Normal and Damaged Female Hazel Flowers John Kelsey - - - April, 2018

The eastern United States and Canada are in want of a solid agricultural plan for a commercial hazelnut industry. The major obstacle has been the Eastern Filbert Blight. Thanks to breeding programs, the solution to that problem seems to be within sight. A second major eastern problem is the erratic production from varieties that perform reliably in traditional hazelnut climates. The core of the erratic production problem in the East is the wild swings of winter temperatures during the hazel’s flowering period. The hazel flowers are cold-tolerant while dormant, but mid-winter warm periods bring flowers out of dormancy. A following arctic spell can damage the exposed flower structure.

We have been observing hazel flowers at arm’s length for several years and have tried to understand the damaged and normal stages of progression at pollination time. It has been rather confusing. This year we invested in some macro photo equipment and were determined to zoom in and learn more.

Hazel Female Flower - - - Normal Progression

Figure 1 – Red Dot Figure 2 Figure 3 – 1mm Red Brush

Figure 4 – 2mm Red spider Figure 5 – 3mm Red Spider Figure 6 – Turning Maroon

Hazel Female Flower - - - Normal Progression

Figure 7 – Maroon Figure 8 – Mostly Black Figure 9 - Black

Figures 1 to 9 show the normal (uninjured) progression of the female hazel flower structure. The exposed sticky red stigmatic filaments capture pollen grains from the wind. Varieties typically spend about a week at each stage shown, but weather around freezing will hold up progress. When the filaments turn maroon, as shown in Figure 6, it seems that the receptive time has elapsed. I don’t think that maroon is a sign of successful pollination, because all the filaments all turn together, but not all are pollinated – I’ve been wrong before.

Not all varieties extend their stigmatic filaments the full 3mm. Some, for example, the clever Yamhill, only extends 1mm and holds 2mm in reserve in case the exposed part gets freeze-damaged.

During dormancy, before the red dot stage, the flower structures are unharmed at temperatures well below zero degF. Once the red filaments are exposed, they are vulnerable to damage at temperatures below the mid 20s degF. (Here is where some varieties may be a more tolerant than others.) Freeze damage would be too late to cause harm after the red stages, because any captured male germ is then protected well inside the female bud.

Hazel Female Flower - - - Freeze Damage

Figure 10 - Black Dot Figure 11 - Black Dot Section Figure 12 – Black Dot Pushed

Figure 13 – New Freeze Damage Figure 14 – Partial Damage

Figures 10 to 14 show various aspects of freeze damage. Figure 10 shows the “black dot” freeze damage during the red dot stage. This winter, Tonda di Giffoni, Slate, and Sacajawea were damaged by exposure to +2 degF during their red dot stage. Figure 11 shows a section of the damaged flowering bud and healthy stigmatic structure protected inside. All three varieties resumed their stigmatic extension after 3 weeks and are probably okay. Figure 12 shows a recovered flower with black dots now pushed out and functional stigmatic surface exposed. I flagged these buds and they are the same buds that were black dots earlier.

During freeze damage, cells burst and the next day the tissue has a pink watery appearance, as shown in Figure 13. About 3 days after the damage, they shrink and turn black. Figure 14 shows freeze damage from +23 degF, which only damaged the outer half of the exposed red spider filaments. Notice that Figure 14 looks quite different from Figure 12, although I expect both can still catch pollen.

So in conclusion, female hazel flowers are tough. They are freeze-resistant before and after the red receptive stages, and they have tricks to succeed despite damage during their receptive exposure. The story, however, is not so good for the boys (coming soon).

Regards - jfk