MURDOCH RESEARCH REPOSITORY

Bennallick, R.A., Colquhoun, I.J., Shearer, B.L. and Hardy, G.E.St.J. (1997) Phosphite: Its phytotoxicity and effectiveness in the protection of Eucalyptus marginata forest from . In: 11th Biennial Conference of the Australasian Pathology Society, 29 September - 2 October, Perth, , pp 186.

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PHOSPHITE: ITS PHYTOTOXICITY AND EFFECTIVENESS IN THE PROTECTION OF Eucalyptus marginata FOREST FROM Phytophthol'a cinnamomi

R. A. Bennallic~, I. JColquhounB, B. L. Shearerc and G. E. St J Hardt' AMurddch University, Murdoch 6150, Western Australia C BAlcoa of Australia Limited, Booragoon 6154, Western Australia Department of Conservation and Land Management, Como 6152, Western Australia

INTRODUCTION Recent trials conducted by the Western Australian Department of Conservation and Land Management 7 1000 have shovvn that phosphite protects trees in E. marginata barbiger 6 800 forest from P. cinnamomi. However, phytotoxicity has 5 been observed in some plant species, and phytotoxic 4 600 .-... concentrations of phosphite have increased the 3! 400 ~ 2 susceptibility of coccinea to P. cinnamomi. 200 ~ The aim of this project was to examine the effect of 1 .on 0 \~ 0 ~ phosphite concentration on phytotoxicity and on § ..:;. colonisation by .P. cinnamomi in three understorey '-' 7 1000 :g 6 6 species of the E. marginata forest. .~ 800 ·E'" 5 .S '§ 4 600 MATERIALS AND METHODS '0 3 400 .§ Adenanthos barbiger, Daviesia decurrens and .....u 2 1ii Xanthorrhoea preissii at Alcoa of Australia 0 1 200 0 a ~u Limited's Jarrahdale mine were sprayed to run-ofIwith § 0, 0.2, 0.5 and 2% phosphite. Plants were monitored J 7 1000 u regularly for phytotoxicity symptoms. One week after 6 BOO ] phosphite treatment, stems of A. barbiger and D. 5 ~ decurrens were underbark inoculated with P. 4 600 f cinnamomi. In X. preissii, roots were underbark 3 400 2 inoculated with 30 days after treatment. P. cinnamomi 1 200 The stems and roots were harvested between 23-31 days 0 a after inoculation, then plated sequentially on a 0.5 1.5 2 Phytophthora-selective agar. The leaves of A. barbiger Phosphite concentration applied (%) and D. decurrens and roots of X. preissii were analysed for phosphite content using gas chromatography and a Figure 1. Phosphite concentration in the foliage of A. flame photometric detector. barbiger and D. decurrenslroots of X. preissii (D) and length of colonisation by P. cinnamomi ( /::,. ) in stems of RESULTS and of in Phosphite at all levels of application restricted A. barbiger D. decurrenslroots X. preissii plants treated with phosphite and inoculated with P. colonisation by P. cinnamomi in the stems of A. cinnamomi. barbiger and D. decurrens plants, but not in the roots of X. preissii plants (Figure]). Very low concentrations of Although phosphite is phloem mobile and has been phosphite were detected in the roots of X. preissii in detected in the roots of treated plants (2), very little is comparison with the phosphite concentration measured knovvn about the distribution of phosphite after foliar in the foliage of A. barbiger and D. decurrens plants application. The low concentration of phosphite treated with phosphite (Figure 1). detected in the roots of X. preiss;i in all treatments . Severe leaf necrosis developed in all three species, suggests that phosphite was not translocated from the Wlth the 2% phosphite treatment, while 0.5% phosphite leaves to the roots. was moderately phytotoxic. Plants with severe The results indicate that phosphite has the potential phytotoxicity symptoms recovered by producing new to contain in native plants. It is generally growth. Phytotoxic concentrations of phosphite did not P. cinnamomi accep~ed that phosphite does not eradicate the pathogen, predispose A. barbiger or D. decurrens to more but It may slow the destruction of native plant colonisation by P. cinnamomi. communities long enough for a more permanent solution DISCUSSION to be found. The foliar application of 0.2, 0.5 and 2% phosphite was effective in restricting colonisation by P. cinnamomi REFERENCES 1. Guest, D. 1. and Grant, B. R. (1991). The complex in stems of A. barbiger and D. decurrens, but not in the action of phosphonates as antifungal agents. Biological roots of X. preissii. However, treatment with 2% Review 66, 159-187. phosphite resulted in severe phytotoxicity symptoms. 2. Ouimette, D. G. and Coffey, M. D. (1989). Leaf necrosis developed in all three species at a Phosphonate levels in avocado (Persea americana) phosphite concentration as low as 0.2%, which is in seedlings and soil following treatment with fosetyl-AI or contrast with the reported low phytotoxicity of phosphite potassium phosphonate. Plant Disease 73(3), 212-215. (I). However, the observed phytotoxicity symptoms were not severe in the 0.2 or 0.5% phosphite treatments.

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