Proc. Amer. Soc. Hort. Sci. 53: 141-142 (1949)
Effect of Boric Acid Sprays Applied During Bloom Upon the Set of Pear Fruits
U. S. Department of Agriculture, Wenatchee, Wash.

Under the conditions prevailing in this experiment it seems evident that boric acid sprays significantly increased the set of Anjou pears.

Planta 148(3):217-21 (Apr 1980)
Pollen tube growth following compatible and incompatible intraspecific pollinations in Petunia hybrida.
Herrero M. Dickinson HG.

The observation that both compatible and incompatible pollen tubes grow at identical speeds on the stigma in many plants with 'gametophytically controlled' self-incompatibility (SI) systems has, in Petunia, been extended to cover all other facets of pollen behaviour on this tissue. On entry into the stylar transmitting tissue both types of tubes accelerate, but the compatible achieve a higher terminal velocity than do the incompatible, which eventually slow and stop. Grafting experiments show that the top 1 mm of the stylar tissue can play an important rôle in determining the future development of the pollen tube. Following mixed pollinations, proportionally too many 'compatible' pollen tubes reach the ovary than would be expected from the results of 'pure' compatible and incompatible pollinations indicating that incompatible pollen in some way helps 'prime' the style for growth of compatible pollen tubes. This data is considered in terms of recent structural studies of these tissues, and related to the pollination conditions pertaining to Petunia populations in the field.

Pollen tube–pistil interaction and fertilization in Lilium longiflorum. p. 3 (1992)
Juliette Janson

Self-incompatibility in lily
— The age of the pistil and the self-incompatibility reaction —

The presence of the incompatibility reaction of L. longiflorum is dependent upon the age of the flower. Till 4 days after anthesis incompatible pollen tubes reach, 48 hours after pollination at room temperature, only half the length of compatible pollen tubes. In older flowers this difference decreases. The same length is reached ten days after anthesis, when the growth of both compatible and incompatible pollen tubes is reduced. Seed set did then not appear. Till nine days after anthesis, compatible pollination resulted in seed set. After incompatible pollination seed set only occurred when carried out between six and nine days after anthesis. Incompatible bud pollination did not result in seed set (Ascher and Peloquin, 1966a).

Plant Science 90(1): 105-115 (1993)
Placental pollination in Lilium longiflorum Thunb.
Juliette Janson

In Lilium longiflorum placental pollination was carried out to study the interaction between the pollen tube and the placenta with ovules. The pollen tube growth between the ovules seems directed and the pollen tubes do find the inner integument. A reaction to the inner integument or the micropyle is observed, but rarely results in ovule penetration. Attempts to activate the ovules did not increase the percentage penetration. Only grafting a style with pollen tubes to the placenta gave a 5-fold increase. The low penetration percentage after placental pollination seems to have its basis in an inability of the pollen tubes to react to signals from the micropyle. The poor results from placental pollination and grafted style pollination are compared mutually and with those from the routinely used cut-style pollination technique in order to give more insight in the processes that attract the pollen tubes to the micropyles.

Acta Bot. Neerl. 42(4): 461-472 (Dec 1993)
Pollen tube growth in Lilium longiflorum following different pollination techniques and flower manipulations
J. Janson M.C. Reinders, J.M. van Tuyl, and C.J. Keijzer

After cut-style pollination of Lilium longiflorum Thunb. using compatible pollen, the percentage of ovules with a pollen tube in the micropyle was very low when compared with pollination at the stigma. Pollen tube growth in the ovary, as observed with scanning electron microscopy, did not show any differences between these two pollination methods until the arrival of the pollen tube at the inner integument. After cut-style pollination, the majority of the pollen tubes either grew past the inner integument and ignored it, or grew over but not into the micropyle. Grafting a stigma just above the ovary did not increase the penetration percentage. Possible activation of the ovary, induced by pollination or pollen tube growth in the style or even in the ovary itself, preceding intrastylar or placental pollination did not result in an increase of the penetration percentage. However, the percentage of ovule penetration after cut-style pollination did increase when a longer part of the style was left at the ovary. The basis of the interaction between pollen tube and pistil, which led to ovule penetration, was built up during pollen tube growth through the style.

North American Lily Society Yearbook. 1975, p. 78.
Interspecific Incompatibility and the Improbable Cross
R. M. Withers
Hawthorn, Victoria, Australia

In this article it is proposed to survey attempts to achieve success in the production of difficult lily hybrids, to outline briefly possible reasons for interspecific incompatibility, and finally to recommend methods by which such crosses can be made with every hope that they will be successful. It is assumed that the seed and pollen parents are of similar chromosome status, and genetically capable of being crossed. The use of colchicine to create polyploid lilies and the make sterile lilies fertile, is quite a separate subject.

Sexual Plant Reproduction 14(2): 77-83 (Sept 2001)
The performance of microgametophytes is affected by inbreeding depression and hybrid vigor in the sporophytic generation
A. G. Stephenson, C. N. Hayes, M. H. Jˇhannsson, J. A. Winsor

Abstract: Inbreeding reduces the level of heterozygosity, thereby exposing deleterious recessives to selection and simultaneously reducing the number of loci expressing heterosis (overdominance). In contrast, hybridization increases the level of heterozygosity, thereby masking deleterious recessives and simultaneously increasing the number of loci expressing heterosis. Most studies of inbreeding depression/hybrid vigor have focused on sporophytic performance such as survivorship, vegetative growth rates, fruit and seed production and (rarely) pollen production. Because the genetic mechanisms that underlie inbreeding depression/hybrid vigor are relevant only to the diploid stage of the life cycle, most studies have tacitly assumed that they have no effects on pollen performance (pollen germination, pollen tube growth rate, ability to achieve fertilization under conditions of pollen competition). However, we reasoned that because pollen is dependent upon the sporophyte for the resources necessary to develop, germinate and initiate tube growth, the level of heterozygosity (vigor) in the pollen-producing parent can affect pollen performance by affecting the ability of the sporophyte to provision its pollen. In a series of studies conducted under field conditions over 7 years, we experimentally varied the level of heterozygosity in wild gourd (Cucurbita pepo) plants (four levels of inbreeding, f = 0.75, 0.50, 0.25, 0 and a zucchini x wild gourd F1). We found that sporophytic vigor (e.g., flower and fruit production) increased with the level of heterozygosity and that the level of heterozygosity of the sporophyte affects the in vitro and in vivo performance of the microgametophytes it produces. These findings are analogous to the "maternal environmental effects" frequently observed in seeds.

Proc. XX EUCARPIA Symp. on New Ornamentals II
Eds. J. Van Huylenbroeck et al.
Acta Hort. 572, ISHS 2002

Controlling prefertilization barriers by in vitro pollination and fertilization of Bromeliaceae
I. Vervaeke, E. Parton, R. Deroose and M.P. De Proft
Laboratory of Plant Culture
Catholic University of Leuven
W. De Croylaan 42 B-3001 Leuven Belgium

Prefertilization barriers between different Bromeliaceae are mostly confined within the style. To control these barriers cut style, placental and placental grafted style pollination were studied. After cut style pollination the fertilization rate increased when a longer style part was left on the ovary of Vriesea C. Possibly less factors that control pollen tube guidance to the ovules are present in the lower style part. After placental pollination pollen germinated on the ovules but only rarely penetration of the micropyle by a pollen tube occurred. No difference in fertilization rate between compatible and incongruent pollination was found. Semi in vivo pollination resulted in a higher pollen tube growth out of the isolated style in comparison to semi in vitro pollination. However for Vriesea C, even after semi in vivo pollination pollen tube growth was inhibited at the stylar end. Grafting a style containing actively growing pollen tubes to the ovules on the placenta (placental grafted style pollination) resulted in a fertilization percentage, which was comparable to this after a classical pollination on the stigma for Aechmea A. Pollen tube growth through the style seems to be necessary for guiding pollen tubes to the ovule micropyle.

Pollen Mixtures