Using digital image analysis to estimate flower numbers of Cootamundra wattle (Acacia baileyana F.Muell.) and hence determine seed production and weed potential

Anne MorganA, Peta AdamsA, Peter KolesikA, Margaret SedgleyA, Sue CarthewB and Kathy HaskardC

A Department of Horticulture, Viticulture and Oenology, The University of Adelaide, Waite Campus, PMB1, Glen Osmond, SA 5064, Australia.

B Department of Animal Science, The University of Adelaide, Roseworthy Campus, Roseworthy, SA 5371, Australia.

C BiometricsSA, SARDI, Waite Campus, GPO Box 397, Adelaide, SA 5001, Australia.


Summary

Acacia baileyana F.Muell. (Cootamundra wattle), a native plant of Australia, is a widely planted ornamental tree that produces attractive displays of yellow inflorescences. Outside its endemic range in Australia and in South Africa it has escaped from cultivation to become a weed. In this study, a non-destructive, digital photographic image method was investigated as a technique for estimating total flower numbers from 10 trees of A. baileyana. This would give a better understanding of the flower and seed characteristics and therefore, the weed potential of this species.

Flower numbers per tree were estimated by obtaining density of flowers in four destructive samples per tree, and scaling up with canopy volume. Numbers ranged from 1.25 million to over 13 million. A relationship was established between density of flowers and proportion of yellow flower colour in photographic digital images, using multiple linear regression on log-transformed data (R2 = 0.40, P = 0.052). This was used to predict number of flowers per plant, although further work could be done to better establish the relationship between proportion yellow and density of flowers. Predicted flower numbers were similar to the estimated, ranging from 1.5 to 16.3 million.The total number of pods and seeds per tree were estimated from branch counts and scaled up from the estimated number of flowers. Average pod set for the 10 trees was 0.12%, and average seeds per pod was 4.0. Nevertheless, because of the large number of flowers, the average seed production was over 19,500. This is a very large reproductive output, partly explaining the weed status of this species.

 

Plant Protection Quarterly (2002) 17 (4) 162-167.