A simple method for detection of Phytophthora nicotianae from soybean soil

Abstract

A high detection rate of Phytophthora nicotianae was obtained from the naturally infested soil of soybean fields. Air-dried soils were firstly moistened in a flask and then pre-incubated at 25 °C for 1-4 weeks before flooding with distilled water and baiting with soybean leaf disks for 6, 12, and 24 h. The baits were then thoroughly washed, flooded with 10-15 ml of distilled water in Petri-dishes and incubated under continuous fluorescent light for 72 h. Sporangia started to emerge from the margins of leaf disks. They were easily observed under the stereomicroscope. Pure culture of the fungus was obtained by spreading zoospore suspension on a 1.5% water-agar containing anti-bacterial antibiotics. This is the first report of recovery of P. nicotianae from naturally infested soybean soils using sensitive leaf disks of soybean (Williams cultivar) as bait in Iran. All isolates were determined to be A2 mating type.