Root and shoot development in Corymbia calophylla and Banksia brownii after the application of the fungicide phosphite

The effects of low-volume foliar application (24, 48, 96 kg ha(-1)) of phosphite on root and shoot development in Corymbia calophylla Lindley and Banksia brownii ex R.Br. were investigated in a glasshouse study. Shoot growth, root and shoot dry weight and root length were not significantly reduced by phosphite application in C. calophylla 2 weeks and 4 months after phosphite application. Shoot growth, shoot dry weight and root length I were not significantly reduced in the non-mycorrhizal B. brownii. However, in plants treated with 24 and 96 kg ha(-1) root dry weight was significantly reduced 4 months but not 2 weeks after spray. A discoloration of the root stele was also observed in phosphite-treated plants of this species. At 2 weeks after spray, root concentrations of phosphite in C. calophylla were up to five times higher than shoot concentrations. At 4 months after application, growth abnormalities were observed in B. brownii and these included spindly new shoot growth with rosetted foliage of reduced leaf size. The results of this study, which assessed one mycorrhizal and one non-mycorrhizal native species, suggest that species may vary in their response to phosphite in terms of root development and phosphite applied at rates of 24 kg ha(-1) or higher may result in reduced root growth, particularly in non-mycorrhizal species. Further studies on root development in a wider range of species are needed to validate these findings.