ELICITATION OF DEFENCE RESPONSES IN PINUS RADIATA SEEDLINGS AND SUSPENSION CELLS, AND INDUCTION OF RESISTANCE TO SPHAEROPSIS SAPINEA
T REGLINSKI, G HOTTER, JT TAYLOR and FJL STAVELY
The Horticulture and Food Research Institute of New Zealand Ltd, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand
Background and objectives
In conifers, elicitors have been shown to induce defence responses in suspension cultures of Pinus elliottii and Pinus banksiana, and at wound sites in Pinus contorta. Here we investigate elicitor induced responses in Pinus radiata seedlings and suspension cultures and the subsequent resistance of seedlings to infection with Sphaeropsis sapinea (Diplodia pinea). S. sapinea causes shoot blight, crown wilt, canker and sap stain on a wide range of conifer species worldwide. The most common symptom associated with S. sapinea infection in P. radiata is shoot blight. Infection of terminal shoots can result in leader dieback or deadtop, this is considered the most damaging form of shoot blight as it results in stem malformation and a reduction in the useable length of the bole.
Results and conclusions
A series of experiments were carried out to assess whether SA and 5CSA affected the susceptibility of P. radiata to subsequent infection by S. sapinea. Only 10-20% of seedlings treated with 1mM 5CSA developed deadtop compared to 40-60% of seedlings treated with 1mM SA. In control seedlings 75-95% developed deadtop. SA had no effect on S sapinea growth at concentrations up to 2mM whilst 1mM and 2mM 5CSA reduced growth rate by 12 and 27%, respectively. However, 5CSA concentrations of 0.5 and 0.25 mM were not directly inhibitory to growth of S. sapinea but still afforded significant reductions in deadtop development (P<0.001) to treated seedlings .
In order to assess the duration of disease control P. radiata seedlings were treated with 1 mM 5CSA up to 64 days before wound inoculation with S. sapinea. Significant reduction in the incidence of deadtop (P<0.05) was observed on seedlings treated between 2 and 32 days before inoculation.
More detailed biochemical studies are in progress to determine the nature and duration of the 5CSA induced responses in P. radiata and to assess the viability of induced resistance for controlling other diseases in forestry nurseries.