Stress Testing Cannabis – Screening for Hermaphrodites

A stress test shows whether a plant tends to turn hermaphrodite. You expose it on purpose to the conditions that trigger male flowers on females. A plant that forms male flowers in the test does not go into breeding. It pays off because the tendency is inherited.

Why test mother and pollen donor, even with feminized seed?

Because the tendency sits in the line, not in the type of seed. Feminized seed is meant to give only females. For it, a female is made into a pollen donor with silver thiosulfate. The spray works however prone she is. So the treatment says nothing about her breeding stability. Daughters of hermaphrodites formed male flowers more often, 34 instead of 23 % in one trial. For monoecy, both flower types on one plant, over 90 % of the difference came down to genes.

  • Test mother and donor separately before crossing.
  • Always test untreated, never under silver thiosulfate.

How does the test work for females?

The test uses the triggers shown to cause male flowers. These are an abrupt light switch and cold of about 13 °C at the switch. After such a switch, 25 to 45 % of females in a prone line carried male flowers. Pruning, heat and light leaks are no use as a test, they are not documented as triggers. How long the cold has to last is not established.

  1. Take four cuttings, rooted clones, from each candidate.
  2. After about 30 days, switch two of them abruptly from 18 to 11 hours of light and keep them around 13 °C.
  3. Flower the other two under normal conditions.
  4. Grow all of them to maturity.
  5. From week four, check low on the stem every week for anthers, the pollen sacs of the male flower.
  6. A single male flower is enough: the candidate is out.

What does a male show under stress?

A male can form female flowers in return. In one case from practice, a plant flowered clearly male for weeks. Two to three days after being cut back, it showed female flowers at the cut, documented with time-stamped photos. Whether the cut caused it or the plant was labile anyway cannot be told from one case. There is no documented test trigger for males.

  • Watch every male until its pollen is ripe.
  • After every cut, check the cut sites for female flowers.
  • Do not use a male with female flowers as a father.

How does a line become more stable over generations?

Through selection in every generation. Because the tendency is inherited, selection can work. How fast the share falls has not been measured. Too much inbreeding, crossing close relatives, has a price. With repeated selfing, malformed flowers in one line rose from 0.4 to 13.7 %. Selfing means pollinating a plant with its own pollen. That line came from male plants; for female lines this has not been measured.

  • With little seed, first multiply it across several parents.
  • Test the males along the way.
  • Test every generation and drop every plant with male flowers.
  • Record the share of affected females per generation.

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