Effect of Base Analogues on Strains of Citrus Tristeza Virus

Inhibitory action of two base analogues viz., 2-thiouracil (pyrimidine base) and 8-azaguanine (Purine base) at 250 and 500 ppm were tested against very mild (S₁) and very severe (S₅) strains of tristeza virus on acid lime after incubating the bud and bark pieces at 6, 12, 24, 36 and 48 hours. The 6-month old acid lime seedlings when inoculated with bark/bud pieces delayed the symptom expression 6 to 12 and 12 to 16 weeks respectively for severe and mild strains. Prolonged inocubation period and increased concentration of base analogues further delayed the symptoms for 4 weeks. Aphid inoculation with one month old seedlings kept in 500 ppm test solutions, showed a delay of only 4 and 6 week respectively for severe and mild strain. Further, the vein clearing and stem pitting pattern has been found altered by the test chemicals.