[A Study of the effectiveness of some applying means to protect the potato crop from Potato Virus Y infection]

Potato virus Y (PVY, genus Potyvirus, family Potyviridae), is the most common and destructive virus found in most potato crop production area. It is considered the main reason for the drop of the class of potato seeds and the the decrease of production; 10-80% yield losses have been reported. Five Syrian isolates of PVY collected from potato fields in various places were characterized by serological, biological and molecular methods. ELISA test showed that all tested samples (60 samples) did not react with the following five virus antisera PVA, PVS, PVM, PVX and PLRV, whereas it showed positive reaction to PVY polyclonal antibodies. RT-PCR test showed that all these five isolates were infected with PVY as the ELISA test demonstrated. After that, 6 separate RT-PCR tests were conducted to characterize the PVY strain. The RTPCR results showed that L1 isolate collected from Lattakia contained mixed infection with PVYNTN-NW and PVYNTN subgroups, whereas H2 isolate collected from Hama and K5 isolate collected from Al-Qaunetra contained PVYNW subgroup, and D3 isolate collected from Damascus as well as A4 isolate collected from Aleppo contained PVYNTN subgroup. When the nucleotide sequences of the 441bp fragment of L1, D3, K5 and AL6 (positive control) isolates were compared with other 8 Syrian and 5 worldwide PVY isolates from GenBank, a 97-99% similarity in nucleotide sequence homology was found between the 4 tested isolates and the Syrian isolates: SYRWi- 11 (AB185832.1), PVY-12 (AB185833.2), PVYSYR (AB270705.1), SYR-II- 2-8 (AB461451.1), SYR-II-Be1 (AB461452.1), SYR-II-DrH (AB461453.1), SYR-III-L4 (AB461454.1), PVY-Bu3 (AB461488.1) and USA (PVYNTN isolate HR1: FJ204166.1), and 83-98% homology with USA isolates (PVY-O5: HQ912901.1; PVYWi: HQ912868.1), UK (PVYN, isolate SASA 207: AJ584851.1) and German (PVYWi, isolate 261-4: AM113988.1). A local Syrian PVY isolate was purified; 3.84 mg purified PVY was obtained from 600 g infected frozen tobacoo leaves. The purified prepapration was injected into a white rabbit and 14 ml crude antiserum were obtained and used to detect PVY in infected tissues by ELISA. IgG was purified from crude antiserum and conjugated to Alkaline phosphatase to produce IgG-Alp. The optimum concentration of IgG was 0.001 mg/ml and the optimum dilation of conjugate (IgG-Alp) was 1/1000 in ELISA test. The antiserum obtained was able to detect PVY by ELISA up to a IgG concentration: 0.00033 mg/ml, and IgG-Alp dilation: 1/3000. This polyclonal antibody succeeds in detecting PVY infection in various samples collected from local potato fields by TBIA and DAS-ELISA tests. No differences in value were detected when it was compared with Bioreba polyclonal antibody, Switzerland. 20 Tubers of two potato cultivars (Marfona and Spunta) which were inoculated with Syrian isolate of PVY (primary infection under field condition) during 2010 and 2011 growing seasons, and which were listed in three groups according to diameter (big: 50 mm, medium: 35-50 mm, small: 35 mm), were tested by TBIA to calculate the translocation rate of the virus through tubers to detect the tuber size which carry the lowest percentage of PVY as an applying means to choose the optimum seed size when natural primary infection occurs in the seed potato field. The observation results showed that no external symptoms, e.g. PTNRD, appeared on the tubers. Serology TBIA results showed different rates of translocation of PVY through tubers according to the cultivars and tubers size in both seasons. The translocation rate of PVY through tubers ranged from 16.4-75.0%, 52.1-81.8% in 2010 and 2011 seasons, respectively. The highest translocation rate of PVY through tubers was in the big size in comparison with other sizes; 75.0%, 81.1% in Spunta cultivar and 44.0%, 81.8% in Marfona cultivar in 2010 and 2011 seasons, respectively. Field experiments were conducted in Trkmanbarh village, Aleppo, during 2010 and 2011 growing seasons to investigate the effects of a number of management components [barrier crops (sorghum and soybean borders), mineral oil (foliar spray with mineral oil) and seed dressing with Gaucho 'Imidacloprid' in two concentrations (2, 4 g / 10 kg potato seed) in comparison with insecticide spray] in reducing the spread of Potato virus Y, which transmitted by aphids in nonpersistent manner in seed potato production fields. Two potato varieties (Marfona and Spunta) were used. Samples were tested by TBIA and PVY and incidence percentage was calculated for each treatment. In the barrier crops experiments results showed that sorghum border was the best by significant differences than other treatments in reducing the PVY infection rate in both seasons. In the mineral oil and Gaucho experiments, the results showed significant differences among most treatments. The treatment of foliar spray with mineral oil and insecticide every 15 days was the best by significant differences than other treatments in both seasons