Grapevine Leaf Rust – Incursion risk assessment and improvement of PCR diagnostics

Abstract

Following the successful eradication of the grapevine leaf rust (GLR) pathogen, Phakopsora euvitis, from Darwin (Northern Territory, Australia) in 2007, the possibility of windborne re-introduction to northern Australia and development of an improved diagnostic test using polymerase chain reaction (PCR) were investigated.

Summary

To investigate the possibility of windborne re-introduction, studies undertaken focused on two aspects of the process:1. The characteristics of airflow between SE Asia and northern Australia and,2. The mortality of detached urediniospores. The airflow between SE Asia and northern Australia during the summer months (December to March) is influenced by the NW monsoon, defined by active and non-active periods. During the active period, airflow over northern Australia isfrom the NW direction across SE Asia and the Timor Sea. This could potentially disseminate viable spores of P. euvitis from other continents in the region. Active monsoons can last several days to weeks but generally about seven days. During non active periods, the airflow does not pose a risk of introducing disease. In general, airflow occurs within the troposphere (between the earth surface and the stratosphere). Conditions in the troposphere can be below freezing at high altitudes, the temperature decreasing by 6.5 ºC per km increase in altitude (Danielson et al, Meteorology, 2003). Sub-zero temperatures would be lethal for the fragile, short-lived urediniospores. However, modelling by the Bureau of Meteorology, Darwin indicated that it is possible for “parcels” of air passing over or leaving the southern East Timor during active monsoon weather to maintain a low altitude (1 km and lower) trajectory and flow to Darwin within a short time frame. If this air contained urediniospores, the moderate temperature conditions experienced at these low altitudes would not be lethal. Urediniospores of P. euvitis have been shown to survive temperatures as low as 5 ºC (Ozoe and Kadowaki, 1971, Daly and Hennessy, 2007).