Current status of ASBVd infection among avocado accessions in the national germplasm collection

Cecile T. Olano, Raymond J. Schnell, David N. Kuhn


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 used to detect the viroid. A survey performed in 1996 found that 19% of the plants were infected with the viroid. The object of the current study was to assess the spread of infection, if any, and the rate and direction of transmission. For this purpose the collection was screened again for ASBVd. Twenty three newly infected trees were detected. Forty eight percent of the newly infected plants were found to be adjacent to previously infected plants. No pattern in direction of spread was discerned for non-adjacent new infections. Fifteen plants found to be positive for the viroid in the 1996 survey are now negative. The failure to detect ASBVd in plants 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 plants in the current collection remains 19%. Thus, important ASBVd infected germplasm can be maintained isolated from non-infected germplasm with proper phytosanitary precautions and continued monitoring of the non-infected accessions using the RTPCR assay.


persea americana; avocado sunblotch viroid; germplasm collection management; viroid indexing; avocado diseases

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283