Biological and Molecular Detection of HSVd - Infecting Peach and Pear Trees in EGYPT

Two isolates of Hop stunt viroid (HSVd) were characterized from naturally infected peach and pear trees during summer season (2007-2008) in Egypt. The two isolates of HSVd were biologically indexed using healthy peach and pear seedlings under insect proof greenhouse. Total RNAs were extracted from peach and pear leaves and used for reverse transcription-polymerase chain reaction (RT-PCR). About 300 bp DNA fragment was amplified from the samples by RT-PCR using HSVd (+) and HSVd (-) specific primers. Fifty-nine pear trees and forty-six peach samples showing stunting, yellowing and leaf blistering were analyzed for the presence of HSVd using tissue print hybridization. The reactivity of HSVd Dig-labeled probe varied from strongly positive, moderately positive and weekly positive reaction with infected samples. Magnified pictures of pear and peach tissue prints indicated that HSVd is phloem restricted as shown from the vascular tissues colored with purple hybridization signals. The percentages of positive infection was 93% in the total collected samples