Characterization of Syrian Apple Chlorotic Leaf Spot Virus Isolates

Khaldoun Al-Jabor
General Commission for Scientific Agricultural Research-
(GCSAR), Sweida Research Center
Faculty of Agriculture, Tishreen University,
2009

Abstract

One thousand seven hundred and sixty leaves and flowers samples of stone (cherry, mahaleb, apricot, plum, peach and almond) and pome fruits (apple, pear, quince and hawthorn) collected from mother blocks, genetic blocks, commercial orchards and nurseries in the provinces of Rural Damascus, Sweida, Qunaitera, Homs, Hama and Lattakia were tested for the presence of Apple chlorotic leaf spot virus (ACLSV) during 2006 season by using modified DAS-ELISA. Abnormal symptoms on the tested trees were reported, grafting incompatibility, chlorotic spots through leaves veins (on apple trees), chlorotic spots through leaves veins, mosaic and leaves deformation (on quince trees), chlorotic spots through leaves veins, pale yellow spots, red ring and Pseudopox  on fruits (on peach). Mod. DAS-ELISA results showed that the total infection rate of tested samples was 15.5%, 21.9% in pome and about 7.0% in stone fruit samples. The highest infection rate was recorded in apple samples (42.5%), while the lowest one was found in seedling peach (2.9%). No viral infection was detected on apricot, plum, mahaleb, seedling pear and hawthorn samples. ACLSV was recorded for the first time in Syria on quince (5%), non-grafted seedling apple (7.1%) and non-grafted seedling peach (2.9%). This ACLSV record on non-grafted seedlings is raising many questions concerning the virus transmission through other vectors except grafting.
Two hundred and eighty apple trees from the genetic block at Sweida Scientific Agricultural Research Center were tested in the same year. Petals were collected in April, then leaves and phloem of shoots collected from the same trees in October, infection rates were 65.36 and 5.36%, respectively. In the Next year, seventy one apple trees from Hasoor mother blocks in Homs and Kasab apple trees genetic block in Lattakia were tested. Petals were collected in April, then leaves and phloem of shoots collected from the same trees in August. Infection rates were 90.14 and 0%, respectively, demonstrating the effect of great sampling kind and date on Mod. DAS-ELISA results.
Mechanical inoculation was conducted on Chinopodium quinoa to identify tested ACLSV isolates, but indicator plants showed abnormal symptoms that led us to investigate mixed infections. So, 80 samples collected from peach trees genetic block in Sweida in August 2006 were tested for the presence of ACLSV, Apple mosaic virus ApMV, Plum pox virus PPV, Prune dwarf virus PDV and Prunus necrotic ring spot virus PNRSV. The results showed high rate of mixed infections (4 of 5 ACLSV infected samples), whereas ACLSV and PNRSV infection rates were 6.25 and 40%, respectively, and no infection was reported for other targeted viruses.
Fifty seven virus isolates were characterized serologically by using treble antibodies sandwich TAS-ELISA and 7 monoclonal antibodies (MAbs). Tested isolates showed great diversity, and they were divided into 23 different serological groups. The most reactive monoclonal antibody with tested isolates was MAb C1, it reacted with 38 isolates, whereas the least reactive monoclonal antibody was MAb A2 (22 isolates). This serological diversity is a result of the difference in the importing sources of fruit trees seedlings joined their early prevalence in Syria.