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United States Department of Agriculture

Agricultural Research Service

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Research Project: Identifying Sources of Resistance to Wood-Canker Diseases in Almond Germplasm

Location: Crops Pathology and Genetics Research

2013 Annual Report


1a.Objectives (from AD-416):
Screen almond cultivars for resistance to the causal agents of Lower Limb Dieback and Bank Canker.


1b.Approach (from AD-416):
Planting disease-resistant cultivars is a time-tested and sustainable approach to disease management. Based on field observations and published research on resistance to wood-canker diseases, we know that a range of resistance exists among commercial cultivars of almond and grape. We propose to improve screening assays for evaluating both commercial cultivars and USDA germplasm repositories for sources of disease resistance. Our approach is to screen plant materials from both commercial nurseries and the USDA-ARS National Clonal Germplasm Respository.


3.Progress Report:

This project was established in support of objective 1 of the in-house project, which is to develop sustainable disease control practices for grapevines. The goal of this project is to determine the potential damage of Botryosphaeriaceae pathogens within almond orchards, frequency of infections within affected orchards, and management of these diseases.

To date, the following has been completed:

1. Orchard Surveys: Six orchards have been surveyed. All orchards have been reported to have problems with fungal cankers located within wind cracks of the scaffolds or pruning wounds. Affected trees were marked, tree specifics were recorded (i.e. variety, age of tree) and symptoms were described. After completion, trees were randomly selected for canker sampling. Windows were cut into the trunk of the tree including the phloem and lower few levels of xylem, removing a sample of the affected wood. Samples were submitted for fungal pathogen isolation to collaborators at the Kearney Agricultural Center and the University of California, Riverside, in the Central Valley of California.

2. Spore Trapping. Based upon the symptoms observed within the field, we hypothesize pruning wounds serve as the primary entrance for these pathogens. One potential change in management practices includes shifting the timing of pruning to a period of time when inoculum levels of these pathogens are low. To determine this timing, slides coated in petroleum jelly were placed throughout a severely diseased field. Slides were collected after 7 days of exposure and replaced with fresh, clean slides. Upon collection, the slides were sent to collaborators within the trial (mentioned above) for isolation and identification. Fungi were identified through both morphological and DNA methods. We found sporulation of Botryosphaeriaceae fungi tend to be associated with rain events. In weeks without rain, we were unable to isolate any of these pathogens.

3. Initiation of a pruning experiment. As described above, one potential change in management may include the shift in pruning young trees. Young trees are traditionally pruned in the dormant period after their first year of growth. The affects on growth of earlier pruning, for example, are unknown. Many growers feel pruning in the fall will reduce tree growth and vigor. With this in mind, we approached targeted growers to gain access to their young trees to initiate a pruning study. This trial will be established in 2014.

In 2012-2013, preliminary results from the surveys were presented at two grower meetings in the region. Both meetings had great attendance (~500 people total), and increased our database of affected orchards. An abstract and presentation was also delivered at the Annual Meeting of the Pacific Division of American Phytopathological Society.


Last Modified: 10/31/2014
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