Potyvirus in Korean radish

This sample came in before the winter break from a grower who specializes in Asian vegetables. A bag full of Korean radishes (also known as tae baek)- white & green very large (~6 inches long and ~3 inches diameter) radishes. This sample presented with leaf curling and dark flecks in the root tissue. Never having encountered a Korean radish before, I had to research the seed catalogs online to see if the green shoulders were normal (they are). The sample was in the cooler for too long and the foliage was beginning to deteriorate, so no picture but symptoms were similar to those caused by viruses.

Possibilities: virus or abiotic (herbicide, nutrient deficiency).

Tests done: CMV (ImmunoStrip assay from Agdia), POTY (elisa assay from Agdia)

Results: (-)CMV, (+)Potyvirus

Pythium root rots of bean and watermelon seedlings

Today was a day of root rots! Two samples of pythium root rot but both came in with complaints of foliage problems on field transplants (browning and death of bean leaves & wilting of watermelon). Luckily, the submitters had included the full root system and soil so we were able to quickly make an accurate diagnosis. Pythium agar was used to confirm the presence of Pythium spp. Note the characteristic stem lesions.
Pythium root rot on snap bean transplants:

And Pythium root rot on watermelon transplants:

Fennel-Unknown problem

Another delicious smelling sample- fennel (Foeniculum vulgare). This sample presented with browning on the edges of stems at the bulb. The very oldest leaves are yellowing and dying. The main cause is likely that the plant is pot bound (roots are curling around at the bottom). There was no internal decay in the bulb and the majority of the foliage was fine. The bulb is incubating to double check.Above photo is a little bleached out, note that the Jiffy pot has been pulled away for the photo.



Cut edges are starting to brown as I took the above photo ~10 mins after cutting.

Lettuce-Powdery Mildew & Rhizoctonia

This was a lettuce sample from an organic hydroponic system. Three heads were submitted-two butter (pictured above) and one that looked like Romaine. There was a lot happening: white powdery growth on the leaves, dieback at the crown, lots of insects crawling around.
Below is a closeup looking across the top of the leaf surface. If you click on the image, you'll see the powdery mildew conidia chains in good detail. This can be seen in the field by rolling the leaf around your finger and looking perpendicular to the leaf with a hand lens. Powdery mildew is caused by the Ascomycete, Erysiphe cichoracearum. Didn't see any cleistothecia on the leaves, but I saved the sample to see they can be induced to form somehow. Here is a closeup of the crown tissue and problem #2. The greenish powdery substance is the growth media, probably an Oasis type media. The arrows are pointing to white mycelium, which turned out to be Rhizoctonia (click photo for bigger image).

Downy Mildew on brassica (cabbage & broccoli) seedlings

Description: Scattered, irregular-shaped, sunken, gray-black lesions on a mixed sample of cabbage and broccoli seedlings. Symptoms ranged from subtle (broccoli) to more severe (cabbage).


Tests done: The diagnostician had already recognized this as downy mildew (based on experience), but I decided to place leaves in a moist chamber to induce sporulation just to double-check.

Final Diagnosis: Downy mildew caused by Peronospora parasitica. Forgot to take a picture of the diagnostic sporangiophores and sporangia! The University of Florida has a good factsheet describing symptoms, although the accompanying photos seem over-exposed.

References used: Compendium of Brassica Diseases