Pruning and Pollen Viability

I happened on this paper today. It’s one of those strange notes that brings together things don’t immediately seem to be related.

This paper can be summarized pretty simply: Less severe pruning increases germinability of pollen. At least in Grapes.

For more detail:
Winkler: Grape Pruning and Pollen Viability (1926)

Probably not out of the ball park with that one. I can see some merit into such a concept. Likewise, there is a relationship between total UV foliar coverage and seed count, set, and viability.

If pruning of various kinds can reduce pollen viability, it seems to me that the viability might be improved by ringing (girdling, binding). Such a treatment blocks the downward flow of carbohydrates, while allowing the continued upward flow of water and soluble minerals.

Of course, I have not found any reports for this specific detail, but plenty that indicate an increase in flowering, fruit set, seed size, etc.
But I did find a couple of items that I had not considered. For instance, Fayek, et al (2011) tried various combinations of ringing and foliar applications of amino solutions. “The general positive effects of amino acid foliar spray applications could be attributed to enhanced pollen tube ovule penetration and delayed ovule senescence which increases fruit set and yield.”

And how many times have I read that pollen must be kept dry if it is to be stored for even a short time? We are left to assume that the sticky surface of the stigma provides all the necessary moisture. Apparently this is not the case for avocados, according to Loupassaki & Vasilakakis (1995). “The most sensitive to relative humidity variation, was the pollen of Fuerte, the germination of which rose from 11.42%, when humidity was 40%, to about 50%, when kept for one hour at a relative humidity equal to 100%.”

A couple of items:

The Pennsylvania State College—Agricultural Experiment Station, Bulletin 230, p. 35 (July 1928)
Effect of Ringing Fruit Trees on Tree Growth and Reproduction. Preliminary work was done on the effect of ringing on the viability of the pollen of varieties that are notoriously poor quality pollen producers. Ringing done a week before blossoming had no effect whatsoever on either the amount or viability of the pollen produced from Winesap and Rhode Island Greening apple trees. (F. N. Fagan and R. H. Sudds.)

I would not expect any great effect just a week after ringing. I am looking for a follow-up to this preliminary report, but no luck yet.

This one may be of more immediate value.

32. Kraus, E. J. The self-sterility problem. Jour. Heredity 6: 549-557 (1916)
pp. 551-552
There is a wide variation in the germinability of apple pollen; it ranges from less than 1% to 100% according to variety. It also should be added that the percentage germination of any variety, even though apparently perfect morphologically, will vary from year to year and is dependent upon many factors such as age and general vitality of the tree, humidity before and during blooming time, soil conditions; in fact, any environmental factor in the broadest sense of the term. Jeffrey recently has pointed out the widespread occurence of morphologically imperfect pollen in many plants, due, as he says, to the hybrid nature of such plants. Whether the same reasoning can be applied to account for morphologically defective pollen in all fruit varieties is still a question; apparently it accounts for some instances.

I keep looking, but cannot find an explicit reference to ringing affecting pollen viability. But I have found some further information.

F. N. Fagan, The Pennsylvania State College—Agricultural Experiment Station
1925: In June of 1922 a few Baldwin trees were ringed in the customary manner, removing a quarter-inch strip of bark completely around the tree. These trees set a good crop of fruit in 1923 and were again ringed in June of that year, resulting in another set of fruit for 1924.
1925: In mid-June of 1924, 18 Stayman Winesap, 18 McIntosh, 18 Rome Beauty, 119 Baldwin fillers received the ringing treatment. The 1925 crop resulting from the ringing is given in the following table:
• Stayman Winesap—18 ringed trees, yielded 4 bushels per tree.
• Stayman Winesap—510 unringed trees, yielded slightly less than 1 bushel per tree. (12 Stayman Winesap trees had been removed for various causes during the past 8 years.)
• Mclntosh—18 ringed trees, yielded 4 bushels per tree.
• Mclntosh—520 unringed trees, yielded slightly less than 1 bushel per tree. (2 trees had been removed from this block during the past 8 years.)
• Rome Beauty—18 ringed trees, yielded 2 bushels per tree.
• Rome Beauty—522 unringed trees, yielded less than 1 bushel per tree.
• Baldwin—103 ringed trees, yielded 110 bushels.
• Baldwin—417 unringed trees, yielded 10 bushels.
1928: Ringing done a week before blossoming had no effect whatsoever on either the amount or viability of the pollen produced from Winesap and Rhode Island Greening apple trees.
1932: The ringing should be done about May 20 to June 5, when terminal growth is very active and before the terminal bud has formed.
1933: As to the technic of ringing, the simple drawing of a sharp knife through the bark was as effective as the removal of a ring of bark and decreased the hazard to the tree.
1937: The ringed McIntosh and Delicious trees show the dwarfing effect that results from heavy early bearing caused by ringing, but no trees have died from ringing. Ringed Northern Spy trees set a heavy crop in 1936 in spite of an outbreak of blossom fire blight. The use of grafting tape over the ring seemed to keep blight from entering the cut. Tree Seal paint was not so satisfactory as tape.

A simple cut through the bark, followed with a grafting tape wrap, is much easier to manage than actually pealing out a strip of bark. This method should be helpful in persuading stubborn species to bloom more freely and set more hips.
American Rose Annual 49: 159-164 (1964)
Stock-Scion Relationships in Roses
Griffith J. Buck
There is some indication that earlier and heavier flower production is stimulated by grafting.4 The presence of a graft union, even in the case of completely compatible stock-scion combinations, has a partial blocking effect on the translocation of nutrient materials, including photosynthetic products, leading to increased starch storage in the stems with a consequent increase in flower bud initiation which is dependent upon high starch reserves. Understock studies with other plants (namely, oranges and persimmon) have shown earlier flowering when budded to themselves than when unbudded, although the size of the plants was similar.

  1. Hodgson, R. W. and S. H. Cameron. 1935. On bud union effect in citrus. California Citrog. 20 (12): 370