Detection of Pseudomonas savastanoi pv. savastanoi from olive and other hosts by polymerase chain reaction (PCR).
Field inspections indicated that olive knot bacteria occur in different olive trees in Amman (Alhashmi Alshamali, Aljubiha, Dahiet Alrashid, Tla'a Ali and Wadi Assir), Madaba'a (Alsamik), Alkarak (Alrabah) and Irbid (Aljohfieh), Jordan. Olive knot bacteria were collected from different host plants grown in different locations (Jerash, Wadi Shouaib and Dairalla) in Jordan. A total of 100 Pseudomonas savastanoi pv. savastanoi isolates were obtained from naturally infected olive trees. Another 30 isolates were obtained from other host plants also from different locations in Jordan. The iaaL gene was detected by PCR amplification from 82% of DNA extracts from the sap of knots formed on naturally infected olives and 97% from bacterial cultures, respectively. Pathogenic P. savastanoi pv. savastanoi was recovered on KB medium from 55% of the collected isolates. The detection of the iaaL gene of the tested isolates was more efficient in detecting P. savastanoi pv. savastanoi than by isolation on KB medium and pathogenicity tests. Culturing the isolates on KB medium prior to iaaL amplification greatly improved PCR efficiency. The iaaL gene was detected in 80, 90 and 90% of the isolates obtained from naturally infected oleander, jasmine and Ziziphus, respectively. Moreover, P. savastanoi pv. savastanoi was isolated from symptomless olive plants and the iaaL gene was detected using PCR amplification. PCR was more efficient in detecting olive knot bacteria by iaaL amplification than by isolation on KB medium followed by pathogenicity tests.