Friday, October 2, 2009

Propagation of Pets - Producing Seeds

Seedpods forming on Petrocosmea forresttii at about 6 weeks after pollination.

Propagation of Petrocosmeas from seeds is unfortunately a rare occurence for most of us. For years, the only option many of us had to grow Pets from seeds was from the small quantities of seed that the late Gesneriad Society Seedfund Chairperson, Maryjane Evans produced. Maryjane was able to produce seeds from gesneriad species when most other people failed. She managed to produce seeds from a few species in the late 1990's and those quickly disappeared from the seedfund list. But, recently I've had some success. I thought I would share what has worked for me, in the hope that others might be able to produce Petrocosmea seeds.

For me, the two key factors that have proven necessary through three flowering seasons now are 1) high humidity, and 2) low temperatures for both seed production and seed sowing. In my conditions, I have been unable to produce any seeds in the absence of either of these factors. When both are present, I get seeds 33% of the time. While not great percentages, it is sufficient to get more seeds than I can grow.

So here's how I do it and what I've learned. First, as the plants start to show buds forming underneath the leaves, I place the entire plant inside a plastic nursery tray that is lined with a section of acrylic blanket cut to fit the tray. This blanket is kept barely moist until I harvest the seed pods. I place a plastic humidity dome over the tray so that the plant is enclosed in a "terrarium" environment. The tray is placed on the light shelves where the Pets normally grow and the plant's care remains the same as always. As the flowers open, I wait until they are open about four or five days. At that time, I note that the stigma has enlarges a bit and if viewed under a magnifying glass, it appears "sticky". At this point it is receptive to fertilization. I remove the pollen from the "father flower" and place as much of the pollen as I can onto the stigma. I label the flower with a small tag containing a number, which I note in my hybrid log with the cross and the date. If fertilization occurs, the stigma will "reorient" itself and will point upwards at approximately a 45 degree angle. The ovary will begin to enlarge. I sometimes remove other flowers and buds on this plant to allow more energy to be focused into the seedpod's formation.

Petrocosmea seeds. This photo was taken by my friend Dale Martens. She photographed a packet of seeds that I had shared with her.

Once the seedpods begin to enlarge, I start to count the days. For me, Petrocosmea seedpods have ripened between 57 and 80 days, depending upon the species used as the pod parent. I harvest the seeds, label them and place most of them into the freezer, inside a double layer of ziplock bags to ensure that no moisture gets to them. In this way, I've had good germination on seeds stored for one year. I only plant a small quantity of the seeds for both insurance in case the first planting does not germinate, and because I do not have the space to grow hundreds of seedlings from each cross. I have now accumulated quite a "bank" of Pet hybrid seeds in my freezer!

Petrocosmea seedlings two weeks after germination. I plant on either straight fine vermiculite or peat pellets that I moisten and sterilize in my microwave for three minutes on high.

I've now sown more than 50 batches of Petrocosmea seeds. I've had some total failures and some thrilling successes. I've learned a couple of critical points. First, the seeds must be sown on sterile medium. I microwave whatever medium I use in the microwave on the high setting for three minutes. I allow it to cool and sow the seeds. I sow the seeds in an enclosed environment, such as a ziplock bag or covered plastic bowl as shown above. The seeds must not dry out. Perhaps the most critical factor, though, seems to be cool temperatures for seedling germination. This has been proven now by myself and four other growers. Petrocosmea seed germination seems to be greatly enhanced by keeping them quite cool...for me around 40 degrees F seems to work best. Warm temperatures in the 60 degree or higher range has resulted in total failure to germinate for me in three seperate experiments and has had the same results for four other growers now. I have no idea why this is a factor for both seed production and germination. Perhaps in nature, the seeds are produced in the winter and early spring months so that the resulting seedlings will have a longer time to produce good root systems before the following winter hits them??? I don't know, but I do know that for me, cool temps are crucial in my environment.

The happy result of persistence in attempts to produce seeds on Petrocosmeas. These are the seedling community pots from three of my current crosses.....where am I going to find the room to grow all of these seedlings???? (Note the tray in front shows the seedlings from a cross I made with the intent of producing miniature Pets....these seedlings are the same age as the seedlings in the other two pots!)

A nursery tray underneath the lights in my basement. These are seedlings from the same cross of P. 'Asa Blue' x begoniifolia. Note the variation in the foliage texture, color and shape.

Once the Petrocosmea seeds germinate, I move them to slightly warmer temperatures to increase the rate of growth. After about a month of age, I begin to fertilize the seedlings as I do my mature Pets. Seedlings usually flower for me in about 8-9 months from seed sowing.
I am often asked if Pets are known to be self-fertile and do the self-pollinate. I have never had a Pet self-pollinate. If I get a seedpod, it is always the result of my crossing activities. So, if the ovary begins to enlarge, I usually always have a successful pollination. Since my success rate is only about 33%, I try to pollinate several flowers. That usually gives me one or two seedpods from each cross. Some pods produce one or two seeds, some hundreds. I've only had an empty seedpod once, on a cross that I attempted to make on a plant that was not in a terrarium. It was the only plant to ever form pods outside of an enclosed environment, but when I opened it, it was empty.
Lastly, I have found that some species seem to be happier to become parents than others. For me, P. forrestii has been a prolific seedpod parent, but has failed as a pollen parent. P. rosettifolia #3 is the same. P. duclouxi, P.barbata 'Keystone' and P. nervosa are also great seedpod parents. P. sericea is a fair parent as either the pollen or seedpod parent. P. minor does not want to cross with any of the other Pets. It has been reluctanct, having only been a pollen parent in two crosses.
So, do try to make some Petrocosmea crosses. I tried every year for ten years before I stumbled upon my current methods. It was just an accident that it worked, but I am most grateful that it did work!!!