired improvements will be found. These new forms can then
be used for further inter-crossing in an effort to combine multiple desirable
features in the one plant.
In contrast to the commercial approach adopted above, the project also included a more speculative element in which wide crosses were attempted. One group of crosses involved the backcrossing existing cut flower varieties to one or other of their parent species. The second group involved crossed between named cultivars and unrelated species or cultivars with desirable floral or adaptive features.
The third group of crosses involved the use of two unrelated species in an attempt to create novel vii hybrids for use as parents in future work with established varieties. In this latter case, with wide crosses between apparently unrelated species, there is of course a greatly reduced expectation of success.
Breeding Technique
Grevilleas are generally
out-breeding plants, but have varying degrees of self-fertility. In order
to make controlled crosses it is necessary to emasculate selected flowers
(remove pollen from florets at a suitable stage of development, typically
10-30 buds per inflorescence), remove the other buds, and a few days later
transfer pollen from the chosen male parent to the stigmas of emasculated
flowers.
Contamination is minimised by covering flower heads with weatherproof paper bags. When closed properly, insects and birds cannot enter with foreign pollen or eat the developing seed. This also prevents pollen transfer from other inflorescences nearby that may rub against the stigmas.
Germination, growing-on and Assessment The seeds often display deep dormancy and are difficult to germinate, but using tissue a tissue culture technique and growth hormones good germination rates were achieved in a short time. Seedlings were then transferred to soil in small pots and eventually planted in the field for growing-on and eventual assessment as they reached the flowering stage. Assessment focussed on the desired characters set out under Objectives, above.
Results
Breeding
Hybrid seed was successfully
produced in a majority of crosses involving varieties that have similar
parentages (Table 1). This was also the case of hybrids that were effectively
backcrossed to the species from which they were derived (Table 2). With
the wider crosses involving either unrelated varieties or unrelated species,
results were generally unsuccessful, but there were some notable exceptions,
including G. decora x G. ‘Sylvia’ and G. georgeana x G. bipinnatifida (Tables
3 and 4).
Material from all classes of crosses was successfully established in the field. Since it typically takes about two years for shrubby Grevilleas to reach flowering (and longer for full flowering), it will be several years before all the products of the crossing programme are assessed. However, of the approximately sixty hybrids which have so far come into flower, nine show novel characteristics of sufficient merit to warrant more detailed evaluation: three for garden use, one for filler foliage use and the remainder for cut flower work. Given these promising early indications we are confident that the project goals of producing advanced breeding lines of merit and of producing PBR protected new varieties will be adequately met.
Other results
In other work related to
the subsidiary objectives, it was found that many existing commercial varieties
are very sensitive to moderate frosts, with damage ranging from bud-burn
to death of the bushes. Since many potential production areas close to
major export airports are frost prone this becomes an important limitation
on the development of the industry. In the assessment of the new hybrids
special attention has been paid to frost susceptibility.
Pruning and training experiments in an attempt to increase the number of first class bloom were generally unsuccessful, the Grevilleas proving to be essentially untrainable. However, there may be some scope for coppicing of older bushes to produce crops of vigorous young shoots with improved production potential. More work is needed on this latter point.
Implications for Stakeholders
Improved cultivars arising
from this project for the cut flower industry will contribute to an expansion
of the area devoted to Grevilleas and to an increased presence of this
genus in the export trade.
Improved garden forms will broader adaptation will increase the popularity of this already important garden shrub. In addition, the propagation industry will benefit from increased demand from both classes of user.
Recommendations
The new cultivars, once
protected by PBR, should be promoted to the industry via field days and
trade shows at cut-flower growers’ conferences.
A commercial partner should be sought to undertake the bulking up and commercialisation of the new PBR-protected cultivars.
Further work should be undertaken
on the potential of coppicing techniques for increasing the proportion
of first class blooms and/or prolonging the life of plantations.
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