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Title: Results of the 2009 ASBVd survey of avocado accessions in the national germplasm collection in Florida

Author
item Tondo, Cecile
item Schnell Ii, Raymond
item Kuhn, David

Submitted to: Journal of Florida State Horticulture Society
Publication Type: Proceedings
Publication Acceptance Date: 7/26/2010
Publication Date: 4/1/2011
Citation: Tondo, C.L., Schnell Ii, R.J., Kuhn, D.N. 2011. Results of the 2009 ASBVd survey of avocado accessions in the national germplasm collection in Florida. Journal of Florida State Horticulture Society. 1.

Interpretive Summary: Avocado Sunblotch Viroid (ASBVd) causes a disease that affects avocado (Persea americana). The disease is of economic importance because the disease symptoms on the fruit renders the fruit unmarketable. Previous studies have demonstrated the presence of ASBVd in the avocado collection at the National Germplasm Repository at Miami. Two surveys have been performed in the past, one in 1996 and another in 2000. This study reports the results of a third survey performed in 2009, in which of all of the plants in the avocado collection were screened for ASBVd. The collection contained 505 trees, 106 of the trees were found to be infected with ASBVd. Fifty of the infected trees are new infections. Twenty four of the newly infected trees were next to infected trees or contaminated plots. Fourteen plants found to be infected in previous surveys, were found to be negative in this survey. As these 14 trees are considered infected, then the proportion of infected trees is 24% (120/505). The increase in ASBVd infections reinforces the importance of establishing back-up collections at different locations. Establishment of collections at the NGR in Hawaii is currently underway.

Technical Abstract: The presence of Avocado Sunblotch Viroid (ASBVd) infection among the avocado (Persea americana Mill.) accessions in the National Germplasm Repository at Miami (NGR-Mia) was established in previous studies. An ASBVd specific reverse transcription-polymerase chain reaction (RT-PCR) protocol was used to detect the viroid. Surveys performed in 1996 and in 2000 found that the proportion of ASBVd positive accessions remained unchanged at 19%, during that time period. 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 in 2009. The germplasm collection increased from 403 to 505 trees. Fifty newly infected trees were detected. Forty eight percent of the newly infected plants were found to be adjacent to previously infected plants, adjacent to plots from which infected plants had been removed or adjacent to other newly infected plants that are adjacent to previously infected plants or contaminated plots. No pattern in direction of spread was discerned for non-adjacent new infections. The proportion of plants found to be positive for the viroid in the current study is 21%. Fourteen plants previously found to be infected, were found to be negative in this survey. The proportion of infected plants (historically and present) in the current collection is 24%. The increase in ASBVd infections reinforces the importance of establishing back-up collections at different locations. Establishment of collections at the NGR in Hawaii is currently underway.