EFFECTS OF CITRUS TRISTEZA VIRUS ON THE GROWTH OF IN VITRO-CULTURED CITRUS

Citrus tristeza virus isolate YC (CTV-YC), a stem pitting-inducing strain, was graft-transmitted to seedlings of Mexican lime [Citrus aurantifolia (Christm.) Swingle], Pineapple sweet orange [C. sinensis (L.) Osbeck] and Arizona Etrog citron 861-SI (C. medica L.). Nodal stem segments from CTV-YC-infected and healthy seedlings of the three species were used as explants for regeneration in vitro. CTV presence reduced significantly the proliferation rate, the vigour and the rooting capacity of regenerated shoots. The most severe effect was observed on Etrog citron, whose regeneration ratio, shoot proliferation and root formation were inhibited to a great extent. CTV infection affected also the survival of transplanted plantlets. In vitro shoot cultures from CTV-infected explants of sweet orange and Mexican lime were successfully sub-cultured for up to 20-24 months, whereas those from infected Etrog usually survived less than 7 months. CTV could be detected in all sub-cultures, but its titer decreased with time.