Detection of Citrus psorosis ophiovirus in Citrus CV. Navel Orange in Egypt

Abstract

Citrus is one of the most important fruit crops worldwide. Most of the citrus cultivars are grown as grafted plants. Virus pathogens transmitted by grafting as well as insect vectors could cause economic problems. Among graft transmissible diseases that have been reported from Egypt as well as in the rest of the Mediterranean countries; citrus psorosis disease that is of the most serious and remain the most spread disease in Egypt (Roistacher, 1991; Sofy, 2008).
In infected trees, scaly bark symptoms appears on the trunk, staining of interior wood of branch and gummy as well as shortened leaf internodes and mottling patterns on leaves (Ghazal et al., 2008; El-Dougdoug et al., 2009).
Citrus psorosis virus (CPsV), the type species of the genus Ophiovirus (Vaira et al., 2005), is the putative causal agent of psorosis, a major graft-transmissible disease of citrus (Roistacher, 1993).
Virus particles are formed by three single-stranded, negative sense RNAs and a coat protein (CP) of 48 kDa (Derrick et al., 1988; Martı´n et al., 2005). RNA1 contains 8184 bp and its complementary strand has two ORFs potentially encoding a 24 kDa protein of unknown function and a 280 kDa protein with motifs characteristic of RNA-dependent RNA polymerases (RdRp). RNA2 contains 1644 bp and its complementary strand encodes a 54 kDa protein without similarities to other known proteins and RNA3 contains 1454 bp and its complementary strand encodes the CP (Barthe et al., 1998; Sa´nchez de la Torre et al., 1998 & 2002; Naum-Onganı´a et al., 2003; Martı´n et al., 2005).
The sensitive, reliable and rapid identification of plant viruses is essential for effective disease control. For many years, laborious and costly indexing on citrus indicators was the only diagnostic method available (Roistacher, 1993).
The first breakthrough in the development of a laboratory diagnostic testing technique came in 1977 with the development of the ELISA (Clark and Adams, 1977).
DAS-ELISA (Garcia et al., 1997) and TAS-ELISA (Alioto et al., 1999) are methods developed and applied for psorosis diagnosis in field trees.
Polymerase chain reaction (PCR) was developed in the early 1990’s and has the ability to selectively amplify a part of the target deoxyribonucleic acid (DNA). Reverse transcription-polymerase chain reaction (RT-PCR) (Garcia et al., 1997; Legarreta et al., 2000; D’Onghia et al., 2001), are now being utilized and several primers have been designed for the CPsV detection by the RT-PCR providing an alternative method for diagnosis (Barthe et al., 1998; Legarreta et al., 2000).
This study aimed to detect CPsV in citrus trees cv. Navel orange via biological, serological and molecular methods.