Variation between plant species of in-planta concentration and effectiveness of low-volume phosphite spray on Phytophthora cinnamomi lesion development

Abstract

Variation between plant species of in-planta concentration and effectiveness of low-volume phosphite spray on lesion development of Phytophthora cinnamomi was determined for 14 species in two native communities of the South-West Botanical Province of Western Australia and 10 species in a glasshouse environment. There was considerable variation in stem phosphite concentrations between environments, phosphite treatment and taxa following low-volume spray. Average stem phosphite concentrations for taxa in the glasshouse environment were 8-fold greater than those in natural environments. In 48% of taxa, phosphite concentrations in stems of plants sprayed with 48 kg phosphite/ha were significantly greater than that for plants sprayed with 24 kg phosphite/ha. There was a 22 to 28-fold difference in stem tissue phosphite concentrations between taxa in the native communities and a 31 to 63-fold difference between taxa in the glasshouse environment. Phosphite was effective in 46% of the taxa based on rate of visible lesion development being significantly less in plants sprayed with 24 or 48 kg phosphite/ha than plants not sprayed. There were significant linear relationships between in-planta phosphite concentration and lesion development. Variation in phosphite effectiveness can be extended into a general hypothesis that plant species may differ in species-specific in-planta phosphite concentration thresholds that must be exceeded before effective control of P. cinnamomi can be achieved. Databases of species falling into phosphite effective or not effective groups can be used to assess variation in phosphite effectiveness between different threatened communities and assist in the development of application procedures aimed at overcoming ineffectiveness of the fungicide.