The Effect of Temperature, Light, and Scoring on the Germination of Some
Hardy Waterlily Seeds

by Donald Stevens, Hamilton, Ontario, Canada
Photos by and © Perry D. Slocum - Click to enlarge

This study was undertaken to investigate the effect of temperature, light and scoring on the germination of hardy waterlilies.

Seeds from the following hardy waterlilies (Nymphaea) were tested: N. alba New Zealand strain (ANZ), N. 'Alba Plenissima' (APL), N. 'Fire Crest' (FIR), N. 'Perry's Fire Opal' (PFO), N. 'Perry's Pink' (PPI), N. 'Texas Dawn' (TDN), N. tetragona (TET) and N. pygmaea (tetragona 'Japan') (PTJ). FIR and TET were purchased locally. All other varieties were obtained from Perry's Water Gardens, North Carolina. ANZ, TET and PTJ represented Nymphaea species. All waterlilies were open pollinated during the summer / fall of 2002 in Hamilton, Ontario, Canada.

All hardy seeds were stored at 5 - 7C (41 - 45F) for 3-4 months. Just before testing, seeds were surface sterilized for 12 minutes in 50 ml 25% bleach (1 part bleach + 3 parts water) containing a drop of dish washing detergent, followed by rinsing four times with "sterile" water. All water used was domestic water that had been "sterilized" for 10 minutes on "high" in a 900W Panasonic microwave in which a rolling boil was maintained for about 4 minutes.

Experiments were carried out in glass aquaria (10 or 29 gal) which were maintained under a fluorescent light fixture [122cm (48")] that held two 40W General Electric "Gro and Sho" wide spectrum and two 40W Philips "Agrolite" bulbs in alternating positions. This was the only source of light. The water surface was about 15cm (6") from the bottom of the lights. The lights were on a 16 hour/day timer. The 10 gallon aquaria was maintained at 22C (72F) by a 100 W heater and the 29 gallon at 29C (85F) by a 150 W heater. Air was gently bubbled through an air stone to help distribute the heat evenly. To help maintain thermal stability, the aquaria were housed in a wooden frame 122cm x 61cm x 96 cm (48"w x 24"d x 37.5"h), enclosed with 6 mil clear plastic. All instruments and containers were surface sterilized with 99% isopropanol between uses to minimize contamination.

Each lot of seeds was randomly assigned to the experimental conditions. The seeds were placed in Zip Lock baggies with 50 mL of sterilized water. Germination was defined as when the emerging radicle protruded past the remnants of the operculum. Germination was evaluated daily for the first 18 days, and then on alternate day until day 28.

The experimental conditions were as follows:

1. The seeds were either unmanipulated or lightly scored by filing the side of the seed with nail file just until the endosperm was exposed.
2. Seeds were maintained in darkness or light. The baggies of seeds in the light were allowed to float freely on the water surface. Dark denoted seeds whose baggies were placed in a floating sealed black plastic bag containing water. Absolute darkness was not obtained, but the light was severely reduced.
3. The seeds were incubated at either 22C (72F) or 29C (85F).

A preliminary study was done with APL, PFO and PPI. Each batch contained 50 seeds that were either scored or not and kept on a shelf at room Temperature 18 - 20C (65 - 69F) in the dark. As seen from Table 1, very poor germination (2 - 12%) was seen for APL and PPI, even by 35 days. For unscored seeds of PFO, only 9/50 (18%) had germinated by 3 weeks, but 44/50 (88%) for the scored seeds at 3 weeks - 38/50 (76%) within 7 days.

Further studies were undertaken to see what effect light and higher temperatures had on germination of hardy waterlily seeds, as seen in Table 2. Most treatments were done with 25 seeds each, but this varied depending on the number of available seeds.

Unscored TET seeds had 100% germination (15/15) by 7 - 8 days at 22C and 29C, under both light and dark conditions. For scored TET seeds, germination decreased, although higher rates were seen at 22C (60 - 73%) than at 29C (23 - 33%).

By 7 - 8 days, 100% (8/8 or 11/11) unscored PTJ seeds had germinated. Again, only slight differences were seen under the various conditions, similar to the unscored TET seeds. No scored PTJ seeds were tested due to low numbers. Of interest was the fact that about half of the stored PTJ seeds had lost their seed coats after being stored at 5C (41F) for 2 - 3 months. These seeds had a very delayed low germination rate (1/15 -4/15).

PFO had a germination rate of 76 - 96% (19 - 24/25) under all conditions for both scored and unscored seeds. At 22C, germination was slightly slower for the unscored seed in light and dark conditions. At 29C, germination was faster by about 3 days than the lower temperature. This was further enhanced by about 1 day for seeds in the dark and an a further day earlier for scored seeds.

FIR had similar results under all conditions as did PFO, with a germination rate of 58 - 89% (11 - 17/25).

Unscored APW seeds germinated 2 - 5 times better than scored seeds, except for the better germination of the scored at 29C (dark). At 22C, for the unscored, there was 96% germination (24/25) in the dark and 52 % (13/25) in the light. Similar results were seen at the higher temperatures, except for the decreased germination of 24% (6/25) at 29C, dark, unscored. For APW, the highest germination rate was at 22C (dark) and unscored. The time frame for this to happen was extended for up to 3 weeks.

The ANZ results were very similar to APW, 28 - 44% (7 - 11/25) germination, under all conditions for both scored and unscored seeds except for 72% (18/25) germination for scored seeds in the dark at 22C.

PPP seeds did not germinate well. Only 1 of 100 seeds exposed to light germinated. In the dark, 12 - 36% germinated, with the unscored seeds germinating slightly better. The highest germination rate (36%) was for unscored seeds at 29C in the dark.

Due to low seed numbers, TDN was only tested at 29C (light). Under these conditions, similar results were seen for scored and unscored seeds, 29% (6/21) and 43% (9/21) respectively.

Most seeds remained "fungus" free. With FIP, the "sterilization" with the bleach did not seem to alter the rate (3 - 5 days) that "fungal" growth appeared around some seeds under most conditions- both scored and unscored. TEW had "fungal" growth in 3 - 5 days for only some of the scored seeds (22C, dark and 29C, light).

What are the best conditions to use? When only small number of seeds are being tested, it is hard to determine whether or not the result was real or just a statistical abstraction (i.e. 4/25 may not be really twice as "good" as 2/25, but there might be a real difference between 10/25 and 20/25). Large numbers would make comparisons much more reliable. It is probably best to look at the results as trends only.

In the preliminary testing at 18 - 20C (65 - 69F), PFO germinated best if scored. Poor germination was seen at this temperature for APW and PPP.

In the current study, two of the species, TET and PTJ, had 100% germination under all conditions tested. The other species, ANJ, had up to 44% germination under all conditions, except for 72% germination for those unscored and incubated at 22C in the dark. Light had no effect on TDN germination, but only the higher temperature was tested. ANW and APW germinated best at 22C in the dark, with ANW having a preference for being scored. PFO and FIR gave similar results for all conditions. PPP had low germination rates.

In general, darkness delayed germination times by about 1 - 2 days, but not the percent germinated. The higher temperature (29C) decreased germination times by about 1 day, but did not affect percent germinated. Scoring did not generally affect percent germination, but decreased germination rate by 1 - 2 days.

In conclusion, for most hobbyists, it would be easiest and just as effective to germinate hardy waterlily seeds at 22C (72F) in the dark. If these conditions gave an unsatisfactory percent germination, the conditions could be altered by increasing the temperature to 29C (85F). Scoring and light might be considered as last resorts.

Table 1 | Table 2 (300K)

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