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Title: CURRENT STATUS OF ASBVD INFECTION AMONG AVOCADO ACCESSIONS IN THE NATIONAL GERMPLASM COLLECTION

Author
item Tondo, Cecile
item Schnell Ii, Raymond
item KUHN, DAVID - FLA. INTL. UNIV.

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: 8/5/2002
Publication Date: 12/15/2002
Citation: Olano, C.T., Schnell II, R.J., Kuhn, D.N. 2002. Current status of ASBVd infection among avocado accessions in the national germplasm collection. Proceedings of Florida State Horticultural Society. 115: 280-282.

Interpretive Summary: Using molecular genetics techniques an assay was developed for Avocado Sunblotch Viroid (ASBVd). This viroid is similar to a virus and causes a decline in production of avocado trees and blemishes on the fruit. The technique was used to survey the Avocado germplasm collection maintained at the Subtropical Horticulture Research Station in Miami, FL in 1996. THis initial survey found that 19% of the trees were infected with the viroid. Since 1996 the collection has been managed to minimize the spread of the viroid with the infected germplasm maintained in a field 763 feet from non-infected accessions. The goal of this study was to re-survey the collection and see if the containment of the viroid has been effective. The results from the 2002 survey found the overall infection rate was still 19%. Of the 23 newly infected plants, 48% were adjacent to previously infected plants and were infected through root grafting. The remaining plants were infected through poor phytosanitary practices. We conclude from the data that maintaining the collections 763 feet apart restricts natural dispersal of ASBVd. Ad long as proper phytosanitary practices are followed, the non-infected accessions will not be at risk of infection with the viroid.

Technical Abstract: Previous studies established the presence of Avocado Sunblotch Viroid (ASBVd) infection among the avocado accessions in the National Germplasm Repository at Miami (NGR-Mia). An ASBVd specific reverse transcription-polymerase chain reaction (RT-PCR) protocol was developed to detect the viroid. A survey performed in 1996 found that 19% of the accessions were infected with the viroid. The object of the current study was to assess the spread of infection and the rate and direction of transmission. For this purpose the collection was screened again for ASBVd. Twenty-three newly infected trees were detected. Fifteen accessions found to be positive for the viroid in the 1996 survey are now negative. The failure to detect ASBVd in accessions previously found to be positive may be due to accuracy of the assay. An alternative hypothesis is viroid induced RNA silencing, a general anti-viral defense mechanism in plants. The proportion of infected accessions in the current collection remains 19%. Forty-eight percent of the newly infected plants were found to be adjacent to previously infected plants.