[nafex] Re: Kiwifruit Pollen Viability

[bjeaj.guthrie@att.net]

Derry,

This spring we have had cool weather that resulted in an 
extended the bloom period of A. kolomikta.  Presently, 
these cold-hardy kiwifruit plants have been blooming for 
two weeks now and this will likely continue into next 
week.  Normally, the flowering period lasts a week to 10 
days.  The lowest temperature encountered (at the 
beginning of) flowering this spring was 29 degrees F 
under breezy conditions.  Temperatures steadily fell 
during the night.  Fortunately, this low occurred at 
sunrise and temperatures quickly rebounded above the 
freezing mark so little damage was done except to the 
tips of some potted A. chinensis plants.  Sustained and 
prolonged cool, wet weather will likely restrict bee 
flight and may limit pollination by these insects.  
However, research suggests that pollination during cold 
temperatures may in some instances help overcome 
incompatibility problems and produce fruit set.

Pollen Viability
If dry, pollen from male kiwifruit plants will remain 
viable at sub-freezing temperatures and can be kept for 
more than a year.  You can use a desiccant such as 
calcium chloride (Damp Rid) or anhydrite (Drierite) to 
remove the moisture.  The latter is a more effective 
desiccant.  Here in Minnesota, kiwifruit pollen is 
extracted, dried, and stored using the following 
procedures.  This approach can be modified to store 
pollen from other fruit plants as well.

1) Pick newly opened flowers from male plants.  The late 
afternoon on a sunny day is a good time to remove these 
blossoms as the pollen has generally reached sufficient 
maturity.

2) Snip the anthers from opened blossoms using manicure 
scissors.  A non-stick (weighing) paper placed on a 
saucer plate is a useful receptor/catcher for the 
anthers.

3) Place the plate in a Ziplock-type bag containing the 
calcium chloride.  Seal, and store overnight.

4) Transfer the dried anthers to gelatin capsules.  The 
weighing paper can be used as a “funnel” to facilitate 
the transfer.

5) Spoon the Drierite into the bottom third of a 40-ml 
vial.  Place a polyester “cotton ball” swab on top of 
the granular desiccant to keep it in place.  Fill the 
remainder of the space with the gelatin capsules, cap 
and seal.  

6) Label and date the vial(s) and place them in a small 
Ziplock-type bag.  Store the bag in the refrigerator for 
one day to remove any residual moisture.  Then transfer 
the vials to the freezer for long-term storage.

Most of the materials mentioned above can be obtained 
from your local discount store or pharmacy.  Gelatin 
capsules may also be available at veterinary-supply 
stores or health food-type shops.  The weighing paper 
and Drierite is available through laboratory-supply 
stores or catalogs.  Drierite can be regenerated by oven 
baking to convert the moisture-containing gypsum back to 
anhydrite.  The 40-ml vials can be obtained from 
environmental laboratories and possibly from some 
environmental consulting firms as they are used in the 
collection of groundwater samples used for volatile 
organic compound (VOC) analyses.  Politely ask for any 
unused vials that were brought out into the field.  As a 
word of caution, many of the 40-ml vials usually contain 
three drops of concentrated hydrochloric acid as a 
preservative.  With gloves, carefully rinse the vials 
out with water and dry thoroughly.  Incidentally, the 40-
ml vials are great for seed storage too!

Controlled Crosses
In Minnesota, A. kolomikta is the first Actinidia 
species to bloom and is the focus of fruit-breeding 
efforts due to its cold-hardiness.  Due to its early 
flowering period, interspecific crosses involving A. 
kolomikta (as the seed parent) must use either shipped 
pollen or dried, frozen, year-old, pollen.  Controlled 
crosses can be made with kiwifruit by bagging female 
blossoms prior to opening (e.g., popcorn stage or 
before) to keep bees, flies and other pollinators out.  
White, wax-lined “donut” bags available at some bakeries 
and party-supply shops work well for this purpose and 
hold up well in rainy weather.  The bag is slipped over 
the unopened blossoms, folded at the opening, and sealed 
by stapling.  Clothespins can also be used to cinch 
openings to the cordon and to help support the bag.

Pollination
Remove the frozen pollen from the freezer and allow it 
reach room temperature before opening the 40-ml vial.  
Remove one or more gelatin capsules and reseal the vial 
and place it back in the refrigerator or freezer.  Empty 
the contents of the gelatin capsule into a separate 
unsealed 40-ml vial so the pollen can rehydrate for an 
hour or two. Recap the vial before bringing out to the 
field.  To pollinate female kiwifruit blossoms in 
controlled crosses, carefully remove the bag from the 
(now opened) flowers.  Shake (side-to-side) the dried 
anthers in 40-ml vial to liberate the pollen.  The 
pollen will appear as a dust coating on the sides of the 
glass vial.  Dip a small watercolor-paint brush into the 
vial to collect the pollen and then gently dab on the 
female flowers.  Repeat as necessary (Note: making a 
buzzing sound is optional).  After pollination, the wood 
is color-coded using acrylic paint and flagging ribbons 
for future identification.  A white “donut” bag is then 
once again placed over the female blossoms and stapled 
until berry set.  Crossing information is then recorded 
into a field notebook.  The paper bags are removed 
following berry set. 

The preceding methods can be adapted to other fruit 
crops.  For self-fertile plants anther removal 
(emasculation) may be needed.  Most kiwifruit plants are 
either male or female so this additional step is not 
necessary.

I hope this information is of some use.   Hope you get 
great yields with your kiwifruit (A. deliciosa-?) plants.

Sincerely,

Bob Guthrie

> Does anyone know the temperature at which kiwi pollen is viable?
> 
> It is  cool and wet outside today 11°C (52°F).
> 
> I've read that in apples, the temp must be 14°C for the apple pollen to be 
> viable.
> 
> Thanks,
> 
> Derry
> 
> Derry Walsh & Bill Chase  email:wchase@interchange.ubc.ca
> Aldergrove,  B. C.,  Canada
> phone/fax (604) 856-9316
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