Presentation Title

Recovery of California black walnut trees following drought induced dieback

Faculty Mentor

Frank W. Ewers

Start Date

18-11-2017 1:30 PM

End Date

18-11-2017 1:45 PM

Location

9-271

Session

Bio Sciences 2

Type of Presentation

Oral Talk

Subject Area

biological_agricultural_sciences

Abstract

Following several years of historic drought, the California black walnut (Juglans californica S. Watson) has been observed to first dieback and then resprout, with resprouts also suffering from apparent water stress and possible fungal attack. Following a year of normal rainfall, trees were sampled at one site on the Pepperdine University campus where the adults had died back totally and resprouted, and a second site at Solstice Canyon where dieback had not occurred in ten-year-old trees. It was hypothesized that the resprouts would exhibit higher water potentials, fv/fm values, and photosynthetic rates, as result of resprouts having less leaf area. It was additionally hypothesized that the primary fungal agent of cankers would be Botryosphaeria dothidea, as is the case for adjacent growing Malosma laurina. Indeed, resprouts had higher mean water potentials, fv/fm values, and photosynthetic rates than the ten-year-old trees. However, we isolated at least five different fungal species from walnut cankers thus far, displaying that there is not a single dominant fungal pathogen. At this time, the resprouts of California black walnut appear to be rather healthy.

Summary of research results to be presented

Resprouts had higher mean water potentials, fv/fm values, and photosynthetic rates than the ten-year-old trees. Tables and statistical analyses will be shown. We isolated at least five different fungal species from walnut cankers thus far, displaying that there is not a single dominant fungal pathogen. Micrographs of the various isolated fungi will be shown.

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Nov 18th, 1:30 PM Nov 18th, 1:45 PM

Recovery of California black walnut trees following drought induced dieback

9-271

Following several years of historic drought, the California black walnut (Juglans californica S. Watson) has been observed to first dieback and then resprout, with resprouts also suffering from apparent water stress and possible fungal attack. Following a year of normal rainfall, trees were sampled at one site on the Pepperdine University campus where the adults had died back totally and resprouted, and a second site at Solstice Canyon where dieback had not occurred in ten-year-old trees. It was hypothesized that the resprouts would exhibit higher water potentials, fv/fm values, and photosynthetic rates, as result of resprouts having less leaf area. It was additionally hypothesized that the primary fungal agent of cankers would be Botryosphaeria dothidea, as is the case for adjacent growing Malosma laurina. Indeed, resprouts had higher mean water potentials, fv/fm values, and photosynthetic rates than the ten-year-old trees. However, we isolated at least five different fungal species from walnut cankers thus far, displaying that there is not a single dominant fungal pathogen. At this time, the resprouts of California black walnut appear to be rather healthy.