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Reforestation requires a constant supply of high quality seed. Different methods have been used to measure seed and fruit production as a proportion of that which potentially could be produced. These estimates coupled with developmental studies permit determination of when and to what extent different biological constraints reduce seed and fruit production. These vary among species, years and sites. Overcoming biological constraints may be possible in seed orchards and seed production areas. Biological constraints include: (1) periodic or inadequate floral initiation, (2) asynchronous development and flowering, (3) floral abortion, (4) ovule abortion, (5) embryo abortion, and (6) failure of seeds and fruits to mature and our inability to determine maturity. Solutions to these constraints are varied but all must begin with an understanding of reproductive biology of each species.

Conifer pollen tubes are an important but underused experimental system in plant biology. They represent a major evolutionary step in male gametophyte development as an intermediate form between the haustorial pollen tubes of cycads and Ginkgo and the structurally reduced and faster growing pollen tubes of flowering plants. Conifer pollen grains are available in large quantities, most can be stored for several years, and they grow very well in culture. The study of pollen tube growth and development furthers our understanding of conifer reproduction and contributes towards our ability to improve on their productivity. This review covers taxonomy and morphology to cell, developmental, and molecular biology. It explores recent advances in research on conifer pollen and pollen tubes in vivo, focusing on pollen wall structure, male gametophyte development within the pollen wall, pollination mechanisms, pollen tube growth and development, and programmed cell death. It also explores recent research in vitro, including the cellular mechanisms underlying pollen tube elongation, in vitro fertilization, genetic transformation and gene expression, and pine pollen tube proteomics. With the ongoing sequencing of the Pinus taeda genome in several labs, we expect the use of conifer pollen tubes as an experimental system to increase in the next decade.

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Cone and seed development in Douglas-fir were studied from pollination until seed release in 1986. Cone abortion at, and shortly after, pollination was high, resulting from a combination of low temperatures and possibly high moisture and populations of microorganisms on cones. Seed potential averaged about 75 seeds per cone with 31 filled seed per cone, giving an average seed efficiency of 39%. The major loss of seed resulted from insufficient pollen in the ovules. Other causes were ovule and embryo abortion at various stages of development. The effects of prezygotic and postzygotic events on seed set are discussed with respect to the reproductive success of Douglas-fir. Key words: Douglas-fir, seed set, cone, ovule, development, abortion.

Details of development and the phenology of postdormancy cone-bud development, microsporogenesis, pollen development, and pollination were similar for Pinus contorta var. contorta and var. latifolia growing near Victoria, B.C., but comparable stages of development for var. latifolia occurred about 1 month later near Prince George, B.C. Several developmental aspects were found which affect the reproductive potential of the species. Only 25% of the ovuliferous scales, mostly in the distal part of the cone, bear fertile ovules. Secretions formed on the ovules and micropylar arms which caused pollen to adhere to these surfaces. Pollination is by means of pollination drops which began to be exuded from the ovules about 2 weeks after the conelets began to emerge from their bud scales. Pollination drops were present within each conelet for 2 to 4 days. At that time conelets were most widely open. Pollination drops were then withdrawn as ovuliferous scales enlarged and sealed the conelets. Pollination drop exudation and withdrawal were affected by humidity and water stress within the tree. Cells lining the micropylar canal enlarged and sealed the micropyle after the conelet closed. Pollen settled into a pollen chamber in the nucellus tip where it germinated about 2 months after pollination. Ovules lacking germinating pollen aborted after megasporogenesis and before free nuclear division began. If many ovules aborted within a conelet, the conelet aborted before winter dormancy. Ovules began free nuclear female gametophyte development and pollen tubes extended into the nucellus before conelets stopped developing in mid-August.

Sacci of conifer pollen do not function primarily to increase the efficiency of wind pollination as is widely thought. Rather, they are bladders and cause pollen to float upwards in a liquid drop into the ovules. This observation is seemingly unsupported in the case of oriental spruce (Picea orientalis (L.) Link), which has saccate pollen. Ovulate cones are pendant at the time of pollination, which requires that pollen sink into the ovules. Pollen of oriental spruce floats at first but within 1-2 min sinks into the ovule. As sinking does not occur in saccate pollen of other Pinaceae, a variety of techniques was used to determine anatomical differences leading to this uncharacteristic tendency. Light, scanning electron, and confocal microscopy of the pollen surface yielded no significant appearing difference between pollen of oriental spruce and white spruce. However, transmission electron microscopy of freeze-fixed/freeze-substituted hydrated pollen revealed that the ektexine of oriental spruce pollen sacci is porous compared to that of white spruce. Confocal microscopy allowed examination of pollen hydration dynamics. Water enters pollen at the distal pole between sacci, and resulting rapid expansion of the tube cell forces air out of the saccate space. White spruce pollen remains buoyant because of enclosed air pockets in the saccus ektexine. Evolutionary change in pollen wall anatomy with resultant loss of saccus function is correlated with a change in ovulate strobilus orientation at pollination in oriental spruce. A suite of characters interact in the conifer pollination mechanism, and concerted change in these characters may lead to speciation.

We describe the phenology and mechanisms of pollen-cone and seed-cone development in lodgepole pine in the interior of British Columbia and the methods for monitoring cone phenology, pollination, seed production, and causes of seed and cone losses in seed orchards over the 15-month reproductive cycle. Pollination lasted about 2 weeks, between mid-May and mid-June. Pollen shedding and female receptivity showed homogamy, protandry, or protogyny depending on weather, site, and year. Morphological and developmental features explain why pollination as early as stage 3 was most successful and why self-pollination led to a seriously reduced production of filled seed. Early pollination increased the seed potential per cone and consequently the filled seed per cone. Cone drop occurred when less than 80% of ovules were pollinated per cone and was higher in trees from Prince George than those in the Okanagan Valley. Misting of trees and mechanical blowing of pollen in the orchards did not increase filled seed per cone. Clonal effect was the most important factor in all trials and has implications for orchard management.