Onions in India often grow a black powdery fungus. Here’s a folscope-look at this fungus and the cells that it grows on.

<figure aria-describedby="caption-attachment-31672" class="wp-caption aligncenter" id="attachment_31672" style="width: 225px">
 <a alt="OnionFungus-9-e1519812520400.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-9-e1519812520400.jpg">
 <img alt="White onion with fungus" class="wp-image-31672 size-medium gcloudimg" data-attachment-id="31672" data-comments-opened="1" data-image-meta='{"aperture":"2.2","credit":"","camera":"iPhone 5s","caption":"","created_timestamp":"1515851612","copyright":"","focal_length":"4.15","iso":"40","shutter_speed":"0.01","title":"","orientation":"0"}' data-image-title="White onion with fungus" data-recalc-dims="1" height="300" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-9.jpg" width="225"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31672">
 White onion with fungus
 </figcaption>
</figure>

 First try – we discarded the dry papery outer peels and looked at the inner wet peel of the onion which was spotted with fungus. We stained it with methylene blue.

<figure aria-describedby="caption-attachment-31664" class="wp-caption aligncenter" id="attachment_31664" style="width: 225px">
 <a alt="OnionFungus-1.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-1.jpg">
 <img alt="Inner wet layer with fungus" class="wp-image-31664 size-medium gcloudimg" data-attachment-id="31664" data-comments-opened="1" data-image-meta='{"aperture":"2.2","credit":"","camera":"iPhone 5s","caption":"","created_timestamp":"1515843219","copyright":"","focal_length":"4.15","iso":"40","shutter_speed":"0.02","title":"","orientation":"1"}' data-image-title="Inner wet layer with fungus" data-recalc-dims="1" height="300" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-1.jpg" width="225"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31664">
 Inner wet layer with fungus
 </figcaption>
</figure>

 It seems like there are nuclei in only some of the cells, hyphae of the fungus are winding their way through the cells and there are black spores. Later trying to figure out the criss-crossing pattern of cells we thought perhaps the peel had got folded on itself.


 Further inside the onion the layers looked free of fungus and we saw nice cells with clear nuclei.

<figure aria-describedby="caption-attachment-31665" class="wp-caption aligncenter" id="attachment_31665" style="width: 300px">
 <a alt="OnionFungus-2.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-2.jpg">
 <img alt="Inner layer without fungus" class="wp-image-31665 size-medium gcloudimg" data-attachment-id="31665" data-comments-opened="1" data-image-meta='{"aperture":"2.2","credit":"","camera":"iPhone 5s","caption":"","created_timestamp":"1515844970","copyright":"","focal_length":"4.15","iso":"50","shutter_speed":"0.01","title":"","orientation":"0"}' data-image-title="Inner layer without fungus" data-recalc-dims="1" height="225" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-2.jpg" width="300"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31665">
 Inner wet layer without fungus
 </figcaption>
</figure>

 This one has two layers with a 3D effect. Seems like only the lower nuclei got stained.

<figure aria-describedby="caption-attachment-31704" class="wp-caption aligncenter" id="attachment_31704" style="width: 300px">
 <a alt="OnionFungus-1-1.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-1-1.jpg">
 <img alt="Two inner layers" class="wp-image-31704 size-medium gcloudimg" data-attachment-id="31704" data-comments-opened="1" data-image-meta='{"aperture":"2.2","credit":"","camera":"iPhone 5s","caption":"","created_timestamp":"1515844205","copyright":"","focal_length":"4.15","iso":"32","shutter_speed":"0.02","title":"","orientation":"0"}' data-image-title="Two inner layers" data-recalc-dims="1" height="225" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-1-1.jpg" width="300"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31704">
 Two inner layers
 </figcaption>
</figure>

 The next time we got a red onion. From the outside it had yellowish patches but inside, sure enough was the fungus.

<figure aria-describedby="caption-attachment-31669" class="wp-caption aligncenter" id="attachment_31669" style="width: 300px">
 <a alt="OnionFungus-6.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-6.jpg">
 <img alt="Discoloured red onion" class="wp-image-31669 size-medium gcloudimg" data-attachment-id="31669" data-comments-opened="1" data-image-meta='{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"1519751695","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0"}' data-image-title="Discoloured red onion" data-recalc-dims="1" height="230" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-6.jpg" width="300"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31669">
 Red patchy onion
 </figcaption>
</figure>
<figure aria-describedby="caption-attachment-31670" class="wp-caption aligncenter" id="attachment_31670" style="width: 171px">
 <a alt="OnionFungus-7.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-7.jpg">
 <img alt="Outer skin peeled to show the fungus" class="wp-image-31670 size-medium gcloudimg" data-attachment-id="31670" data-comments-opened="1" data-image-meta='{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"1519751859","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0"}' data-image-title="Outer skin peeled to show the fungus" data-recalc-dims="1" height="300" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-7.jpg" width="171"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31670">
 Outer skin peeled to show the fungus
 </figcaption>
</figure>

 We looked at this dry fungus-covered skin, without staining.

<figure aria-describedby="caption-attachment-31666" class="wp-caption aligncenter" id="attachment_31666" style="width: 235px">
 <a alt="OnionFungus-3.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-3.jpg">
 <img alt="Fungus on dry skin of onion" class="wp-image-31666 size-medium gcloudimg" data-attachment-id="31666" data-comments-opened="1" data-image-meta='{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"1519750206","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0"}' data-image-title="Fungus on dry skin of onion" data-recalc-dims="1" height="300" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-3.jpg" width="235"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31666">
 Fungus on dry skin of onion
 </figcaption>
</figure>

 Here is an inner wet layer without fungus. This time we used a different, aqueous methylene blue which had undissolved bits that we washed off. It did not work so well. We assume that there are nuclei here but they did not get stained.

<figure aria-describedby="caption-attachment-31667" class="wp-caption aligncenter" id="attachment_31667" style="width: 257px">
 <a alt="OnionFungus-4.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-4.jpg">
 <img alt="Inner layer without fungus" class="wp-image-31667 size-medium gcloudimg" data-attachment-id="31667" data-comments-opened="1" data-image-meta='{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"1519750206","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0"}' data-image-title="Inner layer without fungus" data-recalc-dims="1" height="300" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-4.jpg" width="257"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31667">
 Inner wet layer without fungus
 </figcaption>
</figure>

 At the edge of the dried skin the fungus was clearer to see.

<figure aria-describedby="caption-attachment-31671" class="wp-caption aligncenter" id="attachment_31671" style="width: 218px">
 <a alt="OnionFungus-8.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-8.jpg">
 <img alt="Conidiophore of fungus" class="wp-image-31671 size-medium gcloudimg" data-attachment-id="31671" data-comments-opened="1" data-image-meta='{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"1519752505","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0"}' data-image-title="Conidiophore of fungus" data-recalc-dims="1" height="300" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-8.jpg" width="218"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31671">
 Conidiophore on the edge of the dry onion skin
 </figcaption>
</figure>

 This one is called a “conidiophore”. The hypha (filament) is translucent and segmented. At its tip are the “conidia” or a bunch of spores.  Our best guess from searching on the web is that this is
 <a alt="details" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/details">
 
 Aspergillus niger
 
 </a>
 , which colonises
 <a alt="Datasheet.aspx" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/Datasheet.aspx">
 various parts of over a hundred-odd food plants, from apples to maize
 </a>
 .


 We put a drop of water on one conidiophore and its globular tip burst! Here it is, releasing its conidia into the water.

<figure aria-describedby="caption-attachment-31668" class="wp-caption aligncenter" id="attachment_31668" style="width: 300px">
 <a alt="OnionFungus-5.jpg" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-5.jpg">
 <img alt="Spores eject out under water" class="wp-image-31668 size-medium gcloudimg" data-attachment-id="31668" data-comments-opened="1" data-image-meta='{"aperture":"0","credit":"","camera":"","caption":"","created_timestamp":"1519751203","copyright":"","focal_length":"0","iso":"0","shutter_speed":"0","title":"","orientation":"0"}' data-image-title="Spores eject out under water" data-recalc-dims="1" height="257" src="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/OnionFungus-5.jpg" width="300"/>
 </a>
 <figcaption class="wp-caption-text" id="caption-attachment-31668">
 Spores eject out under water
 </figcaption>
</figure>

 Here’s a video of
 <a alt="watch" class="gcloudimg" href="https://storage.googleapis.com/microcosmosdelta.appspot.com/images/transfer_31703/watch">
 what
 
 Aspergillus niger
 
 can do to its host onion over just 22 days
 </a>
 .


 In Indian kitchens we deal with
 
 A. niger
 
 on a daily basis. We chuck out the infected layers of onion or wash off the powdery fungus. But this close contact with the fungus got us a bit tickly in the nose and throat. Though generally not dangerous,
 
 A. niger
 
 <a href="http://blogs.evergreen.edu/fungalkingdom/aspergillus-niger-not-your-everyday-mold/">
 does contain toxins which could affect you in a variety of ways
 </a>
 . We must take care if we do this with school students, especially in low resource environments where gloves and masks are not available.




 K. Ashalatha
 
 Jayashree Ramadas

Fungus on onion

TCIS Outreach | Thu, Mar 01, 2018, 3:48 AM

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