Presentation Title

The Dehydration Tolerance of a Fungal Pathogen (Botryosphaeria dothidea) Exceeds the Dehydration Tolerance of Chaparral Host Plants

Faculty Mentor

Natalie M Aguirre, Stephen D Davis

Start Date

18-11-2017 1:45 PM

End Date

18-11-2017 2:00 PM

Location

9-271

Session

Bio Sciences 2

Type of Presentation

Oral Talk

Subject Area

biological_agricultural_sciences

Abstract

We tested the hypothesis that an opportunistic endophytic fungus Botryosphaeria dothidea that frequently infects and causes dieback in species of chaparral shrubs in the Santa Monica Mountains continues to elongate and grow in host tissues at dehydration levels that exceed host survival. We did this by collecting large branches from the field from two species of co-occurring chaparral shrubs in the Santa Monica Mountains, Malosma laurina and Ceanothus megacarpus. We allowed branches to dehydrate at increasing lengths of time, up to 6 days, in an air conditioned laboratory, then sealed in plastic bags to allow tissue-water equilibration, and measured water potential at different dehydration levels. Stem segments were then inoculated with the fungal pathogen B. dothidea, sealed into test tubes and allowed to incubate for six days. After six days of fungal growth, lengths of hyphal invasion into stem tissues was recorded and final water potentials were determined using a dew point hygrometer. In Malosma laurina stem segments, incubated at a water potential of -4.4 MPa, fungal elongation continued at 37 mm/week (+ 3.74 SE, n = 12), exceeding the survival limits of the host plant (100% cavitation of stem xylem at -4 MPa). In Ceanothus megacarpus stem segments, incubated at a water potential of -11.4 MPa, fungal elongation continued at 14 mm/week (+ 2.91 SE, n = 12), also exceeding survival limits of the host. This indicates that the invasion and growth of the fungal pathogen B. dothidea in the stem xylem of these co-dominant chaparral species can continue under severe drought conditions recently experienced in California and likely contribute to the whole plant mortality recently observed for these species.

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Nov 18th, 1:45 PM Nov 18th, 2:00 PM

The Dehydration Tolerance of a Fungal Pathogen (Botryosphaeria dothidea) Exceeds the Dehydration Tolerance of Chaparral Host Plants

9-271

We tested the hypothesis that an opportunistic endophytic fungus Botryosphaeria dothidea that frequently infects and causes dieback in species of chaparral shrubs in the Santa Monica Mountains continues to elongate and grow in host tissues at dehydration levels that exceed host survival. We did this by collecting large branches from the field from two species of co-occurring chaparral shrubs in the Santa Monica Mountains, Malosma laurina and Ceanothus megacarpus. We allowed branches to dehydrate at increasing lengths of time, up to 6 days, in an air conditioned laboratory, then sealed in plastic bags to allow tissue-water equilibration, and measured water potential at different dehydration levels. Stem segments were then inoculated with the fungal pathogen B. dothidea, sealed into test tubes and allowed to incubate for six days. After six days of fungal growth, lengths of hyphal invasion into stem tissues was recorded and final water potentials were determined using a dew point hygrometer. In Malosma laurina stem segments, incubated at a water potential of -4.4 MPa, fungal elongation continued at 37 mm/week (+ 3.74 SE, n = 12), exceeding the survival limits of the host plant (100% cavitation of stem xylem at -4 MPa). In Ceanothus megacarpus stem segments, incubated at a water potential of -11.4 MPa, fungal elongation continued at 14 mm/week (+ 2.91 SE, n = 12), also exceeding survival limits of the host. This indicates that the invasion and growth of the fungal pathogen B. dothidea in the stem xylem of these co-dominant chaparral species can continue under severe drought conditions recently experienced in California and likely contribute to the whole plant mortality recently observed for these species.