Pollen released at 1100 h has the highest viability (92.2%) but is no longer viable 3 d (84 h) after anthesis. In vitro pollen-tube growth is fast (140 μm h −1 ) and increases significantly within the first 8 h. In vivo pollen tubes also grow quickly and reach the base of the style within 2 h after pollination and enter the micropyle 8 h after pollination. There is no significant difference between self- and cross-pollination in either the rate and the number of pollen tubes in the pistil and th
e number of ovules penetrated by a pollen tube. Teak has late-acting gametophytic self-incompatibility; the majority of pollen tubes grow through the style but some do not continue to grow from the style towards the embryo sacs. Pollen-tube abnormalities include swollen, reversed, forked and tapered tips and irregular and spiralling tubes. These are most prevalent in self-pollination (20.4%). The index of self-incompatibility of 0.17 and low fruit set following self-pollination (2.49%) indicates that teak is mostly self-incompatible. Drastic fruit abortion occurs within the first week following controlled pollination. Within 14 d, fruit size and fruit set from cross-pollination is generally much greater than from self-pollination.
Floral biology and pollination mechanism of the Acacia hybrid ( A. mangium Willd. × A. auriculiformis A. Cunn. ex Benth.) growing in Thailand are investigated using light and electron microscopy. The hybrid is andromonoecious. A floral spike consists of about 150 loosely arranged flowers. Flowers are cream coloured, fragrant and have no floral nectaries. The pistil has a solid style with a smooth, wet stigma and amphitropous ovules with immature integuments. The anther consists of eight loculi,
each bearing only one 16-grain polyad. The flowers are weakly protogynous. Anthesis is complete at 0500–0600 h but peak female receptivity begins at 0200–0300 h and is completed that day. The stigmatic exudate is of the lipophilic type and is secreted from the stigmatic cells by a holocrine mechanism. Pollen is the main floral reward for the insect pollinators. There are several floral characteristics which facilitate pollen transfer from anthers and deposition on stigmas. Apis mellifera and Ceratina sp. are the most effective pollinators because they are the most common visitors and carry a heavy load of hybrid polyads. However, their behaviour in foraging for pollen in the same tree and weak protogynous dichogamy may promote self-pollination in the hybrid. The hybrid has low pollination success due to low pollinator number. An increase in exposure time of flowers to pollinators or pollinator number may increase pollination success but may not affect the rate of pollen deposition on stigmas due to the relatively small size of the stigma in relation to the polyad. Copyright 1998 Annals of Botany Company
Taxus brevifolia (Nutt.), commonly known as Pacific or western yew, is a conifer native to the Pacific northwest of North America. Contrary to other Taxus species, T. brevifolia staminate strobili are usually located on 2-year-old foliage although they may occur on foliage from 1 to 5-years-old. This delayed staminate strobilus development may be an adaptation to the low light environment where T. brevifolia grows. Microsporogenesis occurred in the autumn preceding pollination. Successive divisi
ons produced isobilateral tetrads visible as early as mid-October. Over-wintering staminate strobili usually contained separate microspores. In 1996 to 1999, pollination occurred in March and April in two natural forest sites on southern Vancouver Island, British Columbia, Canada. The low amounts of airborne pollen and prolonged pollination period indicated low pollination success within T. brevifolia . Female receptivity was measured by the presence of a pollination drop. Protandry up to 18 d was observed. In vitro pollen germination was moderate to good, ranging from 65 to 88% depending on the tree and year. DAPI fluorescence staining showed successful male gametophyte development in vitro . The microspore divided forming a tube nucleus and generative cell within 3 d of culture. The generative cell then divided forming a sterile nucleus and spermatogenous nucleus after 17 d. The spermatogenous nucleus acquired a cell wall then divided forming two equal sperm after 24 d. Copyright 2000 Annals of Botany Company