Tree Growth Stage and Environment after Pathogen Inoculation Alters Susceptibility of Pear Trees to Phytophthora Canker

Authors: LAYWISADKUL, S - Oregon State University; FUCHIGAMI, L - Oregon State University; Scagel, Carolyn; Linderman, Robert

Submitted to: The Open Horticulture Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2010
Publication Date: 3/1/2009
Citation: Laywisadkul, S., Fuchigami, L., Scagel, C.F., Linderman, R.G. 2009. Tree growth stage and environment after pathogen inoculation alters susceptibility of pear trees to Phytophthora canker. The Open Horticulture Journal. 3:11-20.

Interpretive Summary: We investigated whether growth stage of pear tree rootstock and environment after inoculation with Phytophthora syringae influences tree susceptibility to infection. Trees at different stages of dormancy development were inoculated with the pathogen and maintained in different conditions after inoculation. In summary, using a simple disease assay system we determined the susceptibility of pear trees to P. syringae varies between actively growing and dormant trees, and incubation conditions after exposure to the pathogen, particularly temperature, are important for disease development regardless of tree growth stage. Under conditions favorable to the pathogen, P. syringae can infect stems of both actively growing and dormant pear trees. The ability of P. syringae to infect wounds on stems of pear may be restricted by the age of the wound, even in dormant trees. In our test conditions, as trees became more dormant in the autumn their susceptibility to P. syringae was not increased by the influence of urea of tree N status. This information is useful to nursery management practices in areas infested with P. syringae or during transport or cold storage when the potential for exposure to the pathogen is high and highlights the important of inspection and treatment of both dormant and actively growing trees to prevent or reduce the build up of inoculum and avoid epidemics.

Technical Abstract: We investigated whether growth stage of pear (Pyrus communis) tree rootstock and environment after inoculation with Phytophthora syringae influences tree susceptibility to infection. Trees at different stages of dormancy development were inoculated with the pathogen and maintained in different conditions after inoculation. Lesions developed on stems of actively growing trees inoculated before terminal buds had set and increased disease severity was associated with lower temperatures after inoculation. Susceptibility of pear trees to P. syringae in the autumn after terminal buds had set was influenced by environmental conditions after inoculation and tree growth stage. During early stages of dormancy development there was no relationship between temperature and size of lesions. As trees became more dormant a negative relationship developed between temperature and size of lesions. These results suggest a combination of tree growth stage when exposed to the pathogen and environmental conditions afterward play important roles in disease development. Differences in tree susceptibility related to dormancy development may be related to stem nitrogen (N) status or the ability of trees to produce a barrier to infection after stems are wounded. Differences in tree susceptibility may be a direct result of temperature on pathogen activity or an indirect effect on pathogen activity through the effects of temperature on tree metabolic activity. Wounds of different ages on trees after terminal buds had set were differentially susceptible to P. syringae. Lesions developed when fresh wounds were inoculated, but as wounds became older they were less susceptible to infection. Surface wounds inflicted during handling after terminal bud set may serve as infection locations for P syringae; however, the length of time between wound formation and exposure to the pathogen dictates whether infection will occur when trees are in the early stages of dormancy development.