Basal stem rot of vegetables in controlled environment greenhouses in western Saudi Arabia : (A)‎ studies on the causal agent Pythium aphanidermatum

الملخص EN

Samples of diseased cucumber (Cucumis sativus L.), cantaloupe (Cucumis melo var.

cantalopensis) and sweet pepper (capsicum annum L.) exhibiting basal stem rot and damping off were collected from controlled environment greenhouses in the western region of Saudi Arabia.

Based on morphological characterization of vegetative and sexual structures (mycelium, zoospores and oospores), the causal agent was identified as Pythium aphanidermatum (Edson) Fitsp.

Mycelium was hyaline, non-septate.

Oogonia were spherical and terminal with dome-shaped, diclenous (antheridia and oogonia from different hyphae) and intercalary antheridia (one antheridium per oogonium).

Oospores were spherical and aplerotic (partially filling oogonia).

Sporangia were inflated filamentous or lobulate that germinate giving vesicles containing zoospores, which soon be released.

Four different culture broth media, V-8 Juice Broth (V-8JB), Oat Meal Broth (OMB), Corn Meal Broth (CMB) and Potato Broth (PB) were quantitatively evaluated for vegetative growth and induction of reproductive structures.

The highest mycelial dry weight was significantly (at P ≤ 0.05) observed on OMB.

No significant difference (at P ≤ 0.05) were found between PB and V-8JB.

On the other hand, the lowest mycelial growth was detected on CMB.

Oospore density was significantly (at P ≤ 0.05) the highest on CMB followed by V- 8JB then OMB.

However, oospores were not formed on PB.

Zoospore production, on the other hand was the highest when the fungus was grown in V-8JA, followed by OMA, PA then CMA.