Evaluating Powdery Mildew Resistance in CBD Hemp Cultivars – Preliminary Results

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Ali Cala, Nathalia Portilla, Bill Weldon, William Gura, Nicholas King, George Stack, Jacob Toth, Craig Carlson, David Gadoury, Surya Sapkota, Larry Smart, Chris Smart

Hemp powdery mildew – Golovinomyces spadiceus:

  • Hemp powdery mildew is a fungal pathogen that appears as patches of white spores on the surface of leaves (Fig. 1 & 2).
  • It is an emerging pathogen – has been reported in greenhouses and the field.
  • It can cause early leaf drop & reduce flower bud quality (Fig. 3).
  • Disease management strategies for hemp powdery mildew are being developed.
Fig. 1. Powdery mildew on a hemp leaf
Fig. 2. Powdery mildew on a hemp leaf as seen through a microscope
Fig. 3. Powdery mildew can reduce flower bud quality

Is there resistance to powdery mildew in hemp?

  • 30 high CBD cultivars were screened for resistance to powdery mildew
  • Preliminary data from the detached leaf assay showed some differences in susceptibility (Fig. 4).
  • These studies are continuing, and we are screening an additional 37 cultivars.
Fig 4. Chart showing the susceptibility of different hemp cultivars to powdery mildew

Is Hemp Powdery Mildew & Hop Powdery Mildew cross infectivity a concern?

  • Humulus lupulus (hop)  is the closest crop relative to hemp.
  • Hop powdery mildew is caused by Podosphaera macularis (Fig. 5 & 6).
Fig 5. A hop leaf inoculated with powdery mildew
Fig 6. Powdery mildew on hops

Is hemp powdery mildew a threat to hop?

Fig 7. A hop leaf inoculated with hemp powdery mildew, which does not grow well on hop.

Is hop powdery mildew a threat to hemp?

Fig 8. A hemp leaf from cultivar Anka is inoculated with hop powdery mildew. Hemp is a host of hop powdery mildew.

Future questions:

Can we identify resistance genes in hemp against powdery mildew? Which cultivars are most resistant? How diverse is the pathogen population?

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