Biology, impact and preliminary host-specificity testing of the rust fungus, Uromyces salsolae, a potential biological control agent for Salsola kaliin the USA

Russian thistle, Salsola kali (= Salsola australis) (Chenopodiaceae) of Eur asian origin is a troublesome weed in the drier regions of the western USA. The weed commonly infests crops, disturbed wastelands and overgrazed range lands. A rust fungus, Uromyces salsolae, has been found to cause considerab le damage to the weed in Eurasia. Field observations in Turkey revealed tha t S. kali plants infected by the rust were covered with a powdery brown mas s of urediniospores and had stunted growth. Under laboratory conditions, U. salsolae severely infected Salsola plants from France, the USA and Turkey (control). The urediniospores germinated when in contact with water within a minimum period of 2 h and over a wide range of temperatures. S. kali plan ts were also infected at a wide range of temperatures and incubation period s with simulated dew. Fungal attack was very severe and caused mortality or much reduced growth of infected plants without seed production. Preliminar y host specificity testing using 17 plant species or varieties from six fam ilies revealed that the rust infected only the Russian thistle. U. salsolae was imported recently into the USA for further host specificity testing un der quarantine conditions. Its use as a biological control agent for S. kal i in the USA is recommended.