Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2003
Publication Date: 7/10/2003
Citation: POSTMAN, J.D., HUMMER, K.E., POMPER, K.W. VASCULAR DECLINE IN THE OREGON PAWPAW REGIONAL VARIETY TRIAL. HORTTECHNOLOGY. 2003. 13(3):418-420 Interpretive Summary: A regional variety trial of pawpaws was established at the U.S. Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository, Corvallis, Oregon, in the fall of 1995. This orchard contained eight of 28 pawpaw varieties. During the first few years after planting, trees began to die from an unknown disease, and after 2 years half of them died. Survival in some varieties was better than in others. The sick trees turned yellow, wilted and died after about 2 years. Seedling trees initially were not affected by the disease. Eventually they also exhibited symptoms. The disease was not caused by a fungus. Many bacteria were found in the trees, but none could be confirmed as the cause. This report lists the pawpaw varieties that were most susceptible. Research is continuing to determine if a bacterial pathogen was the cause of the pawpaw decline.
Technical Abstract: A pawpaw (Asimina triloba) regional variety trial (RVT) was established at the U.S. Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR), Corvallis, Ore., in the fall of 1995. This orchard was a replicated planting of 28 commercially available varieties or advanced selections from the PawPaw Foundation, with eight replicate trees of each selection grafted onto seedling rootstocks and planted in a randomized block design. Two years after planting, 32 trees had either failed to establish or had died after an initial healthy start. By July 1999, 25% of grafted trees had died due to a vascular wilt-like disease, and 2 years later mortality exceeded 50%. Grafted selections with the lowest symptom severity include 1-7-2, 2-54, 7-90, 8-58, 9-58, 'Mitchell', 'PA-Golden #1', 'Taylor' and 'Wilson'. Seedling guard trees were unaffected until July 2000, when six guard trees of 76 died and 10 more were declining. By July 2001, 14 guard trees were dead. No fungi were consistently isolated from declining trees. A number of bacteria were isolated from infected trees, but no specific pathogen has been confirmed as the causal agent. polymerase chain reaction (PCR) tests for phytoplasmas and for the bacterium Xylella fastidiosa were also negative. Research is ongoing to determine if a bacterial pathogen was the cause of the pawpaw decline in the Oregon RVT.