LAUSR

Phytophthora root rot (PRR) caused by Phytophthora medicaginis (Pm) is an important disease of chickpea in Australia. There are limited control options, with avoiding planting chickpeas in paddocks with a high PRR risk a key management strategy. Currently, risk assessment is based solely on paddock history of PRR, without any measure of Pm inoculum. We developed a qPCR test to quantify Pm inoculum concentrations in soil and evaluated its ability to predict, prior to planting, PRR disease and yield loss in chickpea. The qPCR test was specific to Pm and did not cross react with other Phytophthora species found in Australian agricultural systems and was sensitive, being able to detect <1 Pm oospore/g soil. A field experiment showed no correlation between Pm DNA concentration at seeding and PRR development on the susceptible chickpea variety, Sonali. Field experiments with Yorker, a PRR moderately resistant variety, showed Pm DNA concentration at seeding was correlated with PRR development and grain yield, but relationships varied with season and soil moisture (2015, irrigated r 2 0.752, dryland r 2 0.532; 2017 irrigated r 2 0.52, dryland r 2 0.0005), however above average rainfall in 2016 was highly conducive to PRR and there was no relationship between Pm DNA concentrations at seeding and PRR development or yield. The qPCR could detect moderate to high levels of Pm inoculum, but not low levels capable of causing disease and yield loss in conducive seasons. The Pm qPCR test showed potential to support in-field diagnostics.