Visser et al.: Pollen and Pollination Experiments (1980-1983)

Pollen and pollination experiments. I. The contribution of stray pollen to the seed set of depetalled, hand-pollinated flowers of apple.
Euphytica
29: 379-383 (1980)
T. Visser and J. J. Verhaegh
Summary
Using the finger nails to remove most of the petals is a fast method of preparing apple flowers for hand pollination in the balloon stage. Such flowers still appeared quite attractive to insects; left to open pollination, the seed set per flower averaged two thirds of that of similarly treated, but hand-pollinated flowers. With the aid of 'marker pollen' of scab or mildew resistant donors and the subsequent screening of the seedling progenies for resistance, it was shown that the stray pollen was responsible on average for one of every three seeds formed by unbagged depetalled and hand-pollinated flowers.

Pollen and pollination experiments. II. The influence of the first pollination on the effectiveness of the second one in apple.
Euphytica
29: 385-390 (1980)
T. Visser and J. J. Verhaegh
Summary
Pollinating apple cultivars twice with compatible pollen at an interval of one or two days produced about twice as many seeds per pollinated flower as a single pollination. With the aid of scab- or mildew resistant 'marker pollen', it could be shown that the second pollen formed on average twice as many seeds as the first. The first pollen appears to 'pave the way'—partly at its own cost—for the second and was therefore called 'pioneer pollen'.

Pollen and pollination experiments. III. The viability of apple and pear pollen as affected by irradiation and storage.
Euphytica
30: 65-70 (1981)
T. Visser and E. H. Oost
ABSTRACT
Apple and pear pollen was irradiated with doses of 0, 50, 100, 250 and 500 krad (gamma rays) and stored at 4C and 0–10% r.h. From the in-vitro germination percentages an average LD 50 dose of about 220 krad was estimated. For both irradiated and untreated pollen a close and corresponding linear relationship existed between germination percentage and pollen tube growth. Irradiated pollen was much more sensitive to dry storage conditions than untreated pollen, resulting in less germination and more bursting. Apparently, irradiation caused the pollen cell membrane to lose its flexibility faster than normal. Rehydration of dry-stored, irradiated pollen in water-saturated air restored germination percentages up to their initial levels. The importance of this procedure in germination trials is stressed.

Pollen and pollination experiments. IV. 'Mentor pollen' and 'pioneer pollen' techniques regarding incompatibility and incongruity in apple and pear.
Euphytica 30: 363-369 (1981)
T. Visser
Summary
It was attempted to overcome self-incompatibility in apple and pear and incongruity between these species with the aid of compatible 'mentor' or 'pioneer' pollen. The mentor pollen was applied in a mixture (1:1) with the incompatible/incongruous pollen and the pioneer pollen was applied one day in advance of the other pollination. Two trials in 1976 with dead methanol-treated mentor pollen on apple were moderately successful, probably because of the hot spring weather. In the apple and pear trials of 1979 neither the methanol-treated nor the viable irradiated (100 krad) mentor or pioneer pollen significantly improved the seed set by self pollen or that after intercrossing. Competition and early embryo abortion after selfing or intercrossing probably contributed to the lack of success of these methods. The viable irradiated pollen induced a rather high 'parthenocarpic' fruit set, whether applied on its own or mixed with or in advance of the incompatible pollen; the inviable methanol-treated pollen had no such stimulating influence.

Pollen and pollination experiments. V. An empirical basis for a mentor pollen effect observed on the growth of incompatible pollen tubes in pear.
Euphytica 31(2): 305-312. (1982)
T. Visser and E. H. Oost
ABSTRACT
The self-incompatible pear cultivar Doyenne du Comice was selfed with the aid of the mentor pollen technique (self pollen mixed 1:1 with compatible pollen) and the pioneer pollen method (compatible pollen applied 14 h in advance of the self pollen). Observations on tube growth in the style showed that inviable methylated pollen was ineffective either as mentor or pioneer pollen, having no effect on the performance of the self pollen which stopped growing at about one quarter of the style from the stigma. Calculations made on the basis of the obtained data indicated that the viable untreated or irradiated pioneer and mentor pollen, the former somewhat better than the latter, aided the self pollen tubes to reach the base of the style.

Pollen and pollination experiments. VI. Heat resistance of pollen.
Euphytica 31(2): 287-290 (Sept 1982)
M. Clara Marcucci, T. Visser, J. M. Van Tuyl
Summary
Pollen of dry apple, pear, lily and rose pollen was heated up to 48 h at a range of temperatures. About half or more than half of the pollen grains survived 48 h at 40 C, 24 h at 50 C, 8 16 h at 60 C. 4 8 h at 70 C, more than one hour at 80 C. and between 10 and 20 min at 90 C. Presumably, pollen able to withstand low humidity is also heat resistant, a property which may be usable to make pollen virus free through heat treatment and perhaps to overcome incompatibility.

Pollen and pollination experiments. VII. The effect of pollen treatment and application method on incompatibility and incongruity in Lilium.
Euphytica
31(3): 613-619. (1982)
Jaap M. van Tuyl, M. Clara Marcucci, T. Visser
ABSTRACT
Four methods were investigated for their capacity to overcome incompatibility and incongruity in Lilium longiflorum and the Lilium hybrid Enchantment. Temperature treatments of pollen at 40 to 60C for one hour had no effect on germination capacity. None of the temperature treatments influenced incompatibility or incongruity. Application of cut-style pollination had a positive effect on self-pollination of Enchantment, but did not overcome self-incompatibility in L. longiflorum. With the aid of genetically inactivated (by irradiation) compatible mentor or pioneer pollen self-incompatibility of L. longiflorum could be largely overcome. Both methods also gave promising results in realizing interspecific crosses.

Pollen and pollination experiments. VIII. The effect of successive pollinations with compatible and self-incompatible pollen in apple (Malus) and pear (Pyrus).
Euphytica 32: 57-64 (1983)
Visser. T., Verhaegh, J. J., Marcucci, M. C., and Uijetwaal, B. A.
Summary
In compatible pollen combinations, viable but infertile irradiated pollen Cr appears to compete much more in a mixture (the mentor pollen situation: C+Cr), than when used one day in advance (the pioneer pollen situation: Cr/C). Seed set of Cr/C was usually also greatly superior to that of C/Cr and, using, self, incompatible pollen S instead of Cr, S/C was nearly always much better than C/S. This is in accordance with the promotion of the second by the first (pioneer) pollen. Hence, when Cr or S are applied second in C/Cr or C/S, more ovules are rendered ineffective (blocked or aborted) than in the reverse combination when Cr or S act as pioneer pollen. These observations are consistent with the trend that the combinations C/ C+S, C+S, C/S tended to produce more selfed seeds in that order. Although mentor or pioneer pollen assist in removing the style barrier for self pollen, embryo abortions appears to be a second obstruction towards seed formation. Indications are that high spring temperature during pollination promote the production of selfed seeds in the presence of compatible pollen. The surfeit of self pollen in orchards with a minority of pollinators is not necessarily an unfavourable factor, it may both directly and indirectly contribute to fruit and seed set.

Pollen and pollination experiments. IX. The pioneer pollen effect in apple and pear related to the interval between pollinations and the temperature.
Euphytica
32: 703- 709 (1983)
Visser, T., and Marcucci, M. C.
Summary
Double pollinations of apple and pear may double the seed production, to which the second pollen can contribute 3 times as many seeds as the first (pioneer) pollen, when the interval between pollinations is long enough (48 h) at low (10°C) or short enough (7 h) at high (20°C) temperatures. With shorter or longer intervals, the contribution of the second pollen to seed production diminishes. The dominance of the second pollen was attributed to promotion by the first one, the second pollen probably being optimally stimulated when the tubes of the first have passed about 1/3rd of the style. It is concluded that the effectiveness of the pioneer pollen method to overcome incompatibility, depends on whether the interval between pollinations can be usefully adjusted to both the environmentally (temperature) and inherently determined rate of pollen tube growth of the species.

Pollen and pollination experiments. X. The effect of repeated pollination on fruit and seed set in crosses between the hybrid tea rose CVS. Sonia and Ilona.
Euphytica
32(3): 685-689 (Nov 1983)
D. P. Devries, Lidwein A. M. Dubois
Summary
To improve fruit and seed set in roses, the Hybrid Tea-cultivar Sonia was pollinated with the cv. Ilona 0, 1, 2, 3, 4, 5, 6, and 7 times at 24 h intervals. Unpollinated flowers did not yield fruits. The number of achenes per fruit increased up to 3, fruit weight and weight of achenes increased up to 4, and the number of seeds per pollinated flower (PI) increased up to 5 pollinations.
   Both between and within pollination treatments, highly significant correlations occurred between fruit weight, number of achenes per fruit, and weight of achenes. Effects of repeated pollination in rose and apple are compared. The effect of a relatively low fertilization level in rose crosses is discussed.