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Enzymatic Activity of the Mycelium Compared with Oospore Development During Infection of Pea Roots by Aphanomyces
Abstract:
ABSTRACT To describe the disease cycle of the root pathogen Aphanomyces euteiches, enzymatic activity in the mycelium was compared with the development of oospores in pea roots. Plants were inoculated with two zoospore concentrations to achieve different disease levels. Hyphae were stained for fungal alkaline phosphatase activity in the roots. Additionally, enzyme activity was measured after electrophoresis of an A. euteiches-specific glucose-6-phosphate isozyme. Development of oospores in the roots was measured after staining the oospores with trypan blue. In plants inoculated with the higher zoospore concentration, the enzymatic activity of the pathogen mycelium peaked 10 to 14 days after inoculation, when oospore formation was initiated. Oospore formation was associated with a gradual increase in disease symptoms. At the last harvest, plants inoculated with the higher zoospore concentration had died. In these plants, oospores were found in 90% of the root length, while the enzymatic activity of the mycelium was low. This suggests that the pathogen mycelium is only active on living plants and does not grow saprophytically on dead plant material.
Insights
The root pathogen Aphanomyces euteiches shows peak enzymatic activity during oospore formation in living pea roots. Mycelial activity declines as oospores develop and plants die, indicating it does not grow saprophytically on dead tissue.
Area of Science:
- Plant Pathology
- Mycology
- Molecular Biology
Background:
- Aphanomyces euteiches is a destructive root pathogen affecting legumes.
- Understanding its disease cycle is crucial for developing effective management strategies.
- Enzymatic activity and oospore development are key indicators of pathogen lifecycle progression.
Purpose of the Study:
- To elucidate the disease cycle of Aphanomyces euteiches in pea roots.
- To correlate fungal enzymatic activity with oospore development and disease progression.
- To determine if the pathogen exhibits saprophytic growth on dead plant material.
Main Methods:
- Pea plants were inoculated with Aphanomyces euteiches at varying zoospore concentrations.
- Fungal alkaline phosphatase activity and a specific glucose-6-phosphate isozyme activity were measured in root tissues.
- Oospore development was quantified using trypan blue staining.
- Disease severity and plant mortality were assessed over time.
Main Results:
- Enzymatic activity in Aphanomyces euteiches mycelium peaked 10-14 days post-inoculation, coinciding with the initiation of oospore formation.
- Increased oospore development correlated with enhanced disease symptoms and eventual plant death.
- In dead plants, oospores were abundant (90% root length), but mycelial enzymatic activity was low.
- The pathogen's enzymatic activity was highest when infecting living plant tissues.
Conclusions:
- Aphanomyces euteiches mycelial activity is primarily associated with living host tissue.
- The pathogen does not appear to grow saprophytically on dead plant material after host death.
- Oospore formation is a critical stage in the Aphanomyces euteiches disease cycle, linked to host demise.
