2.2. Soil-bait test
Field soil samples were spread out on paper sheet and air-dried
for seven to 10 days at 22–24 ◦C. The dried soil samples were ground
into fine powder using pestle and mortar and passed through 300
and 200 m sieves, respectively. Twenty grams of fine soil powder
was placed in each of four depressions in stream-sterilized
potting mixture (sand:clay:compost, 1:1:1 ratio v/v) in 1 l plastic
pots. The pots were soaked 10–15 h with tap water in a steel
tray (4 pots/tray/treatment). Four Nicotiana debneyi seedlings were
transplanted into each pot. The pots were placed in glasshouse at
18–20 ◦C. The pots were flooded to half their height in water for
three days, then the water was allowed to drain and the pots were
left with out water for four days. The plants were uprooted after 6–8
weeks for virus testing through back inoculation of sap from leaves
and roots to indicator plants (N. debneyi, Nicotiana benthamiana),
by triple antibody sandwich/double antibody sandwich-enzymelinked
immunosorbent assay (TAS/DAS-ELISA), and by reverse
transcription and polymerase chain reaction (RT-PCR)