Production of Lily Symptomless Virus-free Plants by Shoot Meristem Tip Culture and In Vitro Thermotherapy

Abstract

To produce virus-free plants, a simple and original protocol was established by combining several techniques: repeated shoot meristem excision before and during in vitro culture and thermotherapy applied to bulblets in vitro. Lily symptomless virus (LSV) is a major virus that decreases plant growth vigor and the quality of cut flowers, yet infected plants show no distinct symptoms. Stock bulbs of pollenless Asiatic hybrid lily ( L. × elegans Thunb) lines (‘409’ and ‘599’) were used as explant. Shoot meristems were excised and micropropagated. Thermotherapy (42 days at 35 °C) was applied to in vitro growing bulblets and a second meristem cut was then made from heat-treated material. Leaf tissues from bulblets formed before or postheat treatments were analyzed either by enzyme-linked immunosorbent assay or by reverse transcriptase–polymerase chain reaction. Line ‘499’ produced LSV-free plants without heat treatment, but line ‘599’ produced LSV-free plants only after heat treatment. The virus-free lily bulblets grew vigorously in vitro and acclimatized promptly. It is suggested that thermotherapy given to in vitro growing bulblets effectively eliminated the virus and induced a fast and efficient micropropagation technique for virus-free mother plant stock.