Some factors influencing the sudden death syndrome in cut flower plants : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science at Massey University

Soil/root mixes from plants with the Sudden Collapse Syndrome of cut flower plants were tested for Phytophthora infection using a lupin (Lupinus angustifolius) baiting technique. Boronia heterophylla and Leucadendron 'Wilsons Wonder' root samples both caused the lupin seedlings to exhibit symptoms of Phytophthora infection. The efficacy of phosphorous acid (Foschek® 500 at 1000 ppm and 2000 ppm) and a combination of phosphorous acid and an additional product (Foschek® 500 and C408 at 1000/200 ppm and 2000/400 ppm) in controlling Phytophthora cinnamomi root infections of L. 'Wilsons Wonder', B.heterophylla and B megastigma rooted cuttings was compared with fosetyl- Al (Aliette® 80 SP at 1000 ppm and 2000 ppm) under conditions of high disease pressure The fungicides were applied as a root drench 7 days prior to the roots being inoculated by a split wheat technique and the effect of the fungicides and their concentrations on the rate of plant mortality was measured The results were species dependent. The treatments delaying plant mortality most effectively were fosetyl-AI at 2000 ppm on L 'Wilsons Wonder', phosphorous acid at 2000 ppm on B. heterophylla and both fosetyl-AI at 1000 or 2000 ppm and phosphorous acid at 2000 ppm on B. megastigma. The allelopathic activity of the root bark of Protea cynaroides, L. 'Wilsons Wonder'. Macadamia 'Beaumont' and Knightia excelsa was evaluated as a growth inhibitor for Phytophthora cinnamomi. The results indicate that by day 4 the root bark of M. 'Beaumont' reduced the growth rate of Phytophthora cinnamomi by 76.8% while that of Protea cynaroides inhibited the growth totally. The root bark of L. 'Wilsons Wonder' had no effect on the growth rate but that of K. excelsa enhanced the growth rate by 128% by day 4. The root bark of Protea cynaroides plants previously infected with an unnamed, indigenous Phytophthora species provided greater resistance to the growth rate of Phytophthora cinnamomi than the root bark of uninfected plants On the corn meal agar the leachate of the infected Protea cynaroides root bark exhibited a 'zone of inhibition' which prevented the growth of Phytophthora cinnamomi. Possible reasons for this are discussed