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What the report is about and who the report is targeted at
This project quantified water and nutrient relations in the parasitic tree, quandong (Santalum acuminatum), growing on a range of acacia host species in a semi-arid region at Port Augusta in South Australia. The information collected will aid quandong producers in the selection of suitable hosts and the development of efficient irrigation and fertilisation strategies for quandong production in arid and semi-arid environments, including regions with salinity problems. We also gathered data on the host species, to ensure that our results will also be useful to acacia-seed producers.

Aims and Objectives
Specific objectives were:

1. To quantify water potential gradients between S. acuminatum and a range of acacia host species.
2. To characterise the water relations of S. acuminatum and acacia hosts in response to seasonal changes in water availability.
3. To measure rates of growth and fruit production in S. acuminatum on a range of acacia hosts.
4. To determine chemical composition of host and parasite foliage.

Methods
The research was conducted at the Australian Arid Lands Botanic Garden (AALBG) at Port Augusta, South Australia in an established acacia/quandong plot. The plot consists of eight acacia species (Acacia murrayana, A. victoriae, A. rivalis, A. brumalis, A. calamifolia, A. hakeoides, A. hemiteles and A. argyrophylla), which have been growing in combination with S. acuminatum (quandong) since April 2001. Growth (stem diameter & tree height) and fruiting were measured for parasites on eight acacia hosts in both 2005 and 2006. Water potential and photosynthetic efficiency of A. victoriae, A. argyrophylla, A. hemiteles and A. hakeoides and their attached quandongs (5 replicate pairs) were measured in winter 2005 and summer 2006. The results of this work were analysed and outlined in this report.

Results and Recommendations
Despite having the highest water potentials and the greatest proportion of parasites with fruit, A. victoriae is not an ideal host for sustained parasite growth and fruit production because the parasite has such a negative impact on host growth. In the plot we used, many A. victoriae with parasites had died, and presumably the parasites had subsequently attached to other hosts in the vicinity.

One recommendation from this study would be that A. victoriae, under the present management regime, is only a good host in the first couple of years of parasite establishment, and that growers would be advised to interplant with other more resilient hosts to sustain parasite growth and fruit production in the long term. The best hosts for this purpose, based on our data, would be A. calamifolia, A. hemiteles and A. argyophylla, but not necessarily in that order.

Although A. hakeoides was least affected by the parasites, it was also the least suitable host in terms of both parasite growth and fruit production. Thus, we would not recommend this particular host. In addition to our recommendations, host choice will depend on other factors such as water availability, soil types, salinity and climate. Growers could select the most suitable host from the list of those we recommend on the basis of their particular soil and climate.

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