Plant virus isolation procedures used in this study were modified from [8] . Infected plants showing typical symptoms were harvested, weighed, and homogenized in ice-cold 0.1 M phosphate buffer (pH 7.0 containing 1% of β-mercaptoethanol) at 1 mL/g of plant material for 10 minutes using a mechanical blender. The homogenate was filtered through 2 layers of cheesecloth and then mixed with equal volume of chloroform:butanol (1:1). The mixture was then stirred for 1-2 hours at room temperature and then the organic phase was separated from the mixture through centrifugation at 8000 g for 15 minutes. The aqueous layer was transferred to a beaker, 100 mL of NaCl (4 g/L) and PEG6000 added, and the mixture stirred on ice for 1 hour. The precipitated virus was separated from the solution through centrifugation at 10 000 g for 30 minutes at 4 • C. The resulting pellet was reconstituted in 10 mL of 0.1 M phosphate buffer pH 7.0. Any undissolved material was cleared by centrifugation at 10 000 g for 30 minutes at 12 • C. Then 0.2 M EDTA (pH 7) (50 mL/L) was added to the supernatant and the mixture subjected to centrifugation at 110 000 g for 90 minutes at 4 • C. The supernatant was discarded, and the pellet was left to air dry. The virus pellet was then reconstituted in 100 μL of distilled water and stored at 4 • C until used.