Development of Endophyte-Mediated Disease Resistance in Hybrid Poplar

Hybrid poplar is the predominant woody perennial being developed for the bioeconomy as a purpose-grown source of cellulosic feedstock. P. deltoides — P. trichocarpa has been the most productive hybrid in the Northwest while P. deltoides — P. maximowiczii is likely the Southeast's best hybrid. But durable disease resistance is the principal obstacle in continued commercial use of these hybrids. Breeding for resistance to Melampsora leaf rust the main pathogen in the Northwest has been difficult due to the multiplicity of rust pathotypes. In the Southeast attaining resistance to the principal pathogen Septoria stem canker has been challenging given the disease's broad range of virulence. Our goal is the development of endophyte-mediated resistance technology to overcome these pathogens either by direct antagonism or by prompting host-resistance mechanisms. The proposal therefore responds to program area 8.1's priority to develop "… better methods [and] control strategies for combating … pathogens that attack important woody species…" The objectives are: 1) identification of bacterial endophytes that are antagonistic to Melampsora and Septoria in laboratory and greenhouse assays and 2) evaluation of endophyte technology in hybrid trials in the Northwest and the Southeast. George Newcombe will provide expertise in endophyte selection and application. Anticipated results are improved disease control methods that augment genetic resistance. Phase I will be devoted to endophyte discovery and establishment of field trials. Phase II will complete the fields trials. Phase III's objective is the joint commercialization of hybrids and endophytes in the two regions.