ISHS Acta Horticulturae 386: XVI International Symposium on Fruit Tree Virus diseases
ELIMINATION OF APPLE SCAR SKIN VIROID FROM PEARS BY IN VITRO THERMO - THERAPY AND APICAL MERISTEM CULTURE |
| Authors: | J.D. Postman, A. Hadidi |
| Abstract:
Apple scar skin viroid (ASSVd) has been detected in several pear cultivars imported to the United States from Asia. These cultivars are currently under quarantine at the USDA National Plant Germplasm Quarantine Center, and cannot be released if infected with ASSVd. Shoot tips from the Chinese pear cultivar "Liu Yue Shian" infected with ASSVd were established in vitro and multiplied on Cheng's medium containing benzyladenine (1 mg/L). Following in vitro multiplication, infection was verified in each sample by reverse transcription - polymerase chain reaction (RT-PCR) using DNA primers specific for ASSVd. All in vitro plants tested positive for ASSVd. Plants were transferred to a medium without hormones in heat-sealed, semi-permeable, plastic bags for treatments. Cultures were either (1) maintained in a growth room at 22°C (control); (2) grown in a chamber at temperatures alternating between 30°C and 38°C every 4 hr; or (3) cold hardened for 7 days at temperatures alternating between 22°C (8 hr) and -1°C (16 hr), and then moved to a cold room and grown at 4°C. After 49 – 55 days, apical meristems approximately 0.5 mm long were dissected from each culture and grown into plantlets in vitro. RT-PCR tests for ASSVd after 3 months growth revealed that 86% of plantlets from heat treated meristems and 85% from cold treated meristems were viroid negative. Only 17% of control plantlets tested negative for the viroid. Of 26 in vitro plantlets from all treatments, 11 were successfully established in the greenhouse by tip-grafting onto healthy pear rootstocks. RT-PCR assays of 9 grafted trees for ASSVd, 9 weeks after grafting, produced identical results to assays of the corresponding in vitro cultures. In vitro heat or cold therapy combined with apical meristem culture eliminates ASSVd from infected pear trees and reduces the risk of introducing this pathogen from Asia to the U.S. during the international movement of plant germplasm. | |
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